hauschildt

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Author name code: hauschildt
ADS astronomy entries on 2022-09-14
author:"Hauschildt, Peter H."

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Title: EMISSA (Exploring millimetre indicators of solar-stellar
activity). II. Towards a robust indicator of stellar activity
Authors: Mohan, A.; Wedemeyer, S.; Hauschildt, P. H.; Pandit, S.;
Saberi, M.
2022A&A...664L...9M Altcode: 2022arXiv220804217M
Context. An activity indicator, which can provide a robust quantitative
mapping between the stellar activity and the physical properties of its
atmosphere, is important in exploring the evolution of the observed
active phenomena across main-sequence stars of different spectral
types. Common activity indicators do provide qualitative correlations
with physical properties such as Teff and the rotation
period, among others. However, due to the large variability in their
values, even for a single star, defining robust quantitative mappings
between activity and physical properties is difficult. Millimetre
(mm) wavelengths probe the different atmospheric layers within the
stellar chromosphere, providing a tomographic view of the atmospheric
dynamics. Aims: The project aims to define a robust activity
indicator by characterising mm brightness temperature spectra
(TB(ν)) of the cool main-sequence stars (Teff
∼ 5000-7000 K) compiled by Paper I in this series. The sample
contains 13 stars, including the Sun. Methods: We derived
the mm TB(ν) spectral indices (αmm) for
cool stars, including the Sun, based on observations in the 30-1000
GHz range. The derived values for αmm are explored as
a function of various physical parameters and empirical power-law
functions were derived. We also compared αmm estimates
with other activity indicators. Results: Despite the estimation
errors, αmm values could distinguish the cool stars well,
unlike common activity indicators. The low estimation errors on the
derived trends of αmm vs. physical parameters suggest
that αmm could be a robust activity indicator. Conclusions: We note that αmm, which is linked to
chromospheric thermal stratification and activity in cool stars,
can well distinguish and physically characterise the stars more
robustly than common activity indicators. We emphasise the need for
multi-frequency data across the mm band for stars, with a range of
physical parameters and gathered at multiple epochs during their
activity cycles. This will help to explore αmm in a
statistically robust manner and to study the emergence of chromospheric
heating on the main sequence.

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Title: Solar/Stellar atmospheric tomography with mm - cm data:
Initial catalogue of main sequence stars and results
Authors: Mohan, Atul; Wedemeyer, Sven; Pandit, Sneha; Saberi, Maryam;
Hauschildt, Peter
2022cosp...44.2495M Altcode:
Millimeter - Centimeter (10 - 1000 GHz) bands are particularly
sensitive to emission from various outer atmospheric layers of main
sequence stars, with shorter wavelengths probing deeper layers. This
makes the study of mm - cm spectra (S$_{obs}$) a unique tool to study
the vertical atmospheric stratification of these stars as a function
of various physical parameters. A major challenge in the field of mm
astronomy had been the lack of a sensitive interferometer which can not
only detect the faint $\sim$ 10 - 100 $\mu$Jy level atmospheric fluxes
robustly from these stars, but also provide enough spatial resolution
needed to distinguish any emission from companion stars and stellar
disks. With the advent of the Atacama Large Millimeter/Sub-millimeter
array, the aforementioned hurdles have been overcome to a great extent
for at least the stars within a distance of 10\,pc.\\ In this work, we
gathered the archival data of main sequence stars robustly detected with
ALMA, and additionally reported 10 - 80 GHz fluxes if any, from other
modern interferometric arrays like ATCA, JVLA etc. The data for the Sun
were also gathered and the disk-averaged fluxes were recorded to get
the sun-as-a-star spectrum. The resulting sample comprises of 12 main
sequence stars plus the sun-as-a-star covering an effective temperature
(T$_{eff}$) range of 3000 - 10000 K. We compared their observed fluxes
against respective purely photospheric model fluxes obtained using the
PHOENIX code (S$_{model}$) and obtained the upper atmospheric excess
energy spectrum ($\Delta$S/S$_{model}$ = S$_{obs}$/S$_{model}$ - 1
). We find evidence for a stratified atmosphere which gets progressively
hotter with height in cool stars (T$_{eff}$ &lt; 7000 K). The spectral
index of the observed mm-cm brightness spectrum, was characterised
for every star in the sample with sufficient data. The steepness was
found to decrease with T$_{eff}$, possibly hinting at steeper thermal
gradients in cooler stars. This study demonstrates the potential of mm
- cm band diagnostics to perform atmospheric tomography in cool stars
and that long duration light curves for these stars can be powerful
tools for studying the dynamics across different layers. This calls
for the need to have dedicated long duration surveys of nearby cool
stars in mm - cm bands assisted by state of the art modelling to better
understand the nature of atmospheric stratification and dynamics in
cool stars as a function of stellar type.

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Title: OPTAB: Public code for generating gas opacity tables for
radiation hydrodynamics simulations
Authors: Hirose, Shigenobu; Hauschildt, Peter; Minoshima, Takashi;
Tomida, Kengo; Sano, Takayoshi
2022A&A...659A..87H Altcode: 2021arXiv211205689H
We have developed a public code, OPTAB, that outputs Rosseland, Planck,
and two-temperature Planck mean gas opacity tables for radiation
hydrodynamics simulations in astrophysics. The code is developed for
modern high-performance computing, being written in Fortran 90 and
using Message Passing Interface and Hierarchical Data Format, Version
5. The purpose of this work is to provide a platform on which users can
generate opacity tables for their own research purposes. Therefore,
the code has been designed so that a user can easily modify, change,
or add opacity sources in addition to those already implemented,
which include bremsstrahlung, photoionization, Rayleigh scattering,
line absorption, and collision-induced absorption. In this paper, we
provide details of the opacity calculations in our code and present
validation tests to evaluate the performance of our code.

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Title: EMISSA (Exploring Millimeter Indicators of Solar-Stellar
Activity). I. The initial millimeter-centimeter main-sequence
star sample
Authors: Mohan, A.; Wedemeyer, S.; Pandit, S.; Saberi, M.; Hauschildt,
P. H.
2021A&A...655A.113M Altcode: 2021arXiv211013339M
Context. Due to their wide wavelength coverage across the millimeter
to centimeter (mm-cm) range and their increased sensitivity, modern
interferometric arrays facilitate observations of the thermal and
non-thermal radiation that is emitted from different layers in the
outer atmospheres of stars. Aims: We study the spectral energy
distribution (Sobs(ν)) of main-sequence stars based on
archival observations in the mm-cm range with the aim to study their
atmospheric stratification as a function of stellar type. 
Methods: The main-sequence stars with significant detection in mm
bands were identified in the ALMA Science Archive. These data were
then complemented with spectral flux data in the extreme ultraviolet
to cm range as compiled from various catalogues and observatory
archives. We compared the resultant Sobs(ν) of each star
with a photospheric emission model (Smod(ν)) calculated
with the PHOENIX code. The departures of Sobs(ν) from
Smod(ν) were quantified in terms of a spectral flux
excess parameter (ΔS∕Smod) and studied as a function
of stellar type. Results: The initial sample consists of 12
main-sequence stars across a broad range of spectral types from
A1 to M3.5 and the Sun-as-a-star as reference. The stars with
Teff = 3000-7000 K (F-M type) showed a systematically
higher Sobs(ν) than Smod(ν) in the mm-cm
range. Their ΔS∕Smod exhibits a monotonic rise with
decreasing frequency. The steepness of this rise is higher for cooler
stars in the Teff = 3000-7000 K range, although the single
fully convective star (Teff ~ 3000 K) in the sample deviates
from this trend. Meanwhile, Sobs(ν) of the A-type stars
agrees with Smod(ν) within errors. Conclusions:
The systematically high ΔS∕Smod in F-M stars indicates
hotter upper atmospheric layers, that is, a chromosphere and corona in
these stars, like for the Sun. The mm-cm ΔS∕Smod spectrum
offers a way to estimate the efficiency of the heating mechanisms
across various outer atmospheric layers in main-sequence stars, and
thereby to understand their structure and activity. We emphasise the
need for dedicated surveys of main-sequence stars in the mm-cm range.

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Title: A comparison between X-shooter spectra and PHOENIX models
across the HR-diagram
Authors: Lançon, A.; Gonneau, A.; Verro, K.; Prugniel, P.;
Arentsen, A.; Trager, S. C.; Peletier, R.; Chen, Y. -P.; Coelho,
P.; Falcón-Barroso, J.; Hauschildt, P.; Husser, T. -O.; Jain, R.;
Lyubenova, M.; Martins, L.; Sánchez Blázquez, P.; Vazdekis, A.
2021A&A...649A..97L Altcode: 2020arXiv201209129L
 Aims: The path towards robust near-infrared extensions of stellar
population models involves the confrontation between empirical and
synthetic stellar spectral libraries across the wavelength ranges of
photospheric emission. Indeed, the theory of stellar emission enters
all population synthesis models, even when this is only implicit in the
association of fundamental stellar parameters with empirical spectral
library stars. With its near-ultraviolet to near-infrared coverage, the
X-shooter Spectral Library (XSL) allows us to examine to what extent
models succeed in reproducing stellar energy distributions (SEDs)
and stellar absorption line spectra simultaneously. Methods:
As a first example, this study compares the stellar spectra of XSL with
those of the Göttingen Spectral Library, which are based on the PHOENIX
synthesis code. The comparison was carried out both separately in the
three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and
jointly across the whole spectrum. We did not discard the continuum in
these comparisons; only reddening was allowed to modify the SEDs of the
models. Results: When adopting the stellar parameters published
with data release DR2 of XSL, we find that the SEDs of the models are
consistent with those of the data at temperatures above 5000 K. Below
5000 K, there are significant discrepancies in the SEDs. When leaving
the stellar parameters free to adjust, satisfactory representations
of the SEDs are obtained down to about 4000 K. However, in particular
below 5000 K and in the UVB spectral range, strong local residuals
associated with intermediate resolution spectral features are then seen;
the necessity of a compromise between reproducing the line spectra and
reproducing the SEDs leads to dispersion between the parameters favored
by various spectral ranges. We describe the main trends observed and
we point out localized offsets between the parameters preferred in
this global fit to the SEDs and the parameters in DR2. These depend
in a complex way on the position in the Hertzsprung-Russell diagram
(HRD). We estimate the effect of the offsets on bolometric corrections
as a function of position in the HRD and use this for a brief discussion
of their impact on the studies of stellar populations. A review of
the literature shows that comparable discrepancies are mentioned in
studies using other theoretical and empirical libraries.

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Title: A 3D radiative transfer framework: XII. Many-core, vector
and GPU methods
Authors: Hauschildt, P. H.; Baron, E.
2021A&C....3500450H Altcode: 2021arXiv210201734H
3D detailed radiative transfer is computationally taxing, since the
solution of the radiative transfer equation involves traversing the six
dimensional phase space of the 3D domain. With modern supercomputers
the hardware available for wallclock speedup is rapidly changing,
mostly in response to requirements to minimize the cost of electrical
power. Given the variety of modern computing architectures, we aim to
develop and adapt algorithms for different computing architectures to
improve performance on a wide variety of platforms. We implemented the
main time consuming kernels for solving 3D radiative transfer problems
for vastly different computing architectures using MPI, OpenMP,
OpenACC and vector algorithms. Adapted algorithms lead to massively
improved speed for all architectures, making extremely large model
calculations easily feasible. These calculations would have previously
been considered impossible or prohibitively expensive. Efficient use
of modern computing devices is entirely feasible, but unfortunately
requires the implementation of specialized algorithms for them.

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Title: Probing Spectral Formation of Type Ia Supernovae using PHOENIX
Authors: DerKacy, J.; Baron, E.; Branch, D.; Hoeflich, P.; Hauschildt,
P.; Brown, P.; Wang, L.
2021AAS...23730906D Altcode:
Radiative transfer simulations of Type Ia supernova spectra provide the
opportunity to compare theoretical models to observations, and to probe
the impact of individual physical variations on spectral formation. I
will discuss recent work using the generalized stellar atmospheres
code PHOENIX probing the UV spectra of SN 2011fe, including the first
known detections of C IV and Si IV in a UV supernova spectrum. The
impact of other spectral formation mechanisms on the UV are also
addressed, including photoionization edges, line blanketing by iron
group elements, and spectral temperature dependencies. Additionally
I will discuss work in progress focusing on understanding the origins
of why a subset of broad-lined Ia spectra appear to be Doppler-shifted
versions of core-normal spectra.

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Title: Studying the atmosphere of the close binary star system AADor
with PHOENIX/3D
Authors: Prodoehl, F.; Hauschildt, P.
2021AAS...23743806P Altcode:
Synthetic spectra from model atmospheres are frequently used in the
analysis of observed spectroscopic and photometric data. For the
most part, the models are sufficiently detailed to test the current
theoretical understanding of stellar and sub-stellar mass objects at
various stages in their evolution. However, the vast majority of model
atmospheres are constructed under the assumption that the nearest
stellar neighbor is so far away that it can be safely ignored. This
assumption, while safe for most stars, fails for many short period
binaries. A number of binary systems have orbital separations small
enough so that one of the binary members is significantly heated by its
companion. In order for synthetic spectra to be useful in such cases,
the standard "isolated" modeling approach must be replaced by one that
includes the effects of irradiation. The AADor system is an excellent
example of a well-studied non-mass transferring post-common envelope
binary system. Its members are a sdOB-type primary and an extremely low
mass secondary. We investigate how several PHOENIX/1D models combined
to a 1.5D model can represent the AA Dor secondary and compare these
results to a PHOENIX/3D model that is able to include 3D effects like
transverse radiation and transmission of light close to the terminator.

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Title: Time series of optical spectra of Nova V659 Sct
Authors: Jack, Dennis; Schröder, Klaus-Peter; Eenens, Philippe;
Wolter, Uwe; González-Pérez, José Nicolás.; Schmitt, Jürgen
H. M. M.; Hauschildt, Peter H.
2020AN....341..781J Altcode: 2020arXiv200614052J
With our robotic 1.2 m TIGRE telescope, we were able to obtain eight
optical spectra with intermediate resolution (R ≈ 20,000) of the
Nova V659 Sct during different phases of its outburst. We present a
list of the lines found in the Nova spectra. The most common features
are H I, O I, Na I, Fe II, and Ca II. Studying the spectral evolution
of the strong features, we found that the absorption features move
to higher expansion velocities before disappearing, and the emission
features show (different) asymmetries. Because of the intermediate
spectral resolution, we identified and analyzed the interstellar
medium absorption features present in the spectra. We detected atomic
absorption features of Na I and Ca II. The sodium D lines show more
complex substructures with three main absorption features at a velocity
of around -10, 30, and 85 km s-1. We identified several
diffuse interstellar bands (DIBs) in the Nova V659 Sct spectra and
determined their velocities and equivalent widths.

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Title: Ultraviolet Line Identifications and Spectral Formation Near
Max Light in Type Ia Supernova 2011fe
Authors: DerKacy, James M.; Baron, E.; Branch, David; Hoeflich, Peter;
Hauschildt, Peter; Brown, Peter J.; Wang, Lifan
2020ApJ...901...86D Altcode: 2020arXiv200804402D
We present ultraviolet line identifications of near maximum-light
Hubble Space Telescope observations of SN 2011fe using synthetic
spectra generated from both SYNOW and PHOENIX. We find the spectrum
to be dominated by blends of iron group elements Fe, Co, and Ni
(as expected due to heavy line blanketing by these elements in the
UV) and for the first time identify lines from C IV and Si IV in a
supernova spectrum. We also find that classical delayed detonation
models of SNe Ia are able to accurately reproduce the flux levels of
SN 2011fe in the UV. Further analysis reveals that photionization
edges play an important role in feature formation in the far-UV,
and that temperature variations in the outer layers of the ejecta
significantly alter the Fe III/Fe II ratio producing large flux
changes in the far-UV and velocity shifts in mid-UV features. SN
2011fe is the best observed core-normal SNe Ia; therefore analysis
of its UV spectra shows the power of UV spectra in discriminating
between different metallicities and progenitor scenarios of SNe Ia,
due to the fact that the UV probes the outermost layers of the SN Ia,
which are most sensitive to metallicity and progenitor variations.

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Title: The CARMENES search for exoplanets around M dwarfs. The He
I infrared triplet lines in PHOENIX models of M 2-3 V stars
Authors: Hintz, D.; Fuhrmeister, B.; Czesla, S.; Schmitt,
J. H. M. M.; Schweitzer, A.; Nagel, E.; Johnson, E. N.; Caballero,
J. A.; Zechmeister, M.; Jeffers, S. V.; Reiners, A.; Ribas, I.; Amado,
P. J.; Quirrenbach, A.; Anglada-Escudé, G.; Bauer, F. F.; Béjar,
V. J. S.; Cortés-Contreras, M.; Dreizler, S.; Galadí-Enríquez,
D.; Guenther, E. W.; Hauschildt, P. H.; Kaminski, A.; Kürster, M.;
Lafarga, M.; López del Fresno, M.; Montes, D.; Morales, J. C.
2020A&A...638A.115H Altcode: 2020arXiv200506246H
The He I infrared (IR) line at a vacuum wavelength of 10 833 Å is a
diagnostic for the investigation of atmospheres of stars and planets
orbiting them. For the first time, we study the behavior of the He I
IR line in a set of chromospheric models for M-dwarf stars, whose much
denser chromospheres may favor collisions for the level population over
photoionization and recombination, which are believed to be dominant
in solar-type stars. For this purpose, we use published PHOENIX
models for stars of spectral types M2 V and M3 V and also compute new
series of models with different levels of activity following an ansatz
developed for the case of the Sun. We perform a detailed analysis of
the behavior of the He I IR line within these models. We evaluate the
line in relation to other chromospheric lines and also the influence
of the extreme ultraviolet (EUV) radiation field. The analysis of the
He I IR line strengths as a function of the respective EUV radiation
field strengths suggests that the mechanism of photoionization and
recombination is necessary to form the line for inactive models, while
collisions start to play a role in our most active models. Moreover,
the published model set, which is optimized in the ranges of the Na
I D2, Hα, and the bluest Ca II IR triplet line, gives an
adequate prediction of the He I IR line for most stars of the stellar
sample. Because especially the most inactive stars with weak He I IR
lines are fit worst by our models, it seems that our assumption of
a 100% filling factor of a single inactive component no longer holds
for these stars.

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Title: VizieR Online Data Catalog: GJ 3512 radial velocity and light
curves (Morales+, 2019)
Authors: Morales, J. C.; Mustill, A. J.; Ribas, I.; Davies, M. B.;
Reiners, A.; Bauer, F. F.; Kossakowski, D.; Herrero, E.; Rodriguez,
E.; Lopez-Gonzalez, M. J.; Rodriguez-Lopez, C.; Bejar, V. J. S.;
Gonzalez-Cuesta, L.; Luque, R.; Palle, E.; Perger, M.; Baroch,
D.; Johansen, A.; Klahr, H.; Mordasini, C.; Anglada-Escude, G.;
Caballero, J. A.; Cortes-Contreras, M.; Dreizler, S.; Lafarga, M.;
Nagel, E.; Passegger, V. M.; Reffert, S.; Rosich, A.; Schweitzer,
A.; Tal-Or, L.; Trifonov, T.; Zechmeister, M.; Quirrenbach, A.;
Amado, P. J.; Guenther, E. W.; Hagen, H. -J.; Henning, T.; Jeffers,
S. V.; Kaminski, A.; Kurster, M.; Montes, D.; Seifert, W.; Abellan,
F. J.; Abril, M.; Aceituno, J.; Aceituno, F. J.; Alonso-Floriano,
F. J.; Ammler-von Eiff, M.; Antona, R.; Arroyo-Torres, B.; Azzaro,
M.; Barrado, D.; Becerril-Jarque, S.; Benitez, D.; Berdinas, Z. M.;
Bergond, G.; Brinkmoller, M.; Del Burgo, C.; Burn, R.; Calvo-Ortega,
R.; Cano, J.; Cardenas, M. C.; Cardona Guillen, C.; Carro, J.; Casal,
E.; Casanova, V.; Casasayas-Barris, N.; Chaturvedi, P.; Cifuentes,
C.; Claret, A.; Colome, J.; Czesla, S.; Diez-Alonso, E.; Dorda, R.;
Emsenhuber, A.; Fernandez, M.; Fernandez-Martin, A.; Ferro, I. M.;
Fuhrmeister, B.; Galadi-Enriquez, D.; Gallardo Cava, I.; Garcia Vargas,
M. L.; Garcia-Piquer, A.; Gesa, L.; Gonzalez-Alvarez, E.; Gonzalez
Hernandez, J. I.; Gonzalez-Peinado, R.; Guardia, J.; Guijarro, A.;
de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.;
Hermelo, I.; Hernandez Arabi, R.; Hernandez, Otero F.; Hintz, D.;
Holgado, G.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kehr,
M.; Kemmer, J.; Kim, M.; Kluter, J.; Klutsch, A.; Labarga, F.; Labiche,
N.; Lalitha, S.; Lampon, M.; Lara, L. M.; Launhardt, R.; Lazaro,
F. J.; Lizon, J. -L.; Llamas, M.; Lodieu, N.; Lopez Del Fresno, M.;
Lopez Salas, J. F.; Lopez-Santiago, J.; Magan Madinabeitia, H.; Mall,
U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Martin,
E. L.; Martin-Fernandez, P.; Martin-Ruiz, S.; Martinez-Rodriguez,
H.; Marvin, C. J.; Mirabet, E.; Moya, A.; Naranjo, V.; Nelson, R. P.;
Nortmann, L.; Nowak, G.; Ofir, A.; Pascual, J.; Pavlov, A.; Pedraz,
S.; Perez Medialde, A. D.; Perez-Calpena, A.; Perryman, M. A. C.;
Rabaza, O.; Ramon Ballesta, A.; Rebolo, R.; Redondo, P.; Rix, H. -W.;
Rodler, F.; Rodriguez Trinidad, A.; Sabotta, S.; Sadegi, S.; Salz,
M.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.;
Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schafer, S.; Schlecker,
M.; Schmitt, J. H. M. M.; Schofer, P.; Solano, E.; Sota, A.; Stahl, O.;
Stock, S.; Stuber, T.; Sturmer, J.; Suarez, J. C.; Tabernero, H. M.;
Tulloch, S. M.; Veredas, G.; Vico-Linares, J. I.; Vilardell, F.;
Wagner, K.; Winkler, J.; Wolthoff, V.; Yan, F.; Zapatero Osorio, M. R.
2020yCatp021036502M Altcode:
These tables list the radial velocities measured with the
visual (VIS) and near-infrared (NIR) channels of the CARMENES
spectrograph (Quirrenbach et al. 2018SPIE10702E..0WQ), and the
stellar activity indices computed with SERVAL (Zechmeister et
al. 2018A&amp;A...609A..12Z). Photometry obtained from the Montsec,
Sierra Nevada, and las Cumbres observatories is also listed here as
used in the paper. (4 data files).

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Title: Ultraviolet Line Identifications in Near Max Light Spectra
of Type Ia Supernova 2011fe
Authors: DerKacy, J. M.; Baron, E.; Branch, D.; Hoeflich, P.;
Hauschildt, P.
2020AAS...23527627D Altcode:
We present ultraviolet line identifications of near maximum-light
HST observations of SN 2011fe using synthetic spectra generated
from both SYNOW and PHOENIX. We find the spectrum to be dominated
by blends of iron group elements Fe, Co, and Ni (as expected due to
the heavy line blanketing caused by these elements in the UV) and
selected ions of intermediate mass elements, including C IV, Si IV,
and Mg II. We also examine the abundances of these highly ionized
IME species and their distribution in velocity space. Additionally,
we find that classical DDT models of Type Ia supernovae are able to
accurately reproduce the flux levels of SN 2011fe in the UV. Since SN
2011fe is the best observed core-normal SNe Ia, analysis of UV spectra
shows strong promise in discriminating between different metallicities
and progenitor scenarios of Type Ia supernovae. This is due to the
fact that the UV probes the outermost layers of the Type Ia supernova,
which are most sensitive to metallicity and progenitor variations.

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Title: Predicting the Extreme Ultraviolet Radiation Environment of
Exoplanets around Low-mass Stars: GJ 832, GJ 176, and GJ 436
Authors: Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya L.;
Hauschildt, Peter H.; Baron, E.; Fuhrmeister, Birgit
2019ApJ...886...77P Altcode: 2019arXiv191008053P
Correct estimates of stellar extreme ultraviolet (EUV; 100-1170 Å)
flux are important for studying the photochemistry and stability of
exoplanet atmospheres, as EUV radiation ionizes hydrogen and contributes
to the heating, expansion, and potential escape of a planet’s upper
atmosphere. Contamination from interstellar hydrogen makes observing
EUV emission from M stars particularly difficult, and impossible
past 100 pc, and necessitates other means to predict the flux in this
wavelength regime. We present EUV-infrared (100 Å-5.5 μm) synthetic
spectra computed with the PHOENIX atmospheric code of three early M
dwarf planet hosts: GJ 832 (M1.5 V), GJ 176 (M2.5 V), and GJ 436 (M3.5
V). These one-dimensional, semi-empirical, non-local thermodynamic
equilibrium models include simple temperature prescriptions for the
stellar chromosphere and transition region, from where ultraviolet
(100-3008 Å) fluxes originate. We guide our models with Hubble Space
Telescope far- and near-UV spectra and discuss the ability to constrain
these models using Galaxy Evolution Explorer UV photometry. Our models
closely reproduce the observations and predict the unobservable EUV
spectrum at a wavelength resolution of &lt;0.1 Å. The temperature
profiles that best reproduce the observations for all three stars
are described by nearly the same set of parameters, suggesting that
early M-type stars may have similar thermal structures in their upper
atmospheres. With an impending UV observation gap and the scarcity of
observed EUV spectra for stars less luminous and more distant than the
Sun, upper atmosphere models such as these are important for providing
realistic spectra across short wavelengths and for advancing our
understanding of the effects of radiation on planets orbiting M stars.

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Title: A giant exoplanet orbiting a very-low-mass star challenges
planet formation models
Authors: Morales, J. C.; Mustill, A. J.; Ribas, I.; Davies, M. B.;
Reiners, A.; Bauer, F. F.; Kossakowski, D.; Herrero, E.; Rodríguez,
E.; López-González, M. J.; Rodríguez-López, C.; Béjar, V. J. S.;
González-Cuesta, L.; Luque, R.; Pallé, E.; Perger, M.; Baroch,
D.; Johansen, A.; Klahr, H.; Mordasini, C.; Anglada-Escudé, G.;
Caballero, J. A.; Cortés-Contreras, M.; Dreizler, S.; Lafarga, M.;
Nagel, E.; Passegger, V. M.; Reffert, S.; Rosich, A.; Schweitzer,
A.; Tal-Or, L.; Trifonov, T.; Zechmeister, M.; Quirrenbach, A.;
Amado, P. J.; Guenther, E. W.; Hagen, H. -J.; Henning, T.; Jeffers,
S. V.; Kaminski, A.; Kürster, M.; Montes, D.; Seifert, W.; Abellán,
F. J.; Abril, M.; Aceituno, J.; Aceituno, F. J.; Alonso-Floriano,
F. J.; Ammler-von Eiff, M.; Antona, R.; Arroyo-Torres, B.; Azzaro,
M.; Barrado, D.; Becerril-Jarque, S.; Benítez, D.; Berdiñas, Z. M.;
Bergond, G.; Brinkmöller, M.; del Burgo, C.; Burn, R.; Calvo-Ortega,
R.; Cano, J.; Cárdenas, M. C.; Cardona Guillén, C.; Carro, J.; Casal,
E.; Casanova, V.; Casasayas-Barris, N.; Chaturvedi, P.; Cifuentes,
C.; Claret, A.; Colomé, J.; Czesla, S.; Díez-Alonso, E.; Dorda, R.;
Emsenhuber, A.; Fernández, M.; Fernández-Martín, A.; Ferro, I. M.;
Fuhrmeister, B.; Galadí-Enríquez, D.; Gallardo Cava, I.; García
Vargas, M. L.; Garcia-Piquer, A.; Gesa, L.; González-Álvarez,
E.; González Hernández, J. I.; González-Peinado, R.; Guàrdia,
J.; Guijarro, A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.;
Hedrosa, R. P.; Hermelo, I.; Hernández Arabi, R.; Hernández Otero,
F.; Hintz, D.; Holgado, G.; Huber, A.; Huke, P.; Johnson, E. N.;
de Juan, E.; Kehr, M.; Kemmer, J.; Kim, M.; Klüter, J.; Klutsch,
A.; Labarga, F.; Labiche, N.; Lalitha, S.; Lampón, M.; Lara, L. M.;
Launhardt, R.; Lázaro, F. J.; Lizon, J. -L.; Llamas, M.; Lodieu,
N.; López del Fresno, M.; López Salas, J. F.; López-Santiago, J.;
Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil,
E.; Marín Molina, J. A.; Martín, E. L.; Martín-Fernández, P.;
Martín-Ruiz, S.; Martínez-Rodríguez, H.; Marvin, C. J.; Mirabet,
E.; Moya, A.; Naranjo, V.; Nelson, R. P.; Nortmann, L.; Nowak, G.;
Ofir, A.; Pascual, J.; Pavlov, A.; Pedraz, S.; Pérez Medialdea, D.;
Pérez-Calpena, A.; Perryman, M. A. C.; Rabaza, O.; Ramón Ballesta,
A.; Rebolo, R.; Redondo, P.; Rix, H. -W.; Rodler, F.; Rodríguez
Trinidad, A.; Sabotta, S.; Sadegi, S.; Salz, M.; Sánchez-Blanco,
E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.;
Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schlecker, M.; Schmitt,
J. H. M. M.; Schöfer, P.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.;
Stuber, T.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tulloch,
S. M.; Veredas, G.; Vico-Linares, J. I.; Vilardell, F.; Wagner, K.;
Winkler, J.; Wolthoff, V.; Yan, F.; Zapatero Osorio, M. R.
2019Sci...365.1441M Altcode: 2019arXiv190912174M
Surveys have shown that super-Earth and Neptune-mass exoplanets are more
frequent than gas giants around low-mass stars, as predicted by the core
accretion theory of planet formation. We report the discovery of a giant
planet around the very-low-mass star GJ 3512, as determined by optical
and near-infrared radial-velocity observations. The planet has a minimum
mass of 0.46 Jupiter masses, very high for such a small host star,
and an eccentric 204-day orbit. Dynamical models show that the high
eccentricity is most likely due to planet-planet interactions. We use
simulations to demonstrate that the GJ 3512 planetary system challenges
generally accepted formation theories, and that it puts constraints
on the planet accretion and migration rates. Disk instabilities may
be more efficient in forming planets than previously thought.

---------------------------------------------------------
Title: Endeavours towards precise M-dwarf properties: Activity robust
multi-line modeling in the visual and near-infrared
Authors: Passegger, Vera Maria; Schweitzer, Andreas; Shulyak,
Denis; Nagel, Evangelos; Hauschildt, Peter H.; Reiners, Ansgar;
Amado, Pedro J.; Caballero, José A.; Cortés-Contreras, Miriam;
Domínguez-Fernández, Alejandro J.; Montes, David; Quirrenbach,
Andreas; Ribas, Ignasi
2019ESS.....433301P Altcode:
A precise characterisation of planet-hosting stars is very important to
derive and constrain the physical properties of orbiting planets. The
CARMENES instrument, which is searching for habitable planets around
M dwarfs, provides us with high-resolution spectra in the visual
(0.52-0.96 μm) and near-infrared wavelength range (0.96-1.71
μm). We fit the most recent PHOENIX-SESAM stellar atmosphere
models simultaneously to both wavelength ranges to determine
effective temperature, surface gravity, and metallicity for 282 M
dwarfs. With these temperatures we also derive stellar masses and
radii using luminosities and Gaia DR2 parallaxes. Although stellar
activity is widely unconsidered in stellar parameter determination,
we show the importance of taking into account this property by
carefully selecting magnetically insensitive lines, especially for
the near-infrared wavelength range. For the first time, we directly
compare stellar parameters such as effective temperature, surface
gravity, and metallicity derived from multiple wavelength ranges for
the same spectra. We recommend using a combination of the visual and
near-infrared wavelength ranges for parameter determination in order
to maximise the amount of spectral information and minimise possible
effects due to model imperfections.

---------------------------------------------------------
Title: The CARMENES search for exoplanets around M
dwarfs. Photospheric parameters of target stars from high-resolution
spectroscopy. II. Simultaneous multiwavelength range modeling of
activity insensitive lines
Authors: Passegger, V. M.; Schweitzer, A.; Shulyak, D.; Nagel, E.;
Hauschildt, P. H.; Reiners, A.; Amado, P. J.; Caballero, J. A.;
Cortés-Contreras, M.; Domínguez-Fernández, A. J.; Quirrenbach,
A.; Ribas, I.; Azzaro, M.; Anglada-Escudé, G.; Bauer, F. F.; Béjar,
V. J. S.; Dreizler, S.; Guenther, E. W.; Henning, T.; Jeffers, S. V.;
Kaminski, A.; Kürster, M.; Lafarga, M.; Martín, E. L.; Montes, D.;
Morales, J. C.; Schmitt, J. H. M. M.; Zechmeister, M.
2019A&A...627A.161P Altcode: 2019arXiv190700807P
We present precise photospheric parameters of 282 M dwarfs
determined from fitting the most recent version of PHOENIX models to
high-resolution CARMENES spectra in the visible (0.52-0.96 μm) and NIR
wavelength range (0.96-1.71 μm). With its aim to search for habitable
planets around M dwarfs, several planets of different masses have
been detected. The characterization of the target sample is important
for the ability to derive and constrain the physical properties of any
planetary systems that are detected. As a continuation of previous work
in this context, we derived the fundamental stellar parameters effective
temperature, surface gravity, and metallicity of the CARMENES M-dwarf
targets from PHOENIX model fits using a χ2 method. We
calculated updated PHOENIX stellar atmosphere models that include a
new equation of state to especially account for spectral features
of low-temperature stellar atmospheres as well as new atomic and
molecular line lists. We show the importance of selecting magnetically
insensitive lines for fitting to avoid effects of stellar activity
in the line profiles. For the first time, we directly compare stellar
parameters derived from multiwavelength range spectra, simultaneously
observed for the same star. In comparison with literature values we
show that fundamental parameters derived from visible spectra and
visible and NIR spectra combined are in better agreement than those
derived from the same spectra in the NIR alone. Full Tables
B.1 and B.2 are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A161">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A161</A>

---------------------------------------------------------
Title: The CARMENES search for exoplanets around M dwarfs. Two
temperate Earth-mass planet candidates around Teegarden's Star
Authors: Zechmeister, M.; Dreizler, S.; Ribas, I.; Reiners, A.;
Caballero, J. A.; Bauer, F. F.; Béjar, V. J. S.; González-Cuesta,
L.; Herrero, E.; Lalitha, S.; López-González, M. J.; Luque, R.;
Morales, J. C.; Pallé, E.; Rodríguez, E.; Rodríguez López, C.;
Tal-Or, L.; Anglada-Escudé, G.; Quirrenbach, A.; Amado, P. J.; Abril,
M.; Aceituno, F. J.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von
Eiff, M.; Antona Jiménez, R.; Anwand-Heerwart, H.; Arroyo-Torres,
B.; Azzaro, M.; Baroch, D.; Barrado, D.; Becerril, S.; Benítez,
D.; Berdiñas, Z. M.; Bergond, G.; Bluhm, P.; Brinkmöller, M.;
del Burgo, C.; Calvo Ortega, R.; Cano, J.; Cardona Guillén, C.;
Carro, J.; Cárdenas Vázquez, M. C.; Casal, E.; Casasayas-Barris,
N.; Casanova, V.; Chaturvedi, P.; Cifuentes, C.; Claret, A.; Colomé,
J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Dorda, R.;
Fernández, M.; Fernández-Martín, A.; Fuhrmeister, B.; Fukui, A.;
Galadí-Enríquez, D.; Gallardo Cava, I.; Garcia de la Fuente, J.;
Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Góngora Rueda, J.;
González-Álvarez, E.; González Hernández, J. I.; González-Peinado,
R.; Grözinger, U.; Guàrdia, J.; Guijarro, A.; de Guindos, E.;
Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.;
Henning, T.; Hermelo, I.; Hernández Arabi, R.; Hernández Castaño,
L.; Hernández Otero, F.; Hintz, D.; Huke, P.; Huber, A.; Jeffers,
S. V.; Johnson, E. N.; de Juan, E.; Kaminski, A.; Kemmer, J.; Kim,
M.; Klahr, H.; Klein, R.; Klüter, J.; Klutsch, A.; Kossakowski, D.;
Kürster, M.; Labarga, F.; Lafarga, M.; Llamas, M.; Lampón, M.; Lara,
L. M.; Launhardt, R.; Lázaro, F. J.; Lodieu, N.; López del Fresno,
M.; López-Puertas, M.; López Salas, J. F.; López-Santiago, J.;
Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil,
E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.;
Martín-Fernández, P.; Martín-Ruiz, S.; Marvin, C. J.; Mirabet,
E.; Montañés-Rodríguez, P.; Montes, D.; Moreno-Raya, M. E.;
Nagel, E.; Naranjo, V.; Narita, N.; Nortmann, L.; Nowak, G.; Ofir,
A.; Oshagh, M.; Panduro, J.; Parviainen, H.; Pascual, J.; Passegger,
V. M.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea,
D.; Perger, M.; Perryman, M. A. C.; Rabaza, O.; Ramón Ballesta, A.;
Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode, P.; Rix,
H. -W.; Rodler, F.; Rodríguez Trinidad, A.; Rosich, A.; Sadegi, S.;
Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.;
Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schmitt,
J. H. M. M.; Schöfer, P.; Schweitzer, A.; Seifert, W.; Shulyak, D.;
Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Strachan, J. B. P.; Stuber,
T.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tala Pinto, M.;
Trifonov, T.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner,
K.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2019A&A...627A..49Z Altcode: 2019arXiv190607196Z
Context. Teegarden's Star is the brightest and one of the nearest
ultra-cool dwarfs in the solar neighbourhood. For its late spectral
type (M7.0 V), the star shows relatively little activity and is
a prime target for near-infrared radial velocity surveys such as
CARMENES. Aims: As part of the CARMENES search for exoplanets
around M dwarfs, we obtained more than 200 radial-velocity measurements
of Teegarden's Star and analysed them for planetary signals. 
Methods: We find periodic variability in the radial velocities of
Teegarden's Star. We also studied photometric measurements to rule
out stellar brightness variations mimicking planetary signals. 
Results: We find evidence for two planet candidates, each with 1.1
M⊕ minimum mass, orbiting at periods of 4.91 and 11.4 d,
respectively. No evidence for planetary transits could be found in
archival and follow-up photometry. Small photometric variability is
suggestive of slow rotation and old age. Conclusions: The two
planets are among the lowest-mass planets discovered so far, and they
are the first Earth-mass planets around an ultra-cool dwarf for which
the masses have been determined using radial velocities. Tables
D.1 and D.2 are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A49">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A49</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: CARMENES stars multi wavelength
measurements (Passegger+, 2019)
Authors: Passegger, V. M.; Schweitzer, A.; Shulyak, D.; Nagel, E.;
Hauschildt, P. H.; Reiners, A.; Amado, P. J.; Caballero, J. A.;
Cortes-Contreras, M.; Dominguez-Fernandez, A. J.; Quirrenbach,
A.; Ribas, I.; Azarro, M.; Anglada-Escude, G.; Bauer, F. F.; Bejar,
V. J. S.; Dreizler, S.; Guenther, E. W.; Henning, T.; Jeffers, S. V.;
Kaminski, A.; Kuerster, M.; Lafarga, M.; Martin, E. L.; Montes, D.;
Morales, J. C.; Schmidt, J. H. M. M.; Zechmeister, M.
2019yCat..36270161P Altcode:
We present basic photospheric parameters of 282 M dwarfs within
the CARMENES survey in the visible and near-infrared wavelength
ranges. In table_b1 we provide Carmencita identifier (Karmn), Simbad
name, equatorial coordinates, spectral type, rotational velocity,
assumed age, and an activity flag for each star in our sample. In
table_b2 we give effective temperature, surface gravity and [Fe/H]
for each star in different wavelength ranges (VIS+NIR, NIR, and VIS),
together with their errors. (2 data files).

---------------------------------------------------------
Title: A massively non-LTE model atmosphere for Sirius A
Authors: Aufdenberg, Jason P.; Acosta, Allison; Hauschildt, Peter
2019AAS...23410802A Altcode:
Elemental abundances in the atmosphere of Sirius A reveal a history of
nucleosynthesis. Sirius A has tightly constrained fundamental parameters
due to its orbit with Sirius B, a measured interferometric diameter, and
a precise parallax. Its slow rotation and apparent lack of atmospheric
convection suggest one-dimensional model atmospheres should be a good
approximation. Recent abundance analyses of Sirius A from Landstreet
(2011) and Cowley et al. (2016) have employed local thermodynamic
equilibrium (LTE) models in comparison to high-resolution spectra
from the Hubble Space Telescope Imaging Spectrograph (HST/STIS),
the Goddard High Resolution Spectrograph (GHRS), and the Very Large
Telescope Ultraviolet Visible Echelle Spectrograph (VLT/UVES). In order
to perform an abundance analysis for Sirius A that does not assume
LTE, we have employed the PHOENIX model atmosphere code to compute 1-D
non-LTE models and spectra. These models treat 194 species, 34976 levels
and 600676 transitions in non-LTE for several ions of all elements from
hydrogen to lead except Se, Br, Kr, Sb, Te, I, Xe, Pt, Au, Tc, and Pm
to further constrain Sirius A's elemental abundances. We have thus
far compared our non-LTE abundance results with literature values for 30
elements and find six elements (N, Na, Cu, Mo, Ba, Os) have abundances
which differ by more than 2 standard deviations ( 0.6 dex or more)
from literature values. These results appear to differ from previous
work for three reasons: (1) the latest oscillator strengths from Kurucz
(2014) may differ significantly (2 to 10 times) from earlier values
for specific lines and (2) non-LTE models show enhanced ionization
of trace species relative to LTE which depletes these species and
elevates the abundance needed to match the observed spectrum, and (3)
non-LTE departure coefficient values for specific lines may different
significantly from unity. We also find our model for Sirius A provides
a good match to the observed spectral energy distribution in absolute
units between 100 nm to 1 cm based on recent observations obtained by
White et al. (2019) with ALMA, GBT, and the VLA.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Teegarden's Star RV and Hα curves
(Zechmeister+, 2019)
Authors: Zechmeister, M.; Dreizler, M.; Ribas, I.; Reiners, A.;
Caballero, J. A.; Bauer, F. F.; Bejar, V. J. S.; Gonzalez-Cuesta, L.;
Herrero, E.; Lalitha, S.; Lopez-Gonzalez, M. J.; Luque, R.; Morales,
J. C.; Palle, E.; Rodriguez, E.; Rodriguez Lopez, C.; Tal-Or, L.;
Anglada-Escude, G.; Quirrenbach, A.; Amado, P. J.; Abril, M.; Aceituno,
F. J.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.;
Antona Jimenez, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro,
M.; Baroch, D.; Barrado, D.; Becerril, S.; Benitez, D.; Berdinas,
Z. M.; Bergond, G.; Bluhm, P.; Brinkmoeller, M.; Del Burgo, C.; Calvo
Ortega, R.; Cano, J.; Cardona Guillen, C.; Carro, J.; Cardenas Vazquez,
M. C.; Casal, E.; Casasayas-Barris, N.; Casanova, V.; Chaturvedi, P.;
Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras, M.; Czesla,
S.; Diez-Alonso, E.; Dorda, R.; Fernandez, M.; Fernandez-Martin,
A.; Fuhrmeister, B.; Fukui, A.; Galadi-Enriquez, D.; Gallardo Cava,
I.; Garcia de La Fuente, J.; Garcia-Piquer, A.; Garcia Vargas, M. L.;
Gesa, L.; Gongora Rueda, J.; Gonzalez-Alvarez, E.; Gonzalez Hernandez,
J. I.; Gonzalez-Peinado, R.; Groezinger, U.; Guardia, J.; Guijarro,
A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa,
R. P.; Helmling, J.; Henning, T.; Hermelo, I.; Hernandez Arabi, R.;
Hernandez Castano, L.; Hernandez, Otero F.; Hintz, D.; Huke, P.;
Huber, A.; Jeffers, S. V.; Johnson, E. N.; de Juan, E.; Kaminski,
A.; Kemmer, J.; Kim, M.; Klahr, H.; Klein, R.; Klueter, J.; Klutsch,
A.; Kossakowski, D.; Kuerster, M.; Labarga, F.; Lafarga, M.; Llamas,
M.; Lampon, M.; Lara, L. M.; Launhardt, R.; Lazaro, F. J.; Lodieu,
N.; Lopez Del Fresno, M.; Lopez-Puertas, M.; Lopez Salas, J. F.;
Lopez-Santiago, J.; Magan Madinabeitia, H.; Mall, U.; Mancini, L.;
Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.;
Martin, E. L.; Martin-Fernandez, P.; Martin-Ruiz, S.; Marvin, C. J.;
Mirabet, E.; Montanes-Rodriguez, P.; Montes, D.; Moreno-Raya, M. E.;
Nagel, E.; Naranjo, V.; Narita, N.; Nortmann, L.; Nowak, G.; Ofir,
A.; Oshagh, M.; Panduro, J.; Parviainen, H.; Pascual, J.; Passegger,
V. M.; Pavlov, A.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea,
D.; Perger, M.; Perryman, M. A. C.; Rabaza, O.; Ramon Ballesta,
A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode, P.;
Rix, H. -W.; Rodler, F.; Rodriguez Trinidad, A.; Rosich, A.; Sadegi,
S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.;
Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schaefer, S.; Schmitt,
J. H. M. M.; Schoefer, P.; Schweitzer, A.; Seifert, W.; Shulyak,
D.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Strachan, J. B. P.;
Stuber, T.; Stuermer, J.; Suarez, J. C.; Tabernero, H. M.; Tala Pinto,
M.; Trifonov, T.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.;
Wagner, K.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2019yCat..36270049Z Altcode:
Time series for radial velocities and activity indicators of Teegarden's
Star from CARMENES VIS and NIR spectrograph are presented. See
Zechmeister et al. (2017A&amp;A...609A..12Z) for a detailed description
of the parameters. (2 data files).

---------------------------------------------------------
Title: The MESAS Project: Long-wavelength Follow-up Observations of
Sirius A
Authors: White, Jacob Aaron; Aufdenberg, J.; Boley, A. C.; Devlin,
M.; Dicker, S.; Hauschildt, P.; Hughes, A. G.; Hughes, A. M.; Mason,
B.; Matthews, B.; Moór, A.; Mroczkowski, T.; Romero, C.; Sievers,
J.; Stanchfield, S.; Tapia, F.; Wilner, D.
2019ApJ...875...55W Altcode: 2019arXiv190303481W
Modeling the submillimeter to centimeter emission of stars is
challenging due to a lack of sensitive observations at these
long wavelengths. We launched an ongoing campaign to obtain new
observations entitled Measuring the Emission of Stellar Atmospheres at
Submillimeter/millimeter wavelengths (MESAS). Here we present Atacama
Large Millimeter/submillimeter Array, Green Bank Telescope, and Very
Large Array observations of Sirius A, the closest main-sequence A-type
star, that span from 1.4 to 9.0 mm. These observations complement our
previous millimeter data on Sirius A and are entirely consistent with
the PHOENIX stellar atmosphere models constructed to explain them. We
note that accurate models of long-wavelength emission from stars are
essential not only to understand fundamental stellar processes, but
also to determine the presence of dusty debris in spatially unresolved
observations of circumstellar disks.

---------------------------------------------------------
Title: The CARMENES search for exoplanets around M
dwarfs. Chromospheric modeling of M 2-3 V stars with PHOENIX
Authors: Hintz, D.; Fuhrmeister, B.; Czesla, S.; Schmitt, J. H. M. M.;
Johnson, E. N.; Schweitzer, A.; Caballero, J. A.; Zechmeister, M.;
Jeffers, S. V.; Reiners, A.; Ribas, I.; Amado, P. J.; Quirrenbach, A.;
Anglada-Escudé, G.; Bauer, F. F.; Béjar, V. J. S.; Cortés-Contreras,
M.; Dreizler, S.; Galadí-Enríquez, D.; Guenther, E. W.; Hauschildt,
P. H.; Kaminski, A.; Kürster, M.; Lafarga, M.; López del Fresno,
M.; Montes, D.; Morales, J. C.; Passegger, V. M.; Seifert, W.
2019A&A...623A.136H Altcode: 2019arXiv190203992H
Chromospheric modeling of observed differences in stellar activity
lines is imperative to fully understand the upper atmospheres of
late-type stars. We present one-dimensional parametrized chromosphere
models computed with the atmosphere code PHOENIX using an underlying
photosphere of 3500 K. The aim of this work is to model chromospheric
lines of a sample of 50 M2-3 dwarfs observed in the framework of the
CARMENES, the Calar Alto high-Resolution search for M dwarfs with
Exo-earths with Near-infrared and optical Echelle Spectrographs,
exoplanet survey. The spectral comparison between observed data and
models is performed in the chromospheric lines of Na I D2,
Hα, and the bluest Ca II infrared triplet line to obtain best-fit
models for each star in the sample. We find that for inactive stars a
single model with a VAL C-like temperature structure is sufficient to
describe simultaneously all three lines adequately. Active stars are
rather modeled by a combination of an inactive and an active model, also
giving the filling factors of inactive and active regions. Moreover, the
fitting of linear combinations on variable stars yields relationships
between filling factors and activity states, indicating that more
active phases are coupled to a larger portion of active regions on
the surface of the star.

---------------------------------------------------------
Title: Predicting the Extreme Ultraviolet Radiation Environment of
Exoplanets around Low-mass Stars: The TRAPPIST-1 System
Authors: Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya L.;
Hauschildt, Peter H.; Baron, E.
2019ApJ...871..235P Altcode: 2018arXiv181206159P
The high energy radiation environment around M dwarf stars strongly
impacts the characteristics of close-in exoplanet atmospheres, but these
wavelengths are difficult to observe due to geocoronal and interstellar
contamination. On account of these observational restrictions, a
stellar atmosphere model may be used to compute the stellar extreme
ultraviolet (EUV; 100-912 Å) spectrum. We construct semiempirical
nonlocal thermodynamic equilibrium model spectra of the ultracool M8
star TRAPPIST-1 that span EUV to infrared wavelengths (100 Å-2.5 μm)
using the atmosphere code PHOENIX. These upper atmosphere models contain
prescriptions for the chromosphere and transition region and include
newly added partial frequency redistribution capabilities. In the
absence of broadband UV spectral observations, we constrain our models
using Hubble Space Telescope Lyman α observations from TRAPPIST-1 and
Galaxy Evolution Explorer UV photometric detections from a set of old
M8 stars (&gt;1 Gyr). We find that calibrating the models using both
data sets separately yield similar far-ultraviolet and NUV fluxes,
and EUV fluxes that range from (1.32-17.4) × 10-14
ergs s-1 cm-2. The results from these models
demonstrate that the EUV emission is very sensitive to the temperature
structure in the transition region. Our lower activity models predict
EUV fluxes similar to previously published estimates derived from
semiempirical scaling relationships, while the highest activity model
predicts EUV fluxes a factor of 10 higher. Results from this study
support the idea that the TRAPPIST-1 habitable zone planets likely
do not have much liquid water on their surfaces due to the elevated
levels of high energy radiation emitted by the host star.

---------------------------------------------------------
Title: Stellar Emission as a Source of Flux Bias in Debris Disks
Authors: White, J. A.; Aufdenberg, J.; Boley, A. C.; Hauschildt, P.;
Hughes, A. M.; Matthews, B.; Moór, A.; Wilner, D. J.
2018ASPC..517..171W Altcode:
Our understanding of stellar atmospheres and our ability to infer
architectures of extrasolar planetary systems rely on understanding the
emission of stars at sub-millimeter to centimeter wavelengths. In this
chapter we describe how unconstrained stellar emission can interfere
with the accurate characterization of circumstellar debris. The
ngVLA is the only facility with the sensitivity that allows for the
observations of a broad range of stellar spectral types in a feasible
amount of time. The observations will enable the building and testing
of accurate models of stellar emission, which in turn are required
for evaluating both the occurrence and abundance of debris over the
proposed wavelength range of the ngVLA.

---------------------------------------------------------
Title: Science with an ngVLA: Stellar Emission as a Source of Flux
Bias in Debris Disks
Authors: White, Jacob Aaron; Aufdenberg, Jason; Boley, Aaron C.;
Hauschildt, Peter; Hughes, A. Meredith; Matthews, Brenda; Moór,
Attila; Wilner, David J.
2018arXiv181006565W Altcode:
Our understanding of stellar atmospheres and our ability to infer
architectures of extrasolar planetary systems rely on understanding the
emission of stars at submillimeter to centimeter wavelengths. In this
chapter we describe how unconstrained stellar emission can interfere
with the accurate characterization of circumstellar debris. The
ngVLA is the only facility with the sensitivity that allows for the
observations of a broad range of stellar spectral types in a feasible
amount of time. The observations will enable the building and testing
of accurate models of stellar emission, which in turn are required
for evaluating both the occurrence and abundance of debris over the
proposed wavelength range of the ngVLA

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Title: CARMENES: high-resolution spectra and precise radial velocities
in the red and infrared
Authors: Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.;
Caballero, J. A.; Seifert, W.; Aceituno, J.; Azzaro, M.; Baroch, D.;
Barrado, D.; Bauer, F.; Becerril, S.; Bèjar, V. J. S.; Benítez,
D.; Brinkmöller, M.; Cardona Guillén, C.; Cifuentes, C.; Colomé,
J.; Cortés-Contreras, M.; Czesla, S.; Dreizler, S.; Frölich, K.;
Fuhrmeister, B.; Galadí-Enríquez, D.; González Hernández, J. I.;
González Peinado, R.; Guenther, E. W.; de Guindos, E.; Hagen, H. -J.;
Hatzes, A. P.; Hauschildt, P. H.; Helmling, J.; Henning, Th.; Herbort,
O.; Hernández Castaño, L.; Herrero, E.; Hintz, D.; Jeffers, S. V.;
Johnson, E. N.; de Juan, E.; Kaminski, A.; Klahr, H.; Kürster,
M.; Lafarga, M.; Sairam, L.; Lampón, M.; Lara, L. M.; Launhardt,
R.; López del Fresno, M.; López-Puertas, M.; Luque, R.; Mandel,
H.; Marfil, E. G.; Martín, E. L.; Martín-Ruiz, S.; Mathar, R. J.;
Montes, D.; Morales, J. C.; Nagel, E.; Nortmann, L.; Nowak, G.; Pallé,
E.; Passegger, V. -M.; Pavlov, A.; Pedraz, S.; Pérez-Medialdea, D.;
Perger, M.; Rebolo, R.; Reffert, S.; Rodríguez, E.; Rodríguez López,
C.; Rosich, A.; Sabotta, S.; Sadegi, S.; Salz, M.; Sánchez-López,
A.; Sanz-Forcada, J.; Sarkis, P.; Schäfer, S.; Schiller, J.; Schmitt,
J. H. M. M.; Schöfer, P.; Schweitzer, A.; Shulyak, D.; Solano, E.;
Stahl, O.; Tala Pinto, M.; Trifonov, T.; Zapatero Osorio, M. R.; Yan,
F.; Zechmeister, M.; Abellán, F. J.; Abril, M.; Alonso-Floriano,
F. J.; Ammler-von Eiff, M.; Anglada-Escudé, G.; Anwand-Heerwart, H.;
Arroyo-Torres, B.; Berdiñas, Z. M.; Bergondy, G.; Blümcke, M.; del
Burgo, C.; Cano, J.; Carro, J.; Cárdenas, M. C.; Casal, E.; Claret,
A.; Díez-Alonso, E.; Doellinger, M.; Dorda, R.; Feiz, C.; Fernández,
M.; Ferro, I. M.; Gaisné, G.; Gallardo, I.; Gálvez-Ortiz, M. C.;
García-Piquer, A.; García-Vargas, M. L.; Garrido, R.; Gesa, L.;
Gómez Galera, V.; González-Álvarez, E.; González-Cuesta, L.;
Grohnert, S.; Grözinger, U.; Guàrdia, J.; Guijarro, A.; Hedrosa,
R. P.; Hermann, D.; Hermelo, I.; Hernández Arabí, R.; Hernández
Hernando, F.; Hidalgo, D.; Holgado, G.; Huber, A.; Huber, K.; Huke,
P.; Kehr, M.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Labarga,
F.; Labiche, N.; Lamert, A.; Laun, W.; Lázaro, F. J.; Lemke, U.;
Lenzen, R.; Llamas, M.; Lizon, J. -L.; Lodieu, N.; López González,
M. J.; López-Morales, M.; López Salas, J. F.; López-Santiago,
J.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Marín Molina,
J. A.; Martínez-Rodríguez, H.; Maroto Fernández, D.; Marvin, C. J.;
Mirabet, E.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Naranjo, V.;
Panduro, J.; Pascual, J.; Pérez-Calpena, A.; Perryman, M. A. C.;
Pluto, M.; Ramón, A.; Redondo, P.; Reinhart, S.; Rhode, P.; Rix,
H. -W.; Rodler, F.; Rohloff, R. -R.; Sánchez-Blanco, E.; Sánchez
Carrasco, M. A.; Sarmiento, L. F.; Schmidt, C.; Storz, C.; Strachan,
J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tal-Or, L.;
Tulloch, S. M.; Ulbrich, R. -G.; Veredas, G.; Vico Linares, J. L.;
Vidal-Dasilva, M.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff,
V.; Xu, W.; Zhao, Z.
2018SPIE10702E..0WQ Altcode:
The design and construction of CARMENES has been presented at previous
SPIE conferences. It is a next-generation radial-velocity instrument at
the 3.5m telescope of the Calar Alto Observatory, which was built by a
consortium of eleven Spanish and German institutions. CARMENES consists
of two separate échelle spectrographs covering the wavelength range
from 0.52 to 1.71μm at a spec-tral resolution of R &lt; 80,000, fed by
fibers from the Cassegrain focus of the telescope. CARMENES saw "First
Light" on Nov 9, 2015. During the commissioning and initial operation
phases, we established basic performance data such as throughput and
spectral resolution. We found that our hollow-cathode lamps are suitable
for precise wavelength calibration, but their spectra contain a number
of lines of neon or argon that are so bright that the lamps cannot be
used in simultaneous exposures with stars. We have therefore adopted
a calibration procedure that uses simultaneous star / Fabry Pérot
etalon exposures in combination with a cross-calibration between the
etalons and hollow-cathode lamps during daytime. With this strategy
it has been possible to achieve 1-2 m/s precision in the visible and
5-10 m/s precision in the near-IR; further improvements are expected
from ongoing work on temperature control, calibration procedures
and data reduction. Comparing the RV precision achieved in different
wavelength bands, we find a "sweet spot" between 0.7 and 0.8μm, where
deep TiO bands provide rich RV information in mid-M dwarfs. This is
in contrast to our pre-survey models, which predicted comparatively
better performance in the near-IR around 1μm, and explains in
part why our near-IR RVs do not reach the same precision level as
those taken with the visible spectrograph. We are now conducting a
large survey of 340 nearby M dwarfs (with an average distance of only
12pc), with the goal of finding terrestrial planets in their habitable
zones. We have detected the signatures of several previously known or
suspected planets and also discovered several new planets. We find
that the radial velocity periodograms of many M dwarfs show several
significant peaks. The development of robust methods to distinguish
planet signatures from activity-induced radial velocity jitter is
therefore among our priorities. Due to its large wavelength coverage,
the CARMENES survey is generating a unique data set for studies of M
star atmospheres, rotation, and activity. The spectra cover important
diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II
infrared triplet), as well as FeH lines, from which the magnetic field
can be inferred. Correlating the time series of these features with
each other, and with wavelength-dependent radial velocities, provides
excellent handles for the discrimination between planetary companions
and stellar radial velocity jitter. These data are also generating
new insight into the physical properties of M dwarf atmospheres, and
the impact of activity and flares on the habitability of M star planets.

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Title: VizieR Online Data Catalog: 324 CARMENES M dwarfs velocities
(Reiners+, 2018)
Authors: Reiners, A.; Zechmeister, M.; Caballero, J. A.; Ribas, I.;
Morales, J. C.; Jeffers, S. V.; Schofer, P.; Tal-Or, L.; Quirrenbach,
A.; Amado, P. J.; Kaminski, A.; Seifert, W.; Abril, M.; Aceituno,
J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.;
Anglada-Escude, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro,
M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril, S.; Bejar,
V. J. S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Blumcke, M.;
Brinkmoller, M.; Del Burgo, C.; Cano, J.; Cardenas Vazquez, M. C.;
Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras,
M.; Czesla, S.; Diez-Alonso, E.; Dreizler, S.; Feiz, C.; Fernandez, M.;
Ferro, I. M.; Fuhrmeister, B.; Galadi-Enriquez, D.; Garcia-Piquer, A.;
Garcia Vargas, M. L.; Gesa, L.; Gomez Galera, V.; Gonzalez Hernandez,
J. I.; Gonzalez-Peinado, R.; Grozinger, U.; Grohnert, S.; Guardia,
J.; Guenther, E. W.; Guijarro, A.; de Guindos, E.; Gutierrez-Soto,
J.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa,
R. P.; Helmling, J.; Henning, T.; Hermelo, I.; Hernandez Arabi, R.;
Hernandez Castano, L.; Hernandez Hernando, F.; Herrero, E.; Huber, A.;
Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein, R.; Kluter,
J.; Klutsch, A.; Kurster, M.; Lafarga, M.; Lamert, A.; Lampon, M.;
Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; Lopez
Del Fresno, M.; Lopez-Gonzalez, J.; Lopez-Puertas, M.; Lopez Salas,
J. F.; Lopez-Santiago, J.; Luque, R.; Magan Madinabeitia, H.; Mall,
U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto
Fernandez, D.; Martin, E. L.; Martin-Ruiz, S.; Marvin, C. J.; Mathar,
R. J.; Mirabet, E.; Montes, D.; Moreno-Raya, M. E.; Moya, A.; Mundt,
R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro,
R.; Palle, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pavlov,
A.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger,
M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo,
R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.;
Rodler, F.; Rodriguez, E.; Rodriguez-Lopez, C.; Rodriguez Trinidad,
A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.; Sanchez-Blanco, E.;
Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis,
P.; Sarmiento, L. F.; Schafer, S.; Schmitt, J. H. M. M.; Schiller, J.;
Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Sturmer,
J.; Suarez, J. C.; Tabernero, H. M.; Tala, M.; Trifonov, T.; Tulloch,
S. M.; Ulbrich, R. G.; Veredas, G.; Vico Linares, J. I.; Vilardell,
F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero
Osorio, M. R.
2018yCat..36120049R Altcode:
As part of the GTO agreement, we provide early access to one CARMENES
spectrum for each of our sample targets (Table B.1). They can be
downloaded from the CARMENES GTO Data Archive (Caballero et al., 2016,
in Observatory Operations: Strategies, Processes, and Systems VI,
Proc. SPIE, 9910, 99100E) (http://carmenes.cab.inta-csic.es) (1
data file).

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Title: MESAS: Measuring the Emission of Stellar Atmospheres at
Submillimeter/millimeter Wavelengths
Authors: White, Jacob Aaron; Aufdenberg, Jason; Boley, A. C.;
Hauschildt, Peter; Hughes, Meredith; Matthews, Brenda; Wilner, David
2018ApJ...859..102W Altcode: 2018arXiv180410206W
In the early stages of planet formation, small dust grains grow to
become millimeter-sized particles in debris disks around stars. These
disks can in principle be characterized by their emission at
submillimeter and millimeter wavelengths. Determining both the
occurrence and abundance of debris in unresolved circumstellar disks
of A-type main-sequence stars requires that the stellar photospheric
emission be accurately modeled. To better constrain the photospheric
emission for such systems, we present observations of Sirius A,
an A-type star with no known debris, from the James Clerk Maxwell
Telescope, Submillimeter Array, and Jansky Very Large Array at 0.45,
0.85, 0.88, 1.3, 6.7, and 9.0 mm. We use these observations to inform a
PHOENIX model of Sirius A’s atmosphere. We find the model provides
a good match to these data and can be used as a template for the
submillimeter/millimeter emission of other early A-type stars where
unresolved debris may be present. The observations are part of an
ongoing observational campaign entitled Measuring the Emission of
Stellar Atmospheres at Submillimeter/millimeter wavelengths.

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Title: Convection Enhances Magnetic Turbulence in AM CVn Accretion
Disks
Authors: Coleman, Matthew S. B.; Blaes, Omer; Hirose, Shigenobu;
Hauschildt, Peter H.
2018ApJ...857...52C Altcode: 2018arXiv180304381C
We present the results of local, vertically stratified, radiation
magnetohydrodynamic shearing-box simulations of magnetorotational
instability (MRI) turbulence for a (hydrogen poor) composition
applicable to accretion disks in AM CVn type systems. Many of these
accreting white dwarf systems are helium analogs of dwarf novae
(DNe). We utilize frequency-integrated opacity and equation-of-state
tables appropriate for this regime to accurately portray the relevant
thermodynamics. We find bistability of thermal equilibria in the
effective-temperature, surface-mass-density plane typically associated
with disk instabilities. Along this equilibrium curve (i.e., the
S-curve), we find that the stress to thermal pressure ratio α varied
with peak values of ∼0.15 near the tip of the upper branch. Similar
to DNe, we found enhancement of α near the tip of the upper branch
caused by convection; this increase in α occurred despite our choice
of zero net vertical magnetic flux. Two notable differences we find
between DN and AM CVn accretion disk simulations are that AM CVn
disks are capable of exhibiting persistent convection in outburst,
and ideal MHD is valid throughout quiescence for AM CVns. In contrast,
DNe simulations only show intermittent convection, and nonideal MHD
effects are likely important in quiescence. By combining our previous
work with these new results, we also find that convective enhancement
of the MRI is anticorrelated with mean molecular weight.

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Title: The CARMENES search for exoplanets around M
dwarfs. High-resolution optical and near-infrared spectroscopy of
324 survey stars
Authors: Reiners, A.; Zechmeister, M.; Caballero, J. A.; Ribas,
I.; Morales, J. C.; Jeffers, S. V.; Schöfer, P.; Tal-Or, L.;
Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Seifert, W.; Abril, M.;
Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona,
R.; Anglada-Escudé, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.;
Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril,
S.; Béjar, V. J. S.; Benítez, D.; Berdinas, Z. M.; Bergond,
G.; Blümcke, M.; Brinkmöller, M.; del Burgo, C.; Cano, J.;
Cárdenas Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.;
Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.;
Dreizler, S.; Feiz, C.; Fernández, M.; Ferro, I. M.; Fuhrmeister, B.;
Galadí-Enríquez, D.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa,
L.; Gómez Galera, V.; González Hernández, J. I.; González-Peinado,
R.; Grözinger, U.; Grohnert, S.; Guàrdia, J.; Guenther, E. W.;
Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H. -J.;
Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.;
Henning, Th.; Hermelo, I.; Hernández Arabí, R.; Hernández Castaño,
L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson,
E. N.; de Juan, E.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.;
Kürster, M.; Lafarga, M.; Lamert, A.; Lampón, M.; Lara, L. M.;
Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; López del Fresno,
M.; López-González, J.; López-Puertas, M.; López Salas, J. F.;
López-Santiago, J.; Luque, R.; Magán Madinabeitia, H.; Mall, U.;
Mancini, L.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto
Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C. J.;
Mathar, R. J.; Mirabet, E.; Montes, D.; Moreno-Raya, M. E.; Moya, A.;
Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir,
A.; Oreiro, R.; Pallé, E.; Panduro, J.; Pascual, J.; Passegger,
V. M.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea,
D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramón,
A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.;
Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López, C.;
Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.;
Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.;
Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schmitt,
J. H. M. M.; Schiller, J.; Schweitzer, A.; Solano, E.; Stahl, O.;
Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.;
Tala, M.; Trifonov, T.; Tulloch, S. M.; Ulbrich, R. G.; Veredas, G.;
Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff,
V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2018A&A...612A..49R Altcode: 2017arXiv171106576R
The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to
search for any orbiting planets. In this paper, we present the survey
sample by publishing one CARMENES spectrum for each M dwarf. These
spectra cover the wavelength range 520-1710 nm at a resolution of
at least R &gt;80 000, and we measure its RV, Hα emission, and
projected rotation velocity. We present an atlas of high-resolution
M-dwarf spectra and compare the spectra to atmospheric models. To
quantify the RV precision that can be achieved in low-mass stars over
the CARMENES wavelength range, we analyze our empirical information
on the RV precision from more than 6500 observations. We compare our
high-resolution M-dwarf spectra to atmospheric models where we determine
the spectroscopic RV information content, Q, and signal-to-noise
ratio. We find that for all M-type dwarfs, the highest RV precision can
be reached in the wavelength range 700-900 nm. Observations at longer
wavelengths are equally precise only at the very latest spectral types
(M8 and M9). We demonstrate that in this spectroscopic range, the large
amount of absorption features compensates for the intrinsic faintness
of an M7 star. To reach an RV precision of 1 m s-1 in very
low mass M dwarfs at longer wavelengths likely requires the use of a 10
m class telescope. For spectral types M6 and earlier, the combination
of a red visual and a near-infrared spectrograph is ideal to search
for low-mass planets and to distinguish between planets and stellar
variability. At a 4 m class telescope, an instrument like CARMENES has
the potential to push the RV precision well below the typical jitter
level of 3-4 m s-1.

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Title: The CARMENES search for exoplanets around M dwarfs . First
visual-channel radial-velocity measurements and orbital parameter
updates of seven M-dwarf planetary systems
Authors: Trifonov, T.; Kürster, M.; Zechmeister, M.; Tal-Or,
L.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Ribas, I.;
Reiners, A.; Reffert, S.; Dreizler, S.; Hatzes, A. P.; Kaminski, A.;
Launhardt, R.; Henning, Th.; Montes, D.; Béjar, V. J. S.; Mundt,
R.; Pavlov, A.; Schmitt, J. H. M. M.; Seifert, W.; Morales, J. C.;
Nowak, G.; Jeffers, S. V.; Rodríguez-López, C.; del Burgo, C.;
Anglada-Escudé, G.; López-Santiago, J.; Mathar, R. J.; Ammler-von
Eiff, M.; Guenther, E. W.; Barrado, D.; González Hernández, J. I.;
Mancini, L.; Stürmer, J.; Abril, M.; Aceituno, J.; Alonso-Floriano,
F. J.; Antona, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro,
M.; Baroch, D.; Bauer, F. F.; Becerril, S.; Benítez, D.; Berdiñas,
Z. M.; Bergond, G.; Blümcke, M.; Brinkmöller, M.; Cano, J.; Cárdenas
Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé,
J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Feiz, C.;
Fernández, M.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.;
Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Gómez Galera,
V.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guàrdia,
J.; Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen,
H. -J.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Hermelo, I.;
Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando,
F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E.; de Juan, E.; Kim,
M.; Klein, R.; Klüter, J.; Klutsch, A.; Lafarga, M.; Lampón, M.;
Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; López del Fresno, M.;
López-González, M. J.; López-Puertas, M.; López Salas, J. F.;
Luque, R.; Magán Madinabeitia, H.; Mall, U.; Mandel, H.; Marfil,
E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.;
Martín-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Moya, A.; Moreno-Raya,
M. E.; Nagel, E.; Naranjo, V.; Nortmann, L.; Ofir, A.; Oreiro, R.;
Pallé, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pedraz,
S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman,
M. A. C.; Pluto, M.; Rabaza, O.; Ramón, A.; Rebolo, R.; Redondo,
P.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez,
E.; Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.;
Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.;
Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schiller,
J.; Schöfer, P.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan,
J. B. P.; Suárez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.;
Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler,
J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2018A&A...609A.117T Altcode: 2017arXiv171001595T
Context. The main goal of the CARMENES survey is to find Earth-mass
planets around nearby M-dwarf stars. Seven M dwarfs included in the
CARMENES sample had been observed before with HIRES and HARPS and
either were reported to have one short period planetary companion (GJ
15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary
systems (GJ 581 and GJ 876). Aims: We aim to report new precise
optical radial velocity measurements for these planet hosts and test
the overall capabilities of CARMENES. Methods: We combined our
CARMENES precise Doppler measurements with those available from HIRES
and HARPS and derived new orbital parameters for the systems. Bona-fide
single planet systems were fitted with a Keplerian model. The multiple
planet systems were analyzed using a self-consistent dynamical model
and their best fit orbits were tested for long-term stability. 
Results: We confirm or provide supportive arguments for planets around
all the investigated stars except for GJ 15 A, for which we find that
the post-discovery HIRES data and our CARMENES data do not show a
signal at 11.4 days. Although we cannot confirm the super-Earth planet
GJ 15 Ab, we show evidence for a possible long-period (Pc =
7030-630+970 d) Saturn-mass (mcsini
= 51.8M⊕) planet around GJ 15 A. In addition, based
on our CARMENES and HIRES data we discover a second planet around
GJ 1148, for which we estimate a period Pc = 532.6 days,
eccentricity ec = 0.342 and minimum mass mcsini =
68.1M⊕. Conclusions: The CARMENES optical radial
velocities have similar precision and overall scatter when compared
to the Doppler measurements conducted with HARPS and HIRES. We
conclude that CARMENES is an instrument that is up to the challenge
of discovering rocky planets around low-mass stars. Based on
observations collected at the European Organisation for Astronomical
Research in the Southern Hemisphere under ESO programmes 072.C-0488,
072.C-0513, 074.C-0012, 074.C-0364, 075.D-0614, 076.C-0878, 077.C-0364,
077.C-0530, 078.C-0044, 078.C-0833, 079.C-0681, 183.C-0437, 60.A-9036,
082.C-0718, 183.C-0972, 085.C-0019, 087.C-0831, 191.C-0873. The
appendix tables are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A117">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A117</A>

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Title: The CARMENES search for exoplanets around M dwarfs. HD147379 b:
A nearby Neptune in the temperate zone of an early-M dwarf
Authors: Reiners, A.; Ribas, I.; Zechmeister, M.; Caballero, J. A.;
Trifonov, T.; Dreizler, S.; Morales, J. C.; Tal-Or, L.; Lafarga,
M.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Jeffers, S. V.;
Aceituno, J.; Béjar, V. J. S.; Guàrdia, J.; Guenther, E. W.; Hagen,
H. -J.; Montes, D.; Passegger, V. M.; Seifert, W.; Schweitzer, A.;
Cortés-Contreras, M.; Abril, M.; Alonso-Floriano, F. J.; Ammler-von
Eiff, M.; Antona, R.; Anglada-Escudé, G.; Anwand-Heerwart, H.;
Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer,
F. F.; Becerril, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.;
Blümcke, M.; Brinkmöller, M.; del Burgo, C.; Cano, J.; Cárdenas
Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé, J.;
Czesla, S.; Díez-Alonso, E.; Feiz, C.; Fernández, M.; Ferro, I. M.;
Fuhrmeister, B.; Galadí-Enríquez, D.; Garcia-Piquer, A.; García
Vargas, M. L.; Gesa, L.; Gómez Galera, V.; González Hernández,
J. I.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guijarro,
A.; de Guindos, E.; Gutiérrez-Soto, J.; Hatzes, A. P.; Hauschildt,
P. H.; Hedrosa, R. P.; Helmling, J.; Henning, Th.; Hermelo, I.;
Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando,
F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim,
M.; Klein, R.; Klüter, J.; Klutsch, A.; Kürster, M.; Labarga, F.;
Lamert, A.; Lampón, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen,
R.; Launhardt, R.; López del Fresno, M.; López-González, M. J.;
López-Puertas, M.; López Salas, J. F.; López-Santiago, J.; Luque,
R.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.;
Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín,
E. L.; Martín-Ruiz, S.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.;
Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Nagel, E.; Naranjo, V.;
Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro,
J.; Pascual, J.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez
Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza,
O.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.;
Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López,
C.; Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi,
S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López,
A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.;
Schmitt, J. H. M. M.; Schiller, J.; Schöfer, P.; Solano, E.; Stahl,
O.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.;
Tala, M.; Tulloch, S. M.; Ulbrich, R. -G.; Veredas, G.; Vico Linares,
J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.;
Yan, F.; Zapatero Osorio, M. R.
2018A&A...609L...5R Altcode: 2017arXiv171205797R
We report on the first star discovered to host a planet detected by
radial velocity (RV) observations obtained within the CARMENES survey
for exoplanets around M dwarfs. HD 147379 (V = 8.9 mag, M = 0.58 ±
0.08 M⊙), a bright M0.0 V star at a distance of 10.7 pc,
is found to undergo periodic RV variations with a semi-amplitude of
K = 5.1 ± 0.4 m s-1 and a period of P = 86.54 ± 0.06
d. The RV signal is found in our CARMENES data, which were taken
between 2016 and 2017, and is supported by HIRES/Keck observations
that were obtained since 2000. The RV variations are interpreted
as resulting from a planet of minimum mass mP sin i =
25 ± 2 M⊕, 1.5 times the mass of Neptune, with an
orbital semi-major axis a = 0.32 au and low eccentricity (e &lt;
0.13). HD 147379 b is orbiting inside the temperate zone around the
star, where water could exist in liquid form. The RV time-series and
various spectroscopic indicators show additional hints of variations
at an approximate period of 21.1 d (and its first harmonic), which
we attribute to the rotation period of the star. RV data
(Table A.1) are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/L5">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/L5</A>

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Title: VizieR Online Data Catalog: HD147379 b velocity curve
(Reiners+, 2018)
Authors: Reiners, A.; Ribas, I.; Zechmeister, M.; Caballero, J. A.;
Trifonov, T.; Dreizler, S.; Morales, J. C.; Tal-Or, L.; Lafarga,
M.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Jeffers, S. V.;
Aceituno, J.; Bejar, V. J. S.; Guardia, J.; Guenther, E. W.; Hagen,
H. -J.; Montes, D.; Passegger, V. M.; Seifert, W.; Schweitzer, A.;
Cortes-Contreras, M.; Abril, M.; Alonso-Floriano, F. J.; Ammler-von
Eiff, M.; Antona, R.; Anglada-Escude, G.; Anwand-Heerwart, H.;
Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.;
Becerril, S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Bluemcke,
M.; Brinkmoeller, M.; Del Burgo, C.; Cano, J.; Cardenas Vazquez,
M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Czesla, S.;
Diez-Alonso, E.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister,
B.; Galadi-Enriquez, D.; Garcia-Piquer, A.; Garcia Vargas, M. L.; Gesa,
L.; Gomez Galera, V.; Gonzalez Hernandez, J. I.; Gonzalez-Peinado,
R.; Groezinger, U.; Grohnert, S.; Guijarro, A.; de Guindos, E.;
Gutierrez-Soto, J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa,
R. P.; Helml!, Ing J.; H Enning, Th.; Hermelo, I.; Hernandez Arabi,
R.; Hernandez Castano, L.; Hernandez Hernando, F.; Herrero, E.;
Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein,
R.; Klueter, J.; Klutsch, A.; Kuerster, M.; Labarga, F.; Lamert, A.;
Lampon, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt,
R.; Lopez Del Fresno, M.; Lopez-Gonzalez, M. J.; Lopez-Puertas, M.;
Lopez Salas, J. F.; Lopez-Santiago, J.; Luque, R.; Magan Madinabeitia,
H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina,
J. A.; Maroto Fernandez, D.; Martin, E. L.; Martin-Ruiz, S.; Marvin,
C. J.; Mathar, R. J.; Mirabet, E.; Moreno-Raya, M. E.; Moya, A.;
Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.;
Oreiro, R.; Palle, E.; Panduro, J.; Pascual, J.; Pavlov, A.; Pedraz,
S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger, M.; Perryman,
M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo, R.; Redondo,
P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.;
Rodriguez, E.; Rodriguez-Lopez, C.; Rodriguez Trinidad, A.; Rohloff,
R. -R.; Rosich, A.; ! Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco,
M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento,
L. F.; Schaefer, S.; Schmitt, J. H. M. M.; Schiller, J.; Schoefer,
P.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Stuermer, J.; Suarez,
J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Ulbrich, R. -G.;
Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler,
J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2017yCat..36099005R Altcode:
We analyzed data from the CARMENES VIS channel and HIRES/Keck. The
CARMENES measurements were taken in the context of the CARMENES search
for exoplanets around M dwarfs. The CARMENES instrument consists of two
channels: the VIS channel obtains spectra at a resolution of R=94600 in
the wavelength range 520-960nm, while the NIR channel yields spectra of
R=80400 covering 960-1710nm. Both channels are calibrated in wavelength
with hollow-cathode lamps and use temperature- and pressure-stabilized
Fabry-Perot etalons to interpolate the wavelength solution and
simultaneously monitor the spectrograph drift during nightly operations
(Bauer et al., 2015A&amp;A...581A.117B). (1 data file).

---------------------------------------------------------
Title: VizieR Online Data Catalog: CARMENES radial velocity curves
of 7 M-dwarf (Trifonov+, 2018)
Authors: Trifonov, T.; Kuerster, M.; Zechmeister, M.; Tal-Or, L.;
Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners,
A.; Reffert, S.; Dreizler, S.; Hatzes, A. P.; Kaminski, A.; Launhardt,
R.; Henning, T.; Montes, D.; Bejar, V. J. S.; Mundt, R.; Pavlov,
A.; Schmitt, J. H. M. M.; Seifert, W.; Morales, J. C.; Nowak, G.;
Jeffers, S. V.; Rodriguez-Lopez, C.; Del Burgo, C.; Anglada-Escude,
G.; Lopez-Santiago, J.; Mathar, R. J.; Ammler-von Eiff, M.; Guenther,
E. W.; Barrado, D.; Gonzalez Hernandez, J. I.; Mancini, L.; Stuermer,
J.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Antona, R.;
Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.;
Bauer, F. F.; Becerril, S.; Benitez, D.; Berdinas, Z. M.; Bergond,
G.; Bluemcke, M.; Brinkmoeller, M.; Cano, J.; Cardenas Vazquez, M. C.;
Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras, M.;
Czesla, S.; Diez-Alonso, E.; Feiz, C.; Fernandez, M.; Ferro, I. M.;
Fuhrmeister, B.; Galadi-Enriquez, D.; Garcia-Piquer, A.; Garcia
Vargas, M. L.; Gesa, L.; Gomez Galera, V.; Gonzalez-Peinado, R.;
Groezinger, U.; Grohnert, S.; Guardia, J.; Guijarro, A.; de Guindos,
E.; Gutierrez-Soto, J.; Hagen, H. -J.; Hauschildt, P. H.; Hedrosa,
R. P.; Helmling, J.; Hermelo, I.; Hernandez Arabi, R.; Hernandez
Castano, L.; Hernandez Hernando, F.; Herrero, E.; Huber, A.; Huke, P.;
Johnson, E.; de Juan, E.; Kim, M.; Klein, R.; Klueter, J.; Klutsch, A.;
Lafarga, M.; Lampon, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen,
R.; Lopez Del Fresno, M.; Lopez-Gonzalez, J.; Lopez-Puertas, M.;
Lopez Salas, J. F.; Luque, R.; Magan Madinabeitia, H.; Mall, U.;
Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.;
Martin, E. L.; Martin-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Moya,
A.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Nortmann, L.; Ofir,
A.; Oreiro, R.; Palle, E.; Panduro, J.; Pascual, J.; Passegger,
V. M.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger,
M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo,
R.; Redondo, P.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.;
Rodriguez, E.; Rodriguez Trinidad, A.; Rohlo, R. -R.; Rosich, A.;
Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez,
A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schaefer, S.;
Schiller, J.; Schoefer, P.; Schweitzer, A.; Solano, E.; Stahl, O.;
Strachan, J. B. P.; Suarez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch,
S. M.; Veredas, G.; Vico Linares, J. I.; Vilardel, F.; Wagner, K.;
Winkler, J.; Woltho, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.
2017yCat..36090117T Altcode:
The two CARMENES spectrographs are grism cross-dispersed, white pupil,
echelle spectrograph working in quasi-Littrow mode using a two-beam,
two-slice image slicer. The visible spectrograph covers the wavelength
range from 0.52um to 1.05um with 61 orders, a resolving power of
R=94600, and a mean sampling of 2.8 pixels per resolution element. The data presented in this paper were taken during the early phase
of operation of the CARMENES visible-light spectrograph. (8
data files).

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Title: Optical and ultraviolet spectroscopic analysis of SN 2011fe
at late times
Authors: Friesen, Brian; Baron, E.; Parrent, Jerod T.; Thomas, R. C.;
Branch, David; Nugent, Peter E.; Hauschildt, Peter H.; Foley, Ryan
J.; Wright, Darryl E.; Pan, Yen-Chen; Filippenko, Alexei V.; Clubb,
Kelsey I.; Silverman, Jeffrey M.; Maeda, Keiichi; Shivvers, Isaac;
Kelly, Patrick L.; Cohen, Daniel P.; Rest, Armin; Kasen, Daniel
2017MNRAS.467.2392F Altcode: 2017MNRAS.tmp..243F; 2016arXiv160704784F
We present optical spectra of the nearby Type Ia supernova SN 2011fe
at 100, 205, 311, 349 and 578 d post-maximum light, as well as an
ultraviolet (UV) spectrum obtained with the Hubble Space Telescope at
360 d post-maximum light. We compare these observations with synthetic
spectra produced with the radiative transfer code phoenix. The day +100
spectrum can be well fitted with models that neglect collisional and
radiative data for forbidden lines. Curiously, including these data and
recomputing the fit yields a quite similar spectrum, but with different
combinations of lines forming some of the stronger features. At day +205
and later epochs, forbidden lines dominate much of the optical spectrum
formation; however, our results indicate that recombination, not
collisional excitation, is the most influential physical process driving
spectrum formation at these late times. Consequently, our synthetic
optical and UV spectra at all epochs presented here are formed almost
exclusively through recombination-driven fluorescence. Furthermore,
our models suggest that the UV spectrum even as late as day +360 is
optically thick and consists of permitted lines from several iron-peak
species. These results indicate that the transition to the 'nebular'
phase in Type Ia supernovae is complex and highly wavelength dependent.

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Title: Study of the variability of Nova V5668 Sgr, based on
high-resolution spectroscopic monitoring
Authors: Jack, D.; Robles Pérez, J. de J.; De Gennaro Aquino, I.;
Schröder, K. -P.; Wolter, U.; Eenens, P.; Schmitt, J. H. M. M.;
Mittag, M.; Hempelmann, A.; González-Pérez, J. N.; Rauw, G.;
Hauschildt, P. H.
2017AN....338...91J Altcode: 2017arXiv170201171J
We present results of our dense spectroscopic monitoring of Nova V5668
Sgr. Starting on March 19, 2015, only a few days after its discovery,
we have obtained a series of spectra with the Telescopio Internacional
en Guanajuato, Robótico y Espectroscópico telescope and its Heidelberg
extended range optical spectrograph échelle spectrograph, which offers
a resolution of R = 20,000 and covers the optical wavelength range
3,8008,800 Å. We performed a line identification of the discernible
features for four spectra, which are representative of the respective
phases in the light curve evolution of that nova. We simultaneously
analyzed the variations in the visual light curve and the corresponding
spectra of Nova V5668 Sgr. We found that, during the declining phases
of the nova, the absorption features in all hydrogen and many other
lines had shifted to higher expansion velocities of about -2,000 km
s-1. Conversely, during the rise toward the following
maximum, these observed absorption features had returned to lower
expansion velocities. We found that the absorption features of some
Fe II lines displayed the same behavior, but in addition disappeared
for a few days during some declining phases. Features of several N I
lines also disappeared, while new N II lines appeared in the emission
for a few days during some of the declining phases of the light curve
of Nova V5668 Sgr. The shape of the emission features is changing
during the evolution, and shows a clear double-peak structure after
the deep minimum. Thanks to the dense spectral monitoring we could
observe several interesting developments of the Nova V5668 Sgr.

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Title: A Parallel Numerical Algorithm To Solve Linear Systems Of
Equations Emerging From 3D Radiative Transfer
Authors: Wichert, Viktoria; Arkenberg, Mario; Hauschildt, Peter H.
2016csss.confE..32W Altcode:
Highly resolved state-of-the-art 3D atmosphere simulations will remain
computationally extremely expensive for years to come. In addition
to the need for more computing power, rethinking coding practices is
necessary. We take a dual approach by introducing especially adapted,
parallel numerical methods and correspondingly parallelizing critical
code passages. In the following, we present our respective work on
PHOENIX/3D. With new parallel numerical algorithms, there is a
big opportunity for improvement when iteratively solving the system
of equations emerging from the operator splitting of the radiative
transfer equation J = ΛS. The narrow-banded approximate Λ-operator
Λ* , which is used in PHOENIX/3D, occurs in each iteration
step. By implementing a numerical algorithm which takes advantage of its
characteristic traits, the parallel code's efficiency is further 
increased and a speed-up in computational time can be achieved.

---------------------------------------------------------
Title: Proceeding On : Parallelisation Of Critical Code Passages
In PHOENIX/3D
Authors: Arkenberg, Mario; Wichert, Viktoria; Hauschildt, Peter H.
2016csss.confE..31A Altcode:
Highly resolved state-of-the-art 3D atmosphere simulations will
remain computationally extremely expensive for years to come. In
addition to the need for more computing power, rethinking coding
practices is necessary. We take a dual approach here, by introducing
especially adapted, parallel numerical methods and correspondingly
parallelising time critical code passages. In the following, we
present our work on PHOENIX/3D.While parallelisation is generally
worthwhile, it requires revision of time-consuming subroutines with
respect to separability of localised data and variables in order to
determine the optimal approach. Of course, the same applies to the
code structure. The importance of this ongoing work can be showcased
by recently derived benchmark results, which were generated utilis-
ing MPI and OpenMP. Furthermore, the need for a careful and thorough
choice of an adequate, machine dependent setup is discussed.

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Title: Direct Imaging discovery of a second planet candidate around
the possibly transiting planet host CVSO 30
Authors: Schmidt, T. O. B.; Neuhäuser, R.; Briceño, C.; Vogt, N.;
Raetz, St.; Seifahrt, A.; Ginski, C.; Mugrauer, M.; Buder, S.; Adam,
C.; Hauschildt, P.; Witte, S.; Helling, Ch.; Schmitt, J. H. M. M.
2016A&A...593A..75S Altcode: 2016arXiv160505315S
Context. Direct imaging has developed into a very successful
technique for the detection of exoplanets in wide orbits, especially
around young stars. Directly imaged planets can be both followed
astrometrically on their orbits and observed spectroscopically and
thus provide an essential tool for our understanding of the early
solar system. Aims: We surveyed the 25 Ori association for
direct-imaging companions. This association has an age of only few
million years. Among other targets, we observed CVSO 30, which has
recently been identified as the first T Tauri star found to host a
transiting planet candidate. Methods: We report on photometric
and spectroscopic high-contrast observations with the Very Large
Telescope, the Keck telescopes, and the Calar Alto observatory. They
reveal a directly imaged planet candidate close to the young M3
star CVSO 30. Results: The JHK-band photometry of the newly
identified candidate is at better than 1σ consistent with late-type
giants, early-T and early-M dwarfs, and free-floating planets. Other
hypotheses such as galaxies can be excluded at more than 3.5σ. A lucky
imaging z' photometric detection limit z' = 20.5 mag excludes early-M
dwarfs and results in less than 10 MJup for CVSO 30 c if
bound. We present spectroscopic observations of the wide companion that
imply that the only remaining explanation for the object is that it is
the first very young (&lt;10 Myr) L - T-type planet bound to a star,
meaning that it appears bluer than expected as a result of a decreasing
cloud opacity at low effective temperatures. Only a planetary spectral
model is consistent with the spectroscopy, and we deduce a best-fit
mass of 4-5 Jupiter masses (total range 0.6-10.2 Jupiter masses). Conclusions: This means that CVSO 30 is the first system in which
both a close-in and a wide planet candidate are found to have a common
host star. The orbits of the two possible planets could not be more
different: they have orbital periods of 10.76 h and about 27 000
yr. The two orbits may have formed during a mutual catastrophic event
of planet-planet scattering. Based on observations made with
ESO Telescopes at the La Silla Paranal Observatory under programme
IDs 090.C-0448(A), 290.C-5018(B), 092.C-0488(A) and at the Centro
Astronómico Hispano-Alemán in programme H15-2.2-002.

---------------------------------------------------------
Title: Phoenix Meets CO5BOLD: 3D NLTE Radiative Transfer Calculations
For M-Dwarf Chromospheres
Authors: De Gennaro Aquino, Ivan; Hauschildt, Peter H.; Wedemeyer, Sven
2016csss.confE.149D Altcode:
M-dwarf atmospheres are phenomenologically so rich that is currently
impossible to include all the physical processes in one astrophysical
simulation code. 1D models have greatly improved our understanding
of the radiative properties of M-dwarf photospheres and important
achievements have been obtained in 1D and 3D magneto-hydrodynamic
simulations. Using a snapshot from a CO5BOLD M-dwarf simulation as
input model, we use the 3D atmosphere code PHOENIX/3D to compute the
radiative properties of a M-dwarf photosphere-chromosphere atmosphere
with NLTE treatment for several atomic species and background atomic
and molecular opacities.

---------------------------------------------------------
Title: CARMENES: an overview six months after first light
Authors: Quirrenbach, A.; Amado, P. J.; Caballero, J. A.; Mundt,
R.; Reiners, A.; Ribas, I.; Seifert, W.; Abril, M.; Aceituno, J.;
Alonso-Floriano, F. J.; Anwand-Heerwart, H.; Azzaro, M.; Bauer, F.;
Barrado, D.; Becerril, S.; Bejar, V. J. S.; Benitez, D.; Berdinas,
Z. M.; Brinkmöller, M.; Cardenas, M. C.; Casal, E.; Claret, A.;
Colomé, J.; Cortes-Contreras, M.; Czesla, S.; Doellinger, M.;
Dreizler, S.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister,
B.; Galadi, D.; Gallardo, I.; Gálvez-Ortiz, M. C.; Garcia-Piquer,
A.; Garrido, R.; Gesa, L.; Gómez Galera, V.; González Hernández,
J. I.; Gonzalez Peinado, R.; Grözinger, U.; Guàrdia, J.; Guenther,
E. W.; de Guindos, E.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt,
P. H.; Helmling, J.; Henning, T.; Hermann, D.; Hernández Arabi, R.;
Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber,
A.; Huber, K. F.; Huke, P.; Jeffers, S. V.; de Juan, E.; Kaminski,
A.; Kehr, M.; Kim, M.; Klein, R.; Klüter, J.; Kürster, M.; Lafarga,
M.; Lara, L. M.; Lamert, A.; Laun, W.; Launhardt, R.; Lemke, U.;
Lenzen, R.; Llamas, M.; Lopez del Fresno, M.; López-Puertas, M.;
López-Santiago, J.; Lopez Salas, J. F.; Magan Madinabeitia, H.; Mall,
U.; Mandel, H.; Mancini, L.; Marin Molina, J. A.; Maroto Fernández,
D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C.; Mathar, R. J.;
Mirabet, E.; Montes, D.; Morales, J. C.; Morales Muñoz, R.; Nagel,
E.; Naranjo, V.; Nowak, G.; Palle, E.; Panduro, J.; Passegger, V. M.;
Pavlov, A.; Pedraz, S.; Perez, E.; Pérez-Medialdea, D.; Perger,
M.; Pluto, M.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.;
Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.;
Rodríguez López, C.; Rohloff, R. R.; Rosich, A.; Sanchez Carrasco,
M. A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer,
S.; Schiller, J.; Schmidt, C.; Schmitt, J. H. M. M.; Schöfer,
P.; Schweitzer, A.; Shulyak, D.; Solano, E.; Stahl, O.; Storz, C.;
Tabernero, H. M.; Tala, M.; Tal-Or, L.; Ulbrich, R. -G.; Veredas, G.;
Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Zapatero
Osorio, M. -R.; Zechmeister, M.; Ammler-von Eiff, M.; Anglada-Escudé,
G.; del Burgo, C.; Garcia-Vargas, M. L.; Klutsch, A.; Lizon, J. -L.;
Lopez-Morales, M.; Ofir, A.; Pérez-Calpena, A.; Perryman, M. A. C.;
Sánchez-Blanco, E.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.;
Trifonov, T.; Tulloch, S. M.; Xu, W.
2016SPIE.9908E..12Q Altcode:
The CARMENES instrument is a pair of high-resolution (R&gt; 80,000)
spectrographs covering the wavelength range from 0.52 to 1.71 μm,
optimized for precise radial velocity measurements. It was installed
and commissioned at the 3.5m telescope of the Calar Alto observatory
in Southern Spain in 2015. The first large science program of CARMENES
is a survey of 300 M dwarfs, which started on Jan 1, 2016. We present
an overview of all subsystems of CARMENES (front end, fiber system,
visible-light spectrograph, near-infrared spectrograph, calibration
units, etalons, facility control, interlock system, instrument control
system, data reduction pipeline, data flow, and archive), and give an
overview of the assembly, integration, verification, and commissioning
phases of the project. We show initial results and discuss further
plans for the scientific use of CARMENES.

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Title: An irradiated brown-dwarf companion to an accreting white dwarf
Authors: Hernández Santisteban, Juan V.; Knigge, Christian;
Littlefair, Stuart P.; Breton, Rene P.; Dhillon, Vikram S.; Gänsicke,
Boris T.; Marsh, Thomas R.; Pretorius, Magaretha L.; Southworth,
John; Hauschildt, Peter H.
2016Natur.533..366H Altcode: 2016Natur.533..366S; 2016arXiv160507132H
Interacting compact binary systems provide a natural laboratory in
which to study irradiated substellar objects. As the mass-losing
secondary (donor) in these systems makes a transition from the
stellar to the substellar regime, it is also irradiated by the primary
(compact accretor). The internal and external energy fluxes are both
expected to be comparable in these objects, providing access to an
unexplored irradiation regime. The atmospheric properties of donors
are largely unknown, but could be modified by the irradiation. To
constrain models of donor atmospheres, it is necessary to obtain
accurate observational estimates of their physical properties (masses,
radii, temperatures and albedos). Here we report the spectroscopic
detection and characterization of an irradiated substellar donor in an
accreting white-dwarf binary system. Our near-infrared observations
allow us to determine a model-independent mass estimate for the
donor of 0.055 ± 0.008 solar masses and an average spectral
type of L1 ± 1, supporting both theoretical predictions
and model-dependent observational constraints that suggest that
the donor is a brown dwarf. Our time-resolved data also allow us
to estimate the average irradiation-induced temperature difference
between the dayside and nightside of the substellar donor (57 kelvin)
and the maximum difference between the hottest and coolest parts of
its surface (200 kelvin). The observations are well described by a
simple geometric reprocessing model with a bolometric (Bond) albedo
of less than 0.54 at the 2σ confidence level, consistent with high
reprocessing efficiency, but poor lateral heat redistribution in the
atmosphere of the brown-dwarf donor. These results add to our knowledge
of binary evolution, in that the donor has survived the transition from
the stellar to the substellar regime, and of substellar atmospheres,
in that we have been able to test a regime in which the irradiation
and the internal energy of a brown dwarf are comparable.

---------------------------------------------------------
Title: High spectral resolution monitoring of Nova V339 Delphini
with TIGRE (Corrigendum)
Authors: De Gennaro Aquino, I.; Schröder, K. -P.; Mittag, M.; Wolter,
U.; Jack, D.; Eenens, P.; González-Pérez, J. N.; Hempelmann, A.;
Schmitt, J. H. M. M.; Hauschildt, P. H.; Rauw, G.
2016A&A...589C...4D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

---------------------------------------------------------
Title: Center-to-limb variation of intensity and polarization in
continuum spectra of FGK stars for spherical atmospheres
Authors: Kostogryz, N. M.; Milic, I.; Berdyugina, S. V.; Hauschildt,
P. H.
2016A&A...586A..87K Altcode: 2015arXiv151107213K
 Aims: One of the necessary parameters needed for the
interpretation of the light curves of transiting exoplanets or
eclipsing binary stars (as well as interferometric measurements of a
star or microlensing events) is how the intensity and polarization
of light changes from the center to the limb of a star. Scattering
and absorption processes in the stellar atmosphere affect both the
center-to-limb variation of intensity (CLVI) and polarization (CLVP). In
this paper, we present a study of the CLVI and CLVP in continuum
spectra, taking into consideration the different contributions of
scattering and absorption opacity for a variety of spectral type stars
with spherical atmospheres. Methods: We solve the radiative
transfer equation for polarized light in the presence of a continuum
scattering, taking into consideration the spherical model of a stellar
atmosphere. To cross-check our results, we developed two independent
codes that are based on Feautrier and short characteristics methods,
respectively, Results: We calculate the center-to-limb variation
of intensity (CLVI) and polarization (CLVP) in continuum for the
Phoenix grid of spherical stellar model atmospheres for a range of
effective temperatures (4000-7000 K), gravities (log g = 1.0-5.5), and
wavelengths (4000-7000 Å), which are tabulated and available at the
CDS. In addition, we present several tests of our codes and compare our
calculations for the solar atmosphere with published photometric and
polarimetric measurements. We also show that our two codes provide
similar results in all considered cases. Conclusions: For
sub-giant and dwarf stars (log g = 3.0-4.5), the lower gravity and
lower effective temperature of a star lead to higher limb polarization
of the star. For giant and supergiant stars (log g = 1.0-2.5), the
highest effective temperature yields the largest polarization. By
decreasing the effective temperature of a star down to 4500-5500 K
(depending on log g), the limb polarization decreases and reaches a
local minimum. It increases again with a corresponding decrease in
temperature down to 4000 K. For the most compact dwarf stars (log g =
5.0-5.5), the limb polarization degree shows a maximum for models with
effective temperatures in the range 4200-4600 K (depending on log g) and
decreases toward higher and lower temperatures. The intensity and
polarization profiles are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A87">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A87</A>

---------------------------------------------------------
Title: M dwarfs and the fraction of high carbon-to-oxygen stars in
the solar neighbourhood
Authors: Gizis, John E.; Marks, Zachary; Hauschildt, Peter H.
2016MNRAS.455.3824G Altcode: 2015arXiv151006985G
We investigate the frequency of high carbon-to-oxygen (C/O = 0.9)
M dwarf stars in the solar neighbourhood. Using synthetic spectra, we
find that such M dwarfs would have weaker TiO bands relative to hydride
features. Similar weakening has already been detected in M-subdwarf
(sdM) stars. By comparing to existing spectroscopic surveys of nearby
stars, we show that less than one per cent of nearby stars have high
carbon-to-oxygen ratios. This limit does not include stars with C/O =
0.9, [m/H] &gt; 0.3, and [C/Fe] &gt; 0.1, which we predict to have
low-resolution optical spectra similar to solar metallicity M dwarfs.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Center-to-limb polarization of
FGK stars (Kostogryz+, 2016)
Authors: Kostogryz, N. M.; Milic, I.; Berdyugina, S. V.; Hauschildt,
P. H.
2016yCat..35860087K Altcode:
Calculated center-to-limb variations of intensity (limb darkening)
for different stellar parameters with spherical atmosphere model
approximation. All intensities are normalized to the intensity in
the center of stellar disks, therefore, in the centre of the disks
(mu=1.0), I(mu)/I(1.0)=1.0. The parameters of spherical Phoenix
stellar model atmospheres we considered here are the following:
effective temperature is in the range of 4000K-7000K with the step of
100K and for logg=1.0-5.5 with the step of 0.5. All calculations are
made for such wavelengths: 4000Å, 4500Å, 5000Å, 6000Å, 7000Å. We
also present the position of the stellar limb and calculated stellar
radius. Calculated center-to-limb variations of polarization
(CLVP) for different stellar parameters with spherical atmosphere model
approximation. All intensities are normalized to the intensity in the
center of stellar disks, therefore, in the centre of the disks (mu=1.0),
I(mu)/I(1.0)=1.0. The parameters of spherical Phoenix model atmosphere
we considered here are the following: effective temperature is in
the range of 4000K-7000 K with the step of 100K and for logg=1.0-5.5
with the step of 0.5. All calculations are made for such wavelengths:
4000Å, 4500Å, 5000Å, 6000Å, 7000Å. We also present the position
of the stellar limb. (2 data files).

---------------------------------------------------------
Title: High spectral resolution monitoring of Nova V339 Delphini
with TIGRE
Authors: De Gennaro Aquino, I.; Schröder, K. -P.; Mittag, M.; Wolter,
U.; Jack, D.; Eenens, P.; González-Pérez, J. N.; Hempelmann, A.;
Schmitt, J. H. M. M.; Hauschildt, P. H.; Rauw, G.
2015A&A...581A.134D Altcode:
 Aims: We investigate the early development of the classical nova
<ASTROBJ>V339 Del</ASTROBJ> (<ASTROBJ>Nova Delphini 2013</ASTROBJ>)
through high-resolution optical spectroscopy. To study the structure of
the ejecta, we focus on the evolution of the absorption and emission
features and the changes within the line profiles. Methods: We
obtained spectra with the robotic 1.2 m telescope TIGRE equipped with
the HEROS spectrograph (R = 20 000, wavelength coverage from 3800 to
8800 Å). Our data set covers the outburst from 3 until 121 days after
discovery. Results: We provide a qualitative analysis of the
spectra, describing the line profiles evolution and providing a rich
list of identified lines. During the optically thick phase, we detected
several blue-shifted absorption features from s-processed elements,
whose origin is unclear. The presence of strong lines from C/O and the
absence of Neon features confirm that the nature of the central white
dwarf is a CO type. The later "nebular" phase spectra show evidence of
the non-spherical, inhomogeneous structure of the ejecta. The detailed
evolution of the line profiles and appearance of high ionization species
(e.g. N III, O III, He II, [Fe VII]) are direct consequences of the
re-ionization of the ejecta during the peak of the soft X-ray emission.

---------------------------------------------------------
Title: Synthetic activity indicators for M-type dwarf stars
Authors: Wedemeyer, Sven; Ludwig, Hans-Günter; Hauschildt, Peter;
De Gennaro Aquino, Ivan
2015IAUGA..2255174W Altcode:
Our understanding of the Sun has been substantially progressed
owing to the advances in high-resolution observations during the
last decades. These observations guided the development of numerical
simulation codes for stellar atmospheres towards unprecedented levels
of realism and complexity. Such 3D radiation magnetohydrodynamic (RMHD)
codes can be applied and adapted to cooler stars. Here, we present a
set of time-dependent 3D RMHD simulations for dwarf stars of spectral
type M (representative of AD Leo). "M-dwarfs" are the most abundant
stars in our galaxy and known to exhibit mega-flares. Comparisons
of M-dwarf models with the Sun as fundamental reference case reveal
differences and similarities, which lead to important insights into
the structure and dynamics of quiescent "background" atmospheres. The
models, which extend from the upper convection zone into the
chromosphere, have different initial magnetic field strengths (up to
500G) and topologies, representing regions with different activity
levels. The 3D model atmospheres are characterized by a very dynamic
and intermittent structure on small spatial and temporal scales,
final field strengths reaching a few kG and a wealth of physical
processes, which by nature cannot be described by means of 1D static
model atmospheres.Synthetic observables, i.e. spectra and intensity
images, are calculated by using these models as input for detailed
radiative transfer calculations and can be combined into synthetic full
stellar disks, thus simulating spatially unresolved observations of
M-dwarfs. The considered diagnostics, like, e.g., Halpha, Ca II lines,
or the continuum intensity from UV to millimeter wavelengths, sample
various properties of the dynamics, thermal and magnetic structure
of the photosphere and the chromosphere and thus provide measures of
stellar activity, which can be compared to observations. The complicated
magnetic field structure and its imprint in synthetic diagnostics may
have important implications for the understanding and characterization
of stellar activity and with it possibly for the evaluation of planetary
habitability around active M-dwarf stars.

---------------------------------------------------------
Title: VLTI/AMBER Studies of the Atmospheric Structure and Fundamental
Parameters of Red Giant and Supergiant Stars
Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Abellan,
F. J.; Chiavassa, A.; Fabregat, J.; Freytag, B.; Guirado, J. C.;
Hauschildt, P. H.; Marti-Vidal, I.; Quirrenbach, A.; Scholz, M.;
Wood, P. R.
2015ASPC..497...91A Altcode:
We present recent near-IR interferometric studies of red giant and
supergiant stars, which are aimed at obtaining information on the
structure of the atmospheric layers and constraining the fundamental
parameters of these objects. The observed visibilities of six red
supergiants (RSGs), and also of one of the five red giants observed,
indicate large extensions of the molecular layers, as previously
observed for Mira stars. These extensions are not predicted by
hydrostatic PHOENIX model atmospheres, hydrodynamical (RHD) simulations
of stellar convection, or self-excited pulsation models. All these
models based on parameters of RSGs lead to atmospheric structures
that are too compact compared to our observations. We discuss how
alternative processes might explain the atmospheric extensions for
these objects. As the continuum appears to be largely free of
contamination by molecular layers, we can estimate reliable Rosseland
angular radii for our stars. Together with distances and bolometric
fluxes, we estimate the effective temperatures and luminosities of our
targets, locate them in the HR diagram, and compare their positions
to recent evolutionary tracks.

---------------------------------------------------------
Title: Search with UVES and X-Shooter for signatures of the low-mass
secondary in the post common-envelope binary AA Doradus
Authors: Hoyer, D.; Rauch, T.; Werner, K.; Hauschildt, P. H.; Kruk,
J. W.
2015A&A...578A.125H Altcode: 2015arXiv150407750H
Context. <ASTROBJ>AA Dor</ASTROBJ> is a close, totally eclipsing,
post common-envelope binary with an sdOB-type primary star and an
extremely low-mass secondary star, located close to the mass limit of
stable central hydrogen burning. Within error limits, it may either be a
brown dwarf or a late M-type dwarf. Aims: We aim to extract the
secondary's contribution to the phase-dependent composite spectra. The
spectrum and identified lines of the secondary decide on its nature. Methods: In January 2014, we measured the phase-dependent spectrum
of <ASTROBJ>AA Dor</ASTROBJ> with X-Shooter over one complete orbital
period. Since the secondary's rotation is presumable synchronized with
the orbital period, its surface strictly divides into a day and night
side. Therefore, we may obtain the spectrum of its cool side during its
transit and of its hot, irradiated side close to its occultation. We
developed the Virtual Observatory (VO) tool TLISA to search for weak
lines of a faint companion in a binary system. We successfully applied
it to the observations of <ASTROBJ>AA Dor</ASTROBJ>. Results: We
identified 53 spectral lines of the secondary in the ultraviolet-blue,
visual, and near-infrared X-Shooter spectra that are strongest
close to its occultation. We identified 57 (20 additional) lines in
available Ultraviolet and Visual Echelle Spectrograph (UVES) spectra
from 2001. The lines are mostly from C ii-iii and O ii, typical for a
low-mass star that is irradiated and heated by the primary. We verified
the orbital period of P = 22 597.033201 ± 0.00007 s and determined
the orbital velocity K_sec = 232.9+16.6-6.5 km
s-1 of the secondary. The mass of the secondary is M_sec
= 0.081+0.018-0.010 M_⊙ and, hence, it is
not possible to reliably determine a brown dwarf or an M-type dwarf
nature. Conclusions: Although we identified many emission lines of
the secondary's irradiated surface, the resolution and signal-to-noise
ratio of our UVES and X-Shooter spectra are not good enough to extract
a good spectrum of the secondary's nonirradiated hemisphere. Based
on observations collected at the European Southern Observatory, Chile,
programs 066.D-1800 and 092.C-0692.Based on observations made with the
NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer.Figures 2-5, 9,
and Appendices are available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Identification of the feature that causes the I-band secondary
maximum of a Type Ia supernova
Authors: Jack, D.; Baron, E.; Hauschildt, P. H.
2015MNRAS.449.3581J Altcode: 2015arXiv150303088J
We obtained a time series of spectra covering the secondary maximum in
the I band of the bright Type Ia supernova 2014J in M82 with the TIGRE
telescope. Comparing the observations with theoretical models calculated
with the time dependent extension of the PHOENIX code, we identify the
feature that causes the secondary maximum in the I-band light curve. Fe
II 3d6(3D)4s-3d6(5D)4p and
similar high-excitation transitions produce a blended feature at ∼7500
Å, which causes the rise of the light curve towards the secondary
maximum. The series of observed spectra of SN 2014J and archival data
of SN 2011fe confirm this conclusion. We further studied the plateau
phase of the R-band light curve of SN 2014J and searched for features
which contribute to the flux. The theoretical models do not clearly
indicate a new feature that may cause the R-band plateau phase. However,
Co II features in the range of 6500-7000 Å and the Fe II feature of
the I band are clearly seen in the theoretical spectra, but do not
appear to provide all of the flux necessary for the R-band plateau.

---------------------------------------------------------
Title: What causes the large extensions of red supergiant
atmospheres?. Comparisons of interferometric observations with 1D
hydrostatic, 3D convection, and 1D pulsating model atmospheres
Authors: Arroyo-Torres, B.; Wittkowski, M.; Chiavassa, A.; Scholz,
M.; Freytag, B.; Marcaide, J. M.; Hauschildt, P. H.; Wood, P. R.;
Abellan, F. J.
2015A&A...575A..50A Altcode: 2015arXiv150101560A
 Aims: This research has two main goals. First, we present
the atmospheric structure and the fundamental parameters of three
red supergiants (RSGs), increasing the sample of RSGs observed by
near-infrared spectro-interferometry. Additionally, we test possible
mechanisms that may explain the large observed atmospheric extensions
of RSGs. Methods: We carried out spectro-interferometric
observations of the RSGs V602 Car, HD 95687, and HD 183589 in the
near-infrared K-band (1.92-2.47 μm) with the VLTI/AMBER instrument at
medium spectral resolution (R ~ 1500). To categorize and comprehend
the extended atmospheres, we compared our observational results to
predictions by available hydrostatic PHOENIX, available 3D convection,
and new 1D self-excited pulsation models of RSGs. Results:
Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589
are well reproduced by the PHOENIX model atmospheres. The continuum
visibility values are consistent with a limb-darkened disk as
predicted by the PHOENIX models, allowing us to determine the angular
diameter and the fundamental parameters of our sources. Nonetheless,
in the case of V602 Car and HD 95686, the PHOENIX model visibilities
do not predict the large observed extensions of molecular layers,
most remarkably in the CO bands. Likewise, the 3D convection models
and the 1D pulsation models with typical parameters of RSGs lead
to compact atmospheric structures as well, which are similar to
the structure of the hydrostatic PHOENIX models. They can also not
explain the observed decreases in the visibilities and thus the
large atmospheric molecular extensions. The full sample of our RSGs
indicates increasing observed atmospheric extensions with increasing
luminosity and decreasing surface gravity, and no correlation with
effective temperature or variability amplitude. Conclusions:
The location of our RSG sources in the Hertzsprung-Russell diagram is
confirmed to be consistent with the red limits of recent evolutionary
tracks. The observed extensions of the atmospheric layers of our
sample of RSGs are comparable to those of Mira stars. This phenomenon
is not predicted by any of the considered model atmospheres including
available 3D convection and new 1D pulsation models of RSGs. This
confirms that neither convection nor pulsation alone can levitate the
molecular atmospheres of RSGs. Our observed correlation of atmospheric
extension with luminosity supports a scenario of radiative acceleration
on Doppler-shifted molecular lines. Based on observations made with
the VLT Interferometer (VLTI) at Paranal Observatory under programme
ID 091.D-0275.Figures 2-6 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425212/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: On the atmospheric structure and fundamental parameters of
red supergiants
Authors: Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellan,
F. J.; Chiavassa, A.; Freytag, B.; Scholz, M.; Wood, P. R.; Hauschildt,
P. H.
2015IAUS..307..280W Altcode:
We present near-infrared spectro-interferometric studies of red
supergiant (RSG) stars using the VLTI/AMBER instrument, which are
compared to previously obtained similar observations of AGB stars. Our
observations indicate spatially extended atmospheric molecular layers of
water vapor and CO, similar as previously observed for Mira stars. Data
of VY~CMa indicate that the molecular layers are asymmetric, possibly
clumpy. Thanks to the spectro-interferometric capabilities of the
VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate
fundamental parameters of our sources, locate them in the HR diagram,
and compare their positions to recent evolutionary tracks. For the
example of VY CMa, this puts it close to evolutionary tracks of initial
mass 25-32 M ⊙. Comparisons of our data to hydrostatic
model atmospheres, 3d simulations of convection, and 1d dynamic model
atmospheres based on self-excited pulsation models indicate that
none of these models can presently explain the observed atmospheric
extensions for RSGs. The mechanism that levitates the atmospheres of
red supergiant is thus a currently unsolved problem.

---------------------------------------------------------
Title: Reproduction of the Wilson-Bappu Effect Using PHOENIX
Authors: Olvera, C. M. Guerra; Jack, D.; Shroder, K. -P.; Fuhrmeister,
B.; Mittag, M.; Hauschildt, P.
2015csss...18..405O Altcode:
We use the versatile PHOENIX atmospheric modeling code in its version,
which includes a gravity-scaled chromosphere above the temperature
minimum to model the Ca II K emission line profile for solar-type stars,
all with T_{eff} = 5780K and same turbulence broadening, only with
different surface gravities. Models, which produce the modest emission
observed in relatively inactive stars, reproduce the Wilson-Bappu
effect (WBE) in absolute terms, i.e. the emission line-widths grow
with lower gravity consistent with Δ W ∝ g^{-0.17} in the range
of log{g}=5.0 to 3.5. Further modeling is in process to include lower
gravities. In the solar case, which we used as a first test, we find the
temperature minimum (over height, single component) for a relatively
inactive Sun to reach down to 3930 K. The respective PHOENIX model
(log{g} = 4.4) matches width and typical flux of the chromospheric Ca
II emission of a nearly inactive Sun, as observed with the Hamburg
robotic telescope (see Fig. 1). For comparison, the quiet Sun model
C of tet{1981ApJS...45..635V} had a temperature minimum of 4170 K.

---------------------------------------------------------
Title: 3D Multi-Level Non-LTE Radiative Transfer for the CO Molecule
Authors: Berkner, A.; Schweitzer, A.; Hauschildt, P. H.
2015csss...18..689B Altcode:
The photospheres of cool stars are both rich in molecules and an
environment where the assumption of LTE can not be upheld under all
circumstances. Unfortunately, detailed 3D non-LTE calculations involving
molecules are hardly feasible with current computers. For this reason,
we present our implementation of the super level technique, in which
molecular levels are combined into super levels, to reduce the number
of unknowns in the rate equations and, thus, the computational effort
and memory requirements involved, and show the results of our first
tests against the 1D implementation of the same method.

---------------------------------------------------------
Title: The non-active stellar chromosphere: Ca II basal flux
Authors: Pérez Martínez, M. I.; Schröder, K. -P.; Hauschildt, P.
2014MNRAS.445..270P Altcode:
We analyse high-resolution, high-s/n European Southern Observatories
(ESO)-archive spectra (from UVES, the UV echelle spectrograph)
of 76 inactive or modestly active stars of spectral type G to M,
main sequence and giants. Using PHOENIX model photospheres with Ca
II K lines that match the observed line profiles, we (i) revise the
effective temperatures, (ii) obtain a precise surface flux scale for
each star and (iii) directly determine the exact surface fluxes of each
Ca II K chromospheric emission with respect to the photospheric line
profile. We find that our stellar sample exhibits a lower boundary
to its chromospheric surface flux distribution with an unprecedented
definition. From a subsample of the 25 least active stars, we obtain
a simple empirical formula for the basal Ca II flux as a function of
effective temperature: log {F^basal_{Ca II(H+K)}} = 7.05(± 0.31)
log {T_eff} - 20.86(± 1.15). This is in good agreement with the
Mg II basal flux. In a direct comparison with the large body of Mt
Wilson S-measurements of the chromospheric Ca II emission and its
well-defined cut-off, excellent agreement is achieved as well. A new
result, however, is the small scatter of the least active star's fluxes
about the basal flux. It is about 25 per cent and equals the residual
uncertainties of our approach. At the same time, we do not find any
evidence for a gravity dependence within these limits. This strongly
confirms the basal flux as a well-defined and universal phenomenon,
which characterizes every inactive chromosphere.

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Title: CARMENES instrument overview
Authors: Quirrenbach, A.; Amado, P. J.; Caballero, J. A.; Mundt,
R.; Reiners, A.; Ribas, I.; Seifert, W.; Abril, M.; Aceituno, J.;
Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona Jiménez, R.;
Anwand-Heerwart, H.; Azzaro, M.; Bauer, F.; Barrado, D.; Becerril, S.;
Béjar, V. J. S.; Benítez, D.; Berdiñas, Z. M.; Cárdenas, M. C.;
Casal, E.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla,
S.; Doellinger, M.; Dreizler, S.; Feiz, C.; Fernández, M.; Galadí,
D.; Gálvez-Ortiz, M. C.; García-Piquer, A.; García-Vargas, M. L.;
Garrido, R.; Gesa, L.; Gómez Galera, V.; González Álvarez, E.;
González Hernández, J. I.; Grözinger, U.; Guàrdia, J.; Guenther,
E. W.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H. -J.; Hatzes,
A. P.; Hauschildt, P. H.; Helmling, J.; Henning, T.; Hermann, D.;
Hernández Castaño, L.; Herrero, E.; Hidalgo, D.; Holgado, G.;
Huber, A.; Huber, K. F.; Jeffers, S.; Joergens, V.; de Juan, E.;
Kehr, M.; Klein, R.; Kürster, M.; Lamert, A.; Lalitha, S.; Laun,
W.; Lemke, U.; Lenzen, R.; López del Fresno, Mauro; López Martí,
B.; López-Santiago, J.; Mall, U.; Mandel, H.; Martín, E. L.;
Martín-Ruiz, S.; Martínez-Rodríguez, H.; Marvin, C. J.; Mathar,
R. J.; Mirabet, E.; Montes, D.; Morales Muñoz, R.; Moya, A.; Naranjo,
V.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Passegger, V. -M.;
Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Pluto, M.;
Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode,
P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López, C.;
Rodríguez-Pérez, E.; Rohloff, R. -R.; Rosich, A.; Sánchez-Blanco,
E.; Sánchez Carrasco, M. A.; Sanz-Forcada, J.; Sarmiento, L. F.;
Schäfer, S.; Schiller, J.; Schmidt, C.; Schmitt, J. H. M. M.; Solano,
E.; Stahl, O.; Storz, C.; Stürmer, J.; Suárez, J. C.; Ulbrich,
R. G.; Veredas, G.; Wagner, K.; Winkler, J.; Zapatero Osorio, M. R.;
Zechmeister, M.; Abellán de Paco, F. J.; Anglada-Escudé, G.; del
Burgo, C.; Klutsch, A.; Lizon, J. L.; López-Morales, M.; Morales,
J. C.; Perryman, M. A. C.; Tulloch, S. M.; Xu, W.
2014SPIE.9147E..1FQ Altcode:
This paper gives an overview of the CARMENES instrument and of the
survey that will be carried out with it during the first years of
operation. CARMENES (Calar Alto high-Resolution search for M dwarfs
with Exoearths with Near-infrared and optical Echelle Spectrographs)
is a next-generation radial-velocity instrument under construction
for the 3.5m telescope at the Calar Alto Observatory by a consortium
of eleven Spanish and German institutions. The scientific goal of the
project is conducting a 600-night exoplanet survey targeting ~ 300 M
dwarfs with the completed instrument. The CARMENES instrument consists
of two separate echelle spectrographs covering the wavelength range
from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by
fibers from the Cassegrain focus of the telescope. The spectrographs
are housed in vacuum tanks providing the temperature-stabilized
environments necessary to enable a 1 m/s radial velocity precision
employing a simultaneous calibration with an emission-line lamp
or with a Fabry-Perot etalon. For mid-M to late-M spectral types,
the wavelength range around 1.0 μm (Y band) is the most important
wavelength region for radial velocity work. Therefore, the efficiency
of CARMENES has been optimized in this range. The CARMENES instrument
consists of two spectrographs, one equipped with a 4k x 4k pixel CCD
for the range 0.55 - 1.05 μm, and one with two 2k x 2k pixel HgCdTe
detectors for the range from 0.95 - 1.7μm. Each spectrograph will
be coupled to the 3.5m telescope with two optical fibers, one for
the target, and one for calibration light. The front end contains a
dichroic beam splitter and an atmospheric dispersion corrector, to
feed the light into the fibers leading to the spectrographs. Guiding
is performed with a separate camera; on-axis as well as off-axis
guiding modes are implemented. Fibers with octagonal cross-section
are employed to ensure good stability of the output in the presence
of residual guiding errors. The fibers are continually actuated to
reduce modal noise. The spectrographs are mounted on benches inside
vacuum tanks located in the coudé laboratory of the 3.5m dome. Each
vacuum tank is equipped with a temperature stabilization system
capable of keeping the temperature constant to within +/-0.01°C
over 24 hours. The visible-light spectrograph will be operated near
room temperature, while the near-IR spectrograph will be cooled to
~ 140 K. The CARMENES instrument passed its final design review in
February 2013. The MAIV phase is currently ongoing. First tests at
the telescope are scheduled for early 2015. Completion of the full
instrument is planned for the fall of 2015. At least 600 useable
nights have been allocated at the Calar Alto 3.5m Telescope for the
CARMENES survey in the time frame until 2018. A data base of M stars
(dubbed CARMENCITA) has been compiled from which the CARMENES sample
can be selected. CARMENCITA contains information on all relevant
properties of the potential targets. Dedicated imaging, photometric,
and spectroscopic observations are underway to provide crucial data
on these stars that are not available in the literature.

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Title: A 3D radiative transfer framework. XI. Multi-level NLTE
Authors: Hauschildt, Peter H.; Baron, Edward
2014A&A...566A..89H Altcode: 2014arXiv1404.4376H
Context. Multi-level non-local thermodynamic equilibrium (NLTE)
radiation transfer calculations have become standard throughout the
stellar atmospheres community and are applied to all types of stars as
well as dynamical systems such as novae and supernovae. Nevertheless
even today spherically symmetric 1D calculations with full physics are
computationally intensive. We show that full physics NLTE calculations
can be done with fully 3 dimensional (3D) radiative transfer. Aims: With modern computational techniques and current massive
parallel computational resources, full detailed solution of the
multi-level NLTE problem coupled to the solution of the radiative
transfer scattering problem can be solved without sacrificing the
micro physics description. Methods: We extend the use of a rate
operator developed to solve the coupled NLTE problem in spherically
symmetric 1D systems. In order to spread memory among processors
we have implemented the NLTE/3D module with a hierarchical domain
decomposition method that distributes the NLTE levels, radiative rates,
and rate operator data over a group of processes so that each process
only holds the data for a fraction of the voxels. Each process in a
group holds all the relevant data to participate in the solution of the
3DRT problem so that the 3DRT solution is parallelized within a domain
decomposition group. Results: We solve a spherically symmetric
system in 3D spherical coordinates in order to directly compare our
well-tested 1D code to the 3D case. We compare three levels of tests:
a) a simple H+He test calculation, b) H+He+CNO+Mg, c) H+He+Fe. The last
test is computationally large and shows that realistic astrophysical
problems are solvable now, but they do require significant computational
resources. Conclusions: With presently available computational
resources it is possible to solve the full 3D multi-level problem with
the same detailed micro-physics as included in 1D modeling.

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Title: VLTI/AMBER observations of cold giant stars: atmospheric
structures and fundamental parameters
Authors: Arroyo-Torres, B.; Martí-Vidal, I.; Marcaide, J. M.;
Wittkowski, M.; Guirado, J. C.; Hauschildt, P. H.; Quirrenbach, A.;
Fabregat, J.
2014A&A...566A..88A Altcode: 2014arXiv1404.7384A
 Aims: The main goal of this research is to determine the angular
size and the atmospheric structures of cool giant stars (ɛ Oct, β
Peg, NU Pav, ψ Peg, and γ Hya) and to compare them with hydrostatic
stellar model atmospheres, to estimate the fundamental parameters, and
to obtain a better understanding of the circumstellar environment. Methods: We conducted spectro-interferometric observations of ɛ Oct,
β Peg, NU Pav, and ψ Peg in the near-infrared K band (2.13-2.47
μm), and γ Hya (1.9-2.47 μm) with the VLTI/AMBER instrument
at medium spectral resolution (~1500). To obtain the fundamental
parameters, we compared our data with hydrostatic atmosphere models
(PHOENIX). Results: We estimated the Rosseland angular diameters
of ɛ Oct, β Peg, NU Pav, ψ Peg, and γ Hya to be 11.66±1.50 mas,
16.87±1.00 mas, 13.03±1.75 mas, 6.31±0.35 mas, and 3.78±0.65 mas,
respectively. Together with distances and bolometric fluxes (obtained
from the literature), we estimated radii, effective temperatures, and
luminosities of our targets. In the β Peg visibility, we observed
a molecular layer of CO with a size similar to that modeled with
PHOENIX. However, there is an additional slope in absorption starting
around 2.3 μm. This slope is possibly due to a shell of H2O
that is not modeled with PHOENIX (the size of the layer increases to
about 5% with respect to the near-continuum level). The visibility
of ψ Peg shows a low increase in the CO bands, compatible with the
modeling of the PHOENIX model. The visibility data of ɛ Oct, NU Pav,
and γ Hya show no increase in molecular bands. Conclusions:
The spectra and visibilities predicted by the PHOENIX atmospheres agree
with the spectra and the visibilities observed in our stars (except
for β Peg). This indicates that the opacity of the molecular bands is
adequately included in the model, and the atmospheres of our targets
have an extension similar to the modeled atmospheres. The atmosphere
of β Peg is more extended than that predicted by the model. The role
of pulsations, if relevant in other cases and unmodeled by PHOENIX,
therefore seems negligible for the atmospheric structures of our
sample. The targets are located close to the red limits of the
evolutionary tracks of the STAREVOL model, corresponding to masses
between 1 M⊙ and 3 M⊙. The STAREVOL model
fits the position of our stars in the Hertzsprung-Russell (HR) diagram
better than the Ekström model does. STAREVOL includes thermohaline
mixing, unlike the Ekström model, and complements the latter for
intermediate-mass stars. Based on observations made with the
VLT Interferometer (VLTI) at Paranal Observatory under programme
ID 089.D-0801.Figures 2-4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201323264/olm">http://www.aanda.org</A>

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Title: First spectroscopic observations of the substellar companion
of the young debris disk star PZ Telescopii
Authors: Schmidt, T. O. B.; Mugrauer, M.; Neuhäuser, R.; Vogt, N.;
Witte, S.; Hauschildt, P. H.; Helling, Ch.; Seifahrt, A.
2014A&A...566A..85S Altcode: 2014arXiv1404.2870S
Context. In 2010 a substellar companion to the solar analog pre-main
sequence star PZ Tel and member of the approximately 12 Myr old β Pic
moving group was found by high-contrast direct imaging independently
by two teams. Aims: In order to determine the basic parameters
of this companion more precisely and independent of evolutionary
models, hence age-independent, we obtained follow-up spectroscopic
observations of the primary and companion. Methods: We used
the Spectrograph for INtegral Field Observations in the Near Infrared
(SINFONI) at the Very Large Telescope Unit 4/Yepun of ESO's Paranal
Observatory in the H + K band and processed the data using the
spectral deconvolution technique. The resulting spectrum of the
companion was then compared to a grid of Drift-Phoenix synthetic
model spectra, a combination of a general-purpose model atmosphere
code with a non-equilibrium, stationary cloud and dust model, using a
χ2 minimization analysis. Results: We find a best
fitting spectral type of G6.5 for PZ Tel A. The extracted spectrum
of the substellar companion, at a spatial position compatible with
earlier orbit estimates, yields a temperature Teff
= 2500-115+138 K, a visual extinction
AV = 0.53-0.53+0.84 mag, a surface
gravity of log g = 3.50-0.30+0.51
dex, and a metallicity at the edge of the grid of [M/H] =
0.30-0.30 dex. Conclusions: We derive
a luminosity of log(Lbol/L⊙)
= -2.66-0.08+0.06, a radius of R =
2.42-0.34+0.28 RJup, and a mass of
M = 7.5-4.3+16.9 MJup for the PZ
Tel companion, which is consistent with most earlier estimates using
photometry alone. Combining our results with evolutionary models,
we find a best-fitting mass of about 21 Jupiter masses at an age
corresponding to the recently determined lithium depletion age of
7-2+4 Myr. Hence, the PZ Tel companion is most
likely a wide brown dwarf companion in the 12-4+8
Myr old β Pic moving group. Based on observations made with
ESO Telescopes at the La Silla Paranal Observatory under program ID
087.C-0109(A).

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Title: Characterization of the gaseous companion κ Andromedae b. New
Keck and LBTI high-contrast observations
Authors: Bonnefoy, M.; Currie, T.; Marleau, G. -D.; Schlieder, J. E.;
Wisniewski, J.; Carson, J.; Covey, K. R.; Henning, T.; Biller, B.;
Hinz, P.; Klahr, H.; Marsh Boyer, A. N.; Zimmerman, N.; Janson, M.;
McElwain, M.; Mordasini, C.; Skemer, A.; Bailey, V.; Defrère, D.;
Thalmann, C.; Skrutskie, M.; Allard, F.; Homeier, D.; Tamura, M.;
Feldt, M.; Cumming, A.; Grady, C.; Brandner, W.; Helling, C.; Witte,
S.; Hauschildt, P.; Kandori, R.; Kuzuhara, M.; Fukagawa, M.; Kwon, J.;
Kudo, T.; Hashimoto, J.; Kusakabe, N.; Abe, L.; Brandt, T.; Egner, S.;
Guyon, O.; Hayano, Y.; Hayashi, M.; Hayashi, S.; Hodapp, K.; Ishii, M.;
Iye, M.; Knapp, G.; Matsuo, T.; Mede, K.; Miyama, M.; Morino, J. -I.;
Moro-Martin, A.; Nishimura, T.; Pyo, T.; Serabyn, E.; Suenaga, T.;
Suto, H.; Suzuki, R.; Takahashi; Takami, M.; Takato, N.; Terada, H.;
Tomono, D.; Turner, E.; Watanabe, M.; Yamada, T.; Takami, H.; Usuda, T.
2014A&A...562A.111B Altcode: 2013arXiv1308.3859B
Context. We previously reported the direct detection of a low-mass
companion at a projected separation of 55 ± 2 AU around the B9-type
star κ Andromedae. The properties of the system (mass ratio,
separation) make it a benchmark for understanding the formation and
evolution of gas giant planets and brown dwarfs on wide orbits. Aims: We present new angular differential imaging (ADI) images of
the system at 2.146 (Ks), 3.776 (L'), 4.052 (NB_4.05),
and 4.78 μm (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as
well as more accurate near-infrared photometry of the star with the
MIMIR instrument. We aim to determine the near-infrared spectral
energy distribution of the companion and use it to characterize the
object. Methods: We used analysis methods adapted to ADI
to extract the companion flux. We compared the photometry of the
object to reference young, and old objects and to a set of seven
PHOENIX-based atmospheric models of cool objects accounting for the
formation of dust. We used evolutionary models to derive mass estimates
considering a wide range of plausible initial conditions. Finally,
we used dedicated formation models to discuss the possible origin of
the companion. Results: We derive a more accurate J = 15.86 ±
0.21, H = 14.95 ± 0.13, Ks = 14.32 ± 0.09 mag for κ And
b. We detect the companion in all our high-contrast observations. We
confirm previous contrasts obtained at Ks and L' band. We
derive NB_4.05 = 13.0 ± 0.2, and M' = 13.3 ± 0.3 mag and estimate
log 10(L/L⊙) = -3.76 ± 0.06. Atmospheric
models yield Teff = 1900+100-200
K. They do not set any constraint on the surface gravity. "Hot-start"
evolutionary models predict masses of 14+25-2
MJup based on the luminosity and temperature estimates,
and when considering a conservative age range for the system
(30+120-10 Myr), "warm-start" evolutionary tracks
constrain the mass to M ≥ 10MJup. Conclusions: The
mass of κ Andromedae b mostly falls in the brown-dwarf regime, owing to
remaining uncertainties in age and in mass-luminosity models. According
to the formation models, disk instability in a primordial disk
may account for the position and a wide range of plausible masses
of κ And b. The LBT is an international collaboration among
institutions in the United States, Italy, and Germany. LBT Corporation
partners are: The University of Arizona on behalf of the Arizona
university system; Instituto Nazionale di Astrofisica, Italy; LBT
Beteiligungsgesellschaft, Germany, representing the Max-Planck Society,
the Astrophysical Institute Potsdam, and Heidelberg University; The
Ohio State University, and The Research Corporation, on behalf of the
University of Notre Dame, University of Minnesota, and University
of Virginia.Appendices are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322119/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: The atmospheric structure and fundamental parameters of the
red supergiants AH Scorpii, UY Scuti, and KW Sagittarii
Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.;
Hauschildt, P. H.
2013A&A...554A..76A Altcode: 2013arXiv1305.6179A
 Aims: We present the atmospheric structure and the fundamental
properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW
Sgr based on VLTI/AMBER observations. Methods: We carried
out spectro-interferometric observations of AH Sco, UY Sct, and KW
Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER
instrument with spatial and spectral resolutions of 3 milliarcsec and
1500, respectively, and compared the data to a new grid of hydrostatic
PHOENIX model atmospheres. Results: In our visibility data, we
observe molecular layers of water and CO in extended atmospheres. For
a uniform disk modeling, we observe size increases at the water band
centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5
μm of 20%-35% with respect to the near-continuum bandpass at around
2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr
are well reproduced by the PHOENIX model atmospheres. The continuum
visibility values are consistent with a limb-darkened disk as predicted
by the PHOENIX models. However, the model visibilities do not predict
the large observed extensions of the molecular layers. Comparing
the continuum visibility values to PHOENIX models, we estimate the
Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and
KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas,
respectively. Together with the distance and the spectro-photometry,
we calculate radii of 1411 ± 124 R⊙ for AH Sco, 1708 ±
192 R⊙ for UY Sct, and 1009 ± 142 R⊙ for KW
Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ±
134 K for UY Sct, and 3720 ± 183 K for KW Sgr. Conclusions:
AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of
H2O and CO. The PHOENIX atmosphere models predict the
spectra and the continuum visibility values, but cannot reproduce
the large extensions of the molecular layers. This indicates that
the opacities of the molecular bands are included, but that the model
atmospheres are too compact compared to the observations. The observed
extended layers may be levitated by processes such as pulsation or
convection, which are not included in the hydrostatic atmospheric
models. The location of the targets in the HR-diagram is confirmed to
be close to, and possibly slightly to the right of, the Hayashi limit
of recent evolutionary tracks corresponding to masses between about
20 M⊙ and 40 M⊙.

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Title: A new extensive library of PHOENIX stellar atmospheres and
synthetic spectra
Authors: Husser, T. -O.; Wende-von Berg, S.; Dreizler, S.; Homeier,
D.; Reiners, A.; Barman, T.; Hauschildt, P. H.
2013A&A...553A...6H Altcode: 2013arXiv1303.5632H
 Aims: We present a new library of high-resolution synthetic
spectra based on the stellar atmosphere code PHOENIX that can be used
for a wide range of applications of spectral analysis and stellar
parameter synthesis. Methods: The spherical mode of PHOENIX
was used to create model atmospheres and to derive detailed synthetic
stellar spectra from them. We present a new self-consistent way of
describing micro-turbulence for our model atmospheres. Results:
The synthetic spectra cover the wavelength range from 500 Å to 5.5 μm
with resolutions of R = 500 000 in the optical and near IR, R = 100 000
in the IR and Δλ = 0.1 Å in the UV. The parameter space covers 2300
K ≤ Teff ≤ 12 000 K, 0.0 ≤ log g ≤ +6.0, - 4.0 ≤
[Fe/H] ≤ +1.0, and - 0.2 ≤ [α/Fe] ≤ +1.2. The library is a work
in progress and we expect to extend it up to Teff = 25 000 K.

---------------------------------------------------------
Title: The atmospheric structure and fundamental parameters of
Red Supergiants
Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.;
Hauschildt, P. H.
2013EAS....60...93A Altcode:
We present studies of the atmospheric structure and fundamental
properties of the red supergiants (RSGs) VY CMa, AH Sco, UY Sct,
and KW Sgr based on near-infrared K-band interferometry obtained
with the VLTI/AMBER instrument with a spectral resolution of 1500. In
our visibility data, we observe the presence of molecular layers of
water and CO in extended atmospheres. For a uniform disk modeling, we
observe size increases in the water band centered at 1.9 μm and in the
CO band at 2.3-2.5 μm, with respect to the near-continuum bandpass
(2.20-2.25 μm). With our spectral resolution, we obtain diameters
in the near-continuum, that are free from contamination by molecular
layers. Using PHOENIX atmosphere models, we estimate Rosseland-mean
photospheric angular diameters of VY CMa, AH Sco, UY Sct, and KW Sgr
of 11.13 ± 0.3mas, 5.81 ± 0.15mas, 5.48 ± 0.10mas, and 3.91 ±
0.25mas, respectively. We estimate radii and effective temperatures,
and place the stars in the HR diagram. The PHOENIX atmosphere models
predict the spectra and the continuum visibility values, but do not
predict the molecular layers visibility well: The model atmosphere is
too compact when compared with the observations. This may be caused
by pulsation and/or convection, which are not included in the models.

---------------------------------------------------------
Title: The atmospheric structure and fundamental parameters of the
red supergiants AH Sco, UY Sct, and KW Sgr
Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.;
Hauschildt, P. H.
2013hsa7.conf..516A Altcode:
We present the atmospheric structure and the fundamental parameters
of the Red Supergiants (RSGs) AH Sco, UY Sct, and KW Sgr. We have
carried out spectro-interferometric observations in the near-infrared
bands (between 1.9 μm and 2.5 μm) with the VLTI/AMBER instrument
in medium resolution. In the visibility data, we detect the presence
of molecular layers of water and CO in extended atmospheres. For a
uniform disk modelling, we observe size increases in the water band
centered at 1.9 μm and in the CO band at 2.3--2.5 μm, with respect
to the near-continuun bandpass (2.20-2.25 μm). Our near-infrared
spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the
PHOENIX model. However the synthetic visibility amplitudes of the
model do not predict the large extensions of the molecular bands. The
continuum (2.15-2.25 μm) appears free from contamination by molecular
layers. Thus, the continuum fitting to the PHOENIX can be used to
estimate the diameter. We estimate the Rosseland-mean photospheric
angular diameter of AH Sco, UY Sct, and KW Sgr to be 6.12±0.7
mas, 5.67± 0.55 mas, and 4.07±0.65 mas, respectively (preliminary
values). We estimate radii and effective temperatures, and place the
stars in the HR diagram.

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Title: Extracting the Physical Parameters of a Sample of M-dwarfs
from High-resolution Near-infrared Spectra
Authors: del Burgo, C.; Martín, E. L.; Zapatero Osorio, M. R.;
Deshpande, R.; Witte, S.; Helling, C.; Hauschildt, P. H.
2013ASPC..472...53D Altcode:
This study is part of an effort to determine the physical and
kinematical properties of a sample of 36 nearby late M-dwarfs, with
spectral types M5-M9.5. They are the targets of a program to search
for exoplanets orbiting around them from the radial velocity method
using the near-infrared echelle spectrograph NIRSPEC on the Keck
II telescope. Preliminary results about the effective temperature,
surface gravity, and rotational broadening of a subsample of nine
M-dwarfs are presented. The analysis is based on the comparison of
the spectra obtained in the J-band with a high resolving power of
22,000 and stellar atmosphere synthetic models using the PHOENIX and
the PHOENIX/DRIFT codes. This study shows that the strong potassium
absorption doublet at 12432 and 12522 Å is useful to determine
the effective temperature. Our results are of interest for the new
generation of near-infrared spectrographs that are being developed
to measure radial velocities with unprecedented precisions of a few
ms-1, for which accurate theoretical models for comparison
are needed.

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Title: New limb-darkening coefficients for Phoenix/1d model
atmospheres. II. Calculations for 5000 K ≤ Teff ≤
10 000 K Kepler, CoRot, Spitzer, uvby, UBVRIJHK, Sloan, and 2MASS
photometric systems
Authors: Claret, A.; Hauschildt, P. H.; Witte, S.
2013A&A...552A..16C Altcode:
 Aims: We present an extension of our investigations on
limb-darkening coefficients computed with spherical symmetrical Phoenix
models. The models investigated in this paper cover the range 5000 K
≤ Teff ≤ 10 000 K and complete our previous studies of
low effective temperatures computed with the same code. Methods:
The limb-darkening coefficients are computed for the transmission curves
of the Kepler, CoRoT, and Spitzer space missions and the Strömgren,
Johnson-Cousins, Sloan, and 2MASS passbands. These computations were
performed by adopting the least-squares method. Results: We
have used six laws to describe the specific intensity distribution:
linear, quadratic, square root, logarithmic, exponential, and a
general law with four terms. The computations are presented for
the solar chemical composition and cover the range 3.0 ≤ log g
≤ 5.5. The adopted microturbulent velocity and the mixing-length
parameter are 2.0 km s-1 and 2.0. Tables 2-25
are available in electronic form at the CDS via anonymous ftp
to <A href="http://cdsarc.u-strasbg.fr">cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A16">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A16</A>

---------------------------------------------------------
Title: 3D radiative transfer effects in parametrized starspots
Authors: Berkner, A.; Hauschildt, P. H.; Baron, E.
2013A&A...550A.104B Altcode:
 Aims: We use our 3D radiative transfer framework to investigate
how the presence of a parametrized starspot affects radiative transfer
in stellar atmospheres in general, and molecular CO lines in a stellar
spectrum, in particular. Methods: The equation of state is solved
for a given temperature structure including a simple parametrized
spot model and the 3D scattering problem for line transfer is solved
via an operator splitting technique. The formal solution is based on
a full characteristics solution. We have used both a LTE model and a
test model with a 2 level atom, simulating a single spectral line in
NLTE. Results: We present the resulting CO band spectra showing
both surface resolved and an integrated total emergent flux for the
star and compare the umbral, penumbral, and quiet spectrum for a solar
type star, which clearly shows the presence of spots as an increased
CO line-depth. Furthermore, we show that the opacity structure of the
spot has a significantly different angular variation than the quiet
plane parallel star and its visible shape is strongly influenced by
scattering, where strong scattering disconnects the lateral intensity
profile from the temperature profile of the spot. Conclusions:
Even a simple, small scale parametrized model shows significant
3D effects, in both the resolved and in the surface integrated
spectrum. The 3D model allows for a much more detailed treatment than
simple mixing of spectra with different effective temperatures.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Limb-darkening for CoRoT, Kepler,
Spitzer. II. (Claret+, 2013)
Authors: Claret, A.; Hauschildt, P. H.; Witte, S.
2013yCat..35520016C Altcode: 2013yCat..35529016C
We present an extension of our investigations on limb-darkening
coefficients computed with spherical symmetrical PHOENIX
models. The models investigated in this paper cover the range
5000K&lt;=Teff&lt;=10000K and complete our previous studies of
low effective temperatures computed with the same code. The
limb-darkening coefficients are computed for the transmission curves
of the Kepler, CoRoT, and Spitzer space missions and the Stroemgren,
Johnson-Cousins, Sloan, and 2MASS passbands. These computations were
performed by adopting the least-squares method. We have used
six laws to describe the specific intensity distribution: linear,
quadratic, square root, logarithmic, exponential, and a general law
with four terms. The computations are presented for the solar chemical
composition and cover the range 3.0&lt;=logg&lt;=5.5. The adopted
microturbulent velocity and the mixing-length parameter are 2.0km/s
and 2.0. (17 data files).

---------------------------------------------------------
Title: Characterization of 36 late M-dwarfs using spectral energy
distributions and near-infrared echelle spectra .
Authors: del Burgo, C.; Helling, Ch.; Martín, E. L.; Witte, S.;
Zapatero Osorio, M. R.; Hauschildt, P. H.
2013MmSAI..84.1084D Altcode:
The aim of the study presented here is to determine the physical
and kinematical properties of a sample of 36 nearby M-dwarfs, with
spectral types M5-M9.5. Echelle spectra in the J-band were obtained
using the NIRSPEC spectrograph on the Keck II telescope, with a
resolving power of 22,000, at different epochs. The comparison
of the observed spectra with stellar atmosphere models derived
from the PHOENIX and the DRIFT-PHOENIX codes, has permitted the
determination of the effective temperature (T_{eff }), surface gravity
(log g), and rotational broadening (v_rotsin i) of the 36 M-dwarfs,
assuming solar-like metallicity. This approach turned out to be quite
insensitive to T_{eff } in the spectral type range from M5 to M9.5,
which motivated us to use a different method. Thus, 2MASS J, H and K,
and WISE W1, W2 and W3 photometry, which covers a wide wavelength
range that includes the emission peak of our targets, was compared
with the BT-SETTL-PHOENIX code to alternatively derive T_{eff } for
every M-dwarf. The so obtained values of T_{eff } are consistent with
other near-infrared studies. Our investigation shows some limitations
of current theoretical models and methods. Although late M-dwarfs
are difficult to model given their intrinsic faintness and atmosphere
complexity, a proper characterization of them is necessary to better
conduct the next generation of radial velocity surveys, which are
aimed at searching for rocky planets around those stars.

---------------------------------------------------------
Title: Time-dependent radiative transfer with PHOENIX (Corrigendum)
Authors: Jack, D.; Hauschildt, P. H.; Baron, E.
2013A&A...549C...1J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A 3D radiative transfer framework. X. Arbitrary velocity
fields in the comoving frame
Authors: Baron, E.; Hauschildt, P. H.; Chen, B.; Knop, S.
2012A&A...548A..67B Altcode: 2012arXiv1210.6679B
 Aims: General 3D astrophysical atmospheres will have random
velocity fields. We seek to combine the methods we have developed
for solving the 1D problem with arbitrary flows to those that we
have developed for solving the fully 3D relativistic radiative
transfer problem for monotonic flows. Methods: The methods
developed for 3D atmospheres with monotonic flows, solving the fully
relativistic problem along curves defined by an affine parameter, are
very flexible and can be extended to the case of arbitrary velocity
fields in 3D. Simultaneously, the techniques we developed for treating
the 1D problem with arbitrary velocity fields are easily adapted
to the 3D problem. Results: The algorithm we present can be
used to solve 3D radiative transfer problems that include arbitrary
wavelength couplings. We use a quasi-analytic formal solution of the
radiative transfer equation that significantly improves the overall
computation speed. We show that the approximate lambda operator
developed in previous work gives good convergence, even neglecting
wavelength coupling. Ng acceleration also gives good results. We
present tests that are of similar resolution to what has been presented
using Monte-Carlo techniques, thus our methods will be applicable to
problems outside of our test setup. Additional domain decomposition
parallelization strategies will be explored in future work.

---------------------------------------------------------
Title: New limb-darkening coefficients for PHOENIX/1D model
atmospheres. I. Calculations for 1500 K ≤ Teff ≤
4800 K Kepler, CoRot, Spitzer, uvby, UBVRIJHK, Sloan, and 2MASS
photometric systems
Authors: Claret, A.; Hauschildt, P. H.; Witte, S.
2012A&A...546A..14C Altcode:
 Aims: The knowledge of how the specific intensity is distributed
over the stellar disk is crucial for interpreting the light curves
of extrasolar transiting planets, double-lined eclipsing binaries,
and other astrophysical phenomena. To provide theoretical inputs
for light curve modelling codes, we present new calculations of
limb-darkening coefficients for the spherically symmetric phoenix
models. Methods: The limb-darkening coefficients were
computed by covering the transmission curves of Kepler, CoRoT, and
Spitzer space missions, as well as the passbands of the Strömgren,
Johnson-Cousins, Sloan, and 2MASS. These computations adopted the
least-square method. In addition, we also calculated the linear
and bi-parametric approximations by adopting the flux conservation
method as an additional tool for estimating the theoretical error
bars in the limb-darkening coefficients. Results: Six laws
were used to describe the specific intensity distribution: linear,
quadratic, square root, logarithmic, exponential, and a more general
one with 4 terms. The computations are presented for the solar
chemical composition, with log g varying between 2.5 and 5.5 and
effective temperatures between 1500-4800 K. The adopted microturbulent
velocity and the mixing-length parameters are 2.0 km s-1
and 2.0, respectively. Tables 2-25 are only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A14">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A14</A>

---------------------------------------------------------
Title: A 3D radiative transfer framework. IX. Time dependence
Authors: Jack, D.; Hauschildt, P. H.; Baron, E.
2012A&A...546A..39J Altcode: 2012arXiv1209.5788J
Context. Time-dependent, 3D radiation transfer calculations are
important for the modeling of a variety of objects, from supernovae and
novae to simulations of stellar variability and activity. Furthermore,
time-dependent calculations can be used to obtain a 3D radiative
equilibrium model structure via relaxation in time. Aims:
We extend our 3D radiative transfer framework to include direct time
dependence of the radiation field; i.e., the ∂I/∂t terms are fully
considered in the solution of radiative transfer problems. 
Methods: We build on the framework that we have described in previous
papers in this series and develop a subvoxel method for the ∂I/∂t
terms. Results: We test the implementation by comparing the 3D
results to our well tested 1D time dependent radiative transfer code in
spherical symmetry. A simple 3D test model is also presented. 
Conclusions: The 3D time dependent radiative transfer method is now
included in our 3D RT framework and in PHOENIX/3D.

---------------------------------------------------------
Title: EChO. Exoplanet characterisation observatory
Authors: Tinetti, G.; Beaulieu, J. P.; Henning, T.; Meyer, M.;
Micela, G.; Ribas, I.; Stam, D.; Swain, M.; Krause, O.; Ollivier,
M.; Pace, E.; Swinyard, B.; Aylward, A.; van Boekel, R.; Coradini,
A.; Encrenaz, T.; Snellen, I.; Zapatero-Osorio, M. R.; Bouwman, J.;
Cho, J. Y. -K.; Coudé de Foresto, V.; Guillot, T.; Lopez-Morales, M.;
Mueller-Wodarg, I.; Palle, E.; Selsis, F.; Sozzetti, A.; Ade, P. A. R.;
Achilleos, N.; Adriani, A.; Agnor, C. B.; Afonso, C.; Allende Prieto,
C.; Bakos, G.; Barber, R. J.; Barlow, M.; Batista, V.; Bernath, P.;
Bézard, B.; Bordé, P.; Brown, L. R.; Cassan, A.; Cavarroc, C.;
Ciaravella, A.; Cockell, C.; Coustenis, A.; Danielski, C.; Decin,
L.; De Kok, R.; Demangeon, O.; Deroo, P.; Doel, P.; Drossart, P.;
Fletcher, L. N.; Focardi, M.; Forget, F.; Fossey, S.; Fouqué, P.;
Frith, J.; Galand, M.; Gaulme, P.; González Hernández, J. I.;
Grasset, O.; Grassi, D.; Grenfell, J. L.; Griffin, M. J.; Griffith,
C. A.; Grözinger, U.; Guedel, M.; Guio, P.; Hainaut, O.; Hargreaves,
R.; Hauschildt, P. H.; Heng, K.; Heyrovsky, D.; Hueso, R.; Irwin, P.;
Kaltenegger, L.; Kervella, P.; Kipping, D.; Koskinen, T. T.; Kovács,
G.; La Barbera, A.; Lammer, H.; Lellouch, E.; Leto, G.; Lopez Morales,
M.; Lopez Valverde, M. A.; Lopez-Puertas, M.; Lovis, C.; Maggio, A.;
Maillard, J. P.; Maldonado Prado, J.; Marquette, J. B.; Martin-Torres,
F. J.; Maxted, P.; Miller, S.; Molinari, S.; Montes, D.; Moro-Martin,
A.; Moses, J. I.; Mousis, O.; Nguyen Tuong, N.; Nelson, R.; Orton,
G. S.; Pantin, E.; Pascale, E.; Pezzuto, S.; Pinfield, D.; Poretti,
E.; Prinja, R.; Prisinzano, L.; Rees, J. M.; Reiners, A.; Samuel,
B.; Sánchez-Lavega, A.; Forcada, J. Sanz; Sasselov, D.; Savini, G.;
Sicardy, B.; Smith, A.; Stixrude, L.; Strazzulla, G.; Tennyson, J.;
Tessenyi, M.; Vasisht, G.; Vinatier, S.; Viti, S.; Waldmann, I.;
White, G. J.; Widemann, T.; Wordsworth, R.; Yelle, R.; Yung, Y.;
Yurchenko, S. N.
2012ExA....34..311T Altcode: 2012ExA...tmp...35T; 2011arXiv1112.2728T
A dedicated mission to investigate exoplanetary atmospheres represents
a major milestone in our quest to understand our place in the
universe by placing our Solar System in context and by addressing the
suitability of planets for the presence of life. EChO—the Exoplanet
Characterisation Observatory—is a mission concept specifically geared
for this purpose. EChO will provide simultaneous, multi-wavelength
spectroscopic observations on a stable platform that will allow very
long exposures. The use of passive cooling, few moving parts and well
established technology gives a low-risk and potentially long-lived
mission. EChO will build on observations by Hubble, Spitzer and
ground-based telescopes, which discovered the first molecules and
atoms in exoplanetary atmospheres. However, EChO's configuration
and specifications are designed to study a number of systems in a
consistent manner that will eliminate the ambiguities affecting prior
observations. EChO will simultaneously observe a broad enough spectral
region—from the visible to the mid-infrared—to constrain from
one single spectrum the temperature structure of the atmosphere, the
abundances of the major carbon and oxygen bearing species, the expected
photochemically-produced species and magnetospheric signatures. The
spectral range and resolution are tailored to separate bands belonging
to up to 30 molecules and retrieve the composition and temperature
structure of planetary atmospheres. The target list for EChO includes
planets ranging from Jupiter-sized with equilibrium temperatures T
eq up to 2,000 K, to those of a few Earth masses, with
T eq u223c 300 K. The list will include planets with no
Solar System analog, such as the recently discovered planets GJ1214b,
whose density lies between that of terrestrial and gaseous planets,
or the rocky-iron planet 55 Cnc e, with day-side temperature close to
3,000 K. As the number of detected exoplanets is growing rapidly each
year, and the mass and radius of those detected steadily decreases, the
target list will be constantly adjusted to include the most interesting
systems. We have baselined a dispersive spectrograph design covering
continuously the 0.4-16 μm spectral range in 6 channels (1 in the
visible, 5 in the InfraRed), which allows the spectral resolution to
be adapted from several tens to several hundreds, depending on the
target brightness. The instrument will be mounted behind a 1.5 m class
telescope, passively cooled to 50 K, with the instrument structure and
optics passively cooled to u223c45 K. EChO will be placed in a grand
halo orbit around L2. This orbit, in combination with an optimised
thermal shield design, provides a highly stable thermal environment and
a high degree of visibility of the sky to observe repeatedly several
tens of targets over the year. Both the baseline and alternative
designs have been evaluated and no critical items with Technology
Readiness Level (TRL) less than 4-5 have been identified. We have also
undertaken a first-order cost and development plan analysis and find
that EChO is easily compatible with the ESA M-class mission framework.

---------------------------------------------------------
Title: The Exoplanet Characterization Observatory (EChO): performance
model EclipseSim and applications
Authors: van Boekel, Roy; Benneke, Björn; Heng, Kevin; Hu, Renyu;
Madhusudhan, Nikku; Quanz, Sascha; Bétrémieux, Yan; Bouwman, Jeroen;
Chen, Guo; Decin, Leen; de Kok, Remco; Glauser, Adrian; Güdel,
Manuel; Hauschildt, Peter; Henning, Thomas; Jeffers, Sandra; Jin,
Sheng; Kaltenegger, Lisa; Kerschbaum, Franz; Krause, Oliver; Lammer,
Helmut; Luntzer, Armin; Meyer, Michael; Miguel, Yamila; Mordasini,
Christoph; Ottensamer, Roland; Rank-Lueftinger, Theresa; Reiners,
Ansgar; Reinhold, Timo; Schmid, Hans Martin; Snellen, Ignas; Stam,
Daphne; Sun, Zhao; Vandenbussche, Bart
2012SPIE.8442E..1FV Altcode:
We present EclipseSim, a radiometric model for exoplanet transit
spectroscopy that allows easy exploration of the fundamental
performance limits of any space-based facility aiming to perform such
observations. It includes a library of stellar model atmosphere spectra
and can either approximate exoplanet spectra by simplified models, or
use any theoretical or observed spectrum, to simulate observations. All
calculations are done in a spectrally resolved fashion and the
contributions of the various fundamental noise sources are budgeted
separately, allowing easy assessment of the dominant noise sources,
as a function of wavelength. We apply EclipseSim to the Exoplanet
Characterization Observatory (EChO), a proposed mission dedicated to
exoplanet transit spectroscopy that is currently in competition for
the M3 launch slot of ESA’s cosmic vision programme. We show several
case studies on planets with sizes in the super-Earth to Jupiter range,
and temperatures ranging from the temperate to the ≍1500K regime,
demonstrating the power and versatility of EChO. EclipseSim is publicly
available.*

---------------------------------------------------------
Title: VizieR Online Data Catalog: Limb-darkening for CoRoT, Kepler,
Spitzer (Claret+, 2012)
Authors: Claret, A.; Hauschildt, P. H.; Witte, S.
2012yCat..35460014C Altcode: 2012yCat..35469014C
The knowledge of how the specific intensity is distributed over
the stellar disk is crucial for interpreting the light curves of
extrasolar transiting planets, double-lined eclipsing binaries, and
other astrophysical phenomena. To provide theoretical inputs for light
curve modelling codes, we present new calculations of limb-darkening
coefficients for the spherically symmetric PHOENIX models. The
limb-darkening coefficients were computed by covering the transmission
curves of Kepler, CoRoT, and Spitzer space missions, as well as the
passbands of the Stromgren, Johnson-Cousins, Sloan, and 2MASS. These
computations adopted the least-square method. In addition, we also
calculated the linear and bi-parametric approximations by adopting
the flux conservation method as an additional tool for estimating
the theoretical error bars in the limb-darkening coefficients. Six laws were used to describe the specific intensity distribution:
linear, quadratic, square root, logarithmic, exponential, and a more
general one with 4 terms. The computations are presented for the
solar chemical composition, with logg varying between 2.5 and 5.5 and
effective temperatures between 1500K-4800K. The adopted Microturbulent
velocity and the mixing-length parameters are 2.0km/s and 2.0,
respectively. Model are for solar metallicity. (17 data files).

---------------------------------------------------------
Title: CARMENES. I: instrument and survey overview
Authors: Quirrenbach, Andreas; Amado, Pedro J.; Seifert, Walter;
Sánchez Carrasco, Miguel A.; Mandel, Holger; Caballero, Jose A.;
Mundt, Reinhard; Ribas, Ignasi; Reiners, Ansgar; Abril, Miguel;
Aceituno, Jesus; Alonso-Floriano, Javier; Ammler-von Eiff, Matthias;
Anglada-Escude, Guillem; Antona Jiménez, Regina; Anwand-Heerwart,
Heiko; Barrado y Navascués, David; Becerril, Santiago; Bejar,
Victor; Benitez, Daniel; Cardenas, Concepcion; Claret, Antonio;
Colome, Josep; Cortés-Contreras, Miriam; Czesla, Stefan; del Burgo,
Carlos; Doellinger, Michaela; Dorda, R.; Dreizler, Stefan; Feiz,
Carmen; Fernandez, Matilde; Galadi, David; Garrido, Rafael; González
Hernández, Jonay; Guardia, Josep; Guenther, Eike; de Guindos, Enrique;
Gutiérrez-Soto, Juan; Hagen, Hans J.; Hatzes, Artie; Hauschildt,
Peter; Helmling, Jens; Henning, Thomas; Herrero, Enrique; Huber,
Armin; Huber, Klaus; Jeffers, Sandra; Joergens, Viki; de Juan,
Enrique; Kehr, M.; Klutsch, Alexis; Kürster, Martin; Lalitha, S.;
Laun, Werner; Lemke, Ulrike; Lenzen, Rainer; Lizon, Jean-Louis; López
del Fresno, Mauro; López-Morales, Mercedes; López-Santiago, Javier;
Mall, Ulrich; Martin, Eduardo; Martín-Ruiz, Susana; Mirabet, Eduard;
Montes, David; Morales, Juan Carlos; Morales Muñoz, Rafael; Moya,
Andres; Naranjo, Vianak; Oreiro, Raquel; Pérez Medialdea, David;
Pluto, Michael; Rabaza, Ovidio; Ramon, Alejandro; Rebolo, Rafael;
Reffert, Sabine; Rhode, Petra; Rix, Hans-Walter; Rodler, Florian;
Rodríguez, Eloy; Rodríguez López, Cristina; Rodríguez Pérez,
Emilio; Rodriguez Trinidad, A.; Rohloff, Ralf-Reiner; Sánchez-Blanco,
Ernesto; Sanz-Forcada, Jorge; Schäfer, Sebastian; Schiller, Jörg;
Schmidt, Christof; Schmitt, Jürgen; Solano, Enrique; Stahl, Otmar;
Storz, Clemens; Stürmer, Julian; Suarez, Juan Carlos; Thiele, Ulrich;
Ulbrich, Rainer; Vidal-Dasilva, Manuela; Wagner, Karl; Winkler,
Johannes; Xu, Wenli; Zapatero Osorio, Maria Rosa; Zechmeister, Mathias
2012SPIE.8446E..0RQ Altcode:
CARMENES (Calar Alto high-Resolution search for M dwarfs with
Exo-earths with Near-infrared and optical Echelle Spectrographs)
is a next-generation instrument for the 3.5m telescope at the Calar
Alto Observatory, built by a consortium of eleven Spanish and German
institutions. The CARMENES instrument consists of two separate
échelle spectrographs covering the wavelength range from 0.55 μm
to 1.7 μm at a spectral resolution of R = 82, 000, fed by fibers
from the Cassegrain focus of the telescope. Both spectrographs are
housed in temperature-stabilized vacuum tanks, to enable a long-term
1 m/s radial velocity precision employing a simultaneous calibration
with Th-Ne and U-Ne emission line lamps. CARMENES has been optimized
for a search for terrestrial planets in the habitable zones (HZs)
of low-mass stars, which may well provide our first chance to study
environments capable of supporting the development of life outside the
Solar System. With its unique combination of optical and near-infrared
´echelle spectrographs, CARMENES will provide better sensitivity for
the detection of low-mass planets than any comparable instrument, and
a powerful tool for discriminating between genuine planet detections
and false positives caused by stellar activity. The CARMENES survey
will target 300 M dwarfs in the 2014 to 2018 time frame.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Spectroscopy of very low mass
objects (Patience+, 2012)
Authors: Patience, J.; King, R. R.; De Rosa, R. J.; Vigan, A.; Witte,
S.; Rice, E.; Helling, C.; Hauschildt, P.
2012yCat..35400085P Altcode: 2012yCat..35409085P
With a uniform VLT SINFONI data set of nine targets, we have developed
an empirical grid of J, H, K spectra of the atmospheres of objects
estimated to have very low substellar masses of ~5-20MJup
and young ages ranging from ~1-50Myr. Most of the targets are
companions, objects which are especially valuable for comparison
with atmosphere and evolutionary models, as they present rare
cases in which the age is accurately known from the primary. Based
on the youth of the sample, all objects are expected to have low
surface gravity, and this study investigates the critical early
phases of the evolution of substellar objects. The spectra are
compared with grids of five different theoretical atmosphere models. **************************************************************************
* * * Sorry, but the author(s) never supplied the
tabular material * * announced in the paper * * *
**************************************************************************

---------------------------------------------------------
Title: Fundamental properties and atmospheric structure of the red
supergiant VY Canis Majoris based on VLTI/AMBER spectro-interferometry
Authors: Wittkowski, M.; Hauschildt, P. H.; Arroyo-Torres, B.;
Marcaide, J. M.
2012A&A...540L..12W Altcode: 2012arXiv1203.5194W
 Aims: We investigate the atmospheric structure and fundamental
properties of the red supergiant VY CMa. Methods: We obtained
near-infrared spectro-interferometric observations of VY CMa with
spectral resolutions of 35 and 1500 using the AMBER instrument at the
VLTI. Results: The visibility data indicate the presence of
molecular layers of water vapor and CO in the extended atmosphere with
an asymmetric morphology. The uniform disk diameter in the water band
around 2.0 μm is increased by ~20% compared to the near-continuum
bandpass at 2.20-2.25 μm, and in the CO band at 2.3-2.5 μm it is
increased by up to ~50%. The closure phases indicate relatively
small deviations from point symmetry close to the photospheric
layer, and stronger deviations in the extended H2O and
CO layers. Making use of the high spatial and spectral resolution,
a near-continuum bandpass can be isolated from contamination by
molecular and dusty layers, and the Rosseland-mean photospheric
angular diameter is estimated to 11.3 ± 0.3 mas based on a PHOENIX
atmosphere model. Together with recent high-precision estimates of
the distance and spectro-photometry, this estimate corresponds to a
radius of 1420 ± 120 R⊙ and an effective temperature
of 3490 ± 90 K. Conclusions: VY CMa exhibits asymmetric,
possibly clumpy, atmospheric layers of H2O and CO, which
are not co-spatial, within a larger elongated dusty envelope. Our
revised fundamental parameters put VY CMa close to the Hayashi limit
of recent evolutionary tracks of initial mass 25 M⊙ with
rotation or 32 M⊙ without rotation, shortly before evolving
blueward in the HR-diagram. Based on observations made with the
VLT Interferometer (VLTI) at Paranal Observatory under programme ID
386.D-0012.Figures 2, 3 and 5 are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Spectroscopy across the brown dwarf/planetary mass
boundary. I. Near-infrared JHK spectra
Authors: Patience, J.; King, R. R.; De Rosa, R. J.; Vigan, A.; Witte,
S.; Rice, E.; Helling, Ch.; Hauschildt, P.
2012A&A...540A..85P Altcode: 2012arXiv1201.3921P
With a uniform VLT SINFONI data set of nine targets, we have developed
an empirical grid of J, H, K spectra of the atmospheres of objects
estimated to have very low substellar masses of ~5-20 MJup
and young ages ranging from ~1-50 Myr. Most of the targets are
companions, objects which are especially valuable for comparison with
atmosphere and evolutionary models, as they present rare cases in
which the age is accurately known from the primary. Based on the youth
of the sample, all objects are expected to have low surface gravity,
and this study investigates the critical early phases of the evolution
of substellar objects. The spectra are compared with grids of five
different theoretical atmosphere models. This analysis represents the
first systematic model comparison with infrared spectra of young brown
dwarfs. The fits to the full JHK spectra of each object result in a
range of best fit effective temperatures of ± 150-300 K whether or not
the full model grid or a subset restricted to lower log (g) values is
used. This effective temperature range is significantly larger than the
uncertainty typically assigned when using a single model grid. Fits to
a single wavelength band can vary by up to 1000 K using the different
model grids. Since the overall shape of these spectra is governed
more by the temperature than surface gravity, unconstrained model
fits did not find matches with low surface gravity or a trend in log
(g) with age. This suggests that empirical comparison with spectra of
unambiguously young objects targets (such as those presented here) may
be the most reliable method to search for indications of low surface
gravity and youth. Based on comparison with previous observations,
the SINFONI spectra represent a second epoch for the targets 2M0141
and DH Tau B, and the combined data show no variations in the spectral
morphology over time. The analysis of two other targets, AB Pic B and
CT Cha B, suggests that these objects may have lower temperatures,
and consequently lower masses, than previously estimated. Based
on observations obtained at the Paranal Observatory, Chile for ESO
programs 279.C-5010(A), 080.C-0590(A), 077.C-0264(A), 078.C-0800(B),
&amp; 078.C-0800(A).The spectra are only available at the CDS
via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A85">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A85</A>

---------------------------------------------------------
Title: Modeling the near-UV Band of GK Stars. II. Non-LTE Models
Authors: Short, C. Ian; Campbell, Eamonn A.; Pickup, Heather;
Hauschildt, Peter H.
2012ApJ...747..143S Altcode: 2012arXiv1201.0910S
We present a grid of atmospheric models and synthetic spectral energy
distributions (SEDs) for late-type dwarfs and giants of solar and 1/3
solar metallicity with many opacity sources computed in self-consistent
non-local thermodynamic equilibrium (NLTE), and compare them to the
LTE grid of Short &amp; Hauschildt (Paper I). We describe, for the
first time, how the NLTE treatment affects the thermal equilibrium of
the atmospheric structure (T(τ) relation) and the SED as a finely
sampled function of T eff, log g, and [A/H] among solar
metallicity and mildly metal-poor red giants. We compare the computed
SEDs to the library of observed spectrophotometry described in Paper I
across the entire visible band, and in the blue and red regions of the
spectrum separately. We find that for the giants of both metallicities,
the NLTE models yield best-fit T eff values that are 30-90
K lower than those provided by LTE models, while providing greater
consistency between log g values, and, for Arcturus, T eff
values, fitted separately to the blue and red spectral regions. There
is marginal evidence that NLTE models give more consistent best-fit
T eff values between the red and blue bands for earlier
spectral classes among the solar metallicity GK giants than they do for
the later classes, but no model fits the blue-band spectrum well for
any class. For the two dwarf spectral classes that we are able to study,
the effect of NLTE on derived parameters is less significant. We compare
our derived T eff values to several other spectroscopic and
photometric T eff calibrations for red giants, including
one that is less model dependent based on the infrared flux method
(IRFM). We find that the NLTE models provide slightly better agreement
to the IRFM calibration among the warmer stars in our sample, while
giving approximately the same level of agreement for the cooler stars.

---------------------------------------------------------
Title: Near-infrared light curves of type Ia supernovae
Authors: Jack, D.; Hauschildt, P. H.; Baron, E.
2012A&A...538A.132J Altcode: 2012arXiv1201.1723J
 Aims: With our time-dependent model atmosphere code PHOENIX, our
goal is to simulate light curves and spectra of hydrodynamical models of
all types of supernovae. In this work, we simulate near-infrared light
curves of SNe Ia and confirm the cause of the secondary maximum. Methods: We apply a simple energy solver to compute the evolution
of an SN Ia envelope during the free expansion phase. Included in the
solver are energy changes due to expansion, the energy deposition of
γ-rays and interaction of radiation with the material. Results:
We computed theoretical light curves of several SN Ia hydrodynamical
models in the I, J, H, and K bands and compared them to the observed
SN Ia light curves of SN 1999ee and SN 2002bo. By changing a line
scattering parameter in time, we obtained quite reasonable fits to
the observed near-infrared light curves. This is a strong hint that
detailed NLTE effects in IR lines have to be modeled, which will
be a future focus of our work. Conclusions: We found that IR
line scattering is very important for the near-infrared SN Ia light
curve modeling. In addition, the recombination of Fe III to Fe II and
of Co III to Co II is responsible for the secondary maximum in the
near-infrared bands. For future work the consideration of NLTE for
all lines (including the IR subordinate lines) will be crucial.

---------------------------------------------------------
Title: Dark Matter Powered Stars: Constraints from the Extragalactic
Background Light
Authors: Maurer, A.; Raue, M.; Kneiske, T.; Horns, D.; Elsässer,
D.; Hauschildt, P. H.
2012ApJ...745..166M Altcode: 2012arXiv1201.1305M
The existence of predominantly cold non-baryonic dark matter is
unambiguously demonstrated by several observations (e.g., structure
formation, big bang nucleosynthesis, gravitational lensing, and
rotational curves of spiral galaxies). A candidate well motivated
by particle physics is a weakly interacting massive particle
(WIMP). Self-annihilating WIMPs would affect the stellar evolution
especially in the early universe. Stars powered by self-annihilating
WIMP dark matter should possess different properties compared with
standard stars. While a direct detection of such dark matter powered
stars seems very challenging, their cumulative emission might leave an
imprint in the diffuse metagalactic radiation fields, in particular in
the mid-infrared part of the electromagnetic spectrum. In this work,
the possible contributions of dark matter powered stars (dark stars,
DSs) to the extragalactic background light (EBL) are calculated. It is
shown that existing data and limits of the EBL intensity can already
be used to rule out some DS parameter sets.

---------------------------------------------------------
Title: A new extensive library of synthetic stellar spectra from
PHOENIX atmospheres and its application to fitting VLT MUSE spectra
Authors: Husser, T. -O.; Kamann, S.; Dreizler, S.; Hauschildt, Peter H.
2012ASInC...6...71H Altcode: 2012arXiv1203.1941H
We present a new library of synthetic spectra based on the stellar
atmosphere code phx. It covers the wavelength range from 500 Å to
55 000 Å with a resolution of R=500 000 in the optical and near IR,
R=100 000 in the IR and &amp;Delta&amp;;lambda;=0.1 Å in the UV. The
parameter space covers 2 300 K ≤ T_{eff} ≤ 8 000 K, 0.0 ≤ log(g)
≤ +6.0, -4.0 ≤ [Fe/H] ≤ +1.0 and -0.3 ≤ [α/Fe] ≤ +0.8. The
library is work-in-progress and going to be extended to at least
T_{eff}=25 000 K. We use a new self-consistent way of describing
the microturbulence for our model atmospheres. The entire library
of synthetic spectra will be available for download. Furthermore we
present a method for fitting spectra, especially designed to work
with the new 2nd generation VLT instrument muse. We show that we can
determine stellar parameters (T_{eff}, log(g), [Fe/H] and [α/Fe])
and even single element abundances.

---------------------------------------------------------
Title: Surface convection: from the Sun to red giant stars
Authors: Piau, L.; Kervella, P.; Dib, S.; Hauschildt, P.
2011sf2a.conf..235P Altcode: 2011arXiv1112.1381P
We check how the change in surface conditions between the Sun and red
giant branch stars changes the characteristic surface convection length
scale to be used in models. We investigate the question in the case
of the mixing length theory and of the phenomenology of full spectrum
of turbulence. For the observational part, we rely on independent
measurements of effective temperatures and interferometric radii of
nearby red giants. We find that the local red giant branch cannot
be explained taking into account the solar calibrated convective
length scale.

---------------------------------------------------------
Title: The science of EChO
Authors: Tinetti, Giovanna; Cho, James Y. -K.; Griffith, Caitlin A.;
Grasset, Olivier; Grenfell, Lee; Guillot, Tristan; Koskinen, Tommi T.;
Moses, Julianne I.; Pinfield, David; Tennyson, Jonathan; Tessenyi,
Marcell; Wordsworth, Robin; Aylward, Alan; van Boekel, Roy; Coradini,
Angioletta; Encrenaz, Therese; Snellen, Ignas; Zapatero-Osorio, Maria
R.; Bouwman, Jeroen; Coudé du Foresto, Vincent; Lopez-Morales,
Mercedes; Mueller-Wodarg, Ingo; Pallé, Enric; Selsis, Franck;
Sozzetti, Alessandro; Beaulieu, Jean-Philippe; Henning, Thomas; Meyer,
Michael; Micela, Giuseppina; Ribas, Ignasi; Stam, Daphne; Swain,
Mark; Krause, Oliver; Ollivier, Marc; Pace, Emanuele; Swinyard,
Bruce; Ade, Peter A. R.; Achilleos, Nick; Adriani, Alberto; Agnor,
Craig B.; Afonso, Cristina; Allende Prieto, Carlos; Bakos, Gaspar;
Barber, Robert J.; Barlow, Michael; Bernath, Peter; Bézard, Bruno;
Bordé, Pascal; Brown, Linda R.; Cassan, Arnaud; Cavarroc, Céline;
Ciaravella, Angela; Cockell, Charles; Coustenis, Athéna; Danielski,
Camilla; Decin, Leen; De Kok, Remco; Demangeon, Olivier; Deroo, Pieter;
Doel, Peter; Drossart, Pierre; Fletcher, Leigh N.; Focardi, Matteo;
Forget, Francois; Fossey, Steve; Fouqué, Pascal; Frith, James;
Galand, Marina; Gaulme, Patrick; González Hernández, Jonay I.;
Grassi, Davide; Griffin, Matt J.; Grözinger, Ulrich; Guedel, Manuel;
Guio, Pactrick; Hainaut, Olivier; Hargreaves, Robert; Hauschildt,
Peter H.; Heng, Kevin; Heyrovsky, David; Hueso, Ricardo; Irwin, Pat;
Kaltenegger, Lisa; Kervella, Patrick; Kipping, David; Kovacs, Geza; La
Barbera, Antonino; Lammer, Helmut; Lellouch, Emmanuel; Leto, Giuseppe;
Lopez Morales, Mercedes; Valverde, Lopez Miguel A.; Lopez-Puertas,
Manuel; Lovi, Christophe; Maggio, Antonio; Maillard, Jean-Pierre;
Prado, Jesus Maldonado; Marquette, Jean-Baptiste; Martin-Torres,
Francisco J.; Maxted, Pierre; Miller, Steve; Molinari, Sergio; Montes,
David; Moro-Martin, Amaya; Mousis, Olivier; Tuong, Napoléon Nguyen;
Nelson, Richard; Orton, Glenn S.; Pantin, Eric; Pascale, Enzo; Pezzuto,
Stefano; Poretti, Ennio; Prinja, Raman; Prisinzano, Loredana; Réess,
Jean-Michel; Reiners, Ansgar; Samuel, Benjamin; Sanz Forcada, Jorge;
Sasselov, Dimitar; Savini, Giorgio; Sicardy, Bruno; Smith, Alan;
Stixrude, Lars; Strazzulla, Giovanni; Vasisht, Gautam; Vinatier,
Sandrine; Viti, Serena; Waldmann, Ingo; White, Glenn J.; Widemann,
Thomas; Yelle, Roger; Yung, Yuk; Yurchenko, Sergey
2011IAUS..276..359T Altcode:
The science of extra-solar planets is one of the most rapidly
changing areas of astrophysics and since 1995 the number of
planets known has increased by almost two orders of magnitude. A
combination of ground-based surveys and dedicated space missions has
resulted in 560-plus planets being detected, and over 1200 that await
confirmation. NASA's Kepler mission has opened up the possibility of
discovering Earth-like planets in the habitable zone around some of the
100,000 stars it is surveying during its 3 to 4-year lifetime. The
new ESA's Gaia mission is expected to discover thousands of new
planets around stars within 200 parsecs of the Sun. The key challenge
now is moving on from discovery, important though that remains, to
characterisation: what are these planets actually like, and why are
they as they are? In the past ten years, we have learned how to
obtain the first spectra of exoplanets using transit transmission and
emission spectroscopy. With the high stability of Spitzer, Hubble, and
large ground-based telescopes the spectra of bright close-in massive
planets can be obtained and species like water vapour, methane, carbon
monoxide and dioxide have been detected. With transit science came the
first tangible remote sensing of these planetary bodies and so one can
start to extrapolate from what has been learnt from Solar System probes
to what one might plan to learn about their faraway siblings. As we
learn more about the atmospheres, surfaces and near-surfaces of these
remote bodies, we will begin to build up a clearer picture of their
construction, history and suitability for life. The Exoplanet
Characterisation Observatory, EChO, will be the first dedicated mission
to investigate the physics and chemistry of Exoplanetary Atmospheres. By
characterising spectroscopically more bodies in different environments
we will take detailed planetology out of the Solar System and into
the Galaxy as a whole. EChO has now been selected by the European
Space Agency to be assessed as one of four M3 mission candidates.

---------------------------------------------------------
Title: CoolGrid: Modeling the Right Half of the Hertzsprung-Russell
Diagram
Authors: Short, C. I.; Hauschildt, P. H.
2011ASPC..445..173S Altcode:
We evaluate the ability of PHOENIX LTE models to fit spectrophotometry
throughout the visible and near-UV bands for late-type stars of a wide
range of stellar parameters.

---------------------------------------------------------
Title: A 3D radiative transfer framework. VIII. OpenCL implementation
Authors: Hauschildt, P. H.; Baron, E.
2011A&A...533A.127H Altcode:
 Aims: We discuss an implementation of our 3D radiative transfer
(3DRT) framework with the OpenCL paradigm for general GPU computing. Methods: We implemented the kernel for solving the 3DRT problem
in Cartesian coordinates with periodic boundary conditions in the
horizontal (x,y) plane, including the construction of the nearest
neighbor Λ∗ and the operator splitting step. 
Results: We present the results of both a small and a large test case
and compare the timing of the 3DRT calculations for serial CPUs and
various GPUs. Conclusions: The latest available GPUs can lead to
significant speedups for both small and large grids compared to serial
(single core) computations.

---------------------------------------------------------
Title: Detecting planets around very cool dwarfs at near infrared
wavelengths with the radial velocity technique
Authors: Rodler, F.; Del Burgo, C.; Witte, S.; Helling, Ch.;
Hauschildt, P. H.; Martín, E. L.; Álvarez, C.; Deshpande, R.
2011A&A...532A..31R Altcode: 2011arXiv1105.2287R
Context. Radial velocity monitoring of very cool dwarfs such as
late M- and hot L-dwarfs has become a promising tool in the search
for rocky planets as well as follow-up planetary candidates around
dwarfs detected by transit surveys. These stars are faint at optical
wavelengths, as their spectral flux distribution peaks at near-infrared
(NIR) wavelengths. For this reason, it is desirable to measure the
radial velocities in this wavelength regime. However, in the NIR very
few medium- and high-resolution spectrographs are available at large
telescopes. In the near future, high-resolution spectrographs for
the NIR will be built, which will allow us to search for rocky planets
around cool M-dwarfs and L-dwarfs from radial velocities monitoring. Aims: We investigate the precision that can be attained in radial
velocity measurements of very cool dwarfs in the NIR. The goal is to
determine in which atmospheric window of the Earth's atmosphere the
highest radial velocity precision can be achieved to help in designing
the next generation of NIR high-resolution spectrographs. 
Methods: We use stellar atmosphere synthetic models for an M- and an
L-dwarf with temperatures of 2200 K and 1800 K, respectively, and a
theoretical spectrum of the Earth's transmission in the spectral range
from 0.9 to 2.5 μm. We simulate a series of Doppler-shifted spectra
observed with different resolving powers and signal-to-noise ratios,
and for different rotational broadenings of the dwarf. For different
combinations of the input parameters, we recover the radial velocity by
means of cross-correlation with a high signal-to-noise ratio template
and determine the associate uncertainties. Results: The highest
precision in radial velocity measurements for the cool M-dwarf is found
in the Y band around 1.0 μm, while for the L-dwarf it is determined
in the J band around 1.25 μm. We note that synthetic models may lack
some faint absorption features or underestimate their abundances. In
addition, some instrumental/calibration aspects that are not taken
into account in our estimations would increase the uncertainties.

---------------------------------------------------------
Title: A 3D radiative transfer framework: XIII. OpenCL implementation
Authors: Hauschildt, Peter H.; Baron, E.
2011arXiv1107.5719H Altcode:
We discuss an implementation of our 3D radiative transfer (3DRT)
framework with the OpenCL paradigm for general GPU computing. We
implement the kernel for solving the 3DRT problem in Cartesian
coordinates with periodic boundary conditions in the horizontal $(x,y)$
plane, including the construction of the nearest neighbor $\Lstar$
and the operator splitting step. We present the results of a small and
a large test case and compare the timing of the 3DRT calculations for
serial CPUs and various GPUs. The latest available GPUs can lead to
significant speedups for both small and large grids compared to serial
(single core) computations.

---------------------------------------------------------
Title: Physical parameters of a sample of M dwarfs from
high-resolution near-infrared spectra
Authors: Del Burgo, C.; Deshpande, R.; Martín, E. L.; Zapatero Osorio,
M. R.; Witte, S.; Helling, Ch.; Hauschildt, P. H.
2011EPJWC..1604006D Altcode:
We show preliminary results about the effective temperature, surface
gravity, and projected rotational velocity of eleven M dwarfs from
the comparison of high-resolution near-infrared spectra with resolving
power of ~20,000 and atmosphere synthetic models. Our results are in
good agreement with those found in the literature. We find that the
haze of observed absorption features (mostly water vapor) is relatively
well modeled by the synthetic spectra.

---------------------------------------------------------
Title: Dust in brown dwarfs and extra-solar planets. III. Testing
synthetic spectra on observations
Authors: Witte, S.; Helling, Ch.; Barman, T.; Heidrich, N.; Hauschildt,
P. H.
2011A&A...529A..44W Altcode:
Context. This work is concerned with dust formation in ultra-cool
atmospheres, encompassing the latest type stars, brown dwarfs, and hot
giant exoplanets. Dust represents one of the most important and yet
least understood sources of opacity in these types of objects. 
Aims: We compare our model spectra with SpeX data in order to draw
conclusions about the dust cloud structure and related quantities in
ultra-cool atmospheres. Methods: We use the self-consistent
Drift-Phoenix atmosphere code, which features a kinetic dust
formation mechanism and accounts for the dust cloud influence on the
spectra. Results: We present fits of our latest model spectra
to observations that cover a wide range of our model grid. The results
are remarkably good, yielding significant improvement over the older
Cond-/Dusty-Phoenix models, especially in the L-dwarf regime. The
new models are able to properly reproduce observed spectra, including
complicated features such as the molecular band strengths. This raises
confidence in the reliability of our dust-modeling approach. 
Conclusions: We demonstrate that our code produces excellent results
concerning the fitting with observations. This suggests that our dust
cloud and atmosphere structures are reasonably accurate. Like all
other current cloud models, ours is not able to produce satisfying
results for spectral types later than L6 without manually tuning down
the amount of dust. Our results show the formation of convective cells
within the cloud, which are able to destroy the lower cloud parts. The
dust opacity is reduced significantly without the need to tune the
dust cloud thickness. There are indications that the cycle of dust
accumulation and cloud destruction by convection is time-dependent
on rather long timescales. Considering a statistical distribution of
locally variable dust clouds over a dwarf's surface can result in a
large number of spectral configurations for the same model atmosphere
parameters, hence introducing an additional and more or less random
degree of freedom to those atmospheres. Without resorting to the model
atmosphere parameters, this alone can account for the unusually red
and blue objects that have been discovered.

---------------------------------------------------------
Title: Theoretical light curves of type Ia supernovae
Authors: Jack, D.; Hauschildt, P. H.; Baron, E.
2011A&A...528A.141J Altcode: 2011arXiv1105.3330J
 Aims: We present the first theoretical SN Ia light curves
calculated with the time-dependent version of the general purpose model
atmosphere code PHOENIX. Our goal is to produce light curves and spectra
of hydro models of all types of supernovae. Methods: We extend
our model atmosphere code PHOENIX to calculate type Ia supernovae light
curves. A simple solver was implemented which keeps track of energy
conservation in the atmosphere during the free expansion phase. 
Results: The correct operation of the new additions to PHOENIX were
verified in test calculations. Furthermore, we calculated theoretical
light curves and compared them to the observed SN Ia light curves of
SN 1999ee and SN 2002bo. We obtained LTE as well as NLTE model light
curves. Conclusions: We have verified the correct operation of
our extension into the time domain. We have calculated the first SN
Ia model light curves using PHOENIX in both LTE and NLTE. For future
work the infrared model light curves need to be further investigated.

---------------------------------------------------------
Title: Discovery of an ~23 M Jup Brown Dwarf Orbiting
~700 AU from the Massive Star HIP 78530 in Upper Scorpius
Authors: Lafrenière, David; Jayawardhana, Ray; Janson, Markus;
Helling, Christiane; Witte, Soeren; Hauschildt, Peter
2011ApJ...730...42L Altcode: 2011arXiv1101.4666L
We present the discovery of a substellar companion on a wide orbit
around the ~ 2.5 M sun star HIP 78530, which is a member of
the 5 Myr old Upper Scorpius association. We have obtained follow-up
imaging over two years and show that the companion and primary share
common proper motion. We have also obtained JHK spectroscopy of the
companion and confirm its low surface gravity, in accordance with the
young age of the system. A comparison with DRIFT-PHOENIX synthetic
spectra indicates an effective temperature of 2800 ± 200 K and a
comparison with template spectra of young and old dwarfs indicates
a spectral type of M8 ± 1. The mass of the companion is estimated
to be 19-26 M Jup based on its bolometric luminosity and
the predictions of evolutionary models. The angular separation of the
companion is 4farcs5, which at the distance of the primary star, 156.7
pc, corresponds to a projected separation of ~710 AU. This companion
features one of the lowest mass ratios (~0.009) of any known companion
at separations greater than 100 AU.

---------------------------------------------------------
Title: Surface convection and red-giant radius measurements
Authors: Piau, L.; Kervella, P.; Dib, S.; Hauschildt, P.
2011A&A...526A.100P Altcode: 2010arXiv1010.3649P
Phenomenological models of convection adopt characteristic length
scales that are chosen to fit solar or stellar observations. We
investigate whether changes in these length scales are required
between the Sun and low mass stars on the red giant branch (RGB). The
question is addressed jointly in the frameworks of the mixing length
theory and the full spectrum of turbulence model. For both models,
the convective length scale is assumed to be a fixed fraction of
the local pressure scale height. We use constraints provided by the
observed effective temperatures and linear radii independently. We
consider a sample of 38 nearby giants and subgiants for which surface
temperatures and luminosities are known accurately and the radii are
determined by interferometry to better than 10%. We computed dedicated
models for the few cases where the stellar masses were determined
by asteroseismological measurements. First we calibrated the solar
models. With the same physics, we then computed RGB models for masses
between 0.9 M⊙ and 2.5 M⊙ and metallicities
ranging from [Fe/H] = -0.34 to solar. The evolution is followed up
to 103 L⊙. Special attention is given to the
opacities and the non-grey atmosphere models used as boundary conditions
for which the model of convection is the same as in the interior. For
both the mixing length theory and the full spectrum of turbulence
models, the characteristic solar length scale for convection has to
be slightly reduced to fit the lower edge of the observed RGB. The
corresponding models also agree more closely with the expected mass
distribution on the RGB and the seismic constraints. These results are
robust regardless of effective temperatures determined spectroscopically
or radii determined interferometrically are used.

---------------------------------------------------------
Title: Radiative Trasnfer Calculation Of Light Curves And Spectra
For Type Ia Sne Models
Authors: De, Soma; Baron, E.; Timmes, F.; Hauschildt, P.
2011AAS...21743424D Altcode: 2011BAAS...4343424D
We present calculations of the light curves and spectra from a suite of Type Ia supernovae models, ranging from standard
single degenerate scenarios to double degenerate collisions. We
use a fully relativistic and time dependent radiative transfer
code PHOENIX for our calculations which is time dependent in
both radiative transfer and rate equation. Simple hydrodynamic calculation is used to treat conservation of energy of the gas and
the radiation together and also allow different time-scales for
gas and radiation. Between two time steps for the calculation of
the light curve, the correct distribution of total energy change
among gas and radiation is obtained by iteratively solving for
the radiative transfer equation and hence the new temperature in
the new time step. In our work we explore systematic relationships
between the mass of 56ni mass produced, the mass of silicon group
elements produced, the white dwarf metallicity, and the mass of
unburned material

---------------------------------------------------------
Title: A 3D radiative transfer framework . VII. Arbitrary velocity
fields in the Eulerian frame
Authors: Seelmann, A. M.; Hauschildt, P. H.; Baron, E.
2010A&A...522A.102S Altcode: 2010arXiv1007.3419S
 Aims: A solution of the radiative-transfer problem in 3D with
arbitrary velocity fields in the Eulerian frame is presented. The
method is implemented in our 3D radiative transfer framework and used
in the PHOENIX/3D code. It is tested by comparison to our well-tested
1D co-moving frame radiative transfer code, where the treatment of a
monotonic velocity field is implemented in the Lagrangian frame. The
Eulerian formulation does not need much additional memory and is
useable on state-of-the-art computers, even large-scale applications
with 1000's of wavelength points are feasible. Methods: In the
Eulerian formulation of the problem, the photon is seen by the atom at
a Doppler-shifted wavelength depending on its propagation direction,
which leads to a Doppler-shifted absorption and emission. This leads
to a different source function and a different Λ^* operator in the
radiative transfer equations compared to the static case. 
Results: The results of the Eulerian 3D spherical calculations are
compared to our well-tested 1D Lagrangian spherical calculations,
the agreement is, up to vmax = 1 × 103 km
s-1 very good. Test calculation in other geometries are
also shown.

---------------------------------------------------------
Title: PHOENIX: A General-purpose State-of-the-art Stellar and
Planetary Atmosphere Code
Authors: Baron, E.; Chen, Bin; Hauschildt, P. H.
2010ascl.soft10056B Altcode:
PHOENIX is a general-purpose state-of-the-art stellar and planetary
atmosphere code. It can calculate atmospheres and spectra of stars
all across the HR-diagram including main sequence stars, giants,
white dwarfs, stars with winds, TTauri stars, novae, supernovae,
brown dwarfs and extrasolar giant planets.

---------------------------------------------------------
Title: Studying the Physical Diversity of Late-M Dwarfs with
Dynamical Masses
Authors: Dupuy, Trent J.; Liu, Michael C.; Bowler, Brendan P.; Cushing,
Michael C.; Helling, Christiane; Witte, Soeren; Hauschildt, Peter
2010ApJ...721.1725D Altcode: 2010arXiv1007.4197D
We present a systematic study of the physical properties of
late-M dwarfs based on high-quality dynamical mass measurements and
near-infrared (NIR) spectroscopy. We use astrometry from Keck natural
and laser guide star adaptive optics imaging to determine orbits for
the late-M binaries LP 349 - 25AB (M7.5+M8), LHS 1901AB (M6.5+M6.5),
and Gl 569Bab (M8.5+M9). We find that LP 349 - 25AB (Mtot
= 0.120+0.008 -0.007 Msun) is a pair
of young brown dwarfs for which Lyon and Tucson evolutionary models
jointly predict an age of 140 ± 30 Myr, consistent with the age of
the Pleiades. However, at least the primary component seems to defy
the empirical Pleiades lithium depletion boundary, implying that
the system is in fact older (if the parallax is correct) and that
evolutionary models under-predict the component luminosities for
this magnetically active binary. We find that LHS 1901AB is a pair
of very low-mass stars (Mtot = 0.194+0.025
-0.021 Msun) with evolutionary model-derived
ages consistent with the old age (&gt;6 Gyr) implied by its lack
of activity. Our improved orbit for Gl 569Bab results in a higher
mass for this binary (Mtot = 0.140+0.009
-0.008 Msun) compared to previous work (0.125 ±
0.007 Msun). We use these mass measurements along with our
published results for 2MASS J2206 - 2047AB (M8+M8) to test four sets of
ultracool model atmospheres currently in use. Fitting these models to
our NIR integrated-light spectra provides temperature estimates warmer
by ≈250 K than those derived independently from Dusty evolutionary
models given the measured masses and luminosities. We propose that model
atmospheres are more likely to be the source of this discrepancy, as it
would be difficult to explain a uniform temperature offset over such
a wide range of masses, ages, and activity levels in the context of
evolutionary models. This contrasts with the conclusion of Konopacky
et al. that model-predicted masses (given input T eff
and L bol) are at fault for differences between theory
and observations. In addition, we find an opposite (and smaller) mass
discrepancy from what they report when we adopt their model-testing
approach: masses are too high rather than too low because our T
eff estimates derived from fitting NIR spectra are ≈650 K
higher than their values from fitting broadband photometry alone. Some of the data presented herein were obtained at the W. M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California,
and the National Aeronautics and Space Administration. The Observatory
was made possible by the generous financial support of the W. M. Keck
Foundation. Based partly on observations made with ESO Telescopes
at the Paranal Observatory under program IDs 073.C-0155, 077.C-0783,
and 077.C-0441.

---------------------------------------------------------
Title: Hydrogen recombination with multilevel atoms
Authors: de, Soma; Baron, E.; Hauschildt, P. H.
2010MNRAS.407..658D Altcode: 2010arXiv1005.0580D; 2010MNRAS.tmp..936D
Hydrogen recombination is one of the most important atomic processes
in many astrophysical objects such as Type II supernova (SN II)
atmospheres, the high redshift Universe during the cosmological
recombination era and HII regions in the interstellar medium. Accurate
predictions of the ionization fraction can be quite different from
those given by a simple solution if one takes into account many angular
momentum substates, non-resonant processes and calculates the rates
of all atomic processes from the solution of the radiative transfer
equation instead of using a Planck function under the assumption of
thermal equilibrium. We use the general-purpose model atmosphere
code PHOENIX 1D to compare how the fundamental probabilities such
as the photoionization probability, the escape probability and the
collisional de-excitation probability are affected by the presence of
other metals in the environment, multiple angular momentum substates
and non-resonant processes. Our comparisons are based on a model of
SN 1999em, SNe Type II, 20 d after its explosion.

---------------------------------------------------------
Title: Modeling the Near-ultraviolet Band of GK Stars. I. Local
Thermodynamic Equilibrium Models
Authors: Short, C. Ian; Hauschildt, P. H.
2010ApJ...718.1416S Altcode:
We present a grid of LTE atmospheric models and synthetic spectra that
covers the spectral class range from mid-G to mid-K, and luminosity
classes from V to III, that is dense in T eff sampling (ΔT
eff = 62.5 K), for stars of solar metallicity and moderately
metal-poor scaled solar abundance ([{{A}\over {H}}]=0.0 and -0.5). All
models have been computed with two choices of atomic line list: (1)
the "big" line lists of Kurucz that best reproduce the broadband
solar blue and near-UV f λ level, and (2) the "small"
lists of Kurucz &amp; Peytremann that provide the best fit to the
high-resolution solar blue and near-UV spectrum. We compare our model
spectral energy distributions to a sample of stars carefully selected
from the large catalog of uniformly re-calibrated spectrophotometry of
Burnashev with the goal of determining how the quality of fit varies
with stellar parameters, especially in the historically troublesome blue
and near-UV bands. We confirm that our models computed with the "big"
line list recover the derived T eff values of the PHOENIX
NextGen grid, but find that the models computed with the "small" line
list provide greater internal self-consistency among different spectral
bands, and closer agreement with the empirical T eff scale
of Ramirez &amp; Melendez, but not to the interferometrically derived
T eff values of Baines et al. We find no evidence that the
near-UV band discrepancy between models and observations for Arcturus
(α Boo) reported in two works by Short &amp; Hauschildt is pervasive,
and that Arcturus may be peculiar in this regard.

---------------------------------------------------------
Title: Modeling the near-UV band of GK stars, Paper I: LTE models
Authors: Short, C. Ian; Hauschildt, Peter
2010arXiv1007.1433S Altcode:
We present a grid of LTE atmospheric models and synthetic spectra that
cover the spectral class range from mid-G to mid-K, and luminosity
classes from V to III, that is dense in Teff sampling (Delta Teff=62.5
K), for stars of solar metallicity and moderately metal poor scaled
solar abundance ([A/H]=0.0 and -0.5). All models have been computed
with two choices of atomic line list: a) the "big" line lists of
Kurucz (1992) that best reproduce the broad-band solar blue and near
UV flux level, and b) the "small" lists of Kurucz &amp; Peytremann
(1975) that provide the best fit to the high resolution solar blue
and near-UV spectrum. We compare our model SEDs to a sample of stars
carefully selected from the large catalog of uniformly re-calibrated
spectrophotometry of Burnashev (1985) with the goal of determining
how the quality of fit varies with stellar parameters, especially in
the historically troublesome blue and near-UV bands. We confirm that
our models computed with the "big" line list recover the derived Teff
values of the PHOENIX NextGen grid, but find that the models computed
with the "small" line list provide greater internal self-consistency
among different spectral bands, and closer agreement with the
empirical Teff scale of Ramirez &amp; Melendez (2005), but not to the
interferometrically derived Teff values of Baines et al. (2010). We
find no evidence that the near UV band discrepancy between models
and observations for Arcturus (alpha Boo) reported by Short &amp;
Hauschildt (2003 and 2009) is pervasive, and that Arcturus may be
peculiar in this regard.

---------------------------------------------------------
Title: Resolving debris discs in the far-infrared: Early highlights
from the DEBRIS survey
Authors: Matthews, B. C.; Sibthorpe, B.; Kennedy, G.; Phillips,
N.; Churcher, L.; Duchêne, G.; Greaves, J. S.; Lestrade, J. -F.;
Moro-Martin, A.; Wyatt, M. C.; Bastien, P.; Biggs, A.; Bouvier, J.;
Butner, H. M.; Dent, W. R. F.; di Francesco, J.; Eislöffel, J.;
Graham, J.; Harvey, P.; Hauschildt, P.; Holland, W. S.; Horner, J.;
Ibar, E.; Ivison, R. J.; Johnstone, D.; Kalas, P.; Kavelaars, J.;
Rodriguez, D.; Udry, S.; van der Werf, P.; Wilner, D.; Zuckerman, B.
2010A&A...518L.135M Altcode: 2010arXiv1005.5147D
We present results from the earliest observations of DEBRIS, a Herschel
key programme to conduct a volume- and flux-limited survey for debris
discs in A-type through M-type stars. PACS images (from chop/nod or
scan-mode observations) at 100 and 160 μm are presented toward two
A-type stars and one F-type star: β Leo, β UMa and η Corvi. All
three stars are known disc hosts. Herschel spatially resolves the dust
emission around all three stars (marginally, in the case of β UMa),
providing new information about discs as close as 11 pc with sizes
comparable to that of the Solar System. We have combined these data
with existing flux density measurements of the discs to refine the SEDs
and derive estimates of the fractional luminosities, temperatures and
radii of the discs. Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.

---------------------------------------------------------
Title: PHOENIX Spectra of Red Supergiants - Varying the Surface
Abundances and the Microturbulence
Authors: Lançon, A.; Hauschildt, P. H.
2010ASPC..425...61L Altcode:
Based on PHOENIX models, we briefly discuss effects of surface
abundances and microturbulence on the near-IR spectra of red supergiant
stars.

---------------------------------------------------------
Title: Hydrogen in Type Ib Supernovae
Authors: Baron, Eddie; Branch, David; Hauschildt, Peter; Ketchum,
Wesley; James, Spencer
2010pese.confE...7B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Multi-wavelength observations of a giant flare on CN
Leonis. II. Chromospheric modelling with PHOENIX
Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H.
2010A&A...511A..83F Altcode:
 Aims: In M dwarfs, optical emission lines and continua are
sensitive to changing chromospheric conditions, e.g., during flares. To
study flare conditions for an observed spectrum, a comparison to
synthesised spectra from model atmospheres is needed. Methods:
Using the stellar atmosphere code PHOENIX, we computed a set of 41 1D
NLTE parameterised chromospheric models including the photosphere and
parts of the transition region. By comparison of a linear combination
of the synthesised spectra and a quiescent (observed) chromosphere to
observed UVES/VLT spectra of a giant flare of the M 5.5 dwarf CN Leo
(Gl406), we find the best-fitting flare model chromosphere. 
Results: Our model spectra give a fairly good overall description of
the observed continua and emission lines. In the best-fitting model,
the temperature minimum is deep in the atmosphere resulting in high
electron pressure for the chromospheric flaring area. The inferred
chromospheric filling factor of the flare is about 3 percent, which
declines during the flare. The photospheric flare filling factor is
about 0.3 percent. Based on observations collected at the European
Southern Observatory, Paranal, Chile, 077.D-0011(A) and on observations
obtained with XMM-Newton, an ESA science mission with instruments and
contributions directly funded by ESA Member States and NASA.

---------------------------------------------------------
Title: A 3D radiative transfer framework. VI. PHOENIX/3D example
applications
Authors: Hauschildt, P. H.; Baron, E.
2010A&A...509A..36H Altcode: 2009arXiv0911.3285H
 Aims: We demonstrate the application of our 3D radiative transfer
framework in the model atmosphere code PHOENIX for a number of spectrum
synthesis calculations for very different conditions. Methods:
The 3DRT framework discussed in the previous papers of this series
was added to our general-purpose model atmosphere code PHOENIX/1D
and an extended 3D version PHOENIX/3D was created. The PHOENIX/3D
code is parallelized via the MPI library using a hierarchical domain
decomposition and displays very good strong scaling. Results:
We present the results of several test cases for widely different
atmosphere conditions and compare the 3D calculations with equivalent 1D
models to assess the internal accuracy of the 3D modeling. In addition,
we show the results for a number of parameterized 3D structures. Conclusions: With presently available computational resources it is
possible to solve the full 3D radiative transfer (including scattering)
problem with the same micro-physics as included in 1D modeling.

---------------------------------------------------------
Title: Watching dark matter stars burn - possible signatures of Dark
Stars in the EBL
Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt,
P.; Horns, D.
2010idm..confE..89M Altcode: 2010PoS...110E..89M
No abstract at ADS

---------------------------------------------------------
Title: Cosmic Radiation Fields: Sources in the early Universe
Authors: Raue, Martin; Kneiske, Tanja; Horns, Dieter; Elsaesser,
Dominik; Hauschildt, Peter
2010crf..work.....R Altcode: 2010PoS...121E....R
The workshop "Cosmic Radiation Fields - Sources in the Early Universe"
(CRF 2010) focuses on the connection between the extragalactic
infrared background and sources in the early universe, in particular
stars powered by dark matter burning (Dark Stars; DS). The workshop
covers the following topics: the cosmic infrared background,
formation of early stars, dark stars, effect of dark matter in the
early universe, dark matter halos, primordial star formation rate,
and reionization. Further information can be found on the conference
webpage: http://www.desy.de/crf2010/. Organizing committee: Tanja
Kneiske, Martin Raue, Dominik Elsaesser, Alexander Gewering-Peine,
Peter Hausschildt, Dieter Horns, and Andreas Maurer.

---------------------------------------------------------
Title: Constraints on dark matter powered stars from the extragalactic
background light
Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt,
P.; Horns, D.
2010tsra.confE.229M Altcode: 2010PoS...123E.229M
No abstract at ADS

---------------------------------------------------------
Title: On the hydrogen recombination time in Type II supernova
atmospheres
Authors: de, Soma; Baron, E.; Hauschildt, P. H.
2010MNRAS.401.2081D Altcode: 2009MNRAS.tmp.1740D; 2009arXiv0910.0552D
Non-local thermodynamic equilibrium radiative transfer calculations of
differentially expanding supernovae atmospheres are computationally
intensive and are almost universally performed in a time-independent
snapshot mode, where both the radiative transfer problem and the rate
equations are solved assuming the steady-state approximation. The
validity of the steady-state approximation in the rate equations has
recently been questioned for Type II supernova (SN II) atmospheres
after maximum light on to the plateau. We calculate the effective
recombination time of hydrogen in SN II using our general purpose
model atmosphere code PHOENIX. While we find that the recombination
time for the conditions of SNe II at early times is increased over the
classical value for the case of a simple hydrogen model atom with energy
levels corresponding to just the first two principal quantum numbers,
the classical value of the recombination time is recovered in the case
of a multilevel hydrogen atom. We also find that the recombination time
at most optical depths is smaller in the case of a multilevel atom than
for a simple two-level hydrogen atom. We find that time dependence in
the rate equations is important in the early epochs of a supernova's
lifetime. The changes due to the time-dependent rate equation (at
constant input luminosity) are manifested in physical parameters such as
the level populations which directly affect the spectra. The Hα profile
is affected by the time-dependent rate equations at early times. At
later times, time dependence does not significantly modify the level
populations and therefore the Hα profile is roughly independent of
whether the steady-state or time-dependent approach is used.

---------------------------------------------------------
Title: Time Dependent Radiative Transfer in Cosmic Recombination Epoch
Authors: De, Soma; Baron, E.; Hauschildt, P.
2010AAS...21543709D Altcode: 2010BAAS...42..391D
The Recmbination Epoch in cosmology (redshift of 800-1300) could be a
very useful probe of the early universe and given the potential of high
S/N observations from PLANCK we will be able to extract much information
if we have a consistent radiative transfer framework that can trace
the recombination era as a function of time. One can study a variety
of quantities such as subtle effects in the electron fraction, line
profiles, etc. We consider a patch of the early universe during
the recombination epoch with a set of spatially separated baryonic mass
points moving with a Hubble flow. The density of dark matter and dark
energy is embedded in the Hubble constant at each epoch. We treat this
as an 1D problem. This patch is treated as a snapshot of the universe
at a certain instant of time identified by redshift z and then evolve
the system in time over the recombination era. In order to do this
correctly, the time for a photon to travel across the whole patch should
be smaller than the time interval between two snapshots. We use our
very successful atmosphere code PHOENIX with time dependent radiative
transfer equation and rate equations for hydrogen, helium and lithium
to solve for the radiation field intensity at each radially separated
point at each instant of time. All elements are considered to be in NLTE
and have multi-level atomic structure. We solve the transfer equation
using the short-characteristic approach where the specific intensity
at two intersecting points between a characteristic ray and a radial
layer represent two different directions of photon propagation at a
given point but at two different instants of time. Compton scattering is
being implemented in our calculation, it is an important process in the
recombination epoch and couples the matter and radiation temperatures.

---------------------------------------------------------
Title: Constraints on dark matter powered stars from the extragalactic
background light
Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt,
P.; Horns, D.
2010crf..work...19M Altcode: 2010PoS...121E..19M
No abstract at ADS

---------------------------------------------------------
Title: Dust in brown dwarfs and extra-solar planets. II. Cloud
formation for cosmologically evolving abundances
Authors: Witte, S.; Helling, Ch.; Hauschildt, P. H.
2009A&A...506.1367W Altcode: 2009arXiv0908.3597W
Context: Substellar objects have extremely long life spans. The
cosmological consequence for older objects are low abundances for heavy
elements, which in turn results in a wide distribution of objects
over metallicity, hence over age. Within their cool atmosphere,
dust clouds become a dominant feature, affecting the opacity and
the remaining gas phase abundance of heavy elements. Aims:
We investigate the influence of the stellar metallicity on the dust
formation in substellar atmospheres and on the dust cloud structure
and its feedback on the atmosphere. This work has implications for the
general questions of star formation and of dust formation in the early
universe. Methods: We utilise numerical simulations to solve
a set of moment equations to determine the quasi-static dust cloud
structure (Drift). These equations model the nucleation, the kinetic
growth of composite particles, their evaporation, and the gravitational
settling as a stationary dust formation process. Element conservation
equations augment this system of equations by including the element
replenishment by convective overshooting. The integration with an
atmosphere code (Phoenix) allows determination of a consistent (T, p,
v_conv)-structure (T - local temperature, p - local pressure, v_conv
- convective velocity), hence, to calculate synthetic spectra. Results: A grid of Drift-Phoenix model atmospheres was calculated
for a wide range of metallicity, [M/H] in [ +0.5, -0.0, -0.5, ...,
-6.0] , to allow for systematic study of atmospheric cloud structures
throughout the evolution of the universe. We find dust clouds in even
the most metal-poor ([M/H] = -6.0) atmosphere of brown dwarfs. Only
the most massive among the youngest brown dwarfs and giant gas planets
can resist dust formation. For very low heavy element abundances,
a temperature inversion develops that has a drastic impact on the
dust cloud structure. Conclusions: The combination of metal
depletion by dust formation and the uncertainty of interior element
abundances makes the modelling of substellar atmospheres an intricate
problem in particular for old substellar objects. We furthermore show
that the dust-to-gas ratio does not scale linearly with the object's
[M/H] for a given effective temperature. The mean grain sizes and the
composition of the grains change depending on [M/H], which influences
the dust opacity that determines radiative heating and cooling, as
well as the spectral appearance.

---------------------------------------------------------
Title: Structure and spectra of irradiated secondaries in close
binaries. A model calculation of the pre-cataclysmic variable
UU Sagittae
Authors: Wawrzyn, A. C.; Barman, T. S.; Günther, H. M.; Hauschildt,
P. H.; Exter, K. M.
2009A&A...505..227W Altcode:
Context: The standard stellar model atmosphere ignores the influence
of external radiation. This assumption, while sufficient for
most stars, fails for many short-period binaries. Aims: In
setting up combined model atmospheres for close binaries, we want to
constrain the parameters of both components, especially in the case
of a hot primary component strongly influencing its cool secondary
companion. This situation can be found after common envelope evolution
(CEE). The status of both components today allows one to retrace the
CEE itself. Methods: We used our stellar atmosphere code PHOENIX,
which includes the effect of irradiation in its radiation transport
equation, to investigate the close binary star UU Sge. We combined
our calculated spectra of both components, weighted by their visible
size, and adjusted the input parameters until reasonable agreement
with observations is reached. Results: We derive a range of 80
000-85 000 K for the effective temperature of the primary (Teff,
p) and give a rough estimate for the primary's abundances,
particularly the nitrogen enrichment. The heated day-side of the
secondary has an apparent “effective” or equilibrium temperature
of 24 000-26 000 K, nearly independent of its intrinsic luminosity. It
shows an enhancement in nitrogen and carbon. Conclusions: The
evolution of the primary and secondary stars were strongly influenced
by the other's presence. Radiation from the primary on the secondary's
day-side is still an important factor in understanding the secondary's
atmospheric structure.

---------------------------------------------------------
Title: 3D Radiative Transfer with PHOENIX
Authors: Baron, E.; Chen, Bin; Hauschildt, Peter H.
2009AIPC.1171..148B Altcode: 2009arXiv0908.4273B
Using the methods of general relativity Lindquist derived the
radiative transfer equation that is correct to all orders in
v/c. Mihalas developed a method of solution for the important case
of monotonic velocity fields with spherically symmetry. We have
developed the generalized atmosphere code PHOENIX, which in 1-D has
used the framework of Mihalas to solve the radiative transfer equation
(RTE) in 1-D moving flows. We describe our recent work including 3-D
radiation transfer in PHOENIX and particularly including moving flows
exactly using a novel affine method. We briefly discuss quantitative
spectroscopy in supernovae.

---------------------------------------------------------
Title: 1D and 3D radiative transfer in circumstellar disks
Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt,
P. H.; Barman, T.
2009AIPC.1171...93H Altcode:
We present our code for the calculation of the 1D structure and
synthetic spectra of accretion disks. The code is an extension of the
well-tested stellar atmosphere code PHOENIX and is therefore capable
of including large lists of atomic and molecular lines as well as
a large set of dust species. We assume the standard accretion disk
model for geometrically thin disks and solve the radiative transfer
equation in the vertical direction for a number of disk rings with
different radii. The combination of these rings yields the total disk
spectrum. Comparison to observations of the T Tauri star GQ Lup shows
the capability of our code. Additionally, we will show first results of
3D radiative transfer calculations. We plan to investigate the effect
of rotating disks on the line profile by means of a two-level atom.

---------------------------------------------------------
Title: Methane line opacities in very cool stellar objects
Authors: Hauschildt, P. H.; Warmbier, R.; Schneider, R.; Barman, T.
2009A&A...504..225H Altcode:
Aims: We investigate the effects of different line data for methane
12CH4 on the structures of model atmospheres and low
resolution synthetic spectra for ultra-cool substellar objects. Methods: For each set of methane line data we compare the resulting
model atmospheres and spectra computed with the general purpose model
atmosphere code PHOENIX. Results: The new HGW methane line
data compares well to the HITRAN2004 data. We find the the HITRAN2004
methane lines are in some bands stronger than the HGW lines, resulting
in deeper absorption bands in the synthetic spectra. Conclusions:

---------------------------------------------------------
Title: Time-dependent radiative transfer with PHOENIX
Authors: Jack, D.; Hauschildt, P. H.; Baron, E.
2009A&A...502.1043J Altcode: 2009arXiv0907.1441J
Aims: We present first results and tests of a time-dependent extension
to the general purpose model atmosphere code PHOENIX. We aim to
produce light curves and spectra of hydro models for all types of
supernovae. Methods: We extend our model atmosphere code PHOENIX
to solve time-dependent non-grey, NLTE, radiative transfer in a special
relativistic framework. A simple hydrodynamics solver was implemented
to keep track of the energy conservation of the atmosphere during free
expansion. Results: The correct operation of the new additions
to PHOENIX were verified in test calculations. Conclusions: We
have shown the correct operation of our extension to time-dependent
radiative transfer and will be able to calculate supernova light curves
and spectra in future work.

---------------------------------------------------------
Title: Physical parameters of T dwarfs derived from high-resolution
near-infrared spectra
Authors: Del Burgo, C.; Martín, E. L.; Zapatero Osorio, M. R.;
Hauschildt, P. H.
2009A&A...501.1059D Altcode: 2009arXiv0903.4461D
Aims: We determine the effective temperature, surface gravity and
projected rotational velocity of nine T dwarfs from the comparison of
high-resolution near-infrared spectra and synthetic models, and estimate
the mass and age of the objects from state-of-the-art models. Methods: We use the AMES-COND cloudless solar metallicity models
provided by the PHOENIX code to match the spectra of nine T-type field
dwarfs observed with the near-infrared high-resolution spectrograph
NIRSPEC using ten echelle orders to cover part of the J band from 1.147
to 1.347 μm with a resolving power R∼20 000. The projected rotational
velocity, effective temperature and surface gravity of the objects are
determined based on the minimum root mean square of the differences
between the modelled and observed relative fluxes. Estimates of the mass
and age of the objects are obtained from effective temperature-surface
gravity diagrams, where our results are compared with existing solar
metallicity models. Results: The modelled spectra reproduce quite
well the observed features for most of the T dwarfs, with effective
temperatures in the range of 922-1009 K, and surface gravities between
104.1 and 104.9 cm s-2. Our results
support the assumption of a dust free atmosphere for T dwarfs later
than T5, where dust grains form and then gravitationally sediment
into the low atmosphere. The modelled spectra do not accurately mimic
some individual very strong lines like the K i doublet at 1.2436 and
1.2525 μm. Our modelled spectra does not match well the observed
spectra of the two T dwarfs with earlier spectral types, namely
<ASTROBJ>SDSSp J125453.90-012247.4</ASTROBJ> (T2) and <ASTROBJ>2MASS
J05591914-1404488</ASTROBJ> (T4.5), which is likely due to the presence
of condensate clouds that are not incorporated in the models used
here. By comparing our results and their uncertainties to evolutionary
models, we estimate masses in the interval ≈5-75~MJ for
T dwarfs later than T5, which are in good agreement with those found
in the literature. We found apparent young ages that are typically
between 0.1 and a few Gyr for the same T dwarfs, which is consistent
with recent kinematical studies. Reduced NIRSPEC spectra of
the nine T-type dwarfs are available electronically in fits format
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/1059

---------------------------------------------------------
Title: Comoving-frame radiative transfer in arbitrary velocity
fields. II. Large scale applications
Authors: Knop, S.; Hauschildt, P. H.; Baron, E.
2009A&A...501..813K Altcode: 2009arXiv0909.4264K
Aims: A solution of the radiative-transfer problem in arbitrary
velocity fields introduced in a previous paper, has limitations in its
applicability. For large-scale applications, the methods described
also require large memory sets that are commonly not available
to state-of-the-art computing hardware. In this work, we modify
the algorithm to allow the computation of large-scale problems. Methods: We reduce the memory footprint via a domain decomposition. By
introducing iterative Gauss-Seidel type solvers, we improve the speed
of the overall computation. Because of the domain decomposition, the
new algorithm requires the use of parallel-computing systems. Results: The algorithm that we present permits large-scale
solutions of radiative-transfer problems that include arbitrary
wavelength couplings. In addition, we discover a quasi-analytic formal
solution of the radiative transfer that significantly improves the
overall computation speed. More importantly, this method ensures
that our algorithm can be applied to multi-dimensional Lagrangian
radiative-transfer calculations. In multi-dimensional atmospheres,
velocity fields are in general chaotic ensuring that the inclusion of
arbitrary wavelength couplings are mandatory.

---------------------------------------------------------
Title: Spectral synthesis of circumstellar disks - application to
white dwarf debris disks
Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt, P.
2009JPhCS.172a2060H Altcode: 2009arXiv0905.0329H
Gas and dust disks are common objects in the universe and can be
found around various objects, e.g. young stars, cataclysmic variables,
active galactic nuclei, or white dwarfs. The light that we receive from
disks provides us with clues about their composition, temperature,
and density. In order to better understand the physical and chemical
dynamics of these disks, self-consistent radiative transfer simulations
are inevitable. Therefore, we have developed a 1+1D radiative transfer
code as an extension to the well-established model atmosphere code
PHOENIX. We will show the potential of the application of our code to
model the spectra of white dwarf debris disks.

---------------------------------------------------------
Title: A 3D radiative transfer framework. IV. Spherical and
cylindrical coordinate systems
Authors: Hauschildt, P. H.; Baron, E.
2009A&A...498..981H Altcode: 2009arXiv0903.1949H
Aims: We extend our framework for 3D radiative transfer calculations
with a non-local operator splitting methods along (full) characteristics
to spherical and cylindrical coordinate systems. These coordinate
systems are better suited to a number of physical problems than
Cartesian coordinates. Methods: The scattering problem for
line transfer is solved via means of an operator splitting (OS)
technique. The formal solution is based on a full characteristics
method. The approximate Λ operator is constructed considering nearest
neighbors exactly. The code is parallelized over both wavelength and
solid angle using the MPI library. Results: We present the results
of several test cases with different values of the thermalization
parameter for the different coordinate systems. The results are
directly compared to 1D plane parallel tests. The 3D results agree
very well with the well-tested 1D calculations. Conclusions:
Advances in modern computers will make realistic 3D radiative transfer
calculations possible in the near future.

---------------------------------------------------------
Title: Radiative Transfer Calculations In The Context of Cosmological
Recombination
Authors: De, Soma; Baron, E.; Hauschildt, P.
2009AAS...21441301D Altcode:
We present preliminary results of the ionization fractions and hence
the CMB power spectrum in the cosmological recombination era by solving
both the cosmological rate equations and radiative transfer equations
simultaneously. We use our NLTE moving radiative tranfer code PHOENIX
and multi-level hydrogen and helium atoms. We work in the comoving
frame. Periodic boundary conditions are used and the transfer equation
is iterated to solve for the radiation field. Once we have determined
the radiation field we solve the energy equation to obtain the matter
temperatures which is used to iteratively solve for the ionization
fractions from the time dependent rate equations.

---------------------------------------------------------
Title: A 3D radiative transfer framework. V. Homologous flows
Authors: Baron, E.; Hauschildt, P. H.; Chen, B.
2009A&A...498..987B Altcode: 2009arXiv0903.2486B
Context: Observations and theoretical calculations have shown the
importance of non-spherically symmetric structures in supernovae. Thus,
the interpretation of observed supernova spectra requires the ability
to solve the transfer equation in 3-D moving atmospheres. Aims:
We present an implementation of the solution of the radiative transfer
equation in 3-D homologously expanding atmospheres in spherical
coordinates. The implementation is exact to all orders in v/c. Methods: We use the methods that we have developed in previous
papers in this series as well as a new affine method that makes use
of the fact that photons travel on straight lines. The affine method
greatly facilitates delineating the characteristics and can be used
in the case of strong-gravitational and arbitrary-velocity fields. Results: We compare our results in 3-D for spherically symmetric test
problems with high velocity fields (up to 87% of the speed of light)
and find excellent agreement, when the number of momentum space angles
is high. Our well-tested 1-D results are based on methods where the
momentum directions vary along the characteristic (co-moving momentum
directions). Thus, we are able to verify both the analytic framework
and its numerical implementation. Additionally, we have been able to
test the parallelization over characteristics. Using 5122
momentum angles we ran the code on 16 384 Opteron processors and
achieved excellent scaling. Conclusions: It is now possible to
calculate synthetic spectra from realistic 3D hydro simulations. This
should open an era of progress in hydro modeling, similar to that that
occurred in the 1980s when 1-D models were confronted with synthetic
spectra.

---------------------------------------------------------
Title: Optical and Near-Infrared Spectroscopy of the L Subdwarf
SDSS J125637.13-022452.4
Authors: Burgasser, Adam J.; Witte, Soeren; Helling, Christiane;
Sanderson, Robyn E.; Bochanski, John J.; Hauschildt, Peter H.
2009ApJ...697..148B Altcode: 2009arXiv0903.1567B
Red optical and near-infrared spectroscopy are presented for SDSS
J125637.13-022452.4, one of only four L subdwarfs reported to
date. These data confirm the low-temperature, metal-poor nature of
this source, as indicated by prominent metal-hydride bands, alkali
lines, and collision-induced H2 absorption. The optical
and near-infrared spectra of SDSS J1256-0224 are similar to those
of the sdL4 2MASS J16262034+3925190, and we derive a classification
of sdL3.5 based on the preliminary scheme of Burgasser, Cruz, and
Kirkpatrick. The kinematics of SDSS J1256-0224 are consistent with
membership in the Galactic inner halo, with estimated UVW space
velocities indicating a slightly prograde, eccentric, and inclined
Galactic orbit (3.5 lsim R lsim 11 kpc; midZ maxmid = 7.5
kpc). Comparison to synthetic spectra computed with the PHOENIX code,
including the recent implementation of kinetic condensate formation
(DRIFT-PHOENIX), indicates T eff ≈ 2100-2500 K and [M/H]
≈ -1.5 to -1.0 for log g ≈ 5.0-5.5 (cgs), although there are clear
discrepancies between model and observed spectra particularly in the red
optical region. As such, any conclusions on the role of metallicity in
condensate grain and cloud formation are probably premature. Indeed,
a shift in the temperature scale of L subdwarfs relative to L dwarfs
may obviate the need for modified condensate and grain chemistry in low
metallicity atmospheres. This paper includes data gathered with the
6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Infrared spectra of 9 T dwarfs
(del Burgo+, 2009)
Authors: Del Burgo, C.; Martin, E. L.; Zapatero-Osorio, M. R.;
Hauschildt, P.
2009yCat..35011059D Altcode:
High-resolution near-infrared spectra in the J-band of nine T
dwarfs were obtained using the Keck II telescope and the NIRSPEC
spectrograph. (2 data files).

---------------------------------------------------------
Title: Radiative transfer in circumstellar disks. I. 1D models for
GQ Lupi
Authors: Hügelmeyer, S. D.; Dreizler, S.; Hauschildt, P. H.; Seifahrt,
A.; Homeier, D.; Barman, T.
2009A&A...498..793H Altcode: 2009arXiv0903.2381H
We present a new code for the calculation of the 1D structure and
synthetic spectra of accretion disks. The code is an extension of the
general purpose stellar atmosphere code PHOENIX and is therefore capable
of including extensive lists of atomic and molecular lines as well as
dust in the calculations. We assume that the average viscosity can be
represented by a critical Reynolds number in a geometrically thin disk
and solve the structure and radiative transfer equations for a number
of disk rings in the vertical direction. The combination of these
rings provides the total disk structure and spectrum. Since the warm
inner regions of protoplanetary disks show a rich molecular spectrum,
they are well suited for a spectral analysis with our models. In this
paper we test our code by comparing our models with high-resolution
VLT CRIRES spectra of the T Tauri star GQ Lup.

---------------------------------------------------------
Title: A new formal solution of the radiative transfer in arbitrary
velocity fields
Authors: Knop, S.; Hauschildt, P. H.; Baron, E.
2009A&A...496..295K Altcode: 2009arXiv0902.1876K
Aims: We present a new formal solution of the Lagrangian equation of
radiative transfer that is useful in solving the equation of radiative
transfer in the presence of arbitrary velocity fields. Methods:
Normally a term due to the inclusion of the wavelength derivative
in the Lagrangian equation of radiative transfer is associated
with a generalised opacity. In non-monotonic velocity fields, this
generalised opacity may become negative. To ensure that the opacity
remains positive, this term of the derivative is included in the
formal solution of the radiative transfer problem. Results:
The new definition of the generalised opacity allows for a new
solution of the equation of radiative transfer in the presence of
velocity fields. It is especially useful for arbitrary velocity fields,
where it effectively prevents the occurrences of negative generalised
opacities and still allows the explicit construction of the Λ-operator
of the system needed for an accelerated Λ-iteration. We performed
test calculations, where the results of old, established solutions
were compared with the new solution. The relative deviations never
exceeded 1% and so the new solution is indeed suitable for use in
radiative-transfer modelling. Non-monotonic velocity fields along photon
paths frequently occur in three-dimensional hydrodynamical models of
astrophysical atmospheres. Therefore, the formal solution will be of use
for multidimensional radiative transfer and has immediate applications
in the modelling of pulsating stars and astrophysical shock fronts.

---------------------------------------------------------
Title: Stellar model atmospheres with abundance stratification
Authors: LeBlanc, F.; Monin, D.; Hui-Bon-Hoa, A.; Hauschildt, P. H.
2009A&A...495..937L Altcode:
Context: Atomic diffusion is believed to be an important physical
process in the atmospheres of several types of stars. Stellar
atmospheres, including the stratification of the elements due to
diffusion, are then needed to properly compare theoretical results to
observations for such stars. Aims: This paper aims to estimate
the effect of vertical abundance stratification on the atmospheric
structure of stars and its potential importance regarding observational
anomalies for various types of stars. Methods: Simulations using
a modified version of the PHOENIX atmosphere code will be described,
while taking vertical abundance stratification into account. Results: Our results show that large abundance gradients can exist in
the atmospheres of Ap and blue horizontal branch stars. Stratification
can also lead to relatively large atmospheric structural changes. The
effect of elemental stratification on the atmospheric structure might
well be able to explain the well-known core-wing anomaly of the Balmer
lines observed for cool Ap stars.

---------------------------------------------------------
Title: The Cosmological Evolution of Dust Clouds in Brown Dwarf
Atmospheres
Authors: Witte, S.; Helling, Ch.; Hauschildt, P. H.
2009AIPC.1094..572W Altcode: 2009csss...15..572W
We present our latest DRIFT-PHOENIX model results for dust cloud
formation in cool atmospheres and investigate the influence of the
metallicity [M/H] on the dust cloud structure on the example of a
typical mid-L dwarf (Teff = 2000 K, log (g) = 5.0). Our new dust model
simulates the formation of TiO2 seed particles (nucleation)
and their subsequent gravitational settling, accompanied by kinetic
growth and evaporation of seven solid species on top of these seeds. The
gas phase depletion by each of the considered surface reactions and the
element replenishment by convective up-mixing are consistently coupled
into this mechanism. The result is a stationary cloud structure in
phase-non-equilibrium. We observe a comparably low decrease of the
dust particle number density and a weak increase of the mean grain
size in the lower dust cloud for decreasing metallicities down to
[M/H] = -4.0. For even lower metallicities to [M/H] = -6.0, these
trends are reversed.

---------------------------------------------------------
Title: Non-LTE Modeling of the Near-Ultraviolet Band of Late-Type
Stars
Authors: Short, C. Ian; Hauschildt, P. H.
2009ApJ...691.1634S Altcode: 2008arXiv0811.1145S
We investigate the ability of both LTE and non-LTE (NLTE) models to
fit the near-UV band absolute flux distribution, f λ(λ),
and individual spectral line profiles of three standard stars for
which high-quality spectrophotometry and high-resolution spectroscopy
are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5
IV-V). We investigate (1) the effect of the choice of atomic line list
on the ability of NLTE models to fit the near-UV band f λ
level, (2) the amount of a hypothesized continuous thermal absorption
extinction source required to allow NLTE models to fit the observations,
and (3) the semiempirical temperature structure, T kin(log
τ5000), required to fit the observations with NLTE models
and standard continuous near-UV extinction. We find that all models that
are computed with high-quality atomic line lists predict too much flux
in the near-UV band for Arcturus, but fit the warmer stars well. The
variance among independent measurements of the solar irradiance in
the near-UV is sufficiently large that we cannot definitely conclude
that models predict too much near-UV flux, in contrast to other recent
results. We surmise that the inadequacy of current atmospheric models
of K giants in the near-UV band is best addressed by hypothesizing
that there is still missing continuous thermal extinction, and that
the missing near-UV extinction becomes more important with decreasing
effective temperature for spectral classes later than early G,
suggesting a molecular origin.

---------------------------------------------------------
Title: Ab initio modeling of molecular IR spectra of astrophysical
interest: application to CH4
Authors: Warmbier, R.; Schneider, R.; Sharma, A. R.; Braams, B. J.;
Bowman, J. M.; Hauschildt, P. H.
2009A&A...495..655W Altcode:
Aims: We describe an ab initio-based numerical method of obtaining
infrared spectroscopic data (line list) of polyatomic molecules that
allows calculation of complete sets of lines for temperatures up to
several thousand Kelvin. While the main focus is on completeness
and consistency, not spectroscopic accuracy, the approach is
in principle “exact” for line positions and, although not
exact for line strengths, of sufficient accuracy to be of value,
especially in wavelength regions where there are gaps in reliable
experimental data. Methods: Global potential energy and dipole
moment hypersurfaces are fitted to the results of ab initio electronic
structure calculations. The MULTIMODE software is then used to obtain
rovibrational energy levels and dipole transition matrix elements. This
information is used to calculate a complete set of Einstein coefficients
of spontaneous emission A ij. Results: The method is
applied to obtain a spectroscopic database for methane containing over
1.4 million lines up to an upper state energy of 6200 cm-1
( ∼ 9000 K). The emission spectrum of CH4 at 1000 K is calculated
with the complete set of Einstein coefficients and compared with
the one obtained from the HITRAN database. Gaps in the database are
realistically filled in by the calculated spectrum. Conclusions:
Consistent and complete databases are important for astrophysical
applications. Databases obtained by the method described here fulfill
this requirement and are sufficiently accurate for astrophysical
applications such as model atmosphere calculations and the corresponding
synthetic spectra.

---------------------------------------------------------
Title: Spectral synthesis of inner gaseous protoplanetary disks
with PHOENIX
Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt,
P. H.; Barman, T.
2009AIPC.1094..389H Altcode: 2009csss...15..389H
The inner gaseous regions of protoplanetary disks are of special
interest in the formation and evolution of planets and stars because
they are the likely birthplaces of planets and serve as the accretion
reservoir for young stars. The study of inner disks may give rise to a
better understanding of the dynamics, physical and chemical structure,
and gas content of the region. As a first step, we have developed a 1+1D
disk radiative transfer package as an extension to the well established
multipurpose stellar atmosphere program PHOENIX. The solution of
the equations of momentum and energy conservation as well as the
radiative transfer equation is adopted for the physical conditions in
and the geometry of disks. Irradiation by the central star is treated in
detail. Comparison of our models with high-resolution infrared spectra
will enable us to constrain the structure, dynamics, and gas content of
disks, and thus give new insights on the physical processes governing
star and planet formation. Additionally, we present our current
construction site: a 3D radiative transfer code for accretion disks.

---------------------------------------------------------
Title: Geometry of irradiated stars
Authors: Wawrzyn, A. C.; Günther, H. M.; Barman, T. S.; Hauschildt,
P. H.
2009AIPC.1094..973W Altcode: 2009csss...15..973W
The physical conditions in a variety of objects (e.g. hot exoplanets and
close binaries) are fundamentally influenced by external irradiation. In
static cases this leads to the development of zones of different
temperatures on the `day-side'. In order to combine spectra from all
zones to a full visible circular disk and to obtain a 1.5D spectrum we
need to calculate the weight of each patch. In the following we present
the geometrical considerations and calculate the observed projected
area of constant temperature in an irradiated object for specific
re-radiation angles. This allows non-isotropic models to be used. We
supply an IDL code to calculate the observed projected area for any
patch given the phase and angle between surface and line of sight as
well as a proper weighting for each by numerical integration. We end
up with a simple approach to upgrade a 1D irradiation model to a quasi
1.5D one. This method can be applied e.g. to irradiated secondaries
in close binaries.

---------------------------------------------------------
Title: Medium-resolution infrared integral field spectroscopy of
the brown dwarf TWA 5 B
Authors: Neuhäuser, Ralph; Schmidt, Tobias O. B.; Seifahrt, Andreas;
Bedalov, Ana; Helling, Christiane; Witte, Sören; Hauschildt, Peter
2009AIPC.1094..844N Altcode: 2009csss...15..844N
We obtained medium-resolution infrared K-band integral field
spectroscopy with VLT/Sinfoni for the brown dwarf TWA 5 B, a companion
to the weak-line T Tauri star TWA 5 in the TW Hya association. We
compare the final spectrum with theoretical model atmospheres from
DRIFT-PHOENIX (Dehn et al. 2007, Helling et al. 2008 ab, Witte 2008)
for temperature from 2000 to 3100 K, gravity log g = 3.0, 3.5, and 4.0
(g in cm/s2) and metallicity -0.5, 0.0 (solar), and 0.5;
we also varried the extinction towards TWA 5 B while searching for the
best-fit model between Av = 0.0 and 15 mag. The best-fitting
model spectrum yields the following parameters for TWA 5 B: Effective
temperature Teff~=2800 K, metallicity [M/H]~=-0.5 (for metal content M),
surface gravity log g~=4.0, and extinction Av = 0.0 mag. From
these parameters and the distance towards TWA (~65 pc), we can compute
the mass of the brown dwarf to be roughly 25 Jupiter masses, but with
large error bars including massive planets and low-mass stars. Given its
projected separation from the primary star, ~123 AU, it has certainly
more likely formed star-like, i.e. being a brown dwarf companion.

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Landstreet, John D.; Asplund, Martin; Spite, Monique;
Balachandran, Suchitra B.; Berdyugina, Svetlana V.; Hauschildt, Peter
H.; Ludwig, Hans G.; Mashonkina, Lyudmila I.; Nagendra, K. N.; Puls,
Joachim; Randich, M. Sofia; Tautvaisiene, Grazina
2009IAUTA..27..222L Altcode:
Commission 36 covers the whole field of the physics of stellar
atmospheres. The scientific activity in this large subject has been very
intense during the last triennium and led to the publication of a large
number of papers, which makes a complete report quite impractical. We
have therefore decided to keep the format of the preceding report:
first a list of areas of current research, then Web links for obtaining
further information.

---------------------------------------------------------
Title: Importance of Time-dependence in the Rate Equations in SN
Type II Atmosphere and Estimation of Recombination Time
Authors: De, Soma; Baron, E.; Hauschildt, P.
2009AAS...21349001D Altcode: 2009BAAS...41..465D
We address the issue of importance of time dependence in the
rate equations in the atomospheres of Type II supernovae on the
plateau. Recently, Utrobin and Chugai (2006) argued that time-dependence
is required to obtain the correction ionization state. The showed that
they could better reproduces the Balmer lines in SN 1987A by including
time-dependent rate equations However, there are many degenerate ways
to produce stronger Balmer lines on the plateau, for example, using a
more complex density structure than just a single power-law. Utrobin
and Chugai's argument that the recombination time is long compared
to the age of the supernova is based on a two-level hydrogen atom
model. However, supernova atmospheres include multilevel atoms and hence
more lines and electron donors could affect the ionization state and
hence the recombination time. We calculate the recombination time from
our radiative transfer code PHOENIX from fundamental principles by just
adding up the net continuum transitions for each bound state treated in
NLTE. We treat H, He in NLTE to start with and then add other elements
such as Fe (which are all present in LTE) into NLTE as we proceed. We
compare this recombination time to a typical type II supernova on the
plateau to access the importance of time dependence in rate equations.

---------------------------------------------------------
Title: 3-D Radiative Transfer in the Next Decade
Authors: Baron, E.; Hauschildt, Peter H.
2009astro2010S..11B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Division VIII / Working Group Supernova
Authors: Hillebrandt, Wolfgang; Schmidt, Brian P.; Baron, Edward;
Benetti, Stefano; Blinnikov, Sergey I.; Blinnikov, Sergey I.; Branch,
David R.; Cappellaro, Enrico; Filippenko, Alexei V.; Fransson,
Claes; Garnavich, Peter M.; Green, Daniel W. E.; Goobar, Ariel M.;
Hamuy, Mario; Hauschildt, Peter H.; Kirshner, Robert P.; Leibundgut,
Bruno; Lennon, Daniel J.; Lentz, Eric J.; Lundqvist, Peter; McGraw,
Robert; Mazzali, Paolo A.; Meikle, W. Peter S.; Mezzacappa, Anthony;
Niemeyer, Jens C.; Nomoto, Ken'ichi; Pain, Reynald; Panagia, Nino;
Patat, Ferdinando; Phillips, Mark M.; Pian, Elena; Pignata, Guiliano;
Podsiadlowski, Philipp; Ruiz-Lapuente, María Pilar; Sadler, Elaine
M.; Schmidt, Brian P.; Shull, Peter O.; Spyromilio, Jason; Suntzeff,
Nicholas B.; Thielemann, Friedrich-Karl; Tout, Christopher; Trimble,
Virginia L.; Truran, James W.; Tsvetkov, Dmitry Yu.; Turatto, Massimo;
della Valle, Massimo; Van Dyk, Schuyler; Voges, Wolfgang H.; Walton,
Nicholas A.; Wang, Lifan; Wheeler, J. Craig; Weiler, Kurt W.;
Whitelock, Patricia A.; Woosley, Stanford E.; Yamaoka, Hitoshi;
Zhao, Gang
2009IAUTA..27..295H Altcode:
The Supernova Working Group was re-established at the IAU XXV General
Assembly in Sydney, 21 July 2003, sponsored by Commissions 28 (Galaxies)
and 47 (Cosmology). Here we report on some of its activities since 2005.

---------------------------------------------------------
Title: Reflectance spectra of earth-like exoplanets .
Authors: Wagner, M.; Hauschildt, P. H.
2009MmSAI..80..667W Altcode:
Numerical simulations on irradiated exoplanets provide spectra that
contain informations about the temperature- and density structure and
chemical composition of the exoplanetary atmosphere. The calculation of
cool objects is challenging, because of the much more complex chemistry,
i.e. the strong molecular abundances as well as the occurrence of
dust formation. In order to create an object with planetary features,
such as size, temperature and abundances, the stellar atmosphere
code PHOENIX had to be adapted in an appropriate way. Starting with an
object of Venus-like parameters in 1D (spherical setup), temperature and
optical depth will be reduced to Earth-like values. But in an optically
thin atmosphere, what influence might the surface texture have on the
combined spectrum? An albedo module has already been embedded to serve
the cases of non-angular dependence (e.g. soils, vegetation) and angular
dependence, i.e. water surface. The aim is to expand the work to 3D.

---------------------------------------------------------
Title: A comparison of chemistry and dust cloud formation in ultracool
dwarf model atmospheres
Authors: Helling, Ch.; Ackerman, A.; Allard, F.; Dehn, M.; Hauschildt,
P.; Homeier, D.; Lodders, K.; Marley, M.; Rietmeijer, F.; Tsuji, T.;
Woitke, P.
2008MNRAS.391.1854H Altcode: 2008arXiv0809.3657H; 2008MNRAS.tmp.1310H
The atmospheres of substellar objects contain clouds of oxides,
iron, silicates and other refractory condensates. Water clouds
are expected in the coolest objects. The opacity of these `dust'
clouds strongly affects both the atmospheric temperature-pressure
profile and the emergent flux. Thus, any attempt to model the spectra
of these atmospheres must incorporate a cloud model. However, the
diversity of cloud models in atmospheric simulations is large and it
is not always clear how the underlying physics of the various models
compare. Likewise, the observational consequences of different modelling
approaches can be masked by other model differences, making objective
comparisons challenging. In order to clarify the current state of the
modelling approaches, this paper compares five different cloud models
in two sets of tests. Test case 1 tests the dust cloud models for a
prescribed L-, L-T and T-dwarf atmospheric (temperature T, pressure p,
convective velocity vconv) structures. Test case 2 compares
complete model atmosphere results for given (effective temperature
Teff, surface gravity logg). All models agree on the global
cloud structure but differ in opacity relevant details such as grain
size, amount of dust, dust and gas-phase composition. These models can
loosely be grouped into high- and low-altitude cloud models whereas
the first appears generally redder in near-infrared colours than the
latter. Comparisons of synthetic photometric fluxes translate into a
modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf)
test case of 0.25 &lt;~ Δm &lt;~ 0.875 (0.1 &lt;~ Δm &lt;~ 1.375),
taking into account the Two-Micron All Sky Survey, the UKIRT WFCAM,
the Spitzer IRAC and VLT VISIR filters with UKIRT WFCAM being the most
challenging for the models. Future developments will need closer links
with laboratory astrophysics, and a consistent treatment of the cloud
chemistry and turbulence.

---------------------------------------------------------
Title: Lithium Depletion of Nearby Young Stellar Associations
Authors: Mentuch, Erin; Brandeker, Alexis; van Kerkwijk, Marten H.;
Jayawardhana, Ray; Hauschildt, Peter H.
2008ApJ...689.1127M Altcode: 2008arXiv0808.3584M
We estimate cluster ages from lithium depletion in five
pre-main-sequence groups found within 100 pc of the Sun: the TW Hydrae
association, η Chamaeleontis cluster, β Pictoris moving group,
Tucanae-Horologium association, and AB Doradus moving group. We
determine surface gravities, effective temperatures, and lithium
abundances for over 900 spectra through least-squares fitting to
model-atmosphere spectra. For each group, we compare the dependence of
lithium abundance on temperature with isochrones from pre-main-sequence
evolutionary tracks to obtain model-dependent ages. We find that the η
Cha cluster and the TW Hydrae association are the youngest, with ages
of 12 +/- 6 Myr and 12 +/- 8 Myr, respectively, followed by the β Pic
moving group at 21 +/- 9 Myr, the Tucanae-Horologium association at 27
+/- 11 Myr, and the AB Dor moving group at an age of at least 45 Myr
(whereby we can only set a lower limit, since the models—unlike real
stars—do not show much lithium depletion beyond this age). Here the
ordering is robust, but the precise ages depend on our choice of both
atmospheric and evolutionary models. As a result, while our ages are
consistent with estimates based on Hertzsprung-Russell isochrone fitting
and dynamical expansion, they are not yet more precise. Our observations
do show that with improved models, much stronger constraints should be
feasible, as the intrinsic uncertainties, as measured from the scatter
between measurements from different spectra of the same star, are very
low: around 10 K in effective temperature, 0.05 dex in surface gravity,
and 0.03 dex in lithium abundance.

---------------------------------------------------------
Title: Nova V2362 Cygni (nova Cygni 2006): Spitzer, Swift, and
Ground-Based Spectral Evolution
Authors: Lynch, David K.; Woodward, Charles E.; Gehrz, Robert; Helton,
L. Andrew; Rudy, Richard J.; Russell, Ray W.; Pearson, Richard;
Venturini, Catherine C.; Mazuk, S.; Rayner, John; Ness, Jan-Uwe;
Starrfield, Sumner; Wagner, R. Mark; Osborne, Julian P.; Page, Kim;
Puetter, Richard C.; Perry, R. Brad; Schwarz, Greg; Vanlandingham,
Karen; Black, John; Bode, Michael; Evans, Aneurin; Geballe, Thomas;
Greenhouse, Matthew; Hauschildt, Peter; Krautter, Joachim; Liller,
William; Lyke, James; Truran, Jim; Kerr, T.; Eyres, S. P. S.; Shore,
Steven N.
2008AJ....136.1815L Altcode:
Nova V2362 Cygni has undergone a number of very unusual
changes. Ground-based spectroscopy initially revealed a normal sequence
of events: the object faded and its near-infrared emission lines
gradually shifted to higher excitation conditions until about day 100
when the optical fading reversed and the object slowly brightened. This
was accompanied by a rise in the Swift X-ray telescope flux and a
sudden shift in excitation of the visible and IR spectrum back to low
levels. The new lower excitation spectrum revealed broad line widths
and many P-Cygni profiles, all indicative of the ejection of a second
shell. Eventually, dust formed, the X-ray brightness—apparently
unaffected by dust formation—peaked and then declined, and the object
faded at all wavelengths. The Spitzer dust spectra revealed a number
of solid-state emission features that, at this time, are not identified.

---------------------------------------------------------
Title: Multilayered Spectral Formation in Type Ia Supenovae around
Maximum Light
Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David;
Hauschildt, Peter H.
2008ApJ...687..456B Altcode: 2008arXiv0806.3287B
We use the radiative transfer code PHOENIX to study the line formation
of the wavelength region 5000-7000 Å. This is the region where the SN
Ia-defining Si II feature occurs. This region is important, since the
ratio of the two nearby silicon lines has been shown to correlate with
the absolute blue magnitude. We use a grid of LTE synthetic spectral
models to investigate the formation of line features in the spectra of
SNe Ia. By isolating the main contributors to the spectral formation,
we show that the ions that drive the spectral ratio are Fe III, Fe
II, Si II, and S II. While the former two strongly dominate the flux
transfer, the latter two form in the same physical region inside the
supernova. We also show that the naive blackbody that one would derive
from a fit to the observed spectrum is very different than the true
underlying continuum.

---------------------------------------------------------
Title: Direct evidence of a sub-stellar companion around CT
Chamaeleontis
Authors: Schmidt, T. O. B.; Neuhäuser, R.; Seifahrt, A.; Vogt, N.;
Bedalov, A.; Helling, Ch.; Witte, S.; Hauschildt, P. H.
2008A&A...491..311S Altcode: 2008arXiv0809.2812S
Aims: In our ongoing search for close and faint companions around T
Tauri stars in the Chamaeleon star-forming region, we here present
observations of a new common proper motion companion to the young
T-Tauri star and Chamaeleon member CT Cha and discuss its properties
in comparison to other young, low-mass objects and to synthetic
model spectra from different origins. Methods: Common proper
motion of the companion and CT Cha was confirmed by direct Ks-band
imaging data taken with the VLT Adaptive Optics (AO) instrument NACO
in February 2006 and March 2007, together with a Hipparcos binary
for astrometric calibration. An additional J-band image was taken in
March 2007 to obtain color information for a first classification of
the companion. Moreover, AO integral field spectroscopy with SINFONI
in J, and H+K bands was obtained to deduce physical parameters of
the companion, such as temperature and extinction. Relative flux
calibration of the bands was achieved using photometry from the NACO
imaging data. Results: We found a very faint (Ks = 14.9 mag,
Ks0 = 14.4 mag) object, just ~2.67´´ northwest of CT
Cha corresponding to a projected separation of ~440 AU at 165 ± 30
pc. We show that CT Cha A and this faint object form a common proper
motion pair and that the companion is by ≥4σ significance not a
stationary background object. The near-infrared spectroscopy yields a
temperature of 2600 ± 250 K for the companion and an optical extinction
of AV = 5.2 ± 0.8 mag, when compared to spectra calculated
from Drift-Phoenix model atmospheres. We demonstrate the validity of the
model fits by comparison to several other well-known young sub-stellar
objects. Conclusions: We conclude that the CT Cha companion is a
very low-mass member of Chamaeleon and very likely a physical companion
to CT Cha, as the probability for a by chance alignment is ≤0.01. Due
to a prominent Pa-β emission in the J-band, accretion is probably
still ongoing onto the CT Cha companion. From temperature and luminosity
(log(L_bol/L⊙) = -2.68 ± 0.21), we derive a radius of R =
2.20_-0.60+0.81 RJup. We find a consistent mass
of M = 17 ± 6 MJup for the CT Cha companion from both its
luminosity and temperature when placed on evolutionary tracks. Hence,
the CT Cha companion is most likely a wide brown dwarf companion or
possibly even a planetary mass object. Based on observations
made with ESO telescopes at the Paranal Observatory under program
IDs 076.C-0292(A), 078.C-0535(A), &amp; 279.C-5010(A). Color
versions of Figs. 4, 6, 8 and 11 are only available in electronic form
at http://www.aanda.org

---------------------------------------------------------
Title: A 3D radiative transfer framework. III. Periodic boundary
conditions
Authors: Hauschildt, P. H.; Baron, E.
2008A&A...490..873H Altcode: 2008arXiv0808.0601H
Aims: We present a general method to solve radiative transfer problems
including scattering in the continuum as well as in lines in 3D
configurations with periodic boundary conditions. Methods:
The scattering problem for line transfer is solved via means of an
operator splitting (OS) technique. The formal solution is based on a
full characteristics method. The approximate Λ operator is constructed
considering nearest neighbors exactly. The code is parallelized over
both wavelength and solid angle using the MPI library. Results:
We present the results of several test cases with different values
of the thermalization parameter and two choices for the temperature
structure. The results are directly compared to 1D plane parallel
tests. The 3D results agree very well with the well-tested 1D
calculations. Conclusions: Advances in modern computers will
make realistic 3D radiative transfer calculations possible in the near
future. Our current code scales to very large numbers of processors,
but requires larger memory per processor at high spatial resolution.

---------------------------------------------------------
Title: Irradiated planets
Authors: Hauschildt, P. H.; Barman, T.; Baron, E.
2008PhST..130a4033H Altcode:
We present models for the spectra emitted by irradiated planets and
discuss the numerical methods used in the modeling. In addition, we
show results of simple 3D calculations that are designed as a first
step toward detailed multi-dimensional models of irradiated planets.

---------------------------------------------------------
Title: High-Accuracy Spectral Lines for Radiation Transport in
Stellar Atmospheres
Authors: Sharma, Amit R.; Braams, Bastiaan J.; Bowman, Joel M.;
Warmbier, Robert; Schneider, Ralf; Hauschildt, Peter H.
2008hitr.confE...5S Altcode:
The theory of radiative transfer is an important element for the
understanding of the spectral signature and physical structure
of stellar atmosphere. PHOENIX1 is a such, very general non-Local
Thermodynamic Equilibrium(NLTE) stellar atmosphere computer code which
can handle very large model atoms/molecules as well as line blanketing
by hundreds of millions of atomic and molecular lines. The code is
used to compute model atmospheres and synthetic spectra (solution
of the radiative transport equations) for, e.g., novae, supernovae,
M and brown dwarfs, O to M giants, white dwarfs and accretion disks
in Active Galactic Nuclei (AGN). The radiative transfer in PHOENIX
is solved in spherical geometry and includes the effects of special
relativity (including advection and aberration) in the modeling. The
code includes a large number of NLTE and LTE background spectral lines
and solves transport equation for each of the lines. The numerical
solution requires many wavelength points which arise in the non-LTE
case by balancing all populating and de-populating processes from
each molecular level (typically 150,000 to 300,000 points). Typically,
HITRAN and GEISA are the computer accessible spectroscopic databases
used by such transport codes. However, these spectroscopic databases
are far from adequate and complete and there is constant demand for
more complete and consistent spectral lines for the existing and
newly observed molecules in space. We used the code MULTIMODE2 to
obtain eigenvalues and eigenfunctions of the general so-called Watson
Hamiltonian using variational methods. The procedure begins with a
Hartree form for the wavefunction and then vibrational self-consistent
field (VSCF) equations are solved for the given state (usually the
ground vibrational state) The Hartree form for the wavefunction in
the VSCF method is the representation of the vibrational wavefunction
as a product of single-mode wavefunctions. From the converged single
mode Hamiltonians a basis of virtual states is obtained and these are
used in subsequent virtual space CI calculations. This is very much in
the spirit of CI approaches taken in electronic structure theory. The
application of this methodology for molecules with more than 4 atoms is
made possible by the so-called n-mode representation of the potential3
VSCF method augmented by CI or perturbation theory results in improved
vibrational frequencies. These methods can accurately solve the problem
of coupled vibrations, which physically arise because the vibrationally
excited states of polyatomic molecules exhibit displacements, so
large that anharmonicities become important, causing the harmonic
modes to mix. Following the (ro-)vibrational state calculations we
compute Einstein coefficients and spectral intensities for all allowed
transitions. However, a stringent requirement for these calculations
is a highly accurate potential energy surface. Ab initio-based,
full-dimensional potential energy surfaces (PES) are employed in this
work. These potentials are global fits to of the order of 104 electronic
energies using a basis of polynomials in Morse-like functions of all
the internuclear distances. The polynomial basis is invariant with
respect to all permutations of like atoms and, as a result, yield highly
compact and accurate representations of the PES. Similar techniques
are also employed to represent the dipole moment surface (DMS)4 for
a polyatomic molecules in the normal coordinate space using full
dimensional permutationally invariant potential energy surface. The
VSCF, VCI and PES generation scheme, together, can consistently
deliver high accuracy spectral lines for large number of molecules for
radiation transport application in astrophysics. Chemically interesting
singlet carbocation C2H + 5 , known as the ethyl cation, is of special
interest in the field astrophysics, specially in the ionosphere of
Titan, due to the recent observations by cassini spacecraft. Ethyl
cation exhibits interesting structural minimum and transition state,
namely the bridged structure (or non-classical) and the Y-shape (or
classical) structure. The calculations performed at the Hartree-Fock
level of theory found the classical form to be a real minimum and the
bridged structure to be less stable than the classical form. However,
as soon as correlation effects are taken into account the classical
form turns out to be a first order saddle point and less stable than
the non-classical form. In the lower-lying structure, referred to as
the _bridgedà® structure (or non-classical structure), one hydrogen
forms a bridge with the two carbon nuclei and the other four hydrogen
atoms (two hydrogen on each carbon nuclei) are nearly co-planar with
the two carbon atoms. Semi-global potential energy surface is developed
using the method described above with the electronic structure energy
calculated using the fourth order MÜLLER-PLESSET (MP4) perturbation
theory with contributions due to single, double, triple and quadruple
excitations to the electron correlation energy(MP4(SDTQ)). The dipole
moment surface is calculated at the MP2 level of theory. Multimode code
is used to calculate the vibrational energies up to 4000 cm-1
. Zero point vibrational energy is further compared with Diffusion Monte
Carlo (DMC) calculations. The other most interesting and extensively
studied molecule is methane. Adiabatic rotation approximation is used
to obtain Hamiltonian for rotating molecule. Ro-vibrational energies,
transition matrix elements and Einstein coefficients are calculated
for J = 0, 1, 3, 5, 10, 15, 20, 25, 30. The present calculations are
in good agreement with the well established HITRAN database for methane.

---------------------------------------------------------
Title: Second XMM/RGS spectrum of V2491 Cyg
Authors: Ness, J. -U.; Starrfield, S.; Gonzalez, R.; Kuulkers, E.;
Osborne, J. P.; Page, K.; Schwarz, G.; Vanlandingham, K. M.; Drake,
J. J.; Hernanz, M.; Sala, G.; Evans, A.; Gehrels, N.; Hauschildt,
P.; Krautter, J.; Gehrz, R. D.; Woodward, C. E.
2008ATel.1573....1N Altcode:
A second XMM-Newton observation of the nova V2491 Cyg was obtained on
2008 May 30.3, 49.6 days after the recent outburst and 10 days after
an earlier one obtained on day 39.9 (Ness et al., ATel #1561). The
exposure time in the Reflection Grating Spectrometers (RGS) was
29.8ksec, and the average count rate in the RGS1 was 2.7 counts per
second (c/s). The light curve extracted from the RGS1 is less variable
than during the first observation.

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Title: Comparison of cloud models for Brown Dwarfs
Authors: Helling, Ch.; Ackerman, A.; Allard, F.; Dehn, M.; Hauschildt,
P.; Homeier, D.; Lodders, K.; Marley, M.; Rietmeijer, F.; Tsuji, T.;
Woitke, P.
2008IAUS..249..173H Altcode: 2007arXiv0711.3993H; 2007IAUS..249..173H
A test case comparison is presented for different dust cloud model
approaches applied in brown dwarfs and giant gas planets. We aim to
achieve more transparency in evaluating the uncertainty inherent
to theoretical modelling. We show in how far model results for
characteristic dust quantities vary due to different assumptions. We
also demonstrate differences in the spectral energy distributions
resulting from our individual cloud modelling in 1D substellar
atmosphere simulations.

---------------------------------------------------------
Title: Time-dependent NLTE Rates in Type II Supernovae
Authors: De, Soma; Baron, E.; Hauschildt, P.
2008AAS...212.6402D Altcode: 2008BAAS...40..255D
It has been suggested that the steady-state approximation for
determining NLTE occupation numbers is not sufficient in Type II
supernovae and thus the time-dependent rate equations must be solved
(Utrobin and Chugai 2005). This is because the recombination time
increases due to Lyman alpha trapping causing the recombination time
to become comparable to the age of the supernova. The calculations are
based on the Sobolev approximation and a simple two-level hydrogen
atom. We calculate the recombination time for hydrogen using our
general radiative transfer code PHOENIX. We use a known density,
temperature and velocity structure consistent with the observed spectrum
of SN 1999em, 20 days after maximum light. Since PHOENIX does exact
radiative transfer, we can determine whether the approximations of
Utrobin and Chugai (2005) hold. We study four different systems: a
simple two-level hydrogen atom and a complete multilevel hydrogen atom
in both pure hydrogen and solar compositions to explore the relevance
of time dependence in the rate equations.

---------------------------------------------------------
Title: Erratum: "Consistent Simulations of Substellar Atmospheres
and Nonequilibrium Dust Cloud Formation" (ApJ, 675, L105 [2008])
Authors: Helling, Christiane; Dehn, Matthias; Woitke, Peter;
Hauschildt, Peter H.
2008ApJ...677L.157H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The influence of dust formation modelling on Na I and K I
line profiles in substellar atmospheres
Authors: Johnas, C. M. S.; Helling, Ch.; Dehn, M.; Woitke, P.;
Hauschildt, P. H.
2008MNRAS.385L.120J Altcode: 2008arXiv0801.3544J; 2008MNRAS.tmpL..24J
We aim to understand the correlation between cloud formation and alkali
line formation in substellar atmospheres. We perform line profile
calculations for NaI and KI based on the coupling of our kinetic model
for the formation and composition of dust grains with 1D radiative
transfer calculations in atmosphere models for brown dwarfs and giant
gas planets. The NaI and KI line profiles sensibly depend on the way
clouds are treated in substellar atmosphere simulations. The kinetic
dust formation model results in the highest pseudo-continuum compared
to the limiting cases.

---------------------------------------------------------
Title: Consistent Simulations of Substellar Atmospheres and
Nonequilibrium Dust Cloud Formation
Authors: Helling, Christiane; Dehn, Matthias; Woitke, Peter;
Hauschildt, Peter H.
2008ApJ...675L.105H Altcode: 2008arXiv0801.3733H
We aim to understand cloud formation in substellar objects. We combined
our nonequilibrium, stationary cloud model DRIFT (seed formation,
growth, evaporation, gravitational settling, element conservation)
with the general-purpose model atmosphere code PHOENIX (radiative
transfer, hydrostatic equilibrium, mixing-length theory, chemical
equilibrium) in order to consistently calculate cloud formation and
radiative transfer with their feedback on convection and gas-phase
depletion. We calculate the complete 1D model atmosphere structure
and the chemical details of the cloud layers. The DRIFT-PHOENIX
models enable the first stellar atmosphere simulation that is based
on the actual cloud formation process. The resulting (T, p) -profiles
differ considerably from the previous limiting PHOENIX cases DUSTY and
COND. A tentative comparison with observations demonstrates that the
determination of effective temperatures based on simple cloud models
has to be applied with care. Based on our new models, we suggest
a mean Teff = 1800 K for the L dwarf twin-binary system
DENIS J0205-1159, which is up to 500 K hotter than suggested in the
literature. We show transition spectra for gas-giant planets which
form dust clouds in their atmospheres and evaluate photometric fluxes
for a WASP-1 type system.

---------------------------------------------------------
Title: Atmospheric Properties of Transiting Extrasolar Planets
Authors: Barman, T.; Hauschildt, P.
2008ASPC..398..387B Altcode:
For a few of the nearby transiting extrasolar planets direct flux
measurements have been obtained using the Spitzer Space Telescope. The
atmospheric properties of these planets are discussed below along with
their agreement and disagreement with theoretical models.

---------------------------------------------------------
Title: The Consistent Modeling of Alkali Lines and Dust Formation
in Extreme Exo--Planets
Authors: Johnas, C. M. S.; Helling, Ch.; Witte, S.; Dehn, M.; Woitke,
P.; Hauschildt, P. H.
2008ASPC..398..393J Altcode:
We present the first PHOENIX tep{Hauschildt99} model atmosphere results
for extreme exo-planets where we have coupled a detailed modeling of
the alkali line profiles tep{Johnas06} with non-equilibrium treatment
of the chemically heterogeneous dust clouds (DRIFT) tep{Helling07}. Our
investigation of the Na I D and K I lines show strong differences in
shape and depth of the line profiles compared to commonly used impact
approximated van der Waals profiles and a previously approximative
dust treatment in PHOENIX. Such previous attempts of treating dust
in phase equilibrium lead to a much stronger element depletion of the
atmospheric gas. Consequently, the modelling of dust formation processes
does influence the spectral pseudo-continuum which is determined by
the resonance absorption wings of the alkali lines.

---------------------------------------------------------
Title: Detailed Spectral Modeling of a Three-dimensional Pulsating
Reverse Detonation Model: Too Much Nickel
Authors: Baron, E.; Jeffery, David J.; Branch, David; Bravo, Eduardo;
García-Senz, Domingo; Hauschildt, Peter H.
2008ApJ...672.1038B Altcode: 2007arXiv0709.4177B
We calculate detailed non-LTE synthetic spectra of a pulsating reverse
detonation (PRD) model, a novel explosion mechanism for Type Ia
supernovae. While the hydro models are calculated in three dimensions,
the spectra use an angle-averaged hydro model and thus some of the
three-dimensional (3D) details are lost, but the overall average should
be a good representation of the average observed spectra. We study the
model at three epochs: maximum light, 7 days prior to maximum light,
and 5 days after maximum light. At maximum the defining Si II feature
is prominent, but there is also a prominent C II feature, not usually
observed in normal SNe Ia near maximum. We compare to the early spectrum
of SN 2006D, which did show a prominent C II feature, but the fit to the
observations is not compelling. Finally, we compare to the postmaximum
UV+optical spectrum of SN 1992A. With the broad spectral coverage it
is clear that the iron-peak elements on the outside of the model push
too much flux to the red and thus the particular PRD realizations
studied would be intrinsically far redder than observed SNe Ia. We
briefly discuss variations that could improve future PRD models.

---------------------------------------------------------
Title: Direct Detection of Exo-Planets: GQ Lupi
Authors: Neuhäuser, Ralph; Guenther, Eike; Hauschildt, Peter
2008poii.conf..539N Altcode: 2008poio.conf..539N
No abstract at ADS

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres,
Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt,
Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher;
Tautvaišiené, Grazina; Werner, Klaus
2007IAUTB..26..160S Altcode:
The business meeting of Commission 36 was held during the General
Assembly in Prague on 16 August. It was attended by about 15
members. The issues presented included a review of the work made
by members of Commission 36, and the election of the new Organising
Committee. We note that a comprehensive report on the activities of
the commission during the last triennium has been published in Reports
on Astronomy, Transactions IAU Volume XXVIA. The scientific activity
of the members of the commission has been very intense, and has led
to the publication of a large number of papers.

---------------------------------------------------------
Title: Spitzer, Swift and Ground-based Spectral Evolution of the
Double Thermonuclear Runaway in Nova V2362 Cygni (Nova Cygni 2006)
Authors: Lynch, David K.; Woodward, C. E.; Gehrz, R. D.; Helton,
L. A.; Rudy, R. J.; Russell, R. W.; Pearson, R.; Venturini, C. C.;
Mazuk, S.; Rayner, J.; Ness, J.; Starrfield, S.; Wagner, R. M.;
Osborne, J.; Page, K.; Puetter, R. C.; Perry, R. B.; Schwarz, G.;
Vanlandingham, K.; Block, J.; Bode, M.; Evans, A.; Geballe, T.;
Greenhouse, M.; Hauschildt, P.; Krautter, J.; Liller, W.; Lyke, J.;
Truran, J.; Kerr, T.; Eyres, S. P. S.; Shore, S. N.
2007AAS...211.5112L Altcode: 2007BAAS...39..817L
Nova V2362 Cygni was apparently the result of a rare type of
thermonuclear runaway in which the initial explosion was followed by a
second one a few months later. Spitzer and ground-based spectroscopy
initially revealed a normal sequence of events until about day 100
when the optical fading reversed and the object slowly brightened. This
was accompanied by a rise in the Swift XRT flux and a rejuvenation of
the visible and IR spectrum which had previously been moving toward
higher excitation. The new lower excitation spectrum revealed broad
line widths and many P-Cygni profiles. Eventually dust formed,
the X-Ray brightness peaked and declined and the object faded at all
wavelengths. The Spitzer dust spectra revealed a number of solid-state
emission features which at this time are not identified.

---------------------------------------------------------
Title: Determination of Element Abundances
Authors: Hauschildt, P. H.; Johnas, C. M. S.
2007ASPC..378..111H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lithium abundances of very low mass members of Chamaeleon I
Authors: Johnas, C. M. S.; Guenther, E. W.; Joergens, V.; Schweitzer,
A.; Hauschildt, P. H.
2007A&A...475..667J Altcode:
Aims:We present the first study of the lithium abundances of very
low mass objects in Chamaeleon I close to the hydrogen burning mass
limit based on atmospheric models and high-resolution spectroscopic
observations. The studied objects, Cha Hα 2, 3, 4, 5, 6 and 8,
are very young brown dwarf candidates and very low mass stars on
the verge of lithium depletion. Methods: For this analysis, we
have computed a new “GAIA-cond” class model grid over effective
temperatures from 2600 K to 3100 K, surface gravities from log(g) =
3.5 to 5.5, and lithium abundances from logɛ = 0.0 to 3.7, for two
different line profile setups introduced in previous work. Calculated
synthetic spectra are compared with high-resolution UVES / VLT echelle
spectra of the objects. Results: We find good descriptions of
the lithium resonance doublet lines at 6708 Å and of the surrounding
pseudo-continuum and determine a consistent set of lithium abundances
(log(ɛ) = 1.55). However, the derived lithium abundances are lower than
the meteoritic one (log(ɛ) = 3.31) and that of higher mass stars in
Cha I (log(ɛ) = 3.1/3.4 for LTE-/non-LTE-calculations). By modeling
the TiO-line, we demonstrate that veiling does not make the lithium
lines appear weaker. We can also rule out that the results are spoiled
by the presence of spots. Conclusions: A possible explanation
for these results would be that the objects are either more massive,
or much older, than previously thought, so that the lithium depletion
has already started. Although the uncertainties of the masses and ages
are large, they are not large enough as to explain the observed lithium
depletion. Therefore, the most likely explanation is either a lack
of understanding of the details of the formation of the lithium line,
or a lack of understanding of the internal structure of the very young
low-mass objects. Based on observations obtained at the European
Southern Observatory at Paranal, Chile in program 65.L-0629(A,B)
and 65.I-0011(A).

---------------------------------------------------------
Title: A high resolution spectral atlas of brown dwarfs
Authors: Reiners, A.; Homeier, D.; Hauschildt, P. H.; Allard, F.
2007A&A...473..245R Altcode: 2007arXiv0707.2652R
We present a UVES/VLT high resolution atlas of three L dwarfs and one T
dwarf system, spectral classes at which most of the objects are brown
dwarfs. Our atlas covers the optical region from Hα up to the near
infrared at 1 μm. We present spectral details of ultra-cool atmospheres
at very high resolution (R ∼ 33 000) and compare the spectra to
model calculations. Our comparison shows that molecular features from
VO and CaH, and atomic features from Cs and Rb are reasonably well
fit by current models. On the other hand, features due to TiO, CrH,
and water, and atomic Na and K reveal large discrepancies between
model calculations and our observations. Based on observations
collected at the European Southern Observatory, Paranal, Chile,
077.C-0449.

---------------------------------------------------------
Title: Alkali Line Profiles in Ultra-cool White Dwarfs
Authors: Homeier, D.; Allard, N.; Johnas, C. M. S.; Hauschildt, P. H.;
Allard, F.
2007ASPC..372..277H Altcode: 2007arXiv0707.4138H
We present PHOENIX atmosphere models for metal-rich cool white
dwarfs using improved line shapes for the Na I and K I resonance
doublets. Profiles for collisional broadening due to H_2 and He based
on the adiabatic representation show strong deviations from Van der
Waals interaction at short distances. Comparison with observed spectra
that show extremely broadened Na I lines indicates that a He-rich
atmospheric composition is required to explain the line strengths and
spectral energy distributions. Our current synthetic spectra, using
an expansion in powers of density to the third order optimised for
brown dwarf atmosphere conditions, significantly underestimate the
observed absorption in the far wings, even predicting smaller total
line strength than a Lorentzian profile. This is shown to be due to
the handling of multiple perturber interactions becoming inadequate
for the extreme densities of the coolest white dwarfs. The density
expansion would have to be extended at least to the 7th order for an
accurate treatment of such conditions and might break down altogether
in the densest objects. The results of a direct calculation of the
unified profile should therefore be used for model atmospheres of cool
metal-rich white dwarfs. Qualitative comparison of the full adiabatic
profile to the spectrum of WD 2356-209 indicates good agreement with
the observed line shape. Observations of the coolest white dwarfs may
therefore serve as a laboratory for testing the physics of the deeper
atmospheres and interiors of brown dwarfs and giant planets.

---------------------------------------------------------
Title: Steps for solving the radiative transfer equation for arbitrary
flows in stationary space-times
Authors: Chen, B.; Kantowski, R.; Baron, E.; Knop, S.; Hauschildt,
P. H.
2007MNRAS.380..104C Altcode: 2007MNRAS.tmp..669C; 2006astro.ph..3251C
We derive the radiative transfer equation for arbitrary stationary
relativistic flows in stationary space-times, i.e. for steady-state
transfer problems. We show how the standard characteristics method
of solution developed by Mihalas and used throughout the radiative
transfer community can be adapted to multidimensional applications with
isotropic sources. Because the characteristics always coincide with
geodesics and can always be specified by constants, direct integration
of the characteristics derived from the transfer equation as commonly
done in 1D applications is not required. The characteristics are
known for a specified metric from the geodesics. We give details in
both flat and static spherically symmetric space-times. This work
has direct application in 3D simulations of supernovae, gamma-ray
bursts, and active galactic nuclei, as well as in modelling neutron
star atmospheres.

---------------------------------------------------------
Title: The Influence of Chemi-Ionization and Chemi-Recombination
Processes on H Lines in M Dwarf Atmospheres
Authors: Mihajlov, Anatolij A.; Jevremović, Darko; Hauschildt, Peter;
Dimitrijević, Milan S.; Ignjatović, Ljubinko M.; Allard, France
2007AIPC..938..214M Altcode:
Using general stellar atmosphere code PHOENIX, the influence
of chemi-ionization and inverse chemi-recombination processes,
in H*(n)+H(1s) collisions, on the population of higher
levels and consequently on profiles of Hydrogen lines in the
atmospheres of late type (M) stars was studied. Obtained results are
the first demonstration of the possibility to confirm the considered
processes influence by direct observations of stellar spectra. It is
demonstrated that it is very important to include chemi-ionization and
chemi-recombination processes in modeling of atmospheres of late type
stars, especially if one wants to use line profiles for diagnostics
of stellar photospheres and lower chromospheres.

---------------------------------------------------------
Title: Comparative study of dust cloud modelling for substellar
atmospheres
Authors: Helling, Ch.; Ackerman, A. S.; Allard, F.; Dehen, M.;
Hauschildt, P.; Hubeny, I.; Homeier, D.; Lodders, K.; Marley, M.;
Tsuji, T.; Woitke, P.
2007AN....328..655H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Influence of chemi-ionization and chemi-recombination processes
on hydrogen line shapes in M dwarfs
Authors: Mihajlov, A. A.; Jevremović, D.; Hauschildt, P.;
Dimitrijević, M. S.; Ignjatović, Lj. M.; Alard, F.
2007A&A...471..671M Altcode:
Aims:We study the influence of chemi-ionization in H*(n)
+ H(1s) collisions and inverse chemi-recombination processes on the
population of higher levels and consequently on profiles of hydrogen
lines in the atmospheres of late type (M) stars. Methods:
Modeling, using general stellar atmosphere code PHOENIX to reveal
the importance of the inclusion of such processes. Results:
We demonstrate for the first time observationally detectable effects
of these chemi-processes on stellar spectra. Conclusions: It
is very important to include chemi-ionization and chemi-recombination
processes in modeling of atmospheres of late type stars, especially if
one wants to use line profiles for diagnostics of stellar photospheres
and lower chromospheres.

---------------------------------------------------------
Title: Line spectra and profiles for ultracool substellar objects
Authors: Johnas, Christine M. S.; Hauschildt, Peter H.
2007AIPC..926..120J Altcode:
The pressures in the line forming regions of cool stellar and substellar
objects increase dramatically with lower effective temperatures. This
causes strong pressure broadening of the few remaining atomic lines,
with damping wings more than 0.5 μm wide, dominating the emitted
spectrum. Therefore, there is an essential need for reasonably accurate
line profiles for these lines under high-pressure conditions. We
show the results of model atmosphere calculations using detailed line
profiles for a number of alkali resonance lines and discuss the need
for additional and improved line profile for stellar and planetary
atmosphere simulations.

---------------------------------------------------------
Title: Modelling the Near-IR Spectra of Red Supergiant-dominated
Populations
Authors: Lançon, Ariane; Gallagher, Jay S.; de Grijs, Richard;
Hauschildt, Peter; Ladjal, Djazia; Mouhcine, Mustapha; Smith, Linda
J.; Wood, Peter R.; Förster Schreiber, Natascha
2007IAUS..241..152L Altcode: 2007arXiv0704.0401L
We report on recent progress in the modelling of the near-IR spectra
of young stellar populations, i.e. populations in which red supergiants
(RSGs) are dominant. First, we discuss the determination of fundamental
parameters of RSGs using fits to their near-IR spectra with new PHOENIX
model spectra; RSG-specific surface abundances are accounted for and
effects of the microturbulence parameter are explored. New population
synthesis predictions are then described and, as an example, it is shown
that the spectra of young star clusters in M82 can be reproduced very
well from 0.5 to 2.4 micrometers. We warn of remaining uncertainties
in cluster ages.

---------------------------------------------------------
Title: Quasi-Molecular K-H[2 ]Absorption As An Alternative To The
Resurgence Of CaH Bands In The Spectra Of T-Type Dwarfs: Is The
Cloud-Clearing Scheme At Stake?
Authors: Allard, F.; Allard, N. F.; Johnas, C. M. S.; Hauschildt,
P. H.; Homeier, D.; Kielkopf, J. K.; Spiegelman, F.
2007IAUS..240..332A Altcode:
As brown dwarfs cool off with time, their atmospheres become denser
and more transparent, allowing the emitted thermal flux to escape from
deeper atmospheric layers. Burgasser et al. (2002) have investigated
and classified the red spectra of T dwarfs in a spectral sequence where
a resurgence of the hydride bands, after disappearing in the M to L
spectral transition, occur between the late L to T before disappearing
again in the late T dwarfs. CaH for example is identified in mid-T
dwarfs at around 0.7μm (Burgassser 2003). The authors explain this
resurgence by a cloud-clearing scheme where holes would allow to see
the CaH from deeper enriched layers, while it is settled out from
the uppermost atmospheric layers seen on the rest of the brown dwarf
surface. We present the first synthetic spectra of T dwarfs including
a semi-classical modelling of the pressure broadening of alkalis lines
(Na I D, Li I, K I, Rb I, and Cs I fundamental resonance doublets)
by molecular hydrogen and helium, the most important species in these
atmospheres. We compare the models to the T dwarfs red optical spectra
of Burgasser et al. (2003) and we find that the 0.7μm feature has been
wrongly identified to CaH. In particular, the very strong KI resonance
transition doublet at 0.77μm explains by itself this absorption feature
by producing a quasi-molecular satellite absorption feature at this
wavelength. The strength of this satellite is very sensitive to the
density of perturbers in the lower photosphere and to the background
opacity provided by the Na I D red wing, which explains naturally both
its apparition in late L dwarfs and its vanishing in late T dwarfs. We
find in conclusion that no cloud-clearing scheme or non-equilibrium
processes is necessary to explain this absorption feature, and the
evolution of the red optical spectrum of T dwarfs. And this should teach
us caution about these atmospheres often too enthusiastly considered
planetary. MHR 3D convection models are nevertheless underway to
estimate the likelihood of cloud-clearings in late L and T dwarfs.

---------------------------------------------------------
Title: The SSS Phase of RS Ophiuchi Observed with Chandra and
XMM-Newton. I. Data and Preliminary Modeling
Authors: Ness, J. -U.; Starrfield, S.; Beardmore, A. P.; Bode, M. F.;
Drake, J. J.; Evans, A.; Gehrz, R. D.; Goad, M. R.; Gonzalez-Riestra,
R.; Hauschildt, P.; Krautter, J.; O'Brien, T. J.; Osborne, J. P.;
Page, K. L.; Schönrich, R. A.; Woodward, C. E.
2007ApJ...665.1334N Altcode: 2007arXiv0705.1206N
The phase of supersoft source (SSS) emission of the sixth recorded
outburst of the recurrent nova RS Oph was observed on days 39.7 and
66.9 after outburst with Chandra and on day 54.0 with XMM-Newton. A
~35 s period on day 54.0 originates from the SSS emission and not from
the shock. We discuss the bound-free absorption by neutral elements
in the line of sight, resonance absorption lines plus self-absorbed
emission-line components, collisionally excited emission lines from
the shock, He-like intersystem lines, and spectral changes during an
episode of high-amplitude variability. We find a decrease of the oxygen
K-shell absorption edge that can be explained by photoionization of
oxygen. The absorption component has average velocities of -1286+/-267
km s-1 on day 39.7 and of -771+/-65 km s-1 on
day 66.9. The wavelengths of the emission-line components are at rest
wavelengths, as confirmed by measurements of non-self-absorbed He-like
intersystem lines. We found collisionally excited emission lines from
the radiatively cooling shock at wavelengths shorter than 15 Å that
are systematically blueshifted by -526+/-114 km s-1 on
day 39.7 and are fading. We found anomalous He-like f/i ratios, which
indicates either high densities or significant UV radiation near the
plasma where the emission lines are formed. During the phase of strong
variability the spectral hardness light curve overlies the total light
curve when shifted by 1000 s. This can be explained by photoionization
of neutral oxygen in the line of sight if the densities are of order
1010-1011 cm-3.

---------------------------------------------------------
Title: Analyzing <ASTROBJ>SN 2003Z</ASTROBJ> with PHOENIX
Authors: Knop, S.; Hauschildt, P. H.; Baron, E.; Dreizler, S.
2007A&A...469.1077K Altcode: 2009arXiv0902.1867K
Aims:We present synthetic spectra around maximum for the type
II supernova SN 2003Z, which was first detected on January 29.7
2003. Comparison with observed spectra aim at the determination of
physical parameters for SN 2003Z. Methods: Synthetic spectra
are calculated with our stellar atmosphere code PHOENIX. It solves the
special relativistic equation of radiative transfer, including large
NLTE-calculations and line blanketing by design, in 1-dimensional
spherical symmetry. The observed spectra were obtained at the 3.5
m telescope at Calar Alto. The TWIN instrument was used so that a
spectral range from about 3600 to 7500 Å was covered. The spectra
were taken on Feb. 4, 5, 9, and 11, 2003. Results: The physical
parameters of the models give the luminosities, a range of possible
velocity profiles for the SN, an estimate of the colour excess, and
the observed metalicity. Based on observations collected at the
Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated
jointly by the Max-Planck Institut für Astronomie and the Instituto
de Astrofísica de Andalucía (CSIC).

---------------------------------------------------------
Title: A 3D radiative transfer framework. II. Line transfer problems
Authors: Baron, E.; Hauschildt, P. H.
2007A&A...468..255B Altcode: 2007astro.ph..3437B
Context: Higher resolution telescopes as well as 3D numerical
simulations will require the development of detailed 3D radiative
transfer calculations. Building upon our previous work we extend
our method to include both continuum and line transfer. Aims: We present a general method to calculate radiative transfer
including scattering in the continuum as well as in lines in 3D static
atmospheres. Methods: The scattering problem for line transfer is
solved via means of an operator splitting (OS) technique. The formal
solution is based on a long-characteristics method. The approximate
Λ operator is constructed considering nearest neighbors exactly. The
code is parallelized over both wavelength and solid angle using the
MPI library. Results: We present the results of several test
cases with different values of the thermalization parameter and two
choices for the temperature structure. The results are directly
compared to 1D spherical tests. With our current grid setup the
interior resolution is much lower in 3D than in 1D, nevertheless the
3D results agree very well with the well-tested 1D calculations. We
show that, with relatively simple parallelization, the code scales
to very large number of processors which is mandatory for practical
applications. Conclusions: Advances in modern computers will
make realistic 3D radiative transfer calculations possible in the near
future. Our current code scales to very large numbers of processors,
but requires larger memory per processor at high spatial resolution.

---------------------------------------------------------
Title: Near-IR spectra of red supergiants and giants. I. Models with
solar and with mixing-induced surface abundance ratios
Authors: Lançon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M.
2007A&A...468..205L Altcode: 2007arXiv0704.2120L
Context: It remains difficult to interpret the near-IR emission of young
stellar populations. One main reason is our incomplete understanding
of the spectra of luminous red stars. Aims: This work provides
a grid of theoretical spectra of red giant and supergiant stars,
that extends through optical and near-IR wavelengths. For the first
time, models are also provided with modified surface abundances of C,
N and O, as a step towards accounting for the changes that occur due
to convective dredge-up in red supergiants or may occur at earlier
evolutionary stages in the case of rotation. The aims are (i) to assess
how well current models reproduce observed spectra, in particular in
the near-IR; (ii) to quantify the effects of the abundance changes on
the spectra; and (iii) to determine how these changes affect estimates
of fundamental stellar parameters. Methods: Spectra are computed
with the model atmosphere code PHOENIX and compared with a homogeneous
set of observations. Although the empirical spectra have a resolution
of only λ/Δλ ∼ 1000, we emphasize that models must be calculated at
high spectral resolution in order to reproduce the shapes of line blends
and molecular bands. Results: Giant star spectra of class III can
be fitted extremely well at solar metallicity down to ~3400 K, where
difficulties appear in the modelling of near-IR H2O and TiO absorption
bands. Luminous giants of class II can be fitted well too, with modified
surface abundances preferred in a minority of cases, possibly indicating
mixing in excess of standard first dredge-up. Supergiant stars show
a larger variety of near-IR spectra, and good fits are currently
obtained for about one third of the observations only. Modified surface
abundances help reproducing strong CN bands, but do not suffice to
resolve the difficulties. The effect of the abundance changes on
the estimated Teff depends on the wavelength range of
observation and can amount several 100 K. Conclusions: While
theoretical spectra for giant stars are becoming very satisfactory,
red supergiants require further work. The model grid must be
extended, in particular to larger micro-turbulent velocities. Some
observed spectra may call for models with even lower gravities than
explored here (and therefore probably stellar winds), and/or with more
extreme abundances than predicted by standard non-rotating evolution
models. Non-static atmospheres models should also be envisaged. Selected theoretical spectra (see text) can be retrieved in FITS
format at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5),
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/468/205

---------------------------------------------------------
Title: Reddening, Abundances, and Line Formation in SNe II
Authors: Baron, E.; Branch, David; Hauschildt, Peter H.
2007ApJ...662.1148B Altcode: 2007astro.ph..3068B
We present detailed NLTE spectral synthesis models of the Type II
supernova 2005cs, which occurred in M51 and for which the explosion
time is well determined. We show that previous estimates for the
reddening were significantly too high and briefly discuss how this
will affect the inferred progenitor mass. We also show that standard
CNO-burning-enhanced abundances require far too large an oxygen
depletion, although there is evidence for a single optical N II line,
and the sodium abundance shows clear evidence for enhancement over
solar, both as expected from CNO processing. Finally, we calculate a
distance using the SEAM method. Given the broad range of distances to
M51 in the literature, the determination of a distance using Cepheid
variables would be quite valuable.

---------------------------------------------------------
Title: The influence of convective energy transport on dust formation
in brown dwarf atmospheres
Authors: Dehn, Matthias; Helling, Christiane; Woitke, Peter;
Hauschildt, Peter
2007IAUS..239..227D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The effects of new Na I D line profiles in cool atmospheres
Authors: Johnas, C. M. S.; Hauschildt, P. H.; Schweitzer, A.;
Mullamphy, D. F. T.; Peach, G.; Whittingham, I. B.
2007A&A...466..323J Altcode:
Aims:New Na I D line profiles and their effects on synthetic spectra
of cool dwarfs computed with PHOENIX are studied. Sodium is the most
abundant alkali in cool dwarf atmospheres and mostly responsible for the
shape of the optical spectrum. Methods: In previous work we have
pointed out the importance of atomic hydrogen as a perturber. Here,
broadening due to collisions with atomic hydrogen as well as fully
quantum mechanically calculated profiles for perturbations by helium
are introduced for the Na I resonance line profiles. Furthermore,
the effects of the new line profiles are compared to already existing
line profile calculations. Results: We have calculated a number
of "GAIA-cond" class model atmospheres and synthetic spectra for
effective temperatures from 1100 K to 3000 K considering a gravity
of 4.5. The line formation process has been analyzed with the flux
contribution function. Due to changes in atmospheric structure, the
effects of the line profiles on the synthetic spectra become larger
for smaller effective temperatures. The influence of hydrogen as
perturber is visible at higher effective temperatures although at the
same time the strength of molecular bands increases. Furthermore, the
newly introduced fully quantum mechanically calculated He I broadened
profiles change the synthetic spectra by reducing the flux and the
depths of the sodium absorption lines.

---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.;
Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra,
K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K.
2007IAUTA..26..215S Altcode:
Commission 36 covers all the physics of stellar atmospheres. The
scientific activity in this large field has been very intense during
the last triennium and led to the publication of a large number of
papers which makes an exhaustive report practically not feasible. As
a consequence we decided to keep the format of the preceding report:
first a list of areas of current research, then web links for obtaining
further information.

---------------------------------------------------------
Title: General relativistic radiative transfer
Authors: Knop, S.; Hauschildt, P. H.; Baron, E.
2007A&A...463..315K Altcode: 2006astro.ph.11938K
Aims:We present a general method to calculate radiative transfer
including scattering in the continuum as well as in lines in
spherically symmetric systems that are influenced by the effects
of general relativity (GR). We utilize a comoving wavelength ansatz
that allows to resolve spectral lines throughout the atmosphere. Methods: The used numerical solution is an operator splitting (OS)
technique that uses a characteristic formal solution. The bending of
photon paths and the wavelength shifts due to the effects of GR are
fully taken into account, as is the treatment of image generation in a
curved spacetime. Results: We describe the algorithm we use and
demonstrate the effects of GR on the radiative transport of a two level
atom line in a neutron star like atmosphere for various combinations of
continuous and line scattering coefficients. In addition, we present
grey continuum models and discuss the effects of different scattering
albedos on the emergent spectra and the determination of effective
temperatures and radii of neutron star atmospheres.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Theoretical spectra of red giants
and supergiants (Lancon+, 2007)
Authors: Lancon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M.
2007yCat.6125....0L Altcode:
Each FITS file in this directory contains a theoretical stellar
spectrum. The spherical model atmospheres and the synthetic spectra were
computed with PHOENIX version 13.11.00B as described in the article,
with an initial wavelength sampling step of 0.01nm in the wavelength
range of interest [510nm-2490nm]. The spectra made available here have
been smoothed with a Gaussian with a full width at half maximum of
0.2nm. They are resampled with a wavelength step of 0.025nm. (4
data files).

---------------------------------------------------------
Title: Near-infrared integral-field spectroscopy of the companion
to GQ Lupi
Authors: Seifahrt, A.; Neuhäuser, R.; Hauschildt, P. H.
2007A&A...463..309S Altcode: 2006astro.ph.12250S
Context: The first substellar companion of possibly planetary mass
around a normal star, GQ Lup, has been directly imaged (Neuhäuser et
al. 2005, A&amp;A, 435, L13). Besides the unknown formation history,
the mass of such an object is a criterion to decide about its true
nature. Aims: We aim to determine the physical properties of
the GQ Lup companion - effective temperate (T_eff) and surface gravity
(log{g}), and thus its mass independently from evolutionary models. Methods: We use the adaptive optics integral-field spectrograph
SINFONI at the VLT for near-infrared spectroscopy from 1.1 to 2.5
μm with a resolution of R = 2500-4000. We compare these spectra
with synthetic atmospheric models (GAIA v2.0 cond). Results:
From the complete set of spectra we find a consistent effective
temperature and surface gravity of T_eff = 2650 ± 100 K and log{g}
= 3.7 ± 0.5 dex. Combined with a slightly revised luminosity
of log{L/L⊙} = -2.25 ± 0.24 dex for the companion,
we determine a radius of R = 3.50+1.50-1.03
{R_Jup} and thus a mass of 25 {M_Jup}. The uncertainty of this
value is rather high. Due to the large uncertainty of the surface
gravity, the mass could range from 4 to 155 {M_Jup}. By comparing the
paramaters of the companion of GQ Lup to the ones of <ASTROBJ>2MASS
J05352184-0546085</ASTROBJ>, published by Stassun et al. (2006,
Nature, 440, 311), we conclude that the companion to GQ Lup A has a
mass lower than 36 ± 3 {M_Jup}. Based on observations collected
at the European Southern Observatory, Chile, in programmes 275.C-5033(A)
and 077.C-0264(A).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Spectra of red giants and
supergiants (Lancon+, 2007)
Authors: Lancon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M.
2007yCat..34680205L Altcode:
Each FITS file in this directory contains a theoretical stellar
spectrum. The spherical model atmospheres and the synthetic spectra were
computed with PHOENIX version 13.11.00B as described in the article,
with an initial wavelength sampling step of 0.01nm in the wavelength
range of interest [510nm-2490nm]. The spectra made available here have
been smoothed with a Gaussian with a full width at half maximum of
0.2nm. They are resampled with a wavelength step of 0.025nm. (1
data file).

---------------------------------------------------------
Title: The M Dwarf GJ 436 and its Neptune-Mass Planet
Authors: Maness, H. L.; Marcy, G. W.; Ford, E. B.; Hauschildt, P. H.;
Shreve, A. T.; Basri, G. B.; Butler, R. P.; Vogt, S. S.
2007PASP..119...90M Altcode: 2006astro.ph..8260M
We determine stellar parameters for the M dwarf GJ 436, which hosts a
Neptune-mass planet. We employ primarily spectral modeling at low and
high resolution, examining the agreement between model and observed
optical spectra of five comparison stars of type M0-M3. The modeling
of high-resolution optical spectra suffers from uncertainties in TiO
transitions, affecting the predicted strengths of both atomic and
molecular lines in M dwarfs. The determination of Teff,
gravity, and metallicity from optical spectra remains at ~10%. As
molecules provide opacity both in lines and as an effective continuum,
determining molecular transition parameters remains a challenge
facing models such as the PHOENIX series, best verified with high
resolution and spectrophotometric spectra. Our analysis of GJ 436
yields an effective temperature of Teff = 3350 +/- 300
K and a mass of 0.44 Msolar. New Doppler measurements of
GJ 436 with a precision of 3 m s-1 taken during 6 years
improve the Keplerian model of the planet, giving it a minimum mass
Msini=0.0713MJup = 22.6 M⊕, period P =
2.6439 days, and eccentricity e = 0.16 +/- 0.02. The noncircular
orbit contrasts with the tidally circularized orbits of all close-in
exoplanets, implying either ongoing pumping of eccentricity by a more
distant companion, or a higher Q value for this low-mass planet. The
velocities indeed reveal a long-term trend, indicating a possible
distant companion.

---------------------------------------------------------
Title: Accurate M Dwarf Metallicities from Spectral Synthesis:
A Critical Test of Model Atmospheres
Authors: Bean, Jacob L.; Sneden, Christopher; Hauschildt, Peter H.;
Johns-Krull, Christopher M.; Benedict, G. Fritz
2006ApJ...652.1604B Altcode: 2006astro.ph..8093B
We describe a method for accurately determining M dwarf metallicities
with spectral synthesis based on abundance analyses of visual binary
stars. We obtained high-resolution, high-signal-to-noise ratio
spectra of each component of five visual binary pairs at McDonald
Observatory. The spectral types of the components range from F7 to K3
V for the primaries and from M0.5 to M3.5 V for the secondaries. We
have determined the metallicities of the primaries differentially with
respect to the Sun by fitting synthetic spectra to Fe I line profiles
in the observed spectra. In the course of our analysis of the M dwarf
secondaries, we have made significant improvements to the PHOENIX
cool-star model atmospheres and the spectrum analysis code MOOG. Our
analysis yields an rms deviation of 0.11 dex in metallicity values
between the binary pairs. We estimate the uncertainties in the derived
stellar parameters for the M dwarfs to be 48 K, 0.10 dex, 0.12 dex, 0.15
km s-1, and 0.20 km s-1 for Teff, logg,
[M/H], ξ, and η, respectively. Accurate stellar evolutionary models
are needed to progress further in the analysis of cool-star spectra; the
new model atmospheres warrant recalculation of the evolutionary models.

---------------------------------------------------------
Title: Type Ia Supernova Spectral Line Ratios as Luminosity
Indicators: "From Phenomenology to Radiative Transfer and Back Again"
Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, D.;
Hauschildt, P.
2006AAS...20920001B Altcode: 2006BAAS...38.1178B
Type Ia supernovae have played a crucial role in the discovery of
the dark energy, via the measurement of their light curves and the
determination of the peak brightness via fitting templates to the
observed lightcurve shape. Two spectroscopic indicators (RSi and RCa)
are also known to be well correlated with peak luminosity. Since
the spectroscopic luminosity indicators are obtained directly from
observed spectra, they may emphasize different aspects on the intrinsic
scatter and will have different systematic errors than do measurements
using photometry. We present new variants of such spectroscopic
indicators which are easy to automate and which minimize the effects
of noise. Using the radiative transfer code PHOENIX, we isolate the
main spectral contributions to the RSi wavelength region and propose
an explanation for the counterintuitive correlation of this spectral
indicator with luminosity. Based on these results we introduce RSiS,
a new spectral indicator which correlation with luminosity is twice
as good as RSi. Finally, we quantify the accuracy of the measure of
SNeIa peak brightness with these indicators in the context of SNAP/JDEM.

---------------------------------------------------------
Title: Energy transport, overshoot, and mixing in the atmospheres
of M-type main- and pre-main-sequence objects
Authors: Ludwig, H. -G.; Allard, F.; Hauschildt, P. H.
2006A&A...459..599L Altcode: 2006astro.ph..8264L
We constructed hydrodynamical model atmospheres for mid M-type main-,
as well as pre-main-sequence (PMS) objects. Despite the complex
chemistry encountered in these cool atmospheres a reasonably accurate
representation of the radiative transfer is possible, even in the
context of time-dependent and three-dimensional models. The models
provide detailed information about the morphology of M-type granulation
and statistical properties of the convective surface flows. In
particular, we determined the efficiency of the convective energy
transport, and the efficiency of mixing by convective overshoot. The
convective transport efficiency was expressed in terms of an equivalent
mixing-length parameter α_MLT in the formulation of mixing-length
theory (MLT) given by Mihalas (1978). α_MLT amounts to values around
≈2 for matching the entropy of the deep, adiabatically stratified
regions of the convective envelope, and lies between 2.5 and 3.0 for
matching the thermal structure of the deep photosphere. For current
spectral analysis of PMS objects this implies that MLT models based
on α_MLT=2.0 overestimate the effective temperature by 100 K and
surface gravities by 0.25 dex. The average thermal structure of the
formally convectively stable layers is little affected by convective
overshoot and wave heating, i.e., stays close to radiative equilibrium
conditions. Our models suggest that the rate of mixing by convective
overshoot declines exponentially with geometrical distance to the
Schwarzschild stability boundary. It increases at given effective
temperature with decreasing gravitational acceleration.

---------------------------------------------------------
Title: Type Ia Supernova Spectral Line Ratios as Luminosity Indicators
Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David;
Hauschildt, Peter H.
2006ApJ...647..513B Altcode: 2005astro.ph.12229B
Type Ia supernovae have played a crucial role in the discovery of
the dark energy, via the measurement of their light curves and the
determination of the peak brightness via fitting templates to the
observed light-curve shape. Two spectroscopic indicators are also known
to be well correlated with peak luminosity. Since the spectroscopic
luminosity indicators are obtained directly from observed spectra,
they will have different systematic errors than do measurements using
photometry. In addition, these spectroscopic indicators may be useful
for studies of effects of evolution or age of the SNe Ia progenitor
population. We present several new variants of such spectroscopic
indicators that are easy to automate and that minimize the effects of
noise. We show that these spectroscopic indicators can be measured by
proposed JDEM missions such as SNAP and JEDI.

---------------------------------------------------------
Title: Resolving stellar atmospheres. I. The Hα line and comparisons
to microlensing observations
Authors: Thurl, C.; Sackett, P. D.; Hauschildt, P. H.
2006A&A...455..315T Altcode: 2006astro.ph..4088T
Context: .We present work on {H}α spectral line characteristics in
PHOENIX stellar model atmospheres and their comparison to microlensing
observations. Aims: .We examine in detail the {H}α equivalent
width (EW) and the line shape characteristics for effective temperatures
of 4500 K&lt;T{eff}&lt; 5600 K where {H}α is a strong
spectral feature. Methods: .We find that {H}α EW in models
calculated under the assumption of local thermodynamic equilibrium (LTE)
is up to 15% smaller than in models without this assumption, non-LTE
models (NLTE) and that line shapes vary significantly for the two model
types. A comparison with available high quality microlensing data,
capable of tracing {H}α absorption across the face of one G5III giant,
shows that the LTE model that fits the EW best is about 100 K hotter
than and the best-fitting NLTE model has a similar T{eff}
as predicted by the spectral type analysis of the observed star
but agree within the uncertainties of the observationally derived
temperature. Results: .Neither LTE nor NLTE models fit the line
shape well. We suspect unmodelled chromospheric emission. Line shape
diagnostics suggest lower gravities than derived for the star and
are unacceptable low in the case of the LTE models. We show that EW
alone is insufficient for comparison to stellar model atmospheres, but
combined with a new shape parameter we define is promising. In stellar
parameter ranges where the {H}α line is strong, a NLTE approach of
modeling stellar atmospheres is not only beneficial but mandatory.

---------------------------------------------------------
Title: Spectral Modeling of SNe Ia Near Maximum Light: Probing the
Characteristics of Hydrodynamical Models
Authors: Baron, E.; Bongard, Sebastien; Branch, David; Hauschildt,
Peter H.
2006ApJ...645..480B Altcode: 2006astro.ph..3101B
We have performed detailed non-local thermodynamic equilibrium
(NLTE) spectral synthesis modeling of two types of one-dimensional
hydrodynamical models: the very highly parameterized deflagration
model W7, and two delayed-detonation models. We find that, overall,
both models do about equally well at fitting well-observed SNe Ia near
maximum light. However, the Si II λ6150 feature of W7 is systematically
too fast, whereas for the delayed-detonation models it is also somewhat
too fast but significantly better than that of W7. We find that a
parameterized mixed model does the best job of reproducing the Si II
λ6150 line near maximum light, and we study the differences in the
models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydrodynamical model to fit the spectra of observed SNe
Ia near maximum light.

---------------------------------------------------------
Title: Influence of NLTE calculations on the hydrogen lines in
chromospheric models
Authors: Fuhrmeister, B.; Short, C. I.; Hauschildt, P. H.
2006A&A...452.1083F Altcode:
We present extensive NLTE calculations for a semi-empirical solar
1D chromosphere model based on the VAL C model. We report on a
significant influence of nitrogen, oxygen, and sulfur on the emergent
hydrogen emission with respect to LTE vs. NLTE calculations for these
elements. Moreover, we present a model spectrum with 20 light and
iron group elements computed in NLTE. We compare this to an observed
solar spectrum and to a photospheric model spectrum. We find that the
agreement for this model with the data is less good than the original
VAL C model especially in the UV. This may imply the need of changes
in the chromospheric temperature structure or may point to general
problems of static 1D chromospheric models.

---------------------------------------------------------
Title: Broad-band photometric colors and effective temperature
calibrations for late-type giants. II. Z &lt; 0.02
Authors: Kučinskas, A.; Hauschildt, P. H.; Brott, I.; Vansevičius,
V.; Lindegren, L.; Tanabé, T.; Allard, F.
2006A&A...452.1021K Altcode: 2006astro.ph..3416K
We investigate the effects of metallicity on the broad-band photometric
colors of late-type giants, and make a comparison of synthetic colors
with observed photometric properties of late-type giants over a wide
range of effective temperatures (T_eff=3500-4800 K) and gravities
(log g=0.0-2.5), at [M/H]=-1.0 and -2.0. The influence of metallicity
on the synthetic photometric colors is small at effective temperatures
above 3800 K, but the effects grow larger at lower T_eff, due to the
changing efficiency of molecule formation which reduces molecular
opacities at lower [M/H]. To make a detailed comparison of the
synthetic and observed photometric colors of late type giants in the
T_eff-color and color-color planes (which is done at two metallicities,
[M/H]=-1.0 and -2.0), we derive a set of new T_eff-log g-color relations
based on synthetic photometric colors, at [M/H]=-0.5, -1.0, -1.5,
and -2.0. These relations are based on the T_eff-log g scales that we
derive employing literature data for 178 late-type giants in 10 Galactic
globular clusters (with metallicities of the individual stars between
[M/H]=-0.7 and -2.5), and synthetic colors produced with the PHOENIX,
MARCS and ATLAS stellar atmosphere codes. Combined with the T_eff-log
g-color relations at [M/H]=0.0 (Kučinskas et al. 2005), the set of
new relations covers metallicities [M/H]=0.0dots-2.0 (Δ[M/H]=0.5),
effective temperatures T_eff=3500dots4800 K (Δ T_eff=100 K), and
gravities log g=-0.5dots3.0. The new T_eff-log g-color relations
are in good agreement with published T_eff-color relations based
on observed properties of late-type giants, both at [M/H]=-1.0 and
-2.0. The differences in all T_eff-color planes are typically well
within 100 K. We find, however, that effective temperatures predicted
by the scales based on synthetic colors tend to be slightly higher than
those resulting from the T_eff-color relations based on observations,
with the offsets up to 100 K. This is clearly seen both at [M/H]=-1.0
and -2.0, especially in the T_eff-(B-V) and T_eff-(V-K) planes. The
consistency between T_eff-log g-color scales based on synthetic colors
calculated with different stellar atmosphere codes is very good, with
typical differences being well within Δ T_eff ∼ 70 K at [M/H]=-1.0
and Δ T_eff ∼ 40 K at [M/H]=-2.0.

---------------------------------------------------------
Title: Non-lte Multi-species Modeling of the Hydrogen Lines in Solar
Chromospheric Models
Authors: Short, Ian; Fuhrmeister, B.; Hauschildt, P.
2006AAS...208.1103S Altcode: 2006BAAS...38...90S
We present extensive non-local thermodynamic equilibrium (Non-LTE)
calculations for a semi-empirical one dimensional (1D) solar
chromospheric model based on the historically significant VAL C
model. We report on the significant influence of nitrogen (N), oxygen
(O), and sulfur (S) on the emergent hydrogen (H) continuum and line
emission as computed with these elements in LTE and Non-LTE. Moreover,
we present a model spectrum with 20 light and iron (Fe) group elements
computed in Non-LTE. We compare this to an observed solar spectrum
and to a photospheric model spectrum. We find that the agreement for
this model with the data is less good than the original VAL C model
especially in the UV. This may imply the need for changes in the
chromospheric temperature structure or may point to general problems
of static 1D chromospheric models.

---------------------------------------------------------
Title: The Photosphere and Stellar Wind of Deneb (A2 Ia) in the
Far Ultraviolet
Authors: Aufdenberg, J. P.; Morrison, N. D.; Hauschildt, P. H.;
Adelman, S. J.
2006ASPC..348..124A Altcode:
The A2 Ia-type supergiant star Deneb has been observed by FUSE. A rich
absorption spectrum, dominated by Fe II lines, is revealed between
1085Å and 1185Å. The identified lines show no or only small (-25 km
s-1) blueward Doppler shifts and no P-Cygni profiles are
visible. Apparent emission lines in the spectrum are identified as
windows of low opacity and can be reproduced by a PHOENIX hydrostatic
model atmosphere. Expanding model atmospheres are needed to reproduce
Deneb's excess radio emission and P-Cygni profiles (Hα, Mg II h&amp;k),
but, the wind appears largely transparent in the FUSE region. Expanding
model atmospheres indicate that enhanced non-LTE ionization of Fe
II longrightarrow Fe II can largely hide the wind in the UV and the
FUV. Deneb's Wien tail presents a strong challenge to expanding model
atmospheres and promises to provide strong constraints on wind's
temperature and ionization structure.

---------------------------------------------------------
Title: ToO IRS Observations of Novae
Authors: Woodward, Charles; Black, John; Bode, Michael; Evans, Aneuryn;
Geballe, Thomas; Gehrz, Robert; Greenhouse, Matthew; Hauschildt, Peter;
Helton, Andrew; Krautter, Joachim; Liller, William; Lyke, James; Lynch,
David; Rudy, Richard; Salama, Alberto; Schwarz, Greg; Shore, Steve;
Starrfield, Sumner; Truran, Jim; Vanlandingham, Karen; Wagner, R. Mark
2006sptz.prop30007W Altcode:
Stars are the engines of energy production and chemical evolution
in our Universe. They deposit radiative and mechanical energy into
their environments and enrich the ambient interstellar medium with
elements synthesized in their interiors and dust grains condensed
in their atmospheres. Classical novae (CN) contribute to this cycle
of chemical enrichment through explosive nucleosynthesis and the
violent ejection of material dredged from the white dwarf progenitor
and mixed with the accreted surface layers. Using Spitzer (+IRS),
we propose a 25.8 hrs no-impact ToO program to study (in temporal
detail) the evolutionary stages of CN by targeting 4 Galactic and 2
Magellanic Cloud (MC) novae. Spitzer is a unique facility that enables
us to investigate aspects of the CN phenomenon including the in situ
formation and astromineralogy of nova dust, the elemental abundances
resulting from thermonuclear runaway, the correlation of ejecta masses
with progenitor type, the bolometric luminosities of the outburst,
and the kinematics and structure of the ejected envelopes. Synoptic,
high signal-to-noise IRS spectra permit: 1) determination of the
grain size distribution and mineral composition of nova dust; 2)
estimation of chemical abundances of nova ejecta from coronal and other
emission line spectroscopy; 3) measurement of the density and masses
of the ejecta; 4) characterization of the geometry and structure of
ejected shells at early stages during which the initial mixing of the
chemical abundances can be studied in detail; and 5) exploration of the
characteristics of CN in low metallicity systems (MC) at mid- to far-IR
wavelengths. Observations of CN with Spitzer will be complemented by
extensive ground-based, as well as space-based (e.g., Chandra, Swift,
XMM-Newton), DDT and ToO programs led by team CoIs.

---------------------------------------------------------
Title: A 3D radiative transfer framework. I. Non-local operator
splitting and continuum scattering problems
Authors: Hauschildt, P. H.; Baron, E.
2006A&A...451..273H Altcode: 2006astro.ph..1183H
We describe a highly flexible framework to solve 3D radiation
transfer problems in scattering dominated environments based on a long
characteristics piece-wise parabolic formal solution and an operator
splitting method. We find that the linear systems are efficiently solved
with iterative solvers such as Gauss-Seidel and Jordan techniques. We
use a sphere-in-a-box test model to compare the 3D results to 1D
solutions in order to assess the accuracy of the method. We have
implemented the method for static media, however, it can be used to
solve problems in the Eulerian-frame for media with low velocity fields.

---------------------------------------------------------
Title: NLTE Strontium and Barium in Metal-poor Red Giant Stars
Authors: Short, C. I.; Hauschildt, P. H.
2006ApJ...641..494S Altcode: 2006astro.ph..1210S
We present atmospheric models of red giant stars of various
metallicities, including extremely metal poor (XMP; [Fe/H]&lt;-3.5)
models, with many chemical species, including, significantly, the
first two ionization stages of strontium (Sr) and barium (Ba), treated
in non-local thermodynamic equilibrium (NLTE) with various degrees of
realism. We conclude that (1) for all lines that are useful Sr and Ba
abundance diagnostics, the magnitude and sense of the computed NLTE
effect on the predicted line strength is metallicity dependent, (2)
the indirect NLTE effect of overlap between Ba and Sr transitions
and transitions of other species that are also treated in NLTE
nonnegligibly enhances NLTE abundance corrections for some lines,
(3) the indirect NLTE effect of NLTE opacity of other species on the
equilibrium structure of the atmospheric model is not significant,
(4) the computed NLTE line strengths differ negligibly if collisional
b-b and b-f rates are an order of magnitude smaller or larger than
those calculated with standard analytic formulae, and (5) the effect
of NLTE on the resonance line of Ba II at 4554.03 Å is independent of
whether that line is treated with hyperfine splitting. As a result,
the derivation of abundances of Ba and Sr for metal-poor red giant
stars with LTE modeling that are in the literature should be treated
with caution.

---------------------------------------------------------
Title: Early Infrared Spectral Development of V1187 Scorpii (Nova
Scorpii 2004 No. 2)
Authors: Lynch, D. K.; Woodward, C. E.; Geballe, T. R.; Russell,
R. W.; Rudy, R. J.; Venturini, C. C.; Schwarz, G. J.; Gehrz, R. D.;
Smith, N.; Lyke, J. E.; Bus, S. J.; Sitko, M. L.; Harrison, T. E.;
Fisher, S.; Eyres, S. P.; Evans, A.; Shore, S. N.; Starrfield, S.;
Bode, M. F.; Greenhouse, M. A.; Hauschildt, P. H.; Truran, J. W.;
Williams, R. E.; Perry, R. Brad; Zamanov, R.; O'Brien, T. J.
2006ApJ...638..987L Altcode:
We report on an unprecedented infrared time series of spectra of
V1187 Sco, a very fast ONeMg nova. The observations covered a 56 day
period (2004 August 6-September 30) starting 2 days after the nova's
peak brightness. Time evolution of the spectra revealed changing line
strengths and profiles on timescales of less than a day to weeks as the
nova evolved from early postmaximum to early coronal phases. When our
ground-based optical and Spitzer Space Telescope data were combined,
the wavelength coverage of 0.38-36 μm allowed an accurate spectral
energy distribution to be derived when it was about 6 weeks after
outburst. Developing double structure in the He I lines showed them
changing from narrow to broad in only a few days. Using the O I lines
in combination with the optical spectra, we derived a reddening of
E(B-V)=1.56+/-0.08 and a distance of 4.9+/-0.5 kpc. Modeling of the
ejected material strongly suggested that it was geometrically thick
with ΔR/R=0.8-0.9 (more of a wind than a shell) and a low filling
factor of order a few percent. The line shapes were consistent with
a cylindrical jet, bipolar, or spherical Hubble flow expansion with
a maximum speed of about -3000 km s-1. The central peak
appeared to be more associated with the spherical component, while
the two peaks (especially in Hβ) suggested a ring with either a lower
velocity component or with its axis inclined to the line of sight.

---------------------------------------------------------
Title: Metal Hydride and Alkali Halide Opacities in Extrasolar Giant
Planets and Cool Stellar Atmospheres
Authors: Weck, Philippe F.; Stancil, Phillip C.; Kirby, Kate;
Schweitzer, Andreas; Hauschildt, Peter H.
2006nla..conf..274W Altcode:
The lack of accurate and complete molecular line and continuum opacity
data has been a serious limitation to developing atmospheric models of
cool stars and Extrasolar Giant Planets (EGPs). We report our recent
calculations of molecular opacities resulting from the presence of metal
hydrides and alkali halides. The resulting data have been included in
the PHOENIX stellar atmosphere code ( tealt*{hau99}). The new models,
calculated using spherical geometry for all gravities considered, also
incorporate our latest database of nearly 670 million molecular lines,
and updated equations of state.

---------------------------------------------------------
Title: Dust in the atmospheres of brown dwarfs and young planets:
the effects of gravitational settling and convective overshoot
Authors: Homeier, D.; Ludwig, H. -G.; Allard, F.; Hauschildt, P.;
Dehn, M.
2006IAUS..232..328H Altcode:
Dwarfs of the spectral types late-M, L and T span mass regimes from
very-low-mass stars through brown dwarfs down to young planetary
objects. They all show massive molecular line-blanketing and the
condensation of refractory species with decreasing T_{eff}, leading
to changes in chemical equilibrium composition and absorption due to
dust grains. The spectral evolution from late-M through L to mid- and
late-T classes is now understood as chiefly due to increasing amounts
of condensates in the visible photosphere up to mid-L types, and the
settling of dust clouds into deeper regions at the transition from L
to T, resulting in a depletion of condensable elements in the upper
atmosphere. The ensuing photospheric cooling also drives a change in
carbon chemistry leading to the hallmark methane absorption features
of T dwarfs.Recent observations of brown dwarfs in the L-T spectral
sequence and model atmosphere calculations have shown that these changes
in spectral features reveal differences in the efficiency of cloud
removal that seem to be triggered by an additional parameter besides
effective temperature. We present models describing the settling
of particle clouds as an equilibrium process between condensation,
gravitational sedimentation and convective and turbulent mixing, based
on 3D-hydrodynamical simulations for the description of the velocity
field. These calculations predict a strong dependence of the settling
on gravity, and can therefore explain observed differences between the
spectral energy distributions of brown dwarfs of equal luminosity as an
effect of different mass. Based on these calculations we would expect
even stronger deviations in the colours of young brown dwarfs of very
low mass from those commonly observed in the field. Such predictions
seem to be in aggreement with the first observations of candidate
planetary-mass objects, and would imply that extrasolar planets at very
young ages have spectral energy distributions significantly different
from previous models. Our models al so predict characteristic time
scales for the cloud formation processes that may be compared to
observed variability in brown dwarfs.

---------------------------------------------------------
Title: Photometric colors of late-type giants: theory versus
observations
Authors: Kucinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott,
I.; Vansevicius, V.; Lindegren, L.; Tanabé, T.; Allard, F.
2006IAUS..232..276K Altcode: 2005astro.ph.12354K
Late-type giants (i.e., stars on the red and asymptotic giant branches,
RGB/AGB, respectively) are dominant contributors to the overall spectral
appearance of intermediate age and old stellar populations, especially
in the red/near-infrared part of the spectrum. Being intrinsically
bright, they are well suited for probing distant/obscured populations,
especially those that can not be studied with their fainter members,
like main sequence turn-off stars or subgiants. Late-type giants and
supergiants will be the only stellar types accessible in intermediate
age and old populations beyond the distances of several Mpc with
the future 30-50 m class extremely large telescopes (Olsen et
al. 2003). Indeed, proper understanding of their observable properties
by means of theoretical models is of key importance for studying the
evolution of stellar populations and their host galaxies.

---------------------------------------------------------
Title: A Deep Study of the 3C 273 Field in γ-rays
Authors: Brott, I.; Kreykenbohm, I.; Lubiński, P.; Produit, N.;
Hauschildt, P. H.; Courvoisier, T. J. -L.
2006IAUS..230..459B Altcode:
3C 273 is one of the brightest and best studied quasars. It has
been observed for 770 ks with the imager IBIS (FoV 12 deg) on board
INTEGRAL. To achieve the best possible S/N the dataset has been
screened using several criteria indicating the quality of the data
(i.e., number of good time intervals, etc). We describe the necessary
tools and methods to analyze data of deep fields.

---------------------------------------------------------
Title: Convection and observable properties of late-type giants
Authors: Kucinskas, A.; Ludwig, H. -G.; Hauschildt, P. H.
2006IAUS..232..498K Altcode: 2005astro.ph.12353K
We show that contrary to what is expected from 1D stationary model
atmospheres, 3D hydrodynamical modeling predicts a considerable
influence of convection on the spectral properties of late-type
giants. This is due to the fact that convection overshoots into the
formally stable outer atmospheric layers producing a notable granulation
pattern in the 3D hydrodynamical models, which has a direct influence
on the observable spectra and colors. Within the framework of standard
1D model atmospheres the average thermal stratification of the 3D
hydro model can not be reproduced with any reasonable choice of the
mixing length parameter and formulation of the turbulent pressure. The
differences in individual photometric colors - in terms of 3D versus
1D - reach up to ∼0.2 mag, or Δ T_{eff}∼70 K. We discuss the
impact of full 3D hydrodynamical models on the interpretation of
observable properties of late-type giants, briefly mentioning problems
and challenges which need to be solved for bringing these models to
a routine use within the astronomical community in 5-10 years from now.

---------------------------------------------------------
Title: Infrared spectra of exoplanet candidate GQ Lup b
Authors: Neuhaeuser, R.; Seifahrt, A.; Guenther, E. W.; Mugrauer,
M.; Hauschildt, P.
2006epsc.conf...32N Altcode:
We have presented evidence that the directly detected companion to GQ
Lup could be a planet with mass estimates below 13 Jupiter masses. The
companion is clearly co-moving and bound. The mass estimate was via
theoretical models for formation and atmosphere, hence model-dependant
and uncertain. Originally, we took a K-band spectrum with VLT/NACO with
resolution 700 only. Now, we have taken two much better spectra in the
H and K bands with VLT/Sinfoni with resolution 4000. We will present
and discuss these two spectra regarding temperature and gravity of
the companion and, hence, its mass and nature.

---------------------------------------------------------
Title: Early Spectra of Supernovae
Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt, P. H.
2005ASPC..342..351B Altcode: 2004astro.ph..9659B
We briefly describe the current version of the PHOENIX code. We then
present some results on the modeling of Type II supernovae and show
that fits to observations can be obtained, when account is taken for
spherically symmetric, line-blanketed, expanding atmospheres. We
describe the SEAM method of obtaining distances to supernovae and
briefly discuss its future prospects.

---------------------------------------------------------
Title: The low-mass companion of GQ Lup
Authors: Guenther, E. W.; Neuhäuser, R.; Wuchterl, G.; Mugrauer,
M.; Bedalov, A.; Hauschildt, P. H.
2005AN....326..958G Altcode: 2005astro.ph.10794G
Using NACO on the VLT in the imaging mode we have detected an object at
a distance of only 0.7 arcsec from GQ Lup. The object turns out to be
co-moving. We have taken two K-band spectra with a resolution of \lambda
/ \Delta \lambda=700. In here, we analyze the spectra in detail. We
show that the shape of spectrum is not spoiled by differences in the
Strehl ratio in the blue and in the red part, as well as differential
refraction. We reanalyze the spectra and derive the spectral type of
the companion using classical methods. We find that the object has a
spectral type between M9V and L4V, which corresponds to a T_eff between
1600 and 2500 K. Using GAIA-dusty models, we find that the spectral
type derivation is robust against different log(g)-values. The T_eff
derived from the models is again in the range between 1800 and 2400
K. While the models reproduce nicely the general shape of the spectrum,
the 12CO lines in the spectrum have about half the depth
as those in the model. We speculate that this difference might be
caused by veiling, like in other objects of similar age, and spectral
class. We also find that the absolute brightness of the companion
matches that of other low-mass free-floating objects of similar age
and spectral type. A comparison with the objects in USco observed by
Mohanty et al. (\cite{mohanty04b}) shows that the companion of GQ Lup
has a lower mass than any of these, as it is of later spectral type,
and younger. The same is as true, for the companion of AB Pic. To have
a first estimate of the mass of the object we compare the derived T_eff
and luminosity with those calculated from evolutionary tracks. We also
point out that future instruments, like NAHUAL, will finally allow us
to derive the masses of such objects more precisely.

---------------------------------------------------------
Title: Status of the physics of substellar objects
Authors: Jones, H. R. A.; Viti, S.; Tennyson, J.; Barber, B.; Harris,
G.; Pickering, J. C.; Blackwell-Whitehead, R.; Champion, J. -P.;
Allard, F.; Hauschildt, P. H.; Jorgensen, U. G.; Ehrenfreund, P.;
Stachowska, E.; Ludwig, H. -G.; Martin, E.; Pavlenko, Ya.; Lyubchik,
Yu.; Kurucz, R. L.
2005AN....326..920J Altcode:
A full understanding of the properties of substellar objects is one
of the major challenges facing astrophysics. Since their discovery
in 1995, we have discovered hundreds of brown dwarfs and extrasolar
planets. While these discoveries have enabled important comparisons
with theory, observational progress has been much more rapid than
the theoretical understanding of cool atmospheres. The reliable
determination of mass, abundances, gravities and temperatures is not
yet possible. The key problem is that substellar objects emit their
observable radiation in the infrared region of the spectrum where our
knowledge of atomic, molecular and line broadening data is poor. Here
we report on the status of PoSSO (Physics of SubStellar Objects). In
order to understand brown dwarfs and extrasolar planets increasing
more like those in our solar system, we are studying a wide range of
processes. Here we give an update on the project and sketch an outline
of atoms, molecules and processes requiring study.

---------------------------------------------------------
Title: Broad-band photometric colors and effective temperature
calibrations for late-type giants. I. Z = 0.02
Authors: Kučinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott,
I.; Vansevičius, V.; Lindegren, L.; Tanabé, T.; Allard, F.
2005A&A...442..281K Altcode: 2005astro.ph.10434K
We present new synthetic broad-band photometric colors for
late-type giants based on synthetic spectra calculated with the
PHOENIX model atmosphere code. The grid covers effective temperatures
T_eff=3000dots 5000 K, gravities log g=-0.5dots{+3.5}, and metallicities
[M/H]=+0.5dots{-4.0}. We show that individual broad-band photometric
colors are strongly affected by model parameters such as molecular
opacities, gravity, microturbulent velocity, and stellar mass. Our
exploratory 3D modeling of a prototypical late-type giant shows that
convection has a noticeable effect on the photometric colors too,
as it alters significantly both the vertical and horizontal thermal
structures in the outer atmosphere. The differences between colors
calculated with full 3D hydrodynamical and 1D model atmospheres are
significant (e.g., Δ(V-K)∼0.2 mag), translating into offsets in
effective temperature of up to 70 K. For a sample of 74 late-type
giants in the Solar neighborhood, with interferometric effective
temperatures and broad-band photometry available in the literature,
we compare observed colors with a new PHOENIX grid of synthetic
photometric colors, as well as with photometric colors calculated with
the MARCS and ATLAS model atmosphere codes. We find good agreement of
the new synthetic colors with observations and published T_eff-color
and color-color relations, especially in the T_eff-(V-K), T_eff-(J-K)
and (J-K)-(V-K) planes. Deviations from the observed trends in the
T_eff-color planes are generally within ±100 K for T_eff=3500 to 4800
K. Synthetic colors calculated with different stellar atmosphere models
agree to ±100 K, within a large range of effective temperatures and
gravities. The comparison of the observed and synthetic spectra of
late-type giants shows that discrepancies result from the differences
both in the strengths of various spectral lines/bands (especially
those of molecular bands, such as TiO, H2O, CO) and the continuum
level. Finally, we derive several new T_eff-log g-color relations for
late-type giants at solar-metallicity (valid for T_eff=3500 to 4800
K), based both on the observed effective temperatures and colors of
the nearby giants, and synthetic colors produced with PHOENIX, MARCS
and ATLAS model atmospheres.

---------------------------------------------------------
Title: Quantitative Spectroscopy of Supernovae for Dark Energy Studies
Authors: Baron, E.; Branch, David; Jeffery, David; Nugent, Peter;
Thomas, Rollin; Bongard, Sebastien; Hauschildt, Peter H.; Kasen,
Daniel; Mihalas, Dimitri
2005astro.ph.10166B Altcode:
Detailed quantitative spectroscopy of Type Ia supernovae (SNe~Ia)
provides crucial information needed to minimize systematic effects in
both ongoing SNe Ia observational programs such as the Nearby Supernova
Factory, ESSENCE, and the SuperNova Legacy Survey (SNLS) and in proposed
JDEM missions such as SNAP, JEDI, and DESTINY. Quantitative spectroscopy
is mandatory to quantify and understand the observational strategy of
comparing “like versus like”. It allows us to explore evolutionary
effects, from variations in progenitor metallicity to variations in
progenitor age, to variations in dust with cosmological epoch. It
also allows us to interpret and quantify the effects of asphericity,
as well as different amounts of mixing in the thermonuclear explosion.

---------------------------------------------------------
Title: Phase-Dependent Properties of Extrasolar Planet Atmospheres
Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France
2005ApJ...632.1132B Altcode: 2005astro.ph..7136B
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD 209458b. These observations have provided
the first estimates of the day-side thermal flux from two extrasolar
planets orbiting Sun-like stars. In this paper, synthetic spectra from
atmospheric models are compared to these observations. The day-night
temperature difference is explored and phase-dependent flux densities
are predicted for both planets. For HD 209458b and TrES-1, models
with significant day-to-night energy redistribution are required to
reproduce the observations. However, the observational error bars are
large, and a range of models remains viable.

---------------------------------------------------------
Title: 6Li in the Atmosphere of GJ 117
Authors: Christian, D. J.; Mathioudakis, M.; Jevremović, D.;
Hauschildt, P. H.; Baron, E.
2005ApJ...632L.127C Altcode: 2005astro.ph..9247C
We present high-resolution VLT UVES observations of the active K dwarf
GJ 117. 6Li enhancement has been shown for energetic solar
events, one chromospherically active binary, and several dwarf halo
stars. Our analysis reveals the detection of 6Li on this
source with 6Li/7Li = 0.030 +/- 0.010. We found
no significant contribution from other lines, including Ti I, in the
Li profile of GJ 117 and a template star of similar spectral type and
metallicity. We discuss the possibility for 6Li production
by spallation and find it to be consistent with the activity levels
of the object.

---------------------------------------------------------
Title: Review on low-mass stars and brown dwarfs
Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H.
2005astro.ph..9798C Altcode:
In this review, we examine the successes and weaknesses of modern
low-mass star and brown dwarf theory.(1) We first focus on the
mechanical (equation of state) and thermal (atmosphere) properties
and on the evolution. We then examine the current shortcomings of the
theory and we discuss recent observational analysis which have suggested
discrepancies between models and observations.(2) We then examine the
stellar and brown dwarf IMF and suggest that a power-law above the
average thermal Jeans mass (about 1 Msol) rolling over a lognormal
form below this limit adequately reproduces the observations of field
and young cluster stellar and brown dwarf distributions. This yields
a reasonably accurate estimate of the stellar and brown dwarf Galactic
census. Finally (3) we argue that the combination of turbulence driven
fragmentation at large scale and gravity at small scales provides
an appealing solution for the general star and brown dwarf formation
mechanism. It also provides a physical ground for the aforementioned
power-law + lognormal form for the IMF, whereas a series of different
power laws lacks such a physical motivation. At last, we argue that the
deuterium-burning limit as the distinction between stars and planets
has no physical foundation in this modern star formation scheme. Opacity
limited fragmentation extending down to a few (&lt; 10) jupiter masses,
due to shocks, anisotropy or magnetic fields, provides a much more
robust limit, even though difficult to determine accurately. Therefore,
the various "direct" detections of exoplanets claimed recently in the
literature are most likely regular low-mass brown dwarfs and the direct
detection of an extrasolar planet remains for now elusive.

---------------------------------------------------------
Title: PHOENIX model chromospheres of mid- to late-type M dwarfs
Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H.
2005A&A...439.1137F Altcode: 2005astro.ph..5375F
We present semi-empirical model chromospheres computed with the
atmosphere code PHOENIX. The models are designed to fit the observed
spectra of five mid- to late-type M dwarfs. Next to hydrogen lines
from the Balmer series we used various metal lines, e.g. from Fe i,
for the comparison between data and models. Our computations show that
an NLTE treatment of C, N, O impacts on the hydrogen line formation,
while NLTE treatment of less abundant metals such as nickel influences
the lines of the considered species itself. For our coolest models we
investigated also the influence of dust on the chromospheres and found
that dust increases the emission line flux. Moreover we present an
(electronically published) emission line list for the spectral range
of 3100 to 3900 and 4700 to 6800 Å for a set of 21 M dwarfs and brown
dwarfs. The line list includes the detection of the Na i D lines in
emission for a L3 dwarf.

---------------------------------------------------------
Title: Modeling CHANDRA Low Energy Transmission Grating Spectrometer
Observations of Classical Novae with PHOENIX
Authors: Petz, A.; Hauschildt, P. H.; Ness, J. -U.; Starrfield, S.
2005ASPC..330..299P Altcode: 2005astro.ph..1072P
We use the PHOENIX code package to model the X-ray spectrum of Nova
V4743 Sagittarii observed with the LETGS onboard the Chandra satellite
on March 2003. To analyze nova atmospheres and related systems with
an underlying nuclear burning envelope at X-ray wavelengths, it was
necessary to update the code with new microphysics. We demonstrate
that the X-ray emission is dominated by thermal bremsstrahlung and
that the hard X-rays are dominated by Fe and N absorption. Preliminary
models are calculated assuming solar abundances. It is shown that
the models can be used to determine abundances in the nova ejecta by
increasing the absorption in the shell and considering more elements
in the NLTE calculations.

---------------------------------------------------------
Title: Direct imaging of planets around young stars, the case of GQ
Lup b.
Authors: Neuhaeuser, R.; Guenther, E.; Mugrauer, M.; Wuchterl, G.;
Hauschildt, P.
2005AN....326..630N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model atmospheres of substellar atmospheres at a young age:
influence of gravity and dust.
Authors: Homeier, D.; Allard, F.; Ludwig, H. -G.; Hauschildt, P.;
Dehn, M.
2005AN....326Q.628H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determination of stellar shape in microlensing event MOA
2002-BLG-33
Authors: Rattenbury, N. J.; Abe, F.; Bennett, D. P.; Bond, I. A.;
Calitz, J. J.; Claret, A.; Cook, K. H.; Furuta, Y.; Gal-Yam, A.;
Glicenstein, J. -F.; Hearnshaw, J. B.; Hauschildt, P. H.; Kilmartin,
P. M.; Kurata, Y.; Masuda, K.; Maoz, D.; Matsubara, Y.; Meintjes,
P. J.; Moniez, M.; Muraki, Y.; Noda, S.; Ofek, E. O.; Okajima, K.;
Philpott, L.; Rhie, S. H.; Sako, T.; Sullivan, D. J.; Sumi, T.;
Terndrup, D. M.; Tristram, P. J.; Wood, J.; Yanagisawa, T.; Yock,
P. C. M.
2005A&A...439..645R Altcode: 2005astro.ph..6013R
We report a measurement of the shape of the source star in microlensing
event MOA 2002-BLG-33. The lens for this event was a close binary
whose centre-of-mass passed almost directly in front of the source
star. At this time, the source star was closely bounded on all sides by
a caustic of the lens. This allowed the oblateness of the source star to
be constrained. We found that a/b = 1.02+0.04-0.02
where a and b are its semi-major and semi-minor axes respectively. The
angular resolution of this measurement is approximately 0.04
μ{arcsec}. We also report HST images of the event that confirm
a previous identification of the source star as an F8-G2 turn-off
main-sequence star.

---------------------------------------------------------
Title: Modelling Alkali Line Absorption and Molecular Bands in
Cool DAZs
Authors: Homeier, D.; Allard, N.; Allard, F.; Hauschildt, P. H.;
Schweitzer, A.; Stencil, P. C.; Weck, P. F.
2005ASPC..334..209H Altcode: 2005astro.ph..1077H
Two peculiar stars showing an apparent extremely broadened and strong
Na I D absorption have been discovered in surveys for cool white
dwarfs by Oppenheimer et al. (2001) and Harris et al. (2003, SDSS). We
discuss the nature of these objects using PHOENIX atmosphere models
for metal-poor brown dwarfs/very low mass stars, and new white dwarf
LTE and NLTE models for hydrogen- and helium-dominated atmospheres
with metals. These include complete molecular formation in chemical
equilibrium and a model for the alkali resonance line broadening
based on the damping profiles of Allard et al. (2003), as well as
new molecular line opacities for metal hydrides. First results of
our calculations indicate good agreement with a hydrogen-dominated
WD atmosphere with a Na abundance roughly consistent with a state of
high accretion. We analyse deviations of the abundances of Na, K, Mg
and Ca from the cosmic pattern and comment on implications of these
results for standard accretion scenarios.

---------------------------------------------------------
Title: Modeling CHANDRA Low Energy Transmission Grating Spectrometer
Observations of Classical Novae with PHOENIX
Authors: Petz, A.; Hauschildt, P. H.; Ness, J. U.; Starrfield, S.
2005AIPC..774..357P Altcode:
We use the PHOENIX code package to model the X-ray spectrum of Nova
V4743 Sagittarii observed with the LETGS onboard the Chandra satellite
on 19 March 2003. To analyze nova atmospheres and related systems with
an underlying nuclear burning envelope at X-ray wavelengths, it was
necessary to update the code with new microphysics. We demonstrate
that the X-ray emission is dominated by thermal bremsstrahlung and
that the hard X-rays are dominated by Fe and N absorption. Preliminary
models are calculated assuming solar abundances. It is shown that the
models can be used to determine element abundances in the nova ejecta
by increasing the absorption in the shell.

---------------------------------------------------------
Title: Hot-Jupiters and hot-Neptunes: A common origin?
Authors: Baraffe, I.; Chabrier, G.; Barman, T. S.; Selsis, F.; Allard,
F.; Hauschildt, P. H.
2005A&A...436L..47B Altcode: 2005astro.ph..5054B
We compare evolutionary models for close-in exoplanets coupling
irradiation and evaporation due respectively to the thermal and high
energy flux of the parent star with observations of recently discovered
new transiting planets. The models provide an overall good agreement
with observations, although at the very limit of the quoted error bars
of OGLE-TR-10, depending on its age. Using the same general theory,
we show that the three recently detected hot-Neptune planets (GJ436, ρ
Cancri, μ Ara) may originate from more massive gas giants which have
undergone significant evaporation. We thus suggest that hot-Neptunes
and hot-Jupiters may share the same origin and evolution history. Our
scenario provides testable predictions in terms of the mass-radius
relationships of these hot-Neptunes.

---------------------------------------------------------
Title: Direct detection of exo-planets: GQ Lupi
Authors: Neuhaeuser, Ralph; Guenther, Eike; Hauschildt, Peter
2005astro.ph..6011N Altcode:
We present a comparison of our VLT/NACO K-band spectrum of the GQ Lupi
companion with the new GAIA-dusty model atmosphere grid for T=2000
and 2900 K and log g from 0 to 4. Then, we discuss the mass estimate
for GQ Lup companion.

---------------------------------------------------------
Title: Probing the Chromospheres of M dwarfs with the IRS
Authors: Cushing, Michael; Chabrier, Gilles; Hauschildt, Peter;
Liebert, James; Wehrse, Rainer
2005sptz.prop20409C Altcode:
Arguable the most effective wavelength region to probe the
coolest, outer layers of M dwarf atmospheres is to use mid-infrared
spectrophotometry. Here the continuum opacity is very small, though
if the atmosphere is not heated from below, the opacity due to water
will be very strong. However, if there is any temperature increase
above the minimum temperature layer due to a chromosphere or just weak
acoustic heating, the water opacity weakens greatly, and a substantial
increase in mid-infrared flux is predicted by models. This enhancement
would be expected to increase sharply with increasing wavelength,
reaching perhaps a 50% difference at 30 microns, and exceeding 60% at
36 microns. We thus propose to observe a set of eleven M1-M6 dwarfs,
with and without quiescent H alpha emission. Most of the latter have old
disk / halo space velocities. The observations should test the level of
"basal" chromospheric-like activity for old stars that should have at
most, weak, spun-down dynamos.

---------------------------------------------------------
Title: Detection of red line asymmetries in LHS 2034
Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H.
2005A&A...436..677F Altcode:
We report very pronounced line asymmetries during a long duration flare
on the dM6 star LHS 2034 (AZ Cnc). While all lines of the Balmer series
and all strong He i lines show these asymmetries, the metal lines do
not. This can be explained with the help of PHOENIX model chromospheres
considering the formation depth of the lines involved. Moreover,
the asymmetries persist over about one hour changing shape and
amplitude. Fitting the asymmetries with an additional broad Gaussian
component leads us to the scenario of a series of downward propagating
condensations that decelerate due to the higher density of the lower
chromosphere. In addition, similar but weaker line asymmetries were
found in LHS 2397a.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Late-type giants BVRIJHKL and
Teff calibration (Kucinskas+, 2005)
Authors: Kucinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott,
I.; Vansevicius, V.; Lindegren, L.; Tanabe, T.; Allard, F.
2005yCat..34420281K Altcode:
Table 2 contains synthetic broad-band photometric colors of late-type
giants in the Johnson-Cousins-Glass photometric system. Colors are
based on the synthetic spectra calculated with the PHOENIX stellar
model atmosphere code. Photometric filter definitions used are those
from Bessell (1990PASP..102.1181B) for the Johnson-Cousins BVRI bands,
and from Bessell &amp; Brett (1988PASP..100.1134B) for the Johnson-Glass
JHKL bands. (1 data file).

---------------------------------------------------------
Title: VizieR Online Data Catalog: PHOENIX model chromospheres of
M dwarfs (Fuhrmeister+, 2005)
Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H.
2005yCat..34391137F Altcode:
We present an extensive identification catalog of chromospheric emission
lines in the optical range. The data were obtained with ESO's Kueyen
telescope equipped with the UVES spectrograph from March, 13th to 16th
in 2002. The instrument was operated in dichroic mode (spectral coverage
from 3030 to 3880 and from 4580 to 6680{AA}). The data for the stars
Prox Cen, UV Ceti and LHS 292 were obtained with the same instrument
in winter 2000/2001 with a monochroic setup providing only the blue
part of the spectrum. We tabulated measured wavelength, equivalent
width (EW) and FWHM for every line and star and also provide the rest
wavelength from the Moore catalog which was used for identification
(Moore 1972). Few lines were identified with the NIST database. The
spectra were all corrected for radial velocity besides Kelu-1, DENIS-P
J1058.7-1548 and 2MASSI J1315309-264951. DENIS-P J1058.7-1548 has no
detected lines, and therefore no data in the table. (2 data files).

---------------------------------------------------------
Title: Evidence for a co-moving sub-stellar companion of GQ Lup
Authors: Neuhäuser, R.; Guenther, E. W.; Wuchterl, G.; Mugrauer,
M.; Bedalov, A.; Hauschildt, P. H.
2005A&A...435L..13N Altcode: 2005astro.ph..3691N
We present a companion of the ≤2 Myr young classical T Tauri star
GQ Lup in the Lupus star forming region at 140 ± 50 pc from imaging,
astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO,
we detected an object 6 mag fainter than GQ Lup located 0.7” west of
it. Compared to images obtained 2 to 5 years earlier with Subaru/CIAO
and HST/PC, this object shares the proper motion of GQ Lup by 5 and
7σ, respectively, hence it is a co-moving companion. Its K-L' color is
consistent with a spectral type early to mid L. Our NACO K-band spectrum
yields spectral type M9-L4 with H2O and CO absorption,
consistent with the new GAIA-Dusty template spectrum for log g ≃ 2
to 3 and Teff ≃ 2000 K with ~2 Rjup radius at
∼ 140 pc, hence few Jupiter masses. Using the theoretical models
from Wuchterl &amp; Tscharnuter (2003), Burrows et al. (1997), and
Baraffe et al. (2002), the mass lies between 1 and 42 Jupiter masses.

---------------------------------------------------------
Title: Low-Temperature Opacities
Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France;
Barman, Travis; Bodnarik, Julia G.; Hauschildt, Peter H.; Heffner-Wong,
Amanda; Tamanai, Akemi
2005ApJ...623..585F Altcode: 2005astro.ph..2045F
Previous computations of low-temperature Rosseland and Planck mean
opacities from Alexander &amp; Ferguson are updated and expanded. The
new computations include a more complete equation of state (EOS)
with more grain species and updated optical constants. Grains are now
explicitly included in thermal equilibrium in the EOS calculation,
which allows for a much wider range of grain compositions to be
accurately included than was previously the case. The inclusion of
high-temperature condensates such as Al2O3
and CaTiO3 significantly affects the total opacity over
a narrow range of temperatures before the appearance of the first
silicate grains. The new opacity tables are tabulated for temperatures
ranging from 30,000 to 500 K with gas densities from 10-4 to
10-19 g cm-3. Comparisons with previous Rosseland
mean opacity calculations are discussed. At high temperatures, the
agreement with OPAL and Opacity Project is quite good. Comparisons
at lower temperatures are more divergent as a result of differences
in molecular and grain physics included in different calculations. The
computation of Planck mean opacities performed with the opacity sampling
method is shown to require a very large number of opacity sampling
wavelength points; previously published results obtained with fewer
wavelength points are shown to be significantly in error. Methods for
requesting or obtaining the new tables are provided.

---------------------------------------------------------
Title: Modeling M-dwarf chromospheres with PHOENIX
Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H.
2005ESASP.560..559F Altcode: 2005csss...13..559F
No abstract at ADS

---------------------------------------------------------
Title: NLTE models of extremely metal poor stars
Authors: Short, C. I.; Hauschildt, P. H.
2005ESASP.560..967S Altcode: 2005csss...13..967S
No abstract at ADS

---------------------------------------------------------
Title: The 2002 outburst of V838 Mon: as cool as it gets
Authors: Starrfield, S.; Wagner, R. M.; Hauschildt, P. H.; Bond,
H. E.; Evans, A.; Rushton, M. T.; Munari, U.; Henden, A.; Levay,
Z. G.; Panagia, N.; Sparks, W. B.; Corradi, R. L. M.
2005ESASP.560..359S Altcode: 2005csss...13..359S
No abstract at ADS

---------------------------------------------------------
Title: Evolutionary stellar population synthesis at high spectral
resolution: optical wavelengths
Authors: González Delgado, R. M.; Cerviño, M.; Martins, L. P.;
Leitherer, C.; Hauschildt, P. H.
2005MNRAS.357..945G Altcode: 2005astro.ph..1204D; 2005MNRAS.tmp...89D; 2005astro.ph..1204G;
2005MNRAS.357..945D
We present the single stellar population (SSP) synthesis results of
our new synthetic stellar atmosphere models library with a spectral
sampling of 0.3 Å, covering the wavelength range from 3000 to 7000
Åfor a wide range of metallicities (twice solar, solar, half solar and
1/10 solar). The stellar library is composed of 1650 spectra computed
with the latest improvements in stellar atmospheres. In particular, it
incorporates non-local thermodynamic equilibrium (LTE) line-blanketed
models for hot (Teff&gt;= 27500 K), and LTE line-blanketed
models (Phoenix) for cool (3000 &lt;=Teff&lt;= 4500 K)
stars. Because of the high spectral resolution of this library,
evolutionary synthesis models can be used to predict the strength
of numerous weak absorption lines and the evolution of the profiles
of the strongest lines over a wide range of ages. The SSP results
have been calculated for ages from 1 Myr to 17 Gyr using the stellar
evolutionary tracks provided by the Geneva and Padova groups. For
young stellar populations, our results have a very detailed coverage of
high-temperature stars with similar results for the Padova and Geneva
isochrones. For intermediate and old stellar populations, our results,
once degraded to a lower resolution, are similar to the ones obtained
by other groups (limitations imposed by the stellar evolutionary
physics notwidthstanding). The limitations and advantages of our
models for the analysis of integrated populations are described. The
full set of the stellar library and the evolutionary models are
available for retrieval at the websites http://www.iaa.csic.es/~rosa
and http://www.iaa.csic.es/~mcs/sed@, or on request from the first
two authors.

---------------------------------------------------------
Title: A high-resolution stellar library for evolutionary population
synthesis
Authors: Martins, Lucimara P.; González Delgado, Rosa M.; Leitherer,
Claus; Cerviño, Miguel; Hauschildt, Peter
2005MNRAS.358...49M Altcode: 2005MNRAS.tmp..133M; 2005astro.ph..1225P; 2005astro.ph..1225M
We present a library of 1654 high-resolution stellar spectra, with
a sampling of 0.3 Åand covering the wavelength range from 3000
to 7000 Å. The library was computed with the latest improvements
in stellar atmospheres, incorporating non-local thermodynamic
equilibrium (non-LTE) line-blanketed models for hot, massive
(Teff&gt;= 27500K) and line-blanketed models for cool
(3000 &lt;=Teff&lt;= 4500K) stars. The total coverage of
the grid is 3000 K &lt;=Teff&lt;= 55000 K and -0.5 &lt;=
log g&lt;= 5.5, for four chemical abundance values: twice solar, solar,
half solar and 1/10 solar. Evolutionary synthesis models using this
library are presented in a companion paper. We tested the general
behaviour of the library by calculating and comparing equivalent
widths of numerous H and HeI lines, and some of the commonly used
metallic indices. We also compared the library with the empirical
libraries STELIB and Indo-US. The full set of the synthetic stellar
spectra is available from our websites (http://www.iaa.csic.es/~rosa
and http://www.astro.iag.usp.br/~lucimara/library.htm).

---------------------------------------------------------
Title: Extrasolar planets: atmospheres, spectra, and evolution
Authors: Barman, T. S.; Allard, F.; Baraffe, I.; Chabrier, G.;
Hauschildt, P. H.
2005ESASP.560..437B Altcode: 2005csss...13..437B
No abstract at ADS

---------------------------------------------------------
Title: Modeling of stellar chromospheres: Phoenix vs. Multi
Authors: Jevremović, D.; Baron, E.; Hauschildt, P. H.
2005ESASP.560..673J Altcode: 2005csss...13..673J
No abstract at ADS

---------------------------------------------------------
Title: Modeling CHANDRA low energy transmission grating spectrometer
observations of classical novae with PHOENIX. I. V4743 Sagittarii
Authors: Petz, A.; Hauschildt, P. H.; Ness, J. -U.; Starrfield, S.
2005A&A...431..321P Altcode: 2004astro.ph.10370P
We use the PHOENIX code package to model the X-ray spectrum of Nova
V4743 Sagittarii observed with the LETGS onboard the Chandra satellite
19 March 2003. Our atmosphere models are 1D spherical, expanding,
line blanketed, and in full non-local thermodynamic equilibrium. To
analyze nova atmospheres and related systems with an underlying nuclear
burning envelope at X-ray wavelengths, it was necessary to update the
code with new microphysics, as discussed in this paper. We demonstrate
that the X-ray emission is dominated by thermal bremsstrahlung and that
the hard X-rays are dominated by Fe and N absorption. The best fit to
the observation is provided at a temperature of Teff = 5.8
× 105 K, with Lbol = 50 000 L⊙. The
models are calculated for solar abundances. It is shown that the models
can be used to determine abundances in the nova ejecta.

---------------------------------------------------------
Title: Overview of supernova modeling with PHOENIX
Authors: Baron, E.; Hauschildt, Peter H.
2005MSAIS...7...86B Altcode:
We discuss the information that can be obtained by comparing detailed
NLTE \texttt{PHOENIX} models to observed supernova spectra. We show
that the progenitor chemical composition, total reddening of the
supernova, and accurate distances can be obtained with synthetic
spectra that provide good fits to both the shape of the SED and the
spectral lineshapes in the observed spectra.

---------------------------------------------------------
Title: A PHOENIX Model Atmosphere Grid for Gaia
Authors: Brott, I.; Hauschildt, P. H.
2005ESASP.576..565B Altcode: 2005tdug.conf..565B; 2005astro.ph..3395B
We present the results of a set of model atmospheres and synthetic
spectra computed with the PHOENIX code. The models cover a range of
effective temperatures (2 700 K ≤ Teff ≤ 10 000 K), gravities
(-0.5 ≤ log(g) ≤ 5.5) and metallicities (-4.0 ≤ [Z/H] ≤
+0.5). In addition, variations of alpha elements are considered for
each metallicity. The models are computed with a homogeneous set of
input data in order to allow for direct relative comparison between
the models. For example, all models use a mixing length of l/Hp =
2.0. We provide synthetic spectra with a resolution of 0.2 nm from
the UV to the infrared for all models. We give a brief overview of
the input physics and show illustrative results. All synthetic spectra
are available via ftp.

---------------------------------------------------------
Title: First Steps Towards Modelling a Brown Dwarf Atmosphere
Including the Formation of Dust
Authors: Dehn, M.; Helling, C.; Woitke, P.; Hauschildt, P.
2005prpl.conf.8158D Altcode: 2005LPICo1286.8158D
No abstract at ADS

---------------------------------------------------------
Title: The Deuterium Test for Exo-Planet Candidates Detected Directly
Authors: Neuhäuser, Ralph; Seifahrt, Andreas; Hauschildt, Peter;
Alves, Joao; Guenther, Eike
2005hris.conf..484N Altcode:
In the near future, direct images will be obtained for massive planets
orbiting around other stars. Most likely, the first such objects
detected directly will have masses near the proposed limit between
brown dwarfs and planets, i.e., around 13 Jupiter masses, because the
more massive planets are the brightest. Hence, it may be dubious in
these first few cases, whether the detected object is a brown dwarf or a
real planet. To solve this problem, one can perform the deuterium test,
i.e., one can distinguish between a brown dwarf (defined as an object
able to fuse all deuterium) and an real planet (defined as an object
not being able to fuse any deuterium) by whether or not deuterium can
be identified in a spectrum. Any such object, brown dwarf or planet,
would have spectral type T, defined as those with strong methane lines
in the infrared. We present a model spectrum with the CH3D line at ~
4.5 μm which can be obtained for such objects with CRIRES at the VLT.

---------------------------------------------------------
Title: Cool stellar atmospheres with PHOENIX .
Authors: Hauschildt, P.; Baron, E.
2005MSAIS...7..140H Altcode:
We give an overview about the state-of-the-art in cool stellar (and
sub-stellar) atmosphere simulations. Recent developments in numerical
methods and parallel supercomputers, as well as in the quality of input
data such as atomic and molecular line lists have led to substantial
improvements in the quality of synthetic spectra when compared to
multi-wavelength observations. A wide range of objects from M dwarfs
and giants down to substellar objects is considered. We discuss effects
such as atomic and molecular NLTE (and) line blanketing, external
irradiation, and formation and opacities of dust particles and clouds;
each of which affects the structure of the atmospheres and their
spectra. Current models can simultaneously fit many of the observed
features of a given star with a single model atmosphere, however, a
number of problems remain unsolved and will have to be addressed in the
future, in particular for very low mass stars and substellar objects.

---------------------------------------------------------
Title: A Non-LTE Line-Blanketed Model of a Solar-Type Star
Authors: Short, C. I.; Hauschildt, P. H.
2005ApJ...618..926S Altcode: 2004astro.ph..9693S
We present LTE and non-LTE (NLTE) atmospheric models of a star with
solar parameters and study the effect of treating many thousands of
iron-group lines out of LTE on the computed atmospheric structure, the
overall absolute flux distribution, and the moderately high resolution
spectrum in the visible and near-UV bands. Our NLTE modeling includes
the first two or three ionization stages of 20 chemical elements, up
to and including much of the Fe group, and includes about 20,000 Fe
I and II lines. We investigate separately the effects of treating the
light metals and the Fe-group elements in NLTE. Our main conclusions
are that (1) NLTE line-blanketed models with direct multilevel NLTE
for many actual transitions give results qualitatively similar to
those of the more approximate treatment of L. S. Anderson for both
the Fe statistical equilibrium and the atmospheric Tkin
structure; (2) models with many Fe lines in NLTE have a Tkin
structure that agrees more closely with LTE semiempirical models based
on center-to-limb variation and a wide variety of spectra lines,
whereas LTE models agree more with semiempirical models based only
on an LTE calculation of the Fe I excitation equilibrium; and (3)
the NLTE effects of Fe-group elements on the model structure and
Fλ distribution are much more important than the NLTE
effects of all the light metals combined and serve to substantially
increase the violet and near-UV Fλ level as a result of
NLTE Fe overionization. These results suggest that there may still be
important UV opacity missing from the models. However, the choice of
the species and multiplet-dependent van der Waals broadening enhancement
also plays a significant role in determining whether LTE or NLTE models
provide a close fit to the near-UV flux level. We also find that the
rms deviation of the shape of the rectified high-resolution synthetic
spectrum from that of the observed spectrum is not significantly
affected by the inclusion of NLTE effects.

---------------------------------------------------------
Title: Theoretical Modelling of Late-Type Giant Atmospheres: Preparing
for Gaia
Authors: Kucinskas, A.; Brott, I.; Hauschildt, P. H.; Ludwig, H. -G.;
Lindegren, L.; Tanabé, T.; Vansevicius, V.
2005ESASP.576..591K Altcode: 2005tdug.conf..591K; 2005astro.ph..3208K
Late-type giants (RGB/AGB stars) will be important tracers of the
Galactic morphology and evolution in the framework of Gaia, as they are
intrinsically bright and thus can probe distant stellar populations or
those obscured by interstellar extinction. A realistic representation
of their atmospheres and spectra with stellar atmosphere models is thus
of crucial importance, both for the design and optimization of Gaia
instruments, as well as the interpretation of provided astrophysical
data. Our analysis of synthetic photometric colours of latetype giants
based on PHOENIX, MARCS and ATLAS model atmospheres indicates a general
agreement between the current theoretical predictions and observations
in the framework of stationary 1-D model atmospheres. Presently
available models allow temperature determinations of RGB/AGB stars to
an accuracy of ∼ ±100 K. In an exploratory study we try to quantify
possible residual systematic effects due to the approximations made
in 1-D models using full 3-D hydrodynamical models. We find that
differences in broad-band photometric colours calculated with 1-D and
3-D models are significant, translating to the offsets in effective
temperature of up to μTeff ∼70 K. Clearly, full 3-D hydrodynamical
models will help to alleviate such ambiguities in current theoretical
modelling. Additionally, they will allow to study new phenomena, to
open qualitatively new windows for stellar astrophysics in the Gaia-era.

---------------------------------------------------------
Title: Direct Imaging of Extra-Solar Planets- The Case of GQ Lupi
A and B
Authors: Neuhäuser, R.; Mugrauer, M.; Wuchterl, G.; Guenther, E. W.;
Bedalov, A.; Hauschildt, P.
2005prpl.conf.8327N Altcode: 2005LPICo1286.8327N
No abstract at ADS

---------------------------------------------------------
Title: Spectral Properties of Brown Dwarfs and Hot Jupiters
Authors: Homeier, Derek; Allard, France; Hauschildt, Peter; Barman,
Travis; Schweitzer, Andreas; Baron, Edward
2005hris.conf..465H Altcode: 2004astro.ph..5438H
Brown dwarfs bridge the gap between the stellar and planetary mass
regimes. Evolving from conditions very similar to the lowest-mass stars,
the atmospheres of older brown dwarfs closely resemble those expected
in close-in extrasolar giant planets, and with cooler BDs still being
discovered, more and more approach the properties of gas giants at
wider separation. Interpreting the spectra of BDs is therefore a
crucial step towards understanding and predicting the spectral and
thermal properties of EGPs.

---------------------------------------------------------
Title: PoSSO Physics of SubStellar Objects
Authors: Jones, Hugh; Viti, Serena; Tennyson, Jonathan; Barber, Bob;
Pickering, Juliet; Blackwell-Whitehead, Richard; Champion, Jean-Paul;
Allard, France; Hauschildt, Peter; Jørgensen, Uffe; Ehrenfreund,
Pascale; Stachowska, Ewa; Ludwig, Hans-Günter; Pavlenko, Yakiv;
Lyubchik, Yuri; Kurucz, Robert
2005hris.conf..477J Altcode:
A full understanding of the properties of substellar objects is one
of the major challenges facing astrophysics. Since their discovery
in 1995, we have discovered hundreds of brown dwarfs and extrasolar
planets. While these discoveries have enabled important comparisons
with theory, observational progress has been much more rapid than the
theoretical understanding of cool atmospheres. The determination of
mass, abundances, gravities and temperatures is not yet possible. The
key problem is that substellar objects emit their observable radiation
in the infrared region of the spectrum where our knowledge of atomic,
molecular and line broadening data is poor. In order to understand
these objects, and extra-solar planets increasing more like those our
Solar System, we urge the wider physical chemistry community to engage
in this exciting new field. Here we sketch an outline of the atoms,
molecules and processes requiring study.

---------------------------------------------------------
Title: Alkali Line Formation in the Atmospheres of Extrasolar
Giant Planets
Authors: Allard, N. F.; Allard, F.; Machin, L.; Hauschildt, P.; Louis,
F.; Loeillet, B.; Kielkopf, J. F.; Pascale, J.
2004ASPC..321..197A Altcode:
We present calculations of alkali line profiles and of their formation
in the atmospheres of brown dwarfs and extrasolar giant planets. We
compare our new theoretical spectra to the near-infrared spectrum of
SDSS 1624.

---------------------------------------------------------
Title: Phase-dependent Properties of Extrasolar Giant Planet
Atmospheres
Authors: Barman, T. S.; Allard, F.; Hauschildt, P. H.
2004ASPC..321..201B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Co-moving frame radiative transfer in spherical media with
arbitrary velocity fields
Authors: Baron, E.; Hauschildt, P. H.
2004A&A...427..987B Altcode: 2004astro.ph..8212B
Recently, with the advances in computational speed and availability
there has been a growth in the number and resolution of fully 3D
hydrodynamical simulations. However, all of these simulations are
purely hydrodynamical and there has been little attempt to include
the effects of radiative transfer except in a purely phenomenological
manner because the computational cost is too large even for modern
supercomputers. While there has been an effort to develop 3D Monte Carlo
radiative transfer codes, most of these have been for static atmospheres
or have employed the Sobolev approximation, which limits their
applicability to studying purely geometric effects such as macroscopic
mixing. Also the computational requirements of Monte Carlo methods are
such that it is difficult to couple with 3D hydrodynamics. Here, we
present an algorithm for calculating 1D spherical radiative transfer
in the presence of non-monotonic velocity fields in the co-moving
frame. Non-monotonic velocity flows will occur in convective, and
Raleigh-Taylor unstable flows, in flows with multiple shocks, and
in pulsationally unstable stars such as Mira and Cepheids. This is
a first step to developing fully 3D radiative transfer than can be
coupled with hydrodynamics. We present the computational method and
the results of some test calculations.

---------------------------------------------------------
Title: Spitzer Space Telescope and Coordinated Optical
Spectrophotometry of V1187 Scorpii (Nova Scorpii 2004 #2)
Authors: Woodward, C. E.; Ruch, G.; Gehrz, R. D.; Humphreys, R. M.;
Polomski, E.; Wagner, R. M.; Barlow, M.; Bode, M. F.; Eyres, S.; Evans,
A.; Geballe, T. R.; Greenhouse, M. A.; Hauschildt, P.; Krautter, J.;
Liller, W.; Lyke, J. E.; Rudy, R.; Salama, A.; Schwarz, G.; Shore,
S. N.; Starrfield, S.; Strutskie, M. F.; Truran, J.; Williams, R. E.
2004AAS...205.1923W Altcode: 2004BAAS...36.1374W
Classical nova (CN) explosions are thermonuclear runaway (TNR)
in the accreted H-rich envelope on the white dwarf (WD) in a
cataclysmic variable system. Infrared and optical observations of
CN have established their importance for understanding the formation
of astrophysical grains, and as contributors to abundance anomalies
in the ISM on local scales. Abundance studies of nova ejecta also
provide information about nucleosynthesis in the WD progenitor and in
the TNR. Here, we present Spitzer Space Telescope IRS spectra of the
Galactic Classical nova V1187 Scorpii (Nova Scorpii 2004 #2) as well
as coordinated optical spectroscopy and photometry obtained on the MMT
6.5-m and the 2.0-m robotic Liverpool telescopes. The Spitzer
spectra, obtained on 28.40 September 2004 UT as part of our Cycle
1 ToO nova program, exhibit broad ( ∼ 4800 km/s) H-recombination
line emission (e.g., HI 6-5, HI 7-6, HI 9-8) as well as forbidden line
emission including [Mg VII]5.50 micron, [Mg V]5.61 micron, [Ne II]12.81
micron, and [Ne III]15.55 micron. Of note, the [O IV]25.89 micron line
is present in the spectra of V1187 Sco. The high resolution optical
spectra, obtained on 2004 September 23.01 UT, show double peaked
emission lines with velocity components separated by ∼ 1200 km/s,
suggesting that the ejecta of V1187 Sco is distributed in clumps of
varying ionization states exhibiting a range of ejection velocities
(frequently found in CN). We present a preliminary discussion of
line identification, reddening, abundances, as well as a comparison
of V1187 Sco to other ONeMg nova. Our Spitzer observations are also
supported by complementary ground-based infrared spectra obtain as part
of a large collaborative study of this nova (see posters by Lynch et
al. and Russell et al.). This work is supported in part by NASA
(JPL/SSC) and the NSF (AST02-05814).

---------------------------------------------------------
Title: Type IIP Supernovae as Cosmological Probes: A Spectral-fitting
Expanding Atmosphere Model Distance to SN 1999em
Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt,
Peter H.
2004ApJ...616L..91B Altcode: 2004astro.ph.10153B
Because of their intrinsic brightness, supernovae make excellent
cosmological probes. We describe the spectral-fitting expanding
atmosphere method (SEAM) for obtaining distances to Type IIP supernovae
(SNe IIP) and present a distance to SN 1999em for which a Cepheid
distance exists. Our models give results consistent with the Cepheid
distance, even though we have not attempted to tune the underlying
hydrodynamical model but have simply chosen the best fits. This
is in contradistinction to the expanding photosphere method (EPM),
which yields a distance to SN 1999em that is 50% smaller than the
Cepheid distance. We emphasize the differences between the SEAM and
the EPM. We show that the dilution factors used in the EPM analysis
were systematically too small at later epochs. We also show that the
EPM blackbody assumption is suspect. Since SNe IIP are visible to
redshifts as high as z&lt;~6, with the James Webb Space Telescope,
the SEAM may be a valuable probe of the early universe.

---------------------------------------------------------
Title: The Physics of Extrasolar Gaseous Planets : from Theory to
Observable Signatures
Authors: Chabrier, G.; Allard, F.; Baraffe, I.; Barman, T.; Hauschildt,
P. H.
2004ASPC..321..131C Altcode: 2004astro.ph..1608C
We review our present understanding of the physical properties of
substellar objects, brown dwarfs and irradiated or non-irradiated
gaseous exoplanets. This includes a description of their internal
properties, mechanical structure and heat content, their atmospheric
properties, thermal profile and emergent spectrum, and their evolution,
in particular as irradiated companions of a close parent star. The
general theory can be used to make predictions in term of detectability
for the future observational projects. Special attention is devoted to
the evolution of the two presently detected transit planets, HD 209458b
and OGLE-TR-56B. For this latter, we present a consistent evolution
for its recently revised mass and show that we reproduce the observed
radius within its error bars. We briefly discuss differences between
brown dwarfs and gaseous planets, both in terms of mass function
and formation process. We outline several arguments to show that
the minimum mass for deuterium burning, recently adopted officially
as the limit to distinguish the two types of objects, is unlikely to
play any specific role in star formation, so that such a limit is of
purely semantic nature and is not supported by a physical justification.

---------------------------------------------------------
Title: From Very Low Mass Stars to Extrasolar Planets
Authors: Allard, France; Barman, Travis S.; Paillet, Jimmy; Baraffe,
I.; Chabrier, G.; Hauschildt, P. H.
2004sf2a.conf..193A Altcode: 2004sf2a.confE.265A
We have modeled, using the atmosphere code Phoenix, the photosphere
structures and spectral distribution of brown dwarfs and of all
known Extrasolar Giant Planets (EGPs) to this day. Since EGPs are
often brighter, more massive and larger than telluric planets, they
will be more readily detected in the future transit surveys (COROT,
KEPLER, SIMS, Eddington), and be the most directly observable using
current technology (e.g. by nulling interferometry with the GENIE
experiment). In this paper we summarize the spectral properties of EGPs
as a function of their orbital distance, phase as viewed from the earth,
mass and age, and type of primary star. We establish the most favorable
observation conditions (i.e. maximum luminosity contrast of the planet
to the primary star). We also explore uncertainties tied to the chemical
composition of the atmosphere, and the presence of cloud layers,
and study constraining cases such as HD209458b, OGLE-TR56b and Jupiter.

---------------------------------------------------------
Title: Non-LTE Models of (Cool) Stellar and Giant Planetary
Atmospheres
Authors: Schweitzer, Andreas; Hauschildt, Peter H.
2004AIPC..730..111S Altcode:
The atmospheres of cool stars, brown dwarfs and extrasolar giant
planets are rich with a large mix of molecules producing a complicated
spectrum dominated by molecular absorption bands and, consequently,
highly non-Planckian shape. Additionally, many discovered extrasolar
planets and brown dwarfs are close to a nearby, much hotter,
main sequence star. Either of the above two conditions cause large
deviations from LTE if the collisional processes are insufficient to
restore LTE in the atmospheric layers. Here we review the general
conditions which drive stellar atmospheres in non thermal equilibrium
(Non-LTE). Furthermore, we present recent advances in simulating non-LTE
effects in cool atmospheres for both non-irradiated and irradiated
stars and planets. In non-irradiated atmospheres, the radiative rates
are often too small compared to the collisional rates to drive large
deviations from LTE. However, irradiated atmospheres show significant
non-LTE effects, e.g., in the recently discovered planet HD209458b
eclipsing its parent star.

---------------------------------------------------------
Title: Model Atmospheres for Irradiated Stars in Precataclysmic
Variables
Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France
2004ApJ...614..338B Altcode: 2004astro.ph..6599B
Model atmospheres have been computed for M dwarfs that are strongly
irradiated by nearby hot companions. A variety of primary and secondary
spectral types are explored in addition to models specific to four known
systems: GD 245, NN Ser, AA Dor, and UU Sge. This work demonstrates
that a dramatic temperature inversion is possible on at least one
hemisphere of an irradiated M dwarf and that the emergent spectrum will
be significantly different from an isolated M dwarf or a blackbody flux
distribution. For the first time, synthetic spectra suitable for direct
comparison to high-resolution observations of irradiated M dwarfs in
non-mass-transferring post-common-envelope binaries are presented. The
effects of departures from local thermodynamic equilibrium on the
Balmer line profiles are also discussed.

---------------------------------------------------------
Title: Molecular Line Opacity of LiCl in the Mid-Infrared Spectra
of Brown Dwarfs
Authors: Weck, P. F.; Schweitzer, A.; Kirby, K.; Hauschildt, P. H.;
Stancil, P. C.
2004ApJ...613..567W Altcode: 2004astro.ph..6147W
We present a complete line list for the X1Σ+
electronic ground state of 7Li35Cl, computed
using fully quantum-mechanical techniques. This list includes
transition energies and oscillator strengths in the spectral region
0.3-39,640.7cm-1 for all allowed rovibrational transitions
in absorption within the electronic ground state. The calculations
were performed using an accurate hybrid potential constructed
from a spectral inversion fit of experimental data and from recent
multireference single- and double-excitation configuration interaction
calculations. The line list was incorporated into the stellar atmosphere
code PHOENIX to compute spectra for a range of young to old T dwarf
models. The possibility of observing a signature of LiCl in absorption
near 15.8 μm is addressed and the proposal to use this feature to
estimate the total lithium elemental abundance for these cool objects
is discussed.

---------------------------------------------------------
Title: Mid-Infrared Spectroscopy of the Coldest Known Brown Dwarf
2MASS 0415-0935: Physical Diagnostics and Spectral Modeling
Authors: Burgasser, Adam; Allard, France; Hauschildt, Peter; Homeier,
Derek; Kirkpatrick, J. Davy; McLean, Ian
2004sptz.prop.3259B Altcode:
We propose to obtain 5-22 micron low-resolution spectroscopy for the
coldest known brown dwarf, 2MASS 0415-0935, using the IRS instrument
on Spitzer. With an effective temperature of ~700-800 K, this source
is a benchmark for the study of low temperature atmospheres and a
key starting point for the search for even cooler brown dwarfs. The
proposed observations will sample the brightest continuum emission
region for this object and resolve many individual molecular features,
including the important 10.5 micron band of NH3, the only detectable
nitrogen-bearing molecule in a brown dwarf atmosphere and a tracer
of atmospheric dynamics. By combining the Spitzer data with high
signal-to-noise, moderate resolution optical (0.6-1.0 micron) and
near-infrared (1.0-2.4 micron) ground-based data already obtained
by our group, and matching to our state-of-the-art spectral models,
we will be able to derive the physical properties of this source
(temperature, surface gravity, and metallicity), as well as test
current opacity models for H2O, CH4, and NH3, critical for modeling
and interpreting brown dwarf and planetary atmospheres. The proposed
program is a focused experiment for measuring the physical parameters
of the coolest brown dwarfs now known and soon to be discovered,
and provides a key empirical test of atmosphere models used for both
substellar and planetary studies.

---------------------------------------------------------
Title: ToO Observations of Galactic and Magellanic Cloud Classical
Novae
Authors: Woodward, Charles; Barlow, Michael; Bode, Michael; Evans,
Nye; Geballe, Thomas; Gehrz, Robert; Greenhouse, Mattew; Hauschildt,
Peter; Krautter, Joachim; Liller, William; Lyke, James; Rudy, Richard;
Salama, Alberto; Schwarz, Greg; Shore, Steven; Skrutskie, Michael;
Starrfield, Sumner; Truran, James; Wagner, R. Mark; Williams, Robert
2004sptz.prop.2333W Altcode:
Stars are the engines of energy production and chemical evolution
in our Universe. They deposit radiative and mechanical energy into
their environments, and enrich the ambient interstellar medium with
elements synthesized in their interiors and dust grains condensed
in their atmospheres. Classical novae (CN), a transient phenomenon,
contribute to this cycle of chemical enrichment through explosive
nucleosynthesis and the violent ejection of material dredged from the
white dwarf progenitor and mixed with the accreted surface layers. Using
Spitzer (+IRS), we propose a 10.5 hr, no-impact, multi-cycle (2)
ToO program to study (in temporal detail) the later evolutionary
stages of CN (&gt; 40 days post-outburst) by targeting 4 Galactic
and 3 Magellanic Cloud novae. Spitzer is a unique facility that can
enable us to investigate aspects of CN phenomenon including: the in
situ formation and astromineralogy of dust, the elemental abundances
resulting from thermonuclear runaway, the correllation of ejecta masses
with progenitor type, the bolometric luminosities of the outburst, and
the kinematics and structure of the ejected envelopes. Specifically, our
program addresses four research problems in the study of CN evolution:
1)~determination of the grain size distribution and mineral composition
of nova dust; 2)~estimation of chemical abundances of nova ejecta from
coronal and forbidden emission line spectroscopy; 3)~measurement of
the density and masses of the ejecta; and 4)~characterization of the
nature of novae in the SMC and LMC at mid- to far-infrared wavelengths.

---------------------------------------------------------
Title: Measuring Fundamental Parameters of Substellar
Objects. I. Surface Gravities
Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard,
France; Hauschildt, Peter; Ardila, David
2004ApJ...609..854M Altcode: 2004astro.ph..3265M
We present an analysis of high-resolution optical spectra for a sample
of very young, mid- to late-M, low-mass stellar and substellar objects:
11 in the Upper Scorpius association, and two (GG Tau Ba and Bb) in the
Taurus star-forming region. Effective temperatures and surface gravities
are derived from a multiple-feature spectral analysis using TiO, Na
I, and K I, through comparison with the latest synthetic spectra. We
show that these spectral diagnostics complement each other, removing
degeneracies with temperature and gravity in the behavior of each. In
combination, they allow us to determine temperature to within 50
K and gravity to within 0.25 dex, in very cool young objects. Our
high-resolution spectral analysis does not require extinction
estimates. Moreover, it yields temperatures and gravities independent
of theoretical evolutionary models (although our estimates do depend on
the synthetic spectral modeling). We find that our gravities for most
of the sample agree remarkably well with the isochrone predictions
for the likely cluster ages. However, discrepancies appear in our
coolest targets: these appear to have significantly lower gravity (by
up to 0.75 dex) than our hotter objects, even though our entire sample
covers a relatively narrow range in effective temperature (~300 K). This
drop in gravity is also implied by intercomparisons of the data alone,
without recourse to synthetic spectra. We consider, and argue against,
dust opacity, cool stellar spots, or metallicity differences leading to
the observed spectral effects; a real decline in gravity is strongly
indicated. Such gravity variations are contrary to the predictions of
the evolutionary tracks, causing improbably low ages to be inferred
from the tracks for our coolest targets. Through a simple consideration
of contraction timescales, we quantify the age errors introduced into
the tracks through the particular choice of initial conditions and
demonstrate that they can be significant for low-mass objects that
are only a few megayears old. However, we also find that these errors
appear insufficient to explain the magnitude of the age offsets in
our lowest gravity targets. We venture that this apparent age offset
may arise from evolutionary model uncertainties related to accretion,
deuterium burning and/or convection effects. Finally, when combined with
photometry and distance information, our technique for deriving surface
gravities and effective temperatures provides a way of obtaining masses
and radii for substellar objects independent of evolutionary models;
radius and mass determinations are presented in Paper II.

---------------------------------------------------------
Title: Probing the atmosphere of the bulge G5III star
OGLE-2002-BUL-069 by analysis of microlensed Hα line
Authors: Cassan, A.; Beaulieu, J. P.; Brillant, S.; Coutures, C.;
Dominik, M.; Donatowicz, J.; Jørgensen, U. G.; Kubas, D.; Albrow,
M. D.; Caldwell, J. A. R.; Fouqué, P.; Greenhill, J.; Hill, K.;
Horne, K.; Kane, S.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu,
K. C.; Vinter, C.; Wambsganss, J.; Watson, R.; Williams, A.; Fendt,
C.; Hauschildt, P.; Heinmueller, J.; Marquette, J. B.; Thurl, C.
2004A&A...419L...1C Altcode: 2004astro.ph..1071C
We discuss high-resolution, time-resolved spectra of the caustic exit
of the binary microlensing event OGLE 2002-BLG-069 obtained with
UVES on the VLT. The source star is a G5III giant in the Galactic
Bulge. During such events, the source star is highly magnified, and
a strong differential magnification around the caustic resolves its
surface. Using an appropriate model stellar atmosphere generated by
the PHOENIX v2.6 code we obtain a model light curve for the caustic
exit and compare it with a dense set of photometric observations
obtained by the PLANET microlensing follow up network. We further
compare predicted variations in the Hα equivalent width with those
measured from our spectra. While the model and observations agree in
the gross features, there are discrepancies suggesting shortcomings in
the model, particularly for the Hα line core, where we have detected
amplified emission from the stellar chromosphere after the source
star's trailing limb exited the caustic. This achievement became
possible by the provision of the very efficient OGLE-III Early Warning
System, a network of small telescopes capable of nearly-continuous
round-the-clock photometric monitoring, on-line data reduction,
daily near-real-time modelling in order to predict caustic crossing
parameters, and a fast and efficient response of a 8 m class telescope
to a “Target-of-Opportunity” observation request. Based on
observations made at ESO, 69.D-0261(A), 269.D-5042(A), 169.C-0510(A).

---------------------------------------------------------
Title: The effect of evaporation on the evolution of close-in
giant planets
Authors: Baraffe, I.; Selsis, F.; Chabrier, G.; Barman, T. S.; Allard,
F.; Hauschildt, P. H.; Lammer, H.
2004A&A...419L..13B Altcode: 2004astro.ph..4101B
We include the effect of evaporation in our evolutionary calculations
of close-in giant planets, based on a recent model for thermal
evaporation taking into account the XUV flux of the parent star (Lammer
et al. \cite{Lammer2003}). Our analysis leads to the existence of
a critical mass for a given orbital distance mcrit(a)
below which the evaporation timescale becomes shorter than the
thermal timescale of the planet. For planets with initial masses
below mcrit, evaporation leads to a rapid expansion of
the outer layers and of the total planetary radius, speeding up the
evaporation process. Consequently, the planet does not survive as
long as estimated by a simple application of mass loss rates without
following consistently its evolution. We find out that the transit
planet HD 209458b might be in such a dramatic phase, although with
an extremely small probability. As a consequence, we predict that,
after a certain time, only planets above a value mcrit(a)
should be present at an orbital distance a of a star. For planets with
initial masses above mcrit, evaporation does not affect
the evolution of the radius with time.

---------------------------------------------------------
Title: Improved discretization of the wavelength derivative term in
CMF operator splitting numerical radiative transfer
Authors: Hauschildt, P. H.; Baron, E.
2004A&A...417..317H Altcode: 2004astro.ph..1164H
We describe two separate wavelength discretization schemes that can be
used in the numerical solution of the comoving frame radiative transfer
equation. We present an improved second order discretization scheme
and show that it leads to significantly less numerical diffusion than
the previous scheme. We also show that due to the nature of the second
order term in some extreme cases it can become numerically unstable. We
stabilize the scheme by introducing a mixed discretization scheme and
present the results from several test calculations.

---------------------------------------------------------
Title: The Evolution of Irradiated Planets: Application to Transits
Authors: Chabrier, G.; Barman, T.; Baraffe, I.; Allard, F.; Hauschildt,
P. H.
2004ApJ...603L..53C Altcode: 2004astro.ph..1487C
Extending the theory that we derived recently for HD 209458b to
different cases of strongly irradiated gaseous exoplanets, we have
calculated the consistent evolution of a new transiting planet,
OGLE-TR-56b, for its recently revised mass determination. The theory is
shown to successfully reproduce the observed radius for the proper age
of the system. We also examine the dissipation of kinetic energy at the
planet's internal adiabat due to atmospheric winds and place constraints
on the efficiency of this process. We show that a fraction ~0.1%-0.5%
of the incident flux transformed into thermal energy deposited at the
adiabatic level can accommodate the observed radii of both OGLE-TR-56b
and HD 209458b. The present theory yields quantitative predictions on
the evolution of the emergent spectrum and fundamental properties of
hot jupiters. The predictions for radius, luminosity, temperature as
a function of the planet's mass, and orbital distance can be used as
benchmarks for future detections of transit planets.

---------------------------------------------------------
Title: Examining stellar atmospheres via microlensing
Authors: Thurl, C.; Sackett, P. D.; Hauschildt, P. H.
2004AN....325..247T Altcode:
Resolving stellar atmospheres of stars other than the Sun has
proven very tedious and only possible for the nearest and largest
stars. microlensing offers a solution by providing a “natural”
telescope. Binary lenses create extended caustic lines in the
magnification pattern. As the source star crosses such a caustic,
its light curve not only shows a strong peak of distinctive shape, but
its surface also experiences a substantial differential magnification
and is therefore spatially resolved. As suggested by \cite{schneider,
heyrov, heyrov00, hendry, bryce, fields} microlensing gives us the
opportunity to examine the atmospheres of stars and to test stellar
models against observations.

---------------------------------------------------------
Title: Hunting for the signatures of 3-D explosions with 1-D
synthetic spectra
Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H.
2004cetd.conf..173L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: 2MASS J0516288+260738: a new low-mass eclipsing binary system.
Authors: Schuh, S.; Drechsel, H.; Hauschildt, P.; Handler, G.; Endl,
M.; Dreizler, S.
2004ANS...325R..84S Altcode: 2004ANS...325a..84S; 2004ANS...325..P09S
No abstract at ADS

---------------------------------------------------------
Title: Probing the atmosphere of a solar-like star by galactic
microlensing at high magnification
Authors: Abe, F.; Bennett, D. P.; Bond, I. A.; Calitz, J. J.; Claret,
A.; Cook, K. H.; Furuta, Y.; Gal-Yam, A.; Glicenstein, J. -F.;
Hearnshaw, J. B.; Hauschildt, P. H.; Kent, D.; Kilmartin, P. M.;
Kurata, Y.; Masuda, K.; Maoz, D.; Matsubara, Y.; Meintjes, P. J.;
Moniez, M.; Muraki, Y.; Noda, S.; Ofek, E. O.; Okajima, K.; Philpott,
L.; Rattenbury, N. J.; Rhie, S. H.; Sako, T.; Sullivan, D. J.; Sumi,
T.; Terndrup, D. M.; Tristram, P. J.; Yanagisawa, T.; Yock, P. C. M.
2003A&A...411L.493A Altcode: 2003astro.ph.10410A
We report a measurement of limb darkening of a solar-like star in the
very high magnification microlensing event MOA 2002-BLG-33. A 15 hour
deviation from the light curve profile expected for a single lens was
monitored intensively in V and I passbands by five telescopes spanning
the globe. Our modelling of the light curve showed the lens to be a
close binary system whose centre-of-mass passed almost directly in
front of the source star. The source star was identified as an F8-G2
main sequence turn-off star. The measured stellar profiles agree with
current stellar atmosphere theory to within ~ 4% in two passbands. The
effective angular resolution of the measurements is &lt;1 mu as. These
are the first limb darkening measurements obtained by microlensing
for a Solar-like star.

---------------------------------------------------------
Title: The atmospheres and Evolution of Extrasolar Planets
Authors: Barman, T. S.; Allard, F.; Baraffe, I.; Chabrier, G.;
Hauschildt, P. H.
2003AAS...203.1701B Altcode: 2003BAAS...35Q1234B
Observations of transiting extrasolar giant planet (EGP), HD 209458b,
provided the first tests of atmospheric and evolutionary models for
the shortest period EGPs. To date, most models fail to reproduce the
observed radius of HD 209458b without including mechanisms, such as
tidal heating or strong atmospheric circulations, in addition to
irradiation by the parent star. Based solely on the observations
of HD 209458b it is difficult to say with certainty how crucial
these additional heating sources are to the evolution of close-in
EGPs. Fortunately, new transiting EGP candidates are being discovered
allowing for more robust tests of the theory over a broader parameter
space. In this poster, new atmospheric and evolutionary models are
presented for a variety of orbital separations, stellar spectral types,
and planetary masses. Comparisons are made to the latest EGP transit
observations.

---------------------------------------------------------
Title: The limb-darkening for spherically symmetric NextGen model
atmospheres: A-G main-sequence and sub-giant stars
Authors: Claret, A.; Hauschildt, P. H.
2003A&A...412..241C Altcode:
We compute passband-integrated specific intensities for spherically
symmetric models generated with the PHOENIX code. The models cover the
range 5000 K &lt;=Teff&lt;=10 000 K with surface gravities
between 3.5 and 5.5, in steps of 0.5. The adopted mixing-length
parameter is 2.0 pressure scale heights, while the microturbulent
velocity is 2.0 km s-1. The calculations were carried
out for four photometric systems: Strömgren, Johnson, Geneva and
Walraven, completing 24 filters. The series introduced by Claret
(2000) and a new bi-parametric (exponential) law are shown to be
able to describe the intensity distribution of spherical models
with acceptable sigma . Simple limb-darkening laws do not produce
accurate fits to the computed radiation fields. On the other hand,
the concept of “quasi” spherical models is introduced and we present
the corresponding limb-darkening coefficients for the most commonly
adopted limb-darkening laws for the same filters. Tables 2-17
are only available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: A new model for brown dwarf spectra including accurate unified
line shape theory for the Na I and K I resonance line profiles
Authors: Allard, N. F.; Allard, F.; Hauschildt, P. H.; Kielkopf,
J. F.; Machin, L.
2003A&A...411L.473A Altcode:
We present the first brown dwarf atmosphere models based on theoretical
calculations of absorption profiles of sodium and potassium perturbed by
helium and molecular hydrogen. The synthetic spectra have been compared
to previous calculations with Lorentz profiles and the classic van
der Waals approximation, and to the observed spectrum of the T dwarf
SDSS 1624. The new profiles provide increased opacities in the optical
spectra of methane brown dwarfs. However, the potassium and sodium far
wings alone cannot explain the missing opacity in the 0.85 to 1.1 mu
m range.

---------------------------------------------------------
Title: Alkali Halide Opacity in Brown Dwarf and Cool Stellar
Atmospheres: A Study of Lithium Chloride
Authors: Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.;
Hauschildt, P. H.
2003AAS...203.0605K Altcode: 2003BAAS...35.1212K
Recent thermochemical equilibrium calculations have revealed the
important role played by lithium chloride in the lithium chemistry of
cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl
appears to be the dominant Li-bearing gas over an extended domain of
the (P,T) diagram, typically for temperatures below 1500 K. LiCl has
a large dipole moment in its ground electronic state which can give
rise to intense rovibrational line spectra. In addition, LiCl can
make dipole transitions to several low-lying unbound excited states,
causing dissociation of the molecule. For these reasons, LiCl may be
a significant source of line and continuum opacity in brown dwarf and
cool stellar atmospheres. In this work, we report calculations
of complete lists of line oscillator strengths and photodissociation
cross sections for the low-lying electronic states of LiCl. We have
performed single- and double-excitation configuration interaction
calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991,
MOTECC 91, Elsevier, Leiden) and obtained the potential curves and
the corresponding dipole transition moment functions between the
X 1Σ ^+ ground state and the B 1Σ ^+ and A
1Π excited states. The resulting line oscillator
strengths and molecular photodissociation cross sections have been
included in the PHOENIX stellar atmosphere code (Hauschildt &amp;
Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated
using spherical geometry for all gravities considered, also incorporate
our latest database of nearly 670 million molecular lines, and updated
equations of state (EOS). This work was supported in part by NSF
grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222,
and NAG5-10551 as well as NASA/JPL grant 961582.

---------------------------------------------------------
Title: Modelling the Spectra of SN 1998bw from a Jet Powered
Explosion Model
Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H.
2003AAS...203.4515L Altcode: 2003BAAS...35.1279L
Supernova 1998bw and several other extreme Type Ic supernovae show
strong evidence of asymmetry. We have segmented the jet induced
model for these objects by Maeda &amp; Nomoto into several slices and
modelled each of slices as independent objects. We compare a sequence
of early spectra of SN 1998bw to the spectra of these slice and also
to a composit spectrum made from all of the segments.

---------------------------------------------------------
Title: <ASTROBJ>2MASS J0516288+260738</ASTROBJ>: Discovery of the
first eclipsing late K + Brown dwarf binary system?
Authors: Schuh, S. L.; Handler, G.; Drechsel, H.; Hauschildt, P.;
Dreizler, S.; Medupe, R.; Karl, C.; Napiwotzki, R.; Kim, S. -L.; Park,
B. -G.; Wood, M. A.; Paparó, M.; Szeidl, B.; Virághalmy, G.; Zsuffa,
D.; Hashimoto, O.; Kinugasa, K.; Taguchi, H.; Kambe, E.; Leibowitz,
E.; Ibbetson, P.; Lipkin, Y.; Nagel, T.; Göhler, E.; Pretorius, M. L.
2003A&A...410..649S Altcode: 2003astro.ph..8329S
We report the discovery of a new eclipsing system less than
one arcminute south of the pulsating DB white dwarf <ASTROBJ>KUV
05134+2605</ASTROBJ>. The object could be identified with the point
source <ASTROBJ>2MASS J0516288+260738</ASTROBJ> published by the Two
Micron All Sky Survey. We present and discuss the first light curves
as well as some additional colour and spectral information. The
eclipse period of the system is 1.29 d, and, assuming this to be
identical to the orbital period, the best light curve solution yields
a mass ratio of m2/m1=0.11, a radius ratio of
r2/r1~ 1 and an inclination of 74o. The
spectral anaylsis results in a Teff=4200 K for the
primary. On this basis, we suggest that the new system probably consists
of a late K + Brown dwarf (which would imply a system considerably
younger than ~0.01 Gyr to have r2/r1~ 1), and
outline possible future observations. This paper uses observations
made at the Bohyunsan Optical Astronomy Observatory of Korea Astronomy
Observatory, at the South African Astronomical Observatory (SAAO), at
the 0.9 m telescope at Kitt Peak National Observatory recommissioned
by the Southeastern Association for Research in Astronomy (SARA),
at Gunma Astronomical Observatory established by Gunma prefecture,
Japan, at the Florence and George Wise Observatory, operated by the
Tel-Aviv University, Israel and at Piszkésteto, the mountain station
of Konkoly Observatory of the Hungarian Academy of Science, Hungary. This publication makes use of data products from the Two Micron All
Sky Survey, a joint project of the University of Massachusetts and
the Infrared Processing and Analysis Center / California Institute of
Technology, funded by the National Aeronautics and Space Administration
and the National Science Foundation. The Digitized Sky Survey was
produced at the Space Telescope Science Institute under US Government
grant NAG W-2166. The images of these surveys are based on photographic
data obtained using the Oschin Schmidt Telescope on Palomar Mountain
and the UK Schmidt Telescope. The plates were processed into the present
compressed digital form with the permission of these institutions.

---------------------------------------------------------
Title: High-Precision Limb-Darkening Measurement of a K3 Giant
Using Microlensing
Authors: Fields, Dale L.; Albrow, M. D.; An, J.; Beaulieu, J. -P.;
Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould,
A.; Greenhill, J.; Hill, K.; Jørgensen, U. G.; Kane, S.; Martin,
R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu,
K. C.; Vermaak, P.; Watson, R.; Williams, A.; Glicenstein, J. -F.;
Hauschildt, P. H.; PLANET Collaboration
2003ApJ...596.1305F Altcode: 2003astro.ph..3638F
We obtain high-precision limb-darkening measurements in five
bands (V, VE, IE, I, and H) for the K3 III
(Teff=4200 K, [Fe/H]=+0.3, logg=2.3) source of the Galactic
bulge microlensing event EROS BLG-2000-5. These measurements are
inconsistent with the predictions of atmospheric models at higher
than 10 σ. While the disagreement is present in all bands, it is most
apparent in I, IE, and VE, in part because the
data are better and in part because the intrinsic disagreement is
stronger. We find that when limb-darkening profiles are normalized
to have unit total flux, the I-band models for a broad range of
temperatures all cross each other at a common point. The solar profile
also passes through this point. However, the profile as measured by
microlensing does not. We hypothesize that the models have incorporated
some aspect of solar physics that is not shared by giant atmospheres.

---------------------------------------------------------
Title: Atmospheric Models of Red Giants with Massive-Scale Non-Local
Thermodynamic Equilibrium
Authors: Short, C. I.; Hauschildt, P. H.
2003ApJ...596..501S Altcode: 2003astro.ph..6531S
We present plane-parallel and spherical LTE and non-LTE (NLTE)
atmospheric models of a variety of stellar parameters of the red giant
star Arcturus (α Boo, HD 124897, HR 5340) and study their ability to
fit the measured absolute flux distribution. Our NLTE models include
tens of thousands of the strongest lines in NLTE, and we investigate
separately the effects of treating the light metals and the Fe group
elements Fe and Ti in NLTE. We find that the NLTE effects of Fe group
elements on the model structure and Fλ distribution are
much more important than the NLTE effects of all the light metals
combined, and serve to substantially increase the violet and near-UV
Fλ levels as a result of NLTE Fe overionization. Both the
LTE and NLTE models predict significantly more flux in the blue and UV
bands than is observed. We find that within the moderately metal-poor
metallicity range, the effect of NLTE on the overall UV flux level
decreases with decreasing metallicity. These results suggest that
there may still be important UV opacity missing from the models. We
find that models of solar metallicity giants of spectral type similar
to that of Arcturus fit well the observed flux distributions of those
stars from the red to the near-UV band. This suggests that the blue
and near-UV flux discrepancy is metallicity dependent, increasing with
decreasing metallicity.

---------------------------------------------------------
Title: A Chandra Low Energy Transmission Grating Spectrometer
Observation of V4743 Sagittarii: A Supersoft X-Ray Source and a
Violently Variable Light Curve
Authors: Ness, J. -U.; Starrfield, S.; Burwitz, V.; Wichmann, R.;
Hauschildt, P.; Drake, J. J.; Wagner, R. M.; Bond, H. E.; Krautter,
J.; Orio, M.; Hernanz, M.; Gehrz, R. D.; Woodward, C. E.; Butt, Y.;
Mukai, K.; Balman, S.; Truran, J. W.
2003ApJ...594L.127N Altcode:
V4743 Sagittarii (Nova Sgr 2002 No. 3) was discovered on 2002 September
20. We obtained a 5 ks ACIS-S spectrum in 2002 November and found that
the nova was faint in X-rays. We then obtained a 25 ks Chandra Low
Energy Transmission Grating Spectrometer (LETGS) observation on 2003
March 19. By this time, it had evolved into the supersoft X-ray phase
exhibiting a continuous spectrum with deep absorption features. The
light curve from the observation showed large-amplitude oscillations
with a period of 1325 s (22 minutes) followed by a decline in the total
count rate after ~13 ks of observations. The count rate dropped from
~40 counts s-1 to practically zero within ~6 ks and stayed
low for the rest of the observation (~6 ks). The spectral hardness ratio
changed from maxima to minima in correlation with the oscillations and
then became significantly softer during the decay. Strong H-like and
He-like lines of oxygen, nitrogen, and carbon were found in absorption
during the bright phase, indicating temperatures between 1 and 2
MK, but they were shifted in wavelength corresponding to a Doppler
velocity of -2400 km s-1. The spectrum obtained after
the decline in count rate showed emission lines of C VI, N VI, and N
VII, suggesting that we were seeing expanding gas ejected during the
outburst, probably originating from CNO-cycled material. An XMM-Newton
Target of Opportunity observation, obtained on 2002 April 4 and a
later LETGS observation from 2003 July 18 also showed oscillations,
but with smaller amplitudes.

---------------------------------------------------------
Title: Analysis of the Flux and Polarization Spectra of the Type
Ia Supernova SN 2001el: Exploring the Geometry of the High-Velocity
Ejecta
Authors: Kasen, Daniel; Nugent, Peter; Wang, Lifan; Howell, D. A.;
Wheeler, J. Craig; Höflich, Peter; Baade, Dietrich; Baron, E.;
Hauschildt, P. H.
2003ApJ...593..788K Altcode: 2003astro.ph..1312K
SN 2001el is the first normal Type Ia supernova to show a strong,
intrinsic polarization signal. In addition, during the epochs prior
to maximum light, the Ca II IR triplet absorption is seen distinctly
and separately at both normal photospheric velocities and at very high
velocities. The high-velocity triplet absorption is highly polarized,
with a different polarization angle than the rest of the spectrum. The
unique observation allows us to construct a relatively detailed
picture of the layered geometrical structure of the supernova ejecta:
in our interpretation, the ejecta layers near the photosphere (v~10,000
km s-1) obey a nearly axial symmetry, while a detached,
high-velocity structure (v~18,000-25,000 km s-1) with high
Ca II line opacity deviates from the photospheric axisymmetry. By
partially obscuring the underlying photosphere, the high-velocity
structure causes a more incomplete cancellation of the polarization of
the photospheric light and so gives rise to the polarization peak and
rotated polarization angle of the high-velocity IR triplet feature. In
an effort to constrain the ejecta geometry, we develop a technique
for calculating three-dimensional synthetic polarization spectra and
use it to generate polarization profiles for several parameterized
configurations. In particular, we examine the case in which the inner
ejecta layers are ellipsoidal and the outer, high-velocity structure is
one of four possibilities: a spherical shell, an ellipsoidal shell, a
clumped shell, or a toroid. The synthetic spectra rule out the spherical
shell model, disfavor a toroid, and find a best fit with the clumped
shell. We show further that different geometries can be more clearly
discriminated if observations are obtained from several different lines
of sight. Thus, assuming that the high-velocity structure observed
for SN 2001el is a consistent feature of at least a known subset of
Type Ia supernovae, future observations and analyses such as these may
allow one to put strong constraints on the ejecta geometry and hence
on supernova progenitors and explosion mechanisms.

---------------------------------------------------------
Title: Spectral Types of Planetary Host Star Candidates: New
Transiting Planets?
Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley,
W.; Werner, K.
2003ANS...324....2D Altcode: 2003ANS...324..A03D; 2003ANS...324b...2D
No abstract at ADS

---------------------------------------------------------
Title: News of Effective Temperatures of L Dwarfs
Authors: Schweitzer, Andreas; Gizis, John E.; Allard, France;
Hauschildt, Peter H.
2003IAUS..211..403S Altcode:
In this work we report recent spectral analyses of L dwarfs and our
success in measuring Teff and log(g). Using dust filled
atmospheres for early L dwarfs and rained out atmospheres for late
L dwarfs we could derive Teff of 1400 to 2000 K for L8 to
M9.5 dwarfs respectively. We also give an outlook what we can achieve
with future models that are improving the fits to intermediate L dwarfs
and IR spectra.

---------------------------------------------------------
Title: Evolutionary models for low mass stars and brown dwarfs at
young ages
Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France;
Hauschildt, Peter
2003IAUS..211...41B Altcode:
We analyse evolutionary tracks at young ages for low mass stars with
masses m &lt;e 1.4 M⊙ and brown dwarfs down to one
mass of Jupiter. We analyse current theoretical uncertainties due to
initial conditions. Simple tests on initial conditions show the high
uncertainties of models at ages ∼&lt;= 1 Myr.

---------------------------------------------------------
Title: Model Atmospheres and Spectra: The Role of Dust
Authors: Allard, France; Guillot, Tristan; Ludwig, Hans-Günter;
Hauschildt, Peter H.; Schweitzer, Andreas; Alexander, David R.;
Ferguson, Jason W.
2003IAUS..211..325A Altcode:
Brown dwarf atmospheres form molecules, then high temperature
condensates (corundum, titanates, silicates, and iron compounds),
and then low temperature condensates (ices) as they cool down over
time. These produce large opacities which govern entirely their
spectral energy distribution. Just as it is important to know
molecular opacities (TiO, H_2O, CH_4, etc.) with accuracy, it is
imperative to understand the interplay of processes (e.g. condensation,
sedimentation, coagulation, convection) that determines the radial
and size distribution of grains. Limiting case models have shown that
young, hot brown (L) dwarfs form dust mostly in equilibrium, while at
much cooler stages (late T dwarfs) all high temperature condensates
have sedimented out of their photospheres. But this process is gradual
and all intermediate classes of brown dwarfs can partly be understood
in terms of partial sedimentation of dust. With new models accounting
for these processes, we describe the effects they may have upon brown
dwarf spectral properties.

---------------------------------------------------------
Title: Influence of chemi-ionization and chemi-recombination processes
on the population of hydrogen Rydberg states in atmospheres of late
type dwarfs
Authors: Mihajlov, A. A.; Jevremović, D.; Hauschildt, P.;
Dimitrijević, M. S.; Ignjatović, Lj. M.; Alard, F.
2003A&A...403..787M Altcode:
We study the influence of a group of chemi-ionization and
chemi-recombination processes on the populations of higher states
of hydrogen in the layers of a stellar atmosphere. The group
of processes includes ionization: H*(n)+H(1s)==&gt;
H2++e , H*(n)+H(1s)==&gt;
H(1s)+H++e, and inverse recombination:
H2++e==&gt; H*(n)+H(1s),
H(1s)+H++e==&gt; H*(n)+H(1s), where
H*(n) is the hydrogen atom in a state with the principal
quantum number n &gt;&gt; 1, and H2+ is the
hydrogen molecular ion in a weakly bound rho-vibrational state of the
ground state. These processes have been treated within the framework
of the semi-classical approximation, developed in several previous
papers, and have been included in the general stellar atmosphere
code PHOENIX. We present results for an M dwarf atmosphere with
Teff = 3800 K and find that the inclusion of chemi-ionization
and chemi-recombination processes is significant in the low temperature
parts of the atmosphere.

---------------------------------------------------------
Title: Methane and the Spectra of T Dwarfs
Authors: Homeier, Derek; Hauschildt, Peter H.; Allard, France
2003IAUS..211..419H Altcode: 2002astro.ph..9171H
We have updated our PHOENIX model atmospheres and theoretical spectra
for ultracool dwarfs with new opacity data for methane based on line
strength predictions with the STDS software. By extending the line list
to rotational levels of J = 40 we can significantly improve the shape
of the near-IR absorption features of CH_4, and in addition find an
enhanced blanketing effect, resulting in up to 50% more flux emerging
in the J band than seen in previous models, which may thus contribute
to the brightening in J and blue IR colors observed in T dwarfs.

---------------------------------------------------------
Title: OGLE-TR-3: A possible new transiting planet
Authors: Dreizler, S.; Hauschildt, P. H.; Kley, W.; Rauch, T.; Schuh,
S. L.; Werner, K.; Wolff, B.
2003A&A...402..791D Altcode: 2003astro.ph..3183D
Recently, 59 low-luminosity object transits were reported from
the Optical Gravitational Lensing Experiment (OGLE). Our follow-up
low-resolution spectroscopy of 16 candidates provided two objects,
<ASTROBJ>OGLE-TR-3</ASTROBJ> and <ASTROBJ>OGLE-TR-10</ASTROBJ>,
which have companions with radii compatible with those of gas-giant
planets. Further high-resolution spectroscopy revealed a very low
velocity variation (&lt;500 m s-1) of the host star
<ASTROBJ>OGLE-TR-3</ASTROBJ> which may be caused by its unseen
companion. An analysis of the radial velocity and light curve results
in M&lt;2.5 MJup, R&lt;1.6 RJup, and an orbital
separation of about 5 Rsun, which makes it the planet with
the shortest period known. This allows to identify the low-luminosity
companion of <ASTROBJ>OGLE-TR-3</ASTROBJ> as a possible new gas-giant
planet. If confirmed, this makes <ASTROBJ>OGLE-TR-3</ASTROBJ> together
with <ASTROBJ>OGLE-TR-56</ASTROBJ> the first extrasolar planets
detected via their transit light curves. Based on observations
collected at the European Southern Observatory, Paranal, Chile (ESO
Programme 269.C-5034).

---------------------------------------------------------
Title: Evolutionary models for cool brown dwarfs and extrasolar
giant planets. The case of HD 209458
Authors: Baraffe, I.; Chabrier, G.; Barman, T. S.; Allard, F.;
Hauschildt, P. H.
2003A&A...402..701B Altcode: 2003astro.ph..2293B
We present evolutionary models for cool brown dwarfs and extra-solar
giant planets. The models reproduce the main trends of observed methane
dwarfs in near-IR color-magnitude diagrams. We also present evolutionary
models for irradiated planets, coupling for the first time irradiated
atmosphere profiles and inner structures. We focus on HD 209458-like
systems and show that irradiation effects can substantially affect the
radius of sub-jovian mass giant planets. Irradiation effects, however,
cannot alone explain the large observed radius of HD 209458b. Adopting
assumptions which optimise irradiation effects and taking into account
the extension of the outer atmospheric layers, we still find ~ 20%
discrepancy between observed and theoretical radii. An extra source
of energy seems to be required to explain the observed value of the
first transit planet.

---------------------------------------------------------
Title: Spectrum Modeling of Distorted Stellar Atmospheres and the
X-ray Binary V4641 Sgr
Authors: Lentz, E. J.; Orosz, J. A.; Hauschildt, P. H.
2003AAS...202.3202L Altcode: 2003BAAS...35..743L
We have developed a method to compute synthetic spectra for stars
which have rotationally or tidally distorted atmospheres which vary
in effective temperature and gravity over their surfaces. The spectra
are composited from the specific intensities from high resolution,
spherical, non-LTE model atmospheres for each segment of the surface. We
consider the effects of tidal distortion on the spectrum of the
X-ray binary V4641 Sgr (SAX J1819.3-2525) by comparing the composite
model spectrum to portions of an Echelle spectrum of the star. The
parameters for the component model atmospheres segments, including
effective temperature and gravity and the projected area and velocity,
are taken from a model (Orosz et al. 2003) of the star built using
broadband filter specific intensities from the same atmosphere models.

---------------------------------------------------------
Title: Spectral Analysis of Ultracool Dwarfs
Authors: Homeier, D.; Hauschildt, P. H.; Allard, F.
2003AAS...202.3201H Altcode: 2003BAAS...35..743H
Improvements of opacity data for the molecular bands governing the
spectral energy distribution of the coolest brown dwarfs have brought
about major advances to the modelling of substellar atmospheres. At
this point uncertainties in the lines strengths for the most important
absorbers in the infrared, H2O and CH4, are
becoming secondary to uncertainties in the temperature structure,
e. g. related to the distribution of dust, for objects in the T dwarf
temperature range. Theoretical spectra generated with these models
can set constraints on the temperatures and gravities of ultracool
dwarfs independent from age determinations and cooling models. Thus,
a quantitative analysis of infrared spectra can serve as a test for
evolutionary models and help to identify brown dwarfs in the planetary
mass range (PMOs). We present the latest PHOENIX models for effective
temperatures 700 K&lt; ∼ T eff&lt; ∼1400 K, discussing
the effects of metallicity and gravity on the near infrared absorption
bands. The accuracy currently attainable in determining these parameters
from low resolution spectral fits or infrared colors alone, and using
the additional information available from absolute-flux calibrated
spectra, is assessed.

---------------------------------------------------------
Title: Detectability of Mixed Unburnt C+O in Type Ia Supernova Spectra
Authors: Baron, E.; Lentz, Eric J.; Hauschildt, Peter H.
2003ApJ...588L..29B Altcode: 2003astro.ph..3627B
Motivated by recent three-dimensional calculations of the explosion
of Type Ia supernovae via a pure deflagration, we calculate the
observed spectra at 15-25 days past maximum light of a parameterized
model that has a considerable fraction of unburnt C+O in the central
regions. Rather than attempting a self-consistent three-dimensional
calculation, which is beyond the scope of current computer codes, we
modify the composition structure of the one-dimensional deflagration
model W7. In our exploratory parameterized calculations, we find that
a central concentration of C+O is not ruled out by observations for
the epochs we study. We briefly examine whether nebular phase spectra
could be incompatible with observations.

---------------------------------------------------------
Title: The influence of chemical ionization and chemical recombination
processes on the plasma parameters in low-temperature layers of
stellar atmospheres
Authors: Mihajlov, A. A.; Jevremovi', D.; Ignjatovi', M. Lj.;
Hauschildt, P.; Dimitrijevi', S. M.
2003A&AT...22..513M Altcode:
Available from <A
href="http://taylorandfrancis.metapress.com/openurl.asp?genre=article&amp;issn=1055-6796&amp;volume=22&amp;issue=4&amp;spage=513">http://taylorandfrancis.metapress.com/openurl.asp?genre=article&amp;issn=1055-6796&amp;volume=22&amp;issue=4&amp;spage=513</A>

---------------------------------------------------------
Title: Determination of Primordial Metallicity and Mixing in the
Type II-P Supernova 1993W
Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt,
Peter H.; Turatto, M.; Cappellaro, E.
2003ApJ...586.1199B Altcode: 2002astro.ph.12071B
We present the results of a large grid of synthetic spectra and compare
them to early spectroscopic observations of SN 1993W. This supernova was
discovered close to its explosion date and, at a recession velocity of
5400 km s-1, is located in the Hubble flow. We focus here
on two early spectra that were obtained approximately 5 and 9 days
after explosion. We parameterize the outer supernova envelope as a
power-law density profile in homologous expansion. In order to extract
information on the value of the parameters, a large number of models was
required. We show that very early spectra combined with detailed models
can provide constraints on the value of the power-law index, the ratio
of hydrogen to helium in the surface of the progenitor, the progenitor
metallicity, and the amount of radioactive nickel mixed into the outer
envelope of the supernova. The spectral fits reproduce the observed
spectra exceedingly well. The spectral results combined with the early
photometry predict that the explosion date was 4.7+/-0.7 days before the
first spectrum was obtained. The ability to obtain the metallicity from
early spectra make SNe II-P attractive probes of chemical evolution in
the universe, and by showing that we have the ability to pin down the
parameters of the progenitor and mixing during the supernova explosion,
it is likely to make SNe II-P useful cosmological distance indicators
which are at the same time complementary to SNe Ia. Partially
based on observations performed at ESO La Silla.

---------------------------------------------------------
Title: The Early Ultraviolet Evolution of the ONeMg Nova V382
Velorum 1999
Authors: Shore, Steven N.; Schwarz, Greg; Bond, Howard E.; Downes,
Ronald A.; Starrfield, Sumner; Evans, A.; Gehrz, Robert D.; Hauschildt,
Peter H.; Krautter, Joachim; Woodward, Charles E.
2003AJ....125.1507S Altcode: 2003astro.ph..1415S
We present a multiwavelength study of the ONeMg Galactic nova V382
Velorum 1999 using HST/STIS and FUSE ultraviolet spectra and comparisons
with published ground-based optical spectra. We find a close match to
the basic phenomenology of another well-studied ONeMg nova, V1974 Cygni
(Nova Cyg 1992), in particular, to the spectral development through
the start of the nebular phase. Following an “iron curtain” phase,
the nova proceeded through a stage of P Cygni line profiles on all
important resonance lines, as in many ONeMg novae and unlike the CO
class. Emergent emission lines displayed considerable structure,
as seen in V1974 Cyg, indicating fragmentation of the ejecta at
the earliest stages of the outburst. Analysis and modeling of our
ultraviolet spectra suggest that (4-5)×10-4Msolar
of material was ejected and that the distance to the nova is ~=2.5
kpc. Relative to solar values, we find the following abundances: He=1.0,
C=0.6+/-0.3, N=17+/-4, O=3.4+/-0.3, Ne=17+/-3, Mg=2.6+/-0.1, Al=21+/-2,
and Si=0.5+/-0.3. Finally, we briefly draw comparisons with Nova LMC
2000, another ONeMg nova, for which similar data were obtained with
HST and FUSE. Based on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research
in Astronomy, Inc., under NASA contract 5-26555. These observations
are associated with proposals for programs GO 8540 and GO 8671. Also
based on observations made with the NASA-CNES-CSA Far Ultraviolet
Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins
University under NASA contract NAS 5-32985.

---------------------------------------------------------
Title: Testing spherical, expanding, line-blanketed model atmospheres
of giant stars with interferometry
Authors: Aufdenberg, Jason P.; Hauschildt, Peter H.
2003SPIE.4838..193A Altcode:
We show examples of PHOENIX stellar atmosphere model simulations for
data obtained by long-baseline optical interferometers. A single
spherical, hydrostatic model atmosphere for the M-type giant star
γ Sagittae is shown to be in good agreement with interferometric,
spectrophotometric, and high-dispersion spectroscopic data sets. In
particular we show that the interferometric triple products and
wavelength-dependent uniform disk diameters measured by the Navy
Prototype Optical Interferometer (NPOI) are well matched by our
model. With expanding atmosphere models for the A-type supergiant
α Cygni we predict that the center-to-limb intensity profile is
sensitive to the mass-loss rate of its stellar wind. For one possible
NPOI configuration we show the sensitivity of the squared visibility
amplitudes to the model mass-loss rate at spatial frequencies beyond
the first null. The importance of hot star photospheric interferometry
is discussed.

---------------------------------------------------------
Title: The Molecular Continuum Opacity of 24MgH in Cool
Stellar Atmospheres
Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt,
P. H.; Kirby, K.
2003ApJ...584..459W Altcode: 2002astro.ph..7042W
The opacity due to photodissociation of 24MgH in the
atmospheres of cool stars is investigated. The lowest two electronic
transitions A2Π&lt;--X2Σ+
and B'2Σ+&lt;--
X2Σ+ are considered, where the cross
sections for the latter were published previously (Weck, Stancil,
&amp; Kirby) and the former are presented in this work. Model
atmospheres calculated with the PHOENIX code are used to investigate
the effect of the photodissociation opacity on spectra of cool
stars. The A2Π&lt;--X2Σ+
photodissociation cross sections are obtained using a combination
of ab initio and experimentally derived potential curves and dipole
transition moments. Partial cross sections have been evaluated over
the accessible wavelength range 1770- 4560 Å for all rotational
transitions from the vibrational levels v”=0-11. Assuming
a Boltzmann distribution of the rovibrational levels of the
X2Σ+ state, LTE photodissociation cross
sections are presented for temperatures between 1000 and 5000 K. Shape
resonances, arising from rotational predissociation of quasi-bound
levels of the A2Π state near threshold, characterize the
LTE photodissociation cross sections. A sum rule is proposed as a
check on the accuracy of the photodissociation calculations.

---------------------------------------------------------
Title: The Extraordinary X-ray Light Curve of the Classical Nova V1494
Aquilae (1999 No. 2) in Outburst: The Discovery of Pulsations and a
“Burst”
Authors: Drake, Jeremy J.; Wagner, R. Mark; Starrfield, Sumner; Butt,
Yousaf; Krautter, Joachim; Bond, H. E.; Della Valle, M.; Gehrz, R. D.;
Woodward, Charles E.; Evans, A.; Orio, M.; Hauschildt, P.; Hernanz,
M.; Mukai, K.; Truran, J. W.
2003ApJ...584..448D Altcode: 2002astro.ph.10072D
V1494 Aql (Nova Aql 1999 No. 2) was discovered on 1999 December 2. We
obtained Chandra ACIS-I spectra on 2000 April 15 and June 7 which appear
to show only emission lines. Our third observation, on August 6, showed
that its spectrum had evolved to that characteristic of a Super Soft
X-ray Source. We then obtained Chandra LETG+HRC-S spectra on September
28 (8 ks) and October 1 (17 ks). We analyzed the X-ray light curve of
our grating observations and found both a short timescale “burst”
and oscillations. Neither of these phenomena has previously been seen
in the light curve of a nova in outburst. The “burst” was a factor of
~10 rise in X-ray counts near the middle of the second observation, and
which lasted about 1000 s; it exhibited at least two peaks, in addition
to other structure. Our time series analysis of the combined 25 ks
observation shows a peak at ~2500 s which is present in independent
analyses of both the zeroth-order image and the dispersed spectrum
and is not present in similar analyses of grating data for HZ 43 and
Sirius B. Further analyses of the V1494 Aql data find other periods
present which implies that we are observing nonradial g+
modes from the pulsating, rekindled white dwarf.

---------------------------------------------------------
Title: Brown Dwarfs and Extrasolar Planets
Authors: Allard, F.; Baraffe, I.; Chabrier, G.; Barman, T. S.;
Hauschildt, P. H.
2003ASPC..294..483A Altcode:
Brown dwarfs bridge the gap between the stellar and planetary mass
regimes and, as they cool, their atmospheres evolve towards conditions
most commonly associated with planets. Despite differences (e.g.,
formation and proximity to a stellar companion), it is interesting to
know just how much of the knowledge gained by studying brown dwarfs can
be directly applied when predicting the thermal and spectral properties
of extrasolar planets. This paper briefly summarizes the characteristics
of brown dwarfs and extrasolar giant planet atmospheres, and discusses
the significance of irradiation on the evolution of extrasolar planets.

---------------------------------------------------------
Title: Physics and Chemistry of Molecules and Dust at Low Temperatures
Authors: Ferguson, J. W.; Alexander, D. R.; Tamanai, A.; Bodnarik,
J.; Hauschildt, P. H.; Allard, F.
2003ASPC..294..539F Altcode:
The issues associated with computing the opacity of material at low
temperatures are described. The computation of the opacity requires
both a thorough knowledge of the chemical state of the material
(species populations) and the absorption/scattering behavior of
those species. At low temperatures, both of these issues become
very complex. For temperatures below 1800K, some materials begin to
precipitate out of the gas phase as small solid particles. Because
these small grains are very efficient at absorbing and scattering
light, they dominate the opacity whenever they exist. The abundance of
important molecular and solid absorbers as a function of temperature,
pressure, and the chemical composition will be explored. The effects
of dust on the computation of stellar atmospheres will be discussed.

---------------------------------------------------------
Title: A New Grid of Atmospheres for Early-Type Stars
Authors: Lentz, E. J.; Hauschildt, P. H.; Aufdenberg, J. P.; Baron, E.
2003IAUS..210P.B13L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model atmospheres of massive zero-metallicity stars
Authors: Lentz, Eric J.; Hauschildt, Peter H.; Aufdenberg, Jason P.;
Baron, Ed
2003IAUS..212..416L Altcode:
We have calculated detailed, fully non-LTE, model atomospheres for
massive zero-metal stars. We find the atmospheres of massive primordial
stars become unbound due to radiation pressure on lines and continua
over a much larger fraction of their evolution than previously expected.

---------------------------------------------------------
Title: Gravity &amp; Mass Measurement in Young Substellar Objects
Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard,
France; Hauschildt, Peter; Ardila, David
2003IAUJD..20E..29M Altcode:
We present an analysis of optical high-resolution spectra of very
young ultra-low mass stellar and substellar objects in Upper Scorpius
and Taurus. We show that a multi-feature spectral analysis combined
with the latest synthetic spectra can yield accurate surface gravities
(+/- 0.25 dex) and effective temperatures (+/- 50K). This represents
the most stringent observational constraint so far on gravity in young
ultra-low mass objects. Combining our gravity and temperature results
with observed and synthetic photometry and known cluster distance
we also derive masses and radii for our objects. These are the first
mass and radii measurements in young ultra-low mass objects that are
INDEPENDENT of theoretical evolutionary tracks. We find that two of our
faintest targets have planetary mass (~ 6 Jupiters). We also find that
significant discrepancies exist between our results and the theoretical
tracks for the coolest objects: our derived radii are substantially
larger than predicted. Recent studies of M dwarf eclipsing binaries
also show the theoretical radii to be underestimations. We conclude that
high-resolution spectroscopy is invaluable for guiding the evolutionary
modeling of young low-mass stars and brown dwarfs.

---------------------------------------------------------
Title: Spherical and Expanding Model Atmosphere Predictions for
Interferometry
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
2003ASPC..288..239A Altcode: 2003sam..conf..239A
Direct interferometric measurement of stellar limb-darkening,
unambiguously revealed by the shape of the visibility curve a beyond
the first null, is presently available for a only a few stars. The
vast majority of present day stellar diameter measurements require a
theoretical limb-darkening correction to recover the “true” diameter
and to interpret multi-wavelength uniform disk results. Compilations
of theoretical, wavelength dependent, center-to-limb intensity
profiles needed for such corrections are almost exclusively derived
from plane-parallel model atmospheres and are therefore generally
inappropriate for modeling the atmospheres of giant and supergiant
stars. In our theoretical studies of the angular sizes of both hot and
cool supergiant stars with the general-purpose stellar atmosphere code
PHOENIX, we have found significant and testable differences between
spherical and plane-parallel model predictions. We show examples of
these differences in our studies of 1) the interferometric diameter of
the A-type supergiant α Cygni and 2) interferometric diameter ratios
at wavelengths inside and adjacent to the 712 nm TiO band for normal
M-type giants and supergiants.

---------------------------------------------------------
Title: Parallelization Strategies for ALI Radiative Transfer in
Moving Media
Authors: Baron, E.; Hauschildt, P. H.; Lowenthal, D.
2003ASPC..288..385B Altcode: 2002astro.ph..7043B; 2003sam..conf..385B
We describe the method we have used to parallelize our spherically
symmetric special relativistic short characteristics general radiative
transfer code PHOENIX. We describe some possible parallelization
strategies and show why they would be inefficient. We discuss the
multiple parallelization strategy techniques that we have adopted. We
briefly discuss generalizing these strategies to full 3-D (spatial)
radiation transfer codes.

---------------------------------------------------------
Title: Molecular Absorbers in the Atmospheres of Methane Dwarfs
Authors: Homeier, D.; Allard, F.; Hauschildt, P. H.; Boudon, V.
2003IAUS..210P.E56H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Time-Dependent Moment Equation Method for Supernova Lightcurves
Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H.
2003ASPC..288..275L Altcode: 2003sam..conf..275L
We have developed a time-dependent solution to the moment equations to
solve for the temperature structure and radiation field of objects
where the temperature and structure of the object change slowly
relative to the radiation field, like supernovae. We have restored
the time derivative terms to the transport equation and modified our
method for the formal solution and approximate lambda operator.

---------------------------------------------------------
Title: Stellar atmospheres and synthetic spectra for GAIA
Authors: Hauschildt, P. H.; Allard, F.; Baron, E.; Aufdenberg, J.;
Schweitzer, A.
2003ASPC..298..179H Altcode: 2003gsst.conf..179H
No abstract at ADS

---------------------------------------------------------
Title: The Molecular Line Opacity of MgH in Cool Stellar Atmospheres
Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt,
P. H.; Kirby, K.
2003ApJ...582.1059W Altcode: 2002astro.ph..6219W
A new, complete, theoretical rotational and vibrational line list
for the A2Π&lt;--X2Σ+ electronic
transition in MgH is presented. The list includes transition energies
and oscillator strengths for all possible allowed transitions and was
computed using the best available theoretical potential energies and
dipole transition moment function with the former adjusted to account
for experimental data. The A&lt;--X line list as well as new line
lists for the B'2Σ+&lt;--
X2Σ+ and the
X2Σ+&lt;--X2Σ+ (pure
rovibrational) transitions were included in comprehensive stellar
atmosphere models for M, L, and T dwarfs and solar-type stars. The
resulting spectra, when compared to models lacking MgH, show that
MgH provides significant opacity in the visible between 4400 and 5600
Å. Further comparison of the spectra obtained with the current line
list to spectra obtained using the line list constructed by Kurucz show
that the Kurucz list significantly overestimates the opacity due to MgH,
particularly for the bands near 5150 and 4800 Å, with the discrepancy
increasing with decreasing effective temperature.

---------------------------------------------------------
Title: Temperature Correction Methods
Authors: Hauschildt, P. H.; Barman, T. S.; Baron, E.; Allard, F.
2003ASPC..288..227H Altcode: 2003sam..conf..227H
No abstract at ADS

---------------------------------------------------------
Title: The contrast of magnetic elements across the solar spectrum
Authors: Steiner, O.; Hauschildt, P. H.; Bruls, J.
2003AN....324..398S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model Atmosphere Analyses of Post-Common Envelope Stars
Authors: Rushton, M. T.; Smalley, B.; Ogley, R. N.; Wood, J. H.;
Hauschildt, P.; Bleach, J. N.
2003IAUS..210P.E33R Altcode: 2002astro.ph..8291R
Understanding post-common-envelope evolution is important in the studies
of close-binary systems. The majority of all interacting binaries with
a compact object in their system (e.g. cataclysmic variables, X-ray
binaries) are thought to have passed through a common-envelope (CE)
phase. Current models of interacting binaries all assume, as a starting
point, that there is no significant modification of the secondary star
compared with a normal star of similar spectral type. The extent to
which the CE significantly alters the composition of the secondary
star has yet to be determined. We are studying the M-type secondary
in the pre-CV system EG UMa, in order to determine its atmospheric
parameters by comparison with synthetic spectra generated using
PHOENIX. Absorption lines due to several elements have been used
in investigating the stellar parameters of effective temperature,
gravity and over elemental abundance. In addition, we are searching
for anomalies due to s-process elements (such as Ba, Sr, Rb, Y),
which may have been deposited in the atmosphere during the CE stage,
and prove that CE evolution has occurred. EG UMa displays strong YO
absorption bands, which are normally associated with giants and S
stars. These bands may have been formed as a result of an Y-abundance
enhancement introduced by the CE, which would be consistent with the
observed possible Rb and Sr enrichment.

---------------------------------------------------------
Title: Low Temperature Dust Opacity
Authors: Alexander, David R.; Ferguson, Jason W.; Allard, France;
Hauschildt, Peter H.
2003asdu.confE.126A Altcode:
As temperatures below approximately 1800 K (depending upon the density
and composition) are encountered in an astrophysical environment,
dust grains become important sources of opacity. Because these small
grains are very efficient absorbers and scatterers of light, they
dominate the opacity wherever they exist. The thermodynamic and optical
properties of these materials will be explored, along with deficiencies
in the available laboratory data. Recent results show that even with
relatively low abundances, grains such as Al2O3
and CaTiO3 can have a dramatic impact on the structure of
stellar, sub-stellar and planetary atmospheres, and on star and planet
formation. The effect of dust opacity for temperatures down to 300
K will be discussed. The potential significance of non-equilibrium
effects will also be discussed.

---------------------------------------------------------
Title: Methane Opacities in T Dwarf Atmospheres
Authors: Homeier, D.; Hauschildt, P. H.; Allard, F.
2003ASPC..288..357H Altcode: 2002astro.ph..9163H; 2003sam..conf..357H
We present the current status of PHOENIX model atmospheres for dwarfs
of spectral type T, typical for older field brown dwarfs and low-mass
brown dwarfs. In comparison to warmer L dwarf atmosphers, the spectral
features of these objects can largely be reproduced by treating
the influence of dust in the limiting case of complete settling,
i. e. neglecting the dust opacity (Cond models). One major challenge
in modelling cool brown dwarf atmospheres is the correct treatment of
the molecular lines of H2O and CH4. These are
the dominant opacity sources in the IR and responsible for the very
blue colours of T dwarfs in the near infrared. Reliable opacity
data for these absorbers are thus mandatory for a correct determination
of the temperature structure as well as for detailed modelling of the
characteristic absorption features in the H and K bands, which are the
defining criteria of spectral class T. Line lists extracted from
low temperature atmospheric databases such as HITRAN and GEISA are
generally strongly limited to lower-state energies. To overcome these
limits, a new list of line-by-line predictions for the methane opacities
from the four lowest vibrational states has been computed with the
Spherical Top Database System (STDS). Improvements of these line
lists have been achieved thanks to recent successes in the experimental
calibration of the molecular parameter describing the vibrational and
rotational bands in the spherical top model. This allowed extrapolations
to higher rotational states than previously possible. As a result our
opacity sampling models now allow a much more complete reproduction
of the strong features occuring in the temperature regimes of brown
dwarf atmospheres. A more diffuse background opacity remains due
to the extremely high line density from higher vibrational states,
which at this time can be described only partly by statistical models.

---------------------------------------------------------
Title: NLTE Calculations of a Na D Doublet in the Atmosphere of the
Transiting Planet HD209458b
Authors: Barman, T. S.; Hauschildt, P. H.; Schweitzer, A.; Stancil,
P. C.; Baron, E.; Allard, F.
2003ASPC..294..467B Altcode:
The observation of sodium absorption in the atmosphere of HD209458b,
currently the only EGP known to transit its parent star, is the first
direct evidence of an EGP atmosphere. We explore the possibility that
neutral sodium is not in local thermodynamic equilibrium (LTE) in the
outer atmosphere of irradiated EGPs and that the sodium concentration
may be underestimated by models that make the LTE assumption. Our
results indicate that it may not be necessary to invoke excessive
photoionization, low metallicity, or even high altitude clouds to
explain the observations.

---------------------------------------------------------
Title: Radiation and Chemi-Ionization/Recombination Processes in
Atom-Atom and Ion-Atom Collisions in the Modeling of Low-Temperature
Stellar Atmospheres
Authors: Mihajlov, A. A.; Ignjatovic, Lj.; Dimitrijevic, M. S.;
Jevremovic, D.; Hauschildt, P.
2003IAUS..210P..B2M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Putting Radiation Hydrodynamics into a Detailed Model
Atmosphere Calculation
Authors: Schweitzer, A.; Hauschildt, P. H.
2003ASPC..288..541S Altcode: 2003sam..conf..541S
Non-grey hydrodynamics is still clearly not practicle. However,
it is possible to combine a grey radiation hydrodynamics code and a
non-grey model atmosphere code to obtain more realistic results. In this
presentation we describe our current work in combining the atmosphere
code PHOENIX and the radiation hydrodynaimcs code TITAN. We use
PHOENIX to tabulate the material functions like the equation of state
and the mean opacities. For example, TITAN can then calculate a shock
propagating through an atmosphere for which the initial structure is
provided by PHOENIX. The resulting atmospheric structures will then be
fed back into PHOENIX to calculate high resolution spectra including
NLTE treatment. Our goal is to apply this method to obtain high quality
spectra of Mira variables as a function of phase.

---------------------------------------------------------
Title: Highlights of Stellar Modeling with PHOENIX
Authors: Baron, E.; Hauschildt, P. H.; Allard, F.; Lentz, E. J.;
Aufdenberg, J.; Schweitzer, A.; Barman, T.
2003IAUS..210...19B Altcode: 2002astro.ph..9052B
We briefly describe the current version of the PHOENIX code. We then
present some illustrative results from the modeling of Type Ia and Type
II supernovae, hot stars, and irradiated giant planets. Good fits to
observations can be obtained, when account is taken for spherically
symmetric, line-blanketed, static or expanding atmospheres.

---------------------------------------------------------
Title: Surface Gravity &amp; Mass in Young Brown Dwarfs and Planemos
Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor; Allard,
France; Hauschildt, Peter; Ardila, David
2003ASSL..299..259M Altcode: 2003oils.conf..259M
No abstract at ADS

---------------------------------------------------------
Title: Opacities of Molecules and Dust
Authors: Alexander, D. R.; Ferguson, J. W.; Tamanai, A.; Bodnarik,
J.; Allard, F.; Hauschildt, P. H.
2003ASPC..288..289A Altcode: 2003sam..conf..289A
As progressively lower temperatures are encountered in a stellar
atmosphere, first molecules and finally dust grains become important
sources of opacity. The abundance of important molecular and solid
absorbers depends upon temperature, pressure, and the chemical
composition in complex ways which require detailed equation of state
calculations. Molecular spectra, which usually contain thousands or
millions of spectral lines, are usually treated statistically in the
opacity sampling method. Because of the size of modern line lists and
the computation time required to process them, efficient computation
of molecular opacity requires careful selection of the wavelengths
and the relevant lines. We will discuss these procedures, and the
results obtained for important absorbers such as H2O and
TiO. For temperatures below about 1,800 K, some materials begin to
precipitate out of the gas phase as small solid particles. Because these
small grains are very efficient absorbers and scatterers of light, they
dominate the opacity whenever they exist. The thermodynamic and optical
properties of these materials will be explored. Recent results show that
even grains with relatively low abundances, such as Al2O
3 and CaTiO3, can have a dramatic impact on the
structure of stellar atmospheres. Most atmospheres with Teff
&lt; 3,000 K, both giant and dwarf, have grains in their outer layers
in sufficient quantity to affect the emergent spectrum.

---------------------------------------------------------
Title: Using Superlevels to Calculate Molecular NLTE Problems
Authors: Schweitzer, A.; Hauschildt, P. H.; Baron, E.; Allard, F.
2003ASPC..288..339S Altcode: 2003sam..conf..339S
We present the method we use in the atmosphere code PHOENIX to calculate
molecular NLTE. It is based on the concept of superlevels. Superlevels
consist of many similar levels added together which are assumed to
be populated by a relative LTE distribution. This reduces the size
of the system of rate equations to be solved tremendously. However,
we modified the classical superlevel method and combined it with
our dynamical opacity sampling technique which allows us to treat
millions of lines. Therefore, we can calculate the transitions with
maximum accuracy. We demonstrate the qualities of this method with
the examples of CO and TiO.

---------------------------------------------------------
Title: Chemical Equilibrium of Dust at Low Temperature
Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France;
Hauschildt, Peter H.
2003asdu.confE.127F Altcode:
The opacity of material is required whenever the detailed transfer
of radiation through a gas is modeled. Computation of the opacity
requires both a thorough knowledge of the chemical state of the gas
(species populations) and the absorption/scattering behavior of those
species. At low temperatures the equation of state (EOS) calculations
become particularly complex. Our EOS computations assume chemical
equilibrium and include over 600 solid and liquid species with data
mainly from the JANAF database. We will present and discuss our EOS
computations for gas temperatures from 2000 K to 300 K and a wide
range of gas densities, pressures and chemical compositions. Large
discontinuities in species abundances are seen when an individual grain
species condenses. It has been known for some time that solid silicate
and iron particles play important roles in the chemical equilibrium
and opacity of a cool gas. Many other condensed species, including
Al2 O3, CaTiO3, and even carbon at
very low temperature, can play equally important roles.

---------------------------------------------------------
Title: Resolving Stellar Atmospheres with Microlensing
Authors: Thurl, Christine; Sackett, Penny D.; Hauschildt, Peter H.
2003IAUJD...9E..28T Altcode:
Resolving the stellar surface and determining limb darkening
characteristics in stars other than the Sun has proved to be very
difficult. Observations have not yet yielded a satisfying picture of
stellar surface brightness distributions in distant stars. During
a microlensing event the part of the source star which coincides
with the caustic becomes highly magnified. When the trailing end of
the star leaves the inside of the caustic the limb - and therefore
the stellar atmosphere - contributes much of the measured flux. We
use this to measure surface brightness features of the source star
and determine limb darkening characteristics. It has been shown
previously that commonly-used limb darkening laws fail to match stellar
model atmospheres at the limb of the star (Bryce et al). We examine
this in more detail and also address possible implications for the
use of microlensing to study stellar atmospheres with broad band and
spectroscopic data.

---------------------------------------------------------
Title: Optical Spectroscopy of V838 Monocerotis
Authors: Wagner, R. M.; Starrfield, S. G.; Hauschildt, P. H.
2002AAS...201.4002W Altcode: 2002BAAS...34.1161W
Optical spectroscopy of V838 Mon was obtained on 2002 Feb. 8 (range
415-675 nm, resolution 0.14 nm) and on Sep. 25 (range 390-750 nm,
resolution 0.38 nm) with the 6.5-m MMT of the University of Arizona and
the Smithsonian Institution. The Feb. spectrum exhibits strong emission
lines of the Balmer series, Fe II, Ba II, Na I D, and weaker features
with sharp P Cygni profiles. The width of the emission lines implies an
average expansion velocity of about 150 km/s and a terminal velocity of
about 350 km/s for a wind or expanding envelope. The spectrum indicates
that the progenitor must be a highly evolved object. Preliminary
modeling of this spectrum and a HST/STIS UV spectrum obtained a day
earlier suggests that the object is deficient in hydrogen and similar
in composition to the born-again post-AGB star V4334 Sgr. The Sep. 25th
spectrum is composite. Strong TiO and VO bands are seen in the red
suggesting a late-M-giant component. At shorter wavelengths, there are
strong and narrow absorption lines of the Balmer series and He I (447.1,
587.5 nm). Narrow emission lines arising from [O I] (630.0, 636.3 nm),
Mg I (457.1, 516.7 nm), and many other weaker emission and absorption
lines are also present. Strong interstellar absorption features of Na
I D, 578.0 nm, and perhaps 443.0 nm are present and the equivalent
width of 578.0 nm implies E(B-V) = 0.54 mag. The composite spectrum
suggests that V838 Mon might be a binary system. These spectra and
comparisons with post-AGB stars and eruptive variables such as M31RV
and V4332 Sgr will be presented.

---------------------------------------------------------
Title: Numerical simulations of surface convection in a late M-dwarf
Authors: Ludwig, H. -G.; Allard, F.; Hauschildt, P. H.
2002A&A...395...99L Altcode: 2002astro.ph..8584L
Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)
simulations of time-dependent compressible convection, we have studied
the dynamics and thermal structure of the convective surface layers of a
prototypical late-type M-dwarf (Teffapprox 2800 K, log g=5.0,
solar chemical composition). The RHD models predict stellar granulation
qualitatively similar to the familiar solar pattern. Quantitatively,
the granular cells show a convective turn-over time scale of ~100 s,
and a horizontal scale of 80 km; the relative intensity contrast of
the granular pattern amounts to 1.1%, and root-mean-square vertical
velocities reach 240 m s-1 at maximum. Deviations from
radiative equilibrium in the higher, formally convectively stable
atmospheric layers are found to be insignificant allowing a reliable
modeling of the atmosphere with 1D standard model atmospheres. A
mixing-length parameter of αMLT = 2.1 provides the
best representation of the average thermal structure of the RHD
model atmosphere while alternative values are found when fitting the
asymptotic entropy encountered in deeper layers of the stellar envelope
(αMLT = 1.5), or when matching the vertical velocity
(αMLT = 3.5). The close correspondence between RHD and
standard model atmospheres implies that presently existing discrepancies
between observed and predicted stellar colors in the M-dwarf regime
cannot be traced back to an inadequate treatment of convection in the
1D standard models. The RHD models predict a modest extension of the
convectively mixed region beyond the formal Schwarzschild stability
boundary which provides hints for the distribution of dust grains in
cooler (brown dwarf) atmospheres.

---------------------------------------------------------
Title: Molecular Line and Continuum Opacities for Modeling of
Extrasolar Giant Planet and Cool Stellar Atmospheres
Authors: Weck, P. F.; Stancil, P. C.; Schweitzer, A.; Hauschildt,
P. H.; Kirby, K.; Yamaguchi, Y.; Allen, W.
2002nla..work..165W Altcode:
The molecular hue and continuum opacities are investigated in the
atmospheres of cool stars and Extrasolar Giant Planets (EGPs). Using
a combination of ab inito and experimentally derived potential curves
and dipole transition moments, accurate data have been calculated for
rovibrationally-resolved oscillator strengths and photodissociation
cross sections in the B' 2∑+ ← X 2∑+ and A
2II ← X 2∑+ baud systems in MgH. We
also report our progress on the study of the electronic structure of
LiCl and FeH.

---------------------------------------------------------
Title: Detectability of Hydrogen Mixing in Type Ia Supernova
Premaximum Spectra
Authors: Lentz, Eric J.; Baron, E.; Hauschildt, Peter H.; Branch, David
2002ApJ...580..374L Altcode: 2002astro.ph..7470L
The presence of a small amount of hydrogen is expected in most
single-degenerate scenarios for producing a Type Ia supernova (SN
Ia). While hydrogen may be detected in very early high-resolution
optical spectra, in early radio spectra, and in X-ray spectra, here we
examine the possibility of detecting hydrogen in early low-resolution
spectra such as those that will be obtained by proposed large-scale
searches for nearby SNe Ia. We find that definitive detections will
require both very early spectra (less than 5 days after explosion)
and perhaps slightly higher amounts of hydrogen than are currently
predicted to be mixed into the outer layers of SNe Ia. Thus, the
nondetection of hydrogen so far does not in and of itself rule out any
current progenitor models. Nevertheless, very early spectra of SNe Ia
will provide significant clues to the amount of hydrogen present and
hence to the nature of the SN Ia progenitor system. Spectral coverage
in both the optical and IR will be required to definitively identify
hydrogen in low-resolution spectra.

---------------------------------------------------------
Title: Nova Model Atmopheres
Authors: Hauschildt, Peter H.; Schwarz, G.; Short, C. Ian; Baron,
E.; Starrfield, S.
2002AIPC..637..249H Altcode: 2002cne..conf..249H
We review the basics physics of nova atmospheres and discuss the
physics that has to be included for detailed models of their early
spectra. We also present NLTE calculations for model atmospheres of
novae during outburst. This fully self-consistent NLTE treatment for
a number of model atoms includes &gt; 5000 NLTE levels and &gt; 57000
NLTE primary transitions. We discuss the implication of departures from
LTE for the strengths of the lines in nova spectra. The new results
show that our large set of NLTE lines constitute the majority of the
total line blanketing opacity in nova atmospheres. Although we include
LTE background lines, their effects are small on the model structures
and on the synthetic spectra. We demonstrate that the assumption of
LTE leads to incorrect synthetic spectra and that NLTE calculations
are required for reliably modeling nova spectra. In addition, we show
that detailed NLTE treatment for a number of ionization stages of iron
changes the results of previous calculations and improves the fit to
observed nova spectra. These new models have also been used to fit
the lightcurves of novae during the early phases of the nova outburst.

---------------------------------------------------------
Title: Spectral types of planetary host star candidates: Two new
transiting planets?
Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley,
W.; Werner, K.
2002A&A...391L..17D Altcode: 2002astro.ph..7192D
Recently, 46 low-luminosity object transits were reported from
the Optical Gravitational Lensing Experiment. Our follow-up
spectroscopy of the 16 most promising candidates provides a spectral
classification of the primary. Together with the radius ratio from
the transit measurements, we derived the radii of the low-luminosity
companions. This allows to examine the possible sub-stellar nature
of these objects. Fourteen of them can be clearly identified as
low-mass stars. Two objects, <ASTROBJ>OGLE-TR-03</ASTROBJ> and
<ASTROBJ>OGLE-TR-10</ASTROBJ> have companions with radii of 0.15
R_sun which is very similar to the radius of the transiting planet HD
209458 B. The planetary nature of these two objects should therefore
be confirmed by dynamical mass determinations.

---------------------------------------------------------
Title: Detailed Spectroscopic Analysis of SN 1987A: The Distance
to the Large Magellanic Cloud Using the Spectral-fitting Expanding
Atmosphere Method
Authors: Mitchell, Robert C.; Baron, E.; Branch, David; Hauschildt,
Peter H.; Nugent, Peter E.; Lundqvist, Peter; Blinnikov, Sergei; Pun,
Chun S. J.
2002ApJ...574..293M Altcode: 2002astro.ph..4012M
Supernova 1987A remains the most well studied supernova to
date. Observations produced excellent broadband photometric and
spectroscopic coverage over a wide wavelength range at all epochs. We
model the observed spectra from day 1 to day 81 using a hydrodynamical
model. We show that good agreement can be obtained at times up to
about 60 days if we allow for extended nickel mixing. Later than
about 60 days the observed Balmer lines become stronger than our
models can reproduce. We show that this is likely due to a more
complicated distribution of gamma rays than we allow for in our
spherically symmetric calculations. We present synthetic light curves
in UBVRIJHK and a synthetic bolometric light curve. Using this broad
baseline of detailed spectroscopic models, we find a distance modulus
of μ=18.5+/-0.2 using the spectral-fitting expanding atmosphere method
of determining distances to supernovae. We find that the explosion
time agrees with that of the neutrino burst and is constrained at 68%
confidence to within +/-0.9 days. We argue that the weak Balmer lines
of our detailed model calculations cast doubt on the accuracy of the
purely photometric expanding photosphere method. We also suggest that
Type IIP supernovae will be most useful as distance indicators at
early times because of a variety of effects.

---------------------------------------------------------
Title: Spectra and Evolution of Exrasolar Planets
Authors: Allard, F.; Baraffe, I.; Chabrier, G.; Barman, T.; Hauschildt,
P. H.
2002sf2a.conf..573A Altcode:
We have used our general atmosphere code Phoenix to generate radiative
equilibrium models of irradiated planets located near a dM6 and
a G2 primary. The external radiation, as modeled also by Phoenix,
was explicitly included in the solution of the radiative transfer
equation. A cool (Teff = 500K) and a hot (Teff = 1000K) planet were
modeled at various orbital separations from both the dM6 and the G2
primary. In all scenarios, we compared the effects of the irradiation
in two cases: one where dust clouds form and remain suspended in the
atmosphere and another where dust clouds form but settle out of the
atmosphere. The atmospheric structure and emergent spectrum strongly
depend on the presence or absence of dust clouds.

---------------------------------------------------------
Title: Atmospheric analysis of the M/L and M/T dwarf binary systems
LHS 102 and Gliese 229
Authors: Leggett, S. K.; Hauschildt, Peter H.; Allard, F.; Geballe,
T. R.; Baron, E.
2002MNRAS.332...78L Altcode: 2001astro.ph.12335L
We present 0.9-2.5μm spectroscopy with R ~800 and 1.12-1.22μm
spectroscopy with R ~5800 for the M dwarfs Gl 229A and LHS 102A, and
for the L dwarf LHS 102B. We also report IZJHKL ' photometry for both
components of the LHS 102 system, and L ' photometry for Gl 229A. The
data are combined with previously published spectroscopy and photometry
to produce flux distributions for each component of the kinematically
old disc M/L dwarf binary system LHS 102 and the kinematically young
disc M/T dwarf binary system Gliese 229. The data are analysed using
synthetic spectra generated by the latest `AMES-dusty' and `AMES-cond'
models by Allard &amp; Hauschildt. Although the models are not able to
reproduce the overall slope of the infrared flux distribution of the L
dwarf, most likely because of the treatment of dust in the photosphere,
the data for the M dwarfs and the T dwarf are well matched. We find that
the Gl 229 system is metal-poor despite having kinematics of the young
disc, and that the LHS 102 system has solar metallicity. The observed
luminosities and derived temperatures and gravities are consistent
with evolutionary model predictions if the Gl 229 system is very young
(age~30Myr) with masses (A,B) of (0.38,&gt;~0.007)Msolar
, and the LHS 102 system is older, aged 1-10Gyr with masses (A,B) of
(0.19,0.07)Msolar .

---------------------------------------------------------
Title: The Spectral Energy Distribution and Mass-Loss Rate of the
A-Type Supergiant Deneb
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.; Nordgren,
T. E.; Burnley, A. W.; Howarth, I. D.; Gordon, K. D.; Stansberry, J. A.
2002ApJ...570..344A Altcode: 2002astro.ph..1218A
A stellar wind module has been developed for the PHOENIX stellar
atmosphere code for the purpose of computing non-LTE, line-blanketed,
expanding atmospheric structures and detailed synthetic spectra of hot
luminous stars with winds. We apply the code to observations of Deneb,
for which we report the first positive detections of millimeter and
centimeter emission (obtained using the Submillimeter Common-User
Bolometric Array and the Very Large Array) as well a strong upper
limit on the 870 μm flux (using the Heinrich Hertz Telescope). The
slope of the radio spectrum shows that the stellar wind is partially
ionized. We report a uniform-disk angular diameter measurement
θUD=2.40+/-0.06 mas from the Navy Prototype Optical
Interferometer (NPOI). The measured bolometric flux and corrected
NPOI angular diameter yield an effective temperature of 8600+/-500
K. Least-squares comparisons of synthetic spectral energy distributions
from 1220 Å to 3.6 cm with the observations provide estimates for
the effective temperature and the mass-loss rate of ~=8400+/-100
K and (8+/-3)×10-7 Msolar yr-1,
respectively. This range of mass-loss rates is consistent with that
derived from high-dispersion UV spectra when non-LTE metal-line
blanketing is considered. We are unable achieve a reasonable fit to a
typical Hα P Cygni profile with any model parameters over a reasonable
range. This is troubling because the Hα profile is the observational
basis for the wind momentum-luminosity relationship.

---------------------------------------------------------
Title: Non-LTE Effects of Na I in the Atmosphere of HD 209458b
Authors: Barman, Travis S.; Hauschildt, Peter H.; Schweitzer, Andreas;
Stancil, Phillip C.; Baron, E.; Allard, France
2002ApJ...569L..51B Altcode: 2002astro.ph..3139B
The recent announcement that sodium absorption has been observed in
the atmosphere of HD 209458b, the only extrasolar giant planet (EGP)
observed to transit its parent star, is the first direct detection of
an EGP atmosphere. We explore the possibility that neutral sodium is
not in local thermodynamic equilibrium (LTE) in the outer atmosphere of
irradiated EGPs and that the sodium concentration may be underestimated
by models that make the LTE assumption. Our results indicate that it may
not be necessary to invoke excessive photoionization, low metallicity,
or even high-altitude clouds to explain the observations.

---------------------------------------------------------
Title: Effective Temperatures of Late L Dwarfs and the Onset of
Methane Signatures
Authors: Schweitzer, Andreas; Gizis, John E.; Hauschildt, Peter H.;
Allard, France; Howard, Eric M.; Kirkpatrick, J. Davy
2002ApJ...566..435S Altcode: 2001astro.ph.10316S
We present a spectral analysis of a sample of late L dwarfs. We
use our latest model atmospheres and synthetic spectra and optical
and K-band spectra to determine effective temperatures. We derive
effective temperatures of 1400-1700 K for L8-L6 dwarfs. The analysis
demonstrates that our recent models that rain out the formed dust
completely are applicable to optical spectra of late L dwarfs and that
more consistent models are needed for intermediate L dwarfs and for
infrared spectra. We compare the results for the effective temperatures
with the temperatures of the onset of methane formation. Our models
predict methane absorption at 3.3 μm to occur at temperatures about
400 K higher than methane absorption at 2.2 μm. This is consistent
with our data and previous observations, which show methane absorption
at 3.3 μm, but not at 2.2 μm, in late L dwarfs.

---------------------------------------------------------
Title: Evolutionary models for low-mass stars and brown dwarfs:
Uncertainties and limits at very young ages
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H.
2002A&A...382..563B Altcode: 2001astro.ph.11385B
We analyse pre-Main Sequence evolutionary tracks for low mass stars
with masses m &lt;= 1.4 Msun based on the Baraffe et
al. (\cite{Bar98}) input physics. We also extend the recent Chabrier
et al. (2000) evolutionary models based on dusty atmosphere to
young brown dwarfs down to one mass of Jupiter. We analyse current
theoretical uncertainties due to molecular line lists, convection
and initial conditions. Simple tests on initial conditions show the
high uncertainties of models at ages la 1 Myr. We find a significant
sensitivity of atmosphere profiles to the treatment of convection at
low gravity and Teff &lt; 4000 K, whereas it vanishes as
gravity increases. This effect adds another source of uncertainty
on evolutionary tracks at very early phases. We show that at low
surface gravity (log g &lt;~ 3.5) the common picture of vertical
Hayashi lines with constant Teff is oversimplified. The
effect of a variation of initial deuterium abundance is studied. We
compare our models with evolutionary tracks available in the literature
and discuss the main differences. We finally analyse to what extent
current observations of young systems provide a good test for pre-Main
Sequence tracks.

---------------------------------------------------------
Title: Cool Stellar Atmospheres
Authors: Hauschildt, P. H.; Allard, F.; Schweitzer, A.; Baron, E.
2002ASPC..274...95H Altcode: 2002ohds.conf...95H
No abstract at ADS

---------------------------------------------------------
Title: Cool stellar atmospheres
Authors: Hauschildt, Peter H.; Schweitzer, Andreas; Allard, F.;
Ferguson, J. W.; Alexander, D.; Baron, E.
2002ASSL..274...15H Altcode:
We give an overview about the state-of-the-art in cool stellar (and
sub-stellar) atmosphere simulations. Recent developments in numerical
methods and parallel supercomputers, as well as in the quality of input
data such as atomic and molecular line lists have led to substantial
improvements in the quality of synthetic spectra when compared to
multi-wavelength observations. A wide range of ojbects from M dwarfs
and giants down to substellar objects is considered. We discuss effects
such as atomic and molecular NLTE (and) line blanketing, external
irradiation, and formation and opacities of dust particles and clouds;
each of which affects the structure of the atmospheres and their
spectra. Current models can simultaneously fit many of the observed
features of a given star with a single model atmosphere, however, a
number of problems remain unsolved and will have to be addressed in the
future, in particular for very low mass stars and substellar objects.

---------------------------------------------------------
Title: V838 Monocerotis - a Newly Discovered, Very Peculiar, Slow
Nova-Like Object
Authors: Rauch, Thomas; Hauschildt, Peter; Asplund, Martin; Gredel,
Roland; Käufl, Hans-Ulrich; Kerber, Florian; Rosa, Michael;
Starrfield, Sumner G.; Wagner, R. Mark; Williams, Robert E.
2002ASPC..279..345R Altcode: 2002IAUCo.187..345R; 2002esce.conf..345R
No abstract at ADS

---------------------------------------------------------
Title: From the Sun to Jupiter: Evolution of Low Mass Stars and
Brown Dwarfs down to Planetary Masses
Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France;
Hauschildt, Peter
2002osp..conf...93B Altcode:
We present current models for low mass stars and substellar objects down
to planetary masses and discuss the success and remaining uncertainties
of the theory. We focus on early evolutionary phases during the first
∼ 10 Myr, covering for stars the initial deuterium burning phase to
the zero-age Main Sequence. Uncertainties of models at young ages due
to the choice of initial conditions are emphasized.

---------------------------------------------------------
Title: Spectral types of planetary host star candidates: new
transiting planets ?
Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley,
W.; Werner, K.
2002AGAb...19R...6D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Irradiation of CV secondaries
Authors: Barman, T. S.; Hauschildt, P. H.; Allard, F.
2002ASPC..261...49B Altcode: 2002pcvr.conf...49B
In many cases, the red secondary star in a cataclysmic variable (CV)
system contributes a significant amount to the total near-IR and IR
flux. Over the past decade, several CV secondaries have been observed;
however, the interpretation of these observations is complicated by
the fact that one hemisphere of the secondary is subjected to the
intense radiation fields of the primary, accretion disk, and boundary
layer. Using our general purpose atmosphere code (PHOENIX), we have
modeled the effects of the impinging radiation from a hot white dwarf on
the atmosphere of a CV secondary. We will present preliminary results
for an average CV system.

---------------------------------------------------------
Title: Radiative accelerations in stellar atmospheres
Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H.; Baron, E.
2002A&A...381..197H Altcode:
We present calculations of radiative accelerations obtained with
the general purpose model atmosphere code PHOENIX. The accelerations
are computed simultaneously for all the elements He-Ga; Kr-Nb; Ba;
La, using the opacity sampling method. The calculations are mainly
performed with the LTE approximation. Tests are made to evaluate the
influence of non-LTE effects and the validity of the radiative flux
obtained through the diffusion approximation. It is shown that the
abundances supported in the atmospheres of HgMn and He-weak stars are
generally consistent with those observed.

---------------------------------------------------------
Title: Rovibrational Photodissociation of MgH for Advanced Stellar
Atmosphere Models
Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt,
P. H.; Kirby, K.
2001AAS...199.9208W Altcode: 2001BAAS...33.1441W
For very cool stars (M and later) molecular absorption is the
most important opacity source. The lack of accurate and complete
molecular data has been a serious limitation to developing atmospheric
models of such stars, from which synthetic spectra and important
physical parameters, such as surface chemical composition, can be
calculated. Models generally include molecular bands with hundreds
of millions of spectral lines, but few have considered the effect
of molecular photodissociation processes. Photodissociation from a
range of vibrational (v) and rotational (R) levels of the ground
electronic state of a molecule can provide a significant source
of continuum opacity. We have performed extensive calculations of
photodissociation cross sections for MgH, using the most accurate
available molecular data. Potential curves and transition moments
for the low-lying electronic states of MgH (Saxon et al., 1978),
as well as the ground state dipole moment function, were used to
generate cross sections for photodissociation through the B'-X and
A-X transitions and through the X state, itself. Calculations were
performed for the full range of rovibrational levels (v,R) in the
ground electronic state. These photodissociation cross sections have
been included in the PHOENIX stellar atmosphere code. The new models,
calculated using spherical geometry for all gravities considered,
also incorporate our latest database of nearly 670 million molecular
lines, and updated equations of state (EOS). This work was supported in
part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425,
NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582. Some of the
calculations were performed on the IBM SP2 of the UGA UCNS, on the IBM
SP “Blue Horizon” of the San Diego Supercomputer Center, with support
from the NSF, and on the IBM SP of the NERSC with support from the DoE.

---------------------------------------------------------
Title: Diameters of Cool Giant Stars at 712 nm &amp; 754 nm: Theory
vs. Observations
Authors: Aufdenberg, J. P.; Quirrenbach, A.; Hauschildt, P. H.;
Baron, E.
2001AAS...199.9207A Altcode: 2001BAAS...33.1441A
As reported by Quirrenbach et al. (2000, IAU Symposium No. 205),
the Mark III Interferometer on Mt. Wilson was used to measure the
diameters of 47 cool giant stars in two filters centered at 712 nm
and at 754 nm. These filters probe the stellar atmosphere in a strong
TiO band (712 nm) and in a “continuum” band relatively free of
TiO absorption (754 nm). The measured diameters are systematically
larger at 712 nm than at 754 nm. The diameter ratio increases with
decreasing effective temperature, and it is larger for luminosity class
I than for luminosity class II and III stars. We have been successful
in quantitatively reproducing these trends with the latest set of
cool giant models from the general-purpose stellar atmosphere code
PHOENIX. Spherical, hydrostatic, massively line-blanketed atmosphere
models have been constructed using a depth-impact parameter coordinate
system where parallel rays intersect nested shells. From these models,
synthetic center-to-limb intensity variations in the 712 nm and 754
nm bands have been extracted. From these synthetic limb profiles,
we predict the uniform-disk ratio of the two bands as a function of
model effective temperature and surface gravity. With the exception of
Mira (o Ceti), the diameter ratios of all of the observed oxygen-rich
giants fall within the limits predicted by the models. We find that
the computation of the model atmospheres in a spherical geometry,
with complete as possible atomic and molecular line blanketing, is
required to generate the geometrical extension of the atmosphere and the
limb profiles inferred from the observations. Most of the stars have
well constrained bolometric flux measurements and IR interferometric
angular diameters which provide nearly model-independent effective
temperatures. These measured effective temperatures, along with surface
gravity estimates, provide a consistency check of the models. JPA is
supported by a Harvard-Smithsonian CfA postdoctoral fellowship. This
work was supported in part by NSF grants AST-9720704 and AST-0086246,
NASA grants NAG5-8425, NAG5-9222, as well as NASA/JPL grant 961582 to
the University of Georgia and in part by NSF grants AST-97314508, by
NASA grant NAG5-3505 and an IBM SUR grant to the University of Oklahoma.

---------------------------------------------------------
Title: Spectral Analysis of L dwarfs using PHOENIX
Authors: Schweitzer, A.; Gizis, J. E.; Hauschildt, P. H.; Allard,
F.; Reid, I. N.; Kirkpatrick, J. D.
2001AAS...199.6103S Altcode: 2001BAAS...33.1398S
We present a spectroscopic study of L dwarfs using our latest AMES-Cond
and AMES-Dusty model atmospheres. These model atmospheres are calculated
using the atmosphere code PHOENIX and include dust formation and dust
absorption inside the photosphere. Early L dwarfs turn out to have
a dust filled photosphere and can be described with the AMES-Dusty
models which leave the formed dust completely in the layer in which
it forms. The late L dwarfs turn out to have a dust free (rained out)
photosphere and can be described with the AMES-Cond models which
rain out the formed dust completely. Intermediate L dwarfs, however,
cannot be reproduced with either model yet and require unified models
which consider the settling of dust to produce a self consistent dust
stratification. We derive effective temperatures of 1400 K to 2000 K
for L8 to M9.5 dwarfs respectively. As expected for this field sample
out of the 2MASS catalog, we derive high values for log(g) of 4.5 and
higher. This work was supported in part by NASA ATP grants NAG5-8425,
NAG 5-3018 and LTSA grant NAG 5-3619. Some of the calculations were
performed on the IBM SP2 of the UGA UCNS, on the IBM SP “Blue Horizon”
of the San Diego Supercomputer Center, with support from the NSF, and
on the IBM SP of the NERSC with support from the DoE. The observations
were obtained at the W. M. Keck Observatory, which is operated jointly
by the University of California, the California Institute of Technology
and NASA.

---------------------------------------------------------
Title: Optical - IR stellar astrophysics: Models vs. Observations
Authors: Ferguson, J. W.; Penley, J. J.; Alexander, D. R.; Allard,
F.; Hauschildt, P. H.
2001AAS...19913515F Altcode: 2001BAAS...33.1508F
Recent observational catalogs by Lancon &amp; Wood (2000, A&amp;AS, 146,
217) and Pickles (1998, PASP, 110, 863) among others include the spectra
of dozens of stars covering an unprecedented wavelength range from
the optical to near-infrared. These observations include a wide range
of stellar temperatures, and many types of stars including some with
unusual chemical compositions. Such observations are a vast improvement
over previous "optical-only" or "infrared-only" spectra. Having good
observations with such a broad wavelength range make it possible to
better model the conditions of these stars. Carefully fitting the
effects of molecules such as H2O, CO, VO, and TiO in the
spectra of these stars is paramount in our effort to better understand
these stars. We show the results of PHOENIX (Hauschildt &amp; Baron,
1999, J. Comp. Appl. Math., 102, 41) stellar atmosphere models with
recent improvements in the TiO, H2O and a few other minor
molecular opacity sources. Models computed with different sources of
molecular opacity (H2O for example) show varying degrees of
accuracy of fit, although none of the sources given are perfect fits
to the observed spectral shape. Comparisons with the observations are
made and the resulting effective temperature/spectral class scale is
shown. Low temperature astrophysics at Wichita State University is
supported by NSF grant No. EPS-9874732 with matching support from
the State of Kansas, by a NASA EPSCoR grant NCC5-168 and NASA LTSA
grant NAG5-3435.

---------------------------------------------------------
Title: Stellar Atmospheres: Cool Stars
Authors: Hauschildt, P.
2001eaa..bookE2765H Altcode:
The term `cool stellar atmosphere' is generally applied to the
atmospheres of stars with effective temperatures less than that of
the Sun. In this spirit, this article describes the basic physics of
stellar and substellar atmospheres with effective temperatures below
about 5000 K. This category includes two common subclasses: dwarf
stars and giant stars. From the point of view of the STELLAR ATMO...

---------------------------------------------------------
Title: Infrared spectroscopy of substellar objects in Orion
Authors: Lucas, P. W.; Roche, P. F.; Allard, France; Hauschildt, P. H.
2001MNRAS.326..695L Altcode: 2001astro.ph..5154L
We present broad-band spectra of a sample of 21 low-luminosity
sources in the Trapezium cluster, with masses in the range
0.008-0.10Msolar (assuming an age of 1Myr). These were
selected for low extinction in most cases, and are located west of the
brighter nebulosity. The spectra are in the H bandpass (1.4-1.95μm)
and K bandpass (1.9-2.5μm) also for most of the brighter sources, with
a resolution of 50nm. They were taken with the United Kingdom Infrared
Telescope (UKIRT) using the CGS4 spectrometer. Absorption by water
vapour bands is detected in all the substellar candidates except one,
which is a highly reddened object with strong H2 emission
and an anomalously blue (I-J) colour, implying that it is a very young
cluster member with circumstellar matter. The observation of prominent
water vapour bands confirms the low effective temperatures implied
by our (I-J) colour measurements in an earlier paper, and would imply
late-M or L spectral types if these were older field dwarfs. However,
the profiles of the H-bandpass spectra are very different from those
of field dwarfs with similar water absorption strength, demonstrating
that they are not foreground or background objects. In addition,
the CO absorption bands at 2.3μm and the Nai absorption feature
at 2.21μm are very weak for such cool sources. All these features
are quite well reproduced by the AMES-Dusty-1999 model atmospheres
of Allard et al., and arise from the much lower gravities predicted
for the Trapezium sources (3.5&lt;logg&lt;4.0) compared to evolved
objects (logg~5.5). This represents a new proof of the substellar
status of our sources, independent of the statistical arguments for
low contamination, which are re-examined here. The very late spectral
types of the planetary mass objects and very low-mass brown dwarfs
demonstrate that they are cluster members, since they are too luminous
to be field dwarfs in the background. We also present additional UKIRT
photometry of a small region in the south of the Trapezium cluster
where the extinction and nebular brightness are low, which permitted the
detection of objects with 1-Myr masses slightly lower than our previous
least massive source at 8MJup. Following a minor update to
our previous J-band photometry, due to a new UKIRT filter calibration,
there are ~15 planetary mass candidates in the full data set.

---------------------------------------------------------
Title: Irradiated Planets
Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France
2001ApJ...556..885B Altcode: 2001astro.ph..4262B
We have modeled irradiated planets located near a dM5 and a G2 primary
star. The impinging radiation field was explicitly included in the
solution of the radiative transfer equation and in the computation
of the atmospheric structure. We find that large errors in both
the thermal and reflected flux will result from models that do not
include the impinging radiation in a self-consistent manner. A cool
(Teff=500 K) and a hot (Teff=1000 K) planet were
modeled at various orbital separations from both the dM5 star and the
G2 primary. In all scenarios, we compared the effects of the irradiation
in two extreme cases: one where dust clouds form and remain suspended in
the atmosphere and another where dust clouds form but completely settle
out of the atmosphere. The atmospheric structure and emergent spectrum
strongly depend on the presence or absence of dust clouds. We find that
in the absence of dust opacity, the impinging radiation significantly
alters the innermost layers of an extrasolar giant planet atmosphere and
that they are actually brighter in the optical than dusty planets. Our
models also indicate that the planet-to-star brightness ratio in the
optical will be less that 1×10-5 for objects like τ Bootis,
which is consistent with recently reported upper limit values.

---------------------------------------------------------
Title: Non-LTE Synthetic Spectral Fits to the Type Ia Supernova
1994D in NGC 4526
Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter H.
2001ApJ...557..266L Altcode: 2001astro.ph..4225L
We have fitted the normal, well-observed, Type Ia Supernova (SN Ia)
SN 1994D with non-LTE spectra of the deflagration model W7. We find
that well before maximum luminosity W7 fits the optical spectra of SN
1994D. After maximum brightness the quality of the fits weakens as the
spectrum forms in a core rich in iron-peak elements. We show the basic
structure of W7 is likely to be representative of the typical SN Ia. We
have shown that like W7, the typical SN Ia has a layer of unburned
C+O composition at v&gt;15000 km s-1, followed by layers
of C-burned and O-burned material with a density structure similar to
W7. We present UVOIR (UBVRIJKH) synthetic photometry and colors and
compare with observation. We have computed the distance to the host
galaxy, NGC 4526, obtaining a distance modulus of μ=30.8+/-0.3. We
discuss further application of this direct measurement of SNe Ia
distances. We also discuss some simple modifications to W7 that could
improve the quality of the fits to the observations.

---------------------------------------------------------
Title: 56Ni Mixing in the Outer Layers of SN 1987A
Authors: Mitchell, Robert C.; Baron, E.; Branch, David; Lundqvist,
Peter; Blinnikov, Sergei; Hauschildt, Peter H.; Pun, Chun S. J.
2001ApJ...556..979M Altcode: 2001astro.ph..4148M
Supernova 1987A remains the most well observed and well studied
supernova to date. Observations have produced excellent broadband
photometric and spectroscopic coverage over a wide wavelength
range at all epochs. Here we focus on the very early spectroscopic
observations. Only recently have numerical models been of sufficient
detail to accurately explain the observed spectra. In SN 1987A, good
agreement has been found between observed and synthetic spectra for
day 1, but by day 4, the predicted Balmer lines become much weaker
than the observed lines. We present the results of work based on a
radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic
non-LTE spectra generated from this model by the general radiation
transfer code PHOENIX strongly support the theory that significant
mixing of 56Ni into the outer envelope is required to
maintain strong Balmer lines. Preliminary results suggest a lower limit
to the average nickel mass of 1.0×10-5 Msolar
is required above 5000 km s-1 by day 4. PHOENIX models thus
have the potential to be a sensitive probe for nickel mixing in the
outer layers of a supernova.

---------------------------------------------------------
Title: Grains in the Atmospheres of Red Giant Stars
Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France;
Hauschildt, Peter H.
2001ApJ...557..798F Altcode:
Model atmospheres for cool giant stars are usually computed with
detailed equation of state and opacity calculations that include
many molecular species. We show that models of oxygen-rich stars with
effective temperatures below 3000 K must also include dust grains. The
effects of dust condensation in the equation of state and on the opacity
must be included to obtain accurate temperature structures and spectra.

---------------------------------------------------------
Title: Analysis of Keck HIRES Spectra of Early L-Type Dwarfs
Authors: Schweitzer, Andreas; Gizis, John E.; Hauschildt, Peter H.;
Allard, France; Reid, I. Neill
2001ApJ...555..368S Altcode: 2001astro.ph..3402S
We present analyses of high- and medium-resolution spectra of early L
dwarfs. We have used our latest set of model atmospheres to reproduce
and analyze the observed features. We can model the optical flux
and atomic line profiles with the best accuracy to date. The models
used to reproduce the observations include dust condensation and dust
opacities. Compared with previous studies using older models, we find
that our dust treatment is much improved. The derived parameters for
the objects are well in the expected range for old, very low mass
objects. This is also supported by the absence of Li in most of the
objects. For the objects showing Li, we can be almost certain they
are brown dwarfs. However, a spectral analysis in general, and this
one in particular, can only very roughly determine mass and age.

---------------------------------------------------------
Title: The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.;
Tamanai, Akemi; Schweitzer, Andreas
2001ApJ...556..357A Altcode: 2001astro.ph..4256A
We present opacity sampling model atmospheres, synthetic spectra, and
colors for brown dwarfs and very low mass stars in the following two
limiting cases of dust grain formation: (1) Inefficient gravitational
settling (i.e., the dust is distributed according to the chemical
equilibrium predictions) and (2) efficient gravitational settling
(i.e., the dust forms and depletes refractory elements from the gas,
but their opacity does not affect the thermal structure). The models
include the formation of over 600 gas-phase species and 1000 liquids and
crystals and the opacities of 30 different types of grains including
corundum (Al2O3), the magnesium aluminum spinel
MgAl2O4, iron, enstatite (MgSiO3),
forsterite (Mg2SiO4), amorphous carbon, SiC, and a
number of calcium silicates. The models extend from the beginning of the
grain formation regime well into the condensation regime of water ice
(Teff=3000-100 K) and encompass the range of logg=2.5-6.0 at
solar metallicity. We find that silicate dust grains can form abundantly
in the outer atmospheric layers of red and brown dwarfs with a spectral
type later than M8. The greenhouse effects of dust opacities provide a
natural explanation for the peculiarly red spectroscopic distribution
of the latest M dwarfs and young brown dwarfs. The grainless (cond)
models, on the other hand, correspond closely to methane brown dwarfs
such as Gliese 229B. We also discover that the λλ5891, 5897 Na I D
and λλ7687, 7701 K I resonance doublets play a critical role in T
dwarfs, in which their red wings define the pseudocontinuum from the
I to the Z bandpass.

---------------------------------------------------------
Title: Parallel Implementation of the PHOENIX Generalized Stellar
Atmosphere Program. III. A Parallel Algorithm for Direct Opacity
Sampling
Authors: Hauschildt, Peter H.; Lowenthal, David K.; Baron, E.
2001ApJS..134..323H Altcode: 2001astro.ph..4258H
We describe two parallel algorithms for line opacity calculations based
on a local file and on a global file approach. The performance and
scalability of both approaches is discussed for different test cases
and very different parallel computing systems. The results show that
a global file approach is more efficient on high-performance parallel
supercomputers with dedicated parallel I/O subsystem, whereas the
local file approach is very useful on farms of workstations, e.g.,
cheap PC clusters.

---------------------------------------------------------
Title: Radiative properties of magnetic elements. I. Why are vec
G-band bright points bright?
Authors: Steiner, O.; Hauschildt, P. H.; Bruls, J.
2001A&A...372L..13S Altcode:
Photospheric magnetic elements are most conspicuously visible in
high-resolution G-band filtergrams. We show that their enhanced
contrast in the G-band is due to a reduction of the CH abundance by
dissociation in the deep photospheric layers of the flux tube, where
it is hotter than in the surrounding atmosphere. As a consequence, the
CH-lines weaken, allowing more of the continuum to “shine” through
the forest of G-band CH-lines. We suggest that other molecular bands
or atomic lines may exhibit a similar behaviour.

---------------------------------------------------------
Title: The Extraordinary CHANDRA Light Curve of V1494 Aql
Authors: Starrfield, S.; Drake, J.; Wagner, R. M.; Butt, Y.;
Hauschildt, P. H.; Krautter, J.; Gehrz, R. D.; Woodward, C. E.;
Della Valle, M.; Orio, M.; Mukai, K.; Hernanz, M.; Truran, J. W.;
Evans, A. E.
2001AAS...198.1109S Altcode: 2001BAAS...33Q.804S
V1494 Aql (Nova Aql 1999 No. 2) was discovered on 2 December
1999. It reached Vmax ~4 making it the brightest nova in
the northern hemisphere since V1500 Cyg erupted in 1975. Our early
optical spectra showed that it was an “Fe II” class nova (Williams:
AJ, 104, 725, 1992). We activated our CHANDRA Target of Opportunity
proposal for bright novae in outburst and obtained ACIS-I spectra
on 15 April and 7 June 2000 which showed only emission lines. Our
third observation on 6 August showed that it had evolved to a sharp
“emission line” spectrum characteristic of a Super Soft X-ray Source
(peak ~ 0.5 keV). We obtained HRC-S+LETG spectra on 28 Sept. (8 ksec)
and 1 October (17 ksec). These spectra qualitatively resemble those
of CAL 83 obtained with XMM (Paerels, F., et al. 2001, A&amp;A, 365,
L308.). More exciting, we have analyzed the light curve of our grating
observations and find that there is a factor of 6 rise in counts near
the middle of the second observation which lasts about 1000 seconds
and has a complex structure. Our time series analyses of these data
show a 2500 sec periodicity that is not present in similar analyses of
the observations of HZ 43 or Sirius B. An analysis of our HRC-S+LETG
observation of V382 Vel (Nova Vel 1999) is in progress and further
analyses of these data are underway. We gratefully acknowledge partial
support from NASA CHANDRA grants to CFA, OSU, UGA, and ASU.

---------------------------------------------------------
Title: A Galactic Distance Scale Using Type-II Supernovae
Authors: Mitchell, R. C.; Baron, E.; Branch, D.; Lundqvist, P.;
Blinnikov, S. I.; Hauschildt, P. H.; Pun, C. S. J.
2001AAS...198.3904M Altcode: 2001BAAS...33..839M
Supernovae count among the most luminous phenomena in the universe,
and as such they have been long sought after to serve as cosmological
distance indicators. Type Ia supernova are currently the most favored,
since theoretically they are the most uniform in luminosity. Type II
supernovae, on the other hand, have a much larger variance in luminosity
and therefore cannot provide an accurate distance by photometry
alone. The Spectral-fitting Expanding Atmosphere Method (SEAM)
calculates the luminosity of a supernova by matching computer models of
the object's spectra to observed spectra, a feat that requires excellent
radiative-transfer and hydrodynamic models and an equally powerful and
accurate code. This study will introduce the program PHOENIX, and use
it to examine the SN 1987A hydrodynamic models of Sergei Blinnikov and
collaborators from Day 1 to Day 103. We will show that PHOENIX can be
used to assess the accuracy of hydrodynamic models of supernovae, and
to simulate their spectral evolution with unparalleled detail. With
PHOENIX, we will be able to determine the luminosity and distance to
Type II supernovae with remarkable precision. This work was supported
in part by NSF grant AST-9731450, NASA grant NAG5-3505, and an IBM SUR
grant to the University of Oklahoma. Some of the calculations presented
in this poster were performed at the San Diego Supercomputer Center
(SDSC), supported by the NSF, and at the National Energy Research
Supercomputer Center (NERSC), supported by the U.S. DOE. We thank both
these institutions for a generous allocation of computer time.

---------------------------------------------------------
Title: Solar Mn I 5432/5395 Å line formation explained
Authors: Doyle, J. G.; Jevremović, D.; Short, C. I.; Hauschildt,
P. H.; Livingston, W.; Vince, I.
2001A&A...369L..13D Altcode:
We present a solution for the long standing problem concerning the
“chromospheric” behaviour of the Mn i 5395/5432 Å lines in the
solar spectrum using multi-line/multi-species NLTE modelling. Using
comprehensive spectral line formation modelling, we show that the
Mn i lines are very sensitive to optical pumping in a transition
which overlaps with Mg ii k. It therefore follows that one has to be
careful with the choice of lines as temperature indicators and for
the determination of the Mn abundances although on the other hand,
due to the formation process of these lines they may be useful as a
solar and stellar activity diagnostic.

---------------------------------------------------------
Title: Hα Equivalent Width Variations across the Face of a
Microlensed K Giant in the Galactic Bulge
Authors: Albrow, M.; An, J.; Beaulieu, J. -P.; Caldwell, J. A. R.;
Dominik, M.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies,
J.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson,
R.; Williams, A.; PLANET Collaboration; Hauschildt, P. H.
2001ApJ...550L.173A Altcode: 2000astro.ph.11380A
We present Very Large Telescope FORS1 spectroscopy that temporally
resolves the second caustic crossing of the Galactic bulge K giant
source of microlensing event EROS 2000-BLG-5, the first time this has
been accomplished for several phases of a caustic transit. The ~1 Å Hα
equivalent width of the source star increases slightly as the center
of the star egresses the caustic and then plummets by 30% during the
final limb crossing. These changes are not seen in contemporaneous
spectra of control stars in the FORS1 slit but are qualitatively
consistent with expectations from stellar atmosphere models as the
caustic differentially magnifies different portions of the stellar face
of the target. Observations such as these in a variety of stellar lines
are equivalent to atmospheric tomography and are expected to provide
a direct test of stellar models. Based on observations at the
European Southern Observatory (programs 265.C-5728 and 265.C-5729).

---------------------------------------------------------
Title: Non-LTE Modeling of Nova Cygni 1992
Authors: Short, C. Ian; Hauschildt, Peter H.; Starrfield, S.; Baron, E.
2001ApJ...547.1057S Altcode: 2000astro.ph..9502S
We present a grid of nova models that have an extremely large number of
species treated in non-LTE and apply it to the analysis of an extensive
time series of ultraviolet spectroscopic data for Nova Cygni 1992. We
use ultraviolet colors to derive the time development of the effective
temperature of the expanding atmosphere during the fireball phase and
the first 10 days of the optically thick wind phase. We find that the
nova has a pure, optically thick wind spectrum until about 10 days
after the explosion. During this interval, we find that synthetic
spectra based on our derived temperature sequence agree very well with
the observed spectra. We find that a sequence of hydrogen-deficient
models provides an equally good fit, provided the model effective
temperature is shifted upward by ~1000 K. We find that high-resolution
UV spectra of the optically thick wind phase are fit moderately well
by the models. We find that a high-resolution spectrum of the fireball
phase is better fit by a model with a steep density gradient, similar
to that of a supernova, than by a nova model.

---------------------------------------------------------
Title: Infrared Spectra and Spectral Energy Distributions of Late
M and L Dwarfs
Authors: Leggett, S. K.; Allard, F.; Geballe, T. R.; Hauschildt,
P. H.; Schweitzer, Andreas
2001ApJ...548..908L Altcode: 2000astro.ph.10174L
We have obtained 1.0-2.5 μm spectra at R~600 of 14 disk dwarfs
with spectral types M6-L7. For four of the dwarfs, we have also
obtained infrared spectra at R~3000 in several narrow intervals. In
addition, we present new L' photometry for four of the dwarfs in
the sample, which allows improved determinations of their bolometric
luminosities. While obtaining the photometry we resolved the L dwarf
Denis-P J0205-1159 into an identical pair of objects separated by
0.35". The spectra together with the published energy distribution
for one other L5 dwarf are compared to synthetic spectra generated
by upgraded model atmospheres. Good matches are found for 2200
K&gt;=Teff&gt;=1900 K (spectral types around M9-L3),
but discrepancies exist at Teff&gt;=2300 K (M8) and
Teff&lt;=1800 K (L4-L7). At the higher temperatures the
mismatches are due to incompleteness in the water vapor opacity line
list. At the lower temperatures the disagreement is probably due
to our treatment of dust; we assume a photospheric distribution in
equilibrium with the gas phase and neglect any diffusion mechanisms. We
derive effective temperatures for the sample from the comparison with
synthetic spectra and also by comparing our observed total intrinsic
luminosities to structural model calculations (which are mostly
independent of the atmosphere but are dependent on the unknown masses
and ages of the targets). The two derivations agree to about 200 K
except for the faintest object in the sample, where the discrepancy
is larger. Agreement with other temperature determinations is also
+/-~200 K, except for the L7 dwarf.

---------------------------------------------------------
Title: Radiation-hydrodynamics Simulations of Surface Convection in
a Late M-dwarf
Authors: Ludwig, Hans-Günter; Hauschildt, Peter
2001AGM....18..P15L Altcode:
Based on detailed 2D and 3D numerical radiation hydrodynamics
calculations of time-dependent compressible convection, we have
studied the dynamics and thermal structure of the convective surface
layers of a prototypical late-type M-dwarf at Teff=2800 K,
and log g=5.0 with solar chemical composition. The thermal structure
of the atmosphere is dominated by molecular absorption, the formation
of dust grains is not important for the chosen model parameters. In
the multi dimensional models the radiative transfer is treated
by a multi-group (4 groups) approach which provides a simplified,
nevertheless rather realistic treatment of the complex radiative energy
transport. The equation of state includes the important contribution
of H2 molecule formation. Our models predict a convective
pattern at the surface of an late M-dwarf qualitatively similar to
solar granulation. Quantitatively, the convective turn-over timescale
amounts to ≈ 100 s, a typical horizontal scale of convective cells
to 80 km, and a relative intensity contrast of the granular pattern to
1.1 %. The efficiency of convective energy transport corresponds to
an effective mixing-length parameter between 1.5 to 2.1 depending on
the thermal property which is represented. The models provide mixing
timescales due to atmospheric overshoot which can be extrapolated to
lower effective temperatures where dust grains are present and mixed
into optically thin layers.

---------------------------------------------------------
Title: X-ray Pulsations and a “Burst” in the X-ray Light Curve of
Classical Nova V1494 Aql (1999 #2) in Outburst
Authors: Krautter, J.; Drake, J.; Starrfield, S.; Wagner, R. M.; Butt,
Y.; Bond, H. E.; della Valle, M.; Gehrz, R. D.; Woodward, C. E.; Evans,
A. E.; Orio, M.; Hauschildt, P.; Hernanz, M.; Mukai, K.; Truran, J. W.
2001AGM....18S0101K Altcode: 2001AGAb...18....5K
Nova V1494 Aql was discovered on Dec. 2, 1999. We activated our CHANDRA
T-o-O proposal for bright novae in outburst and obtained ACIS-I spectra
on Apr. 15 and Jun. 7, 2000, which showed only emission lines. Our third
observation on Aug. 6 found that it had evolved into that characteristic
of a Super Soft X-ray source (peak ~ 0.5 keV). We obtained HRC-S+LETG
spectra on 28 Sept. (8 ksec) and 1 October (17 ksec). These spectra
demonstrated that we were observing the atmosphere of a hot white dwarf
which was probably still undergoing nuclear hydrogen burning on top of
its surface. We analyzed the light curve of our grating observations
and found both a short time scale “burst” and periodic variations of
the count rate. Neither of these phenomena have ever been seen in the
light curve of a nova in outburst. The “burst” was a factor of 6 rise
in X-ray counts which lasted about 1000 sec and exhibited at least two
peaks plus other structure. Our time series analyses of the combined 25
ksec observation showed a peak at 2501.6 sec. Further analysis of the
V1494 Aql data found other periods present which implies that we were
observing non-radial g modes from the pulsating, rekindled white dwarf.

---------------------------------------------------------
Title: The Physics of Low-mass Stars and Substellar Objects. Galactic
Implications (CD-ROM Directory: contribs/chabrier)
Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H.
2001ASPC..223...49C Altcode: 2001csss...11...49C
No abstract at ADS

---------------------------------------------------------
Title: Effective Temperatures for Very Cool Objects, from Resonance
Lines of Cs I and Rb I (CD-ROM Directory: contribs/mohanty)
Authors: Mohanty, S.; Basri, G.; Allard, F.; Hauschildt, P. H.;
Delfosse, X.; Martín, E. L.; Forveille, T.; Goldman, B.
2001ASPC..223..838M Altcode: 2001csss...11..838M
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE Modeling of Nova Cygni 1992
Authors: Short, C. I.; Hauschildt, P. H.; Baron, E.
2001ASPC..231..548S Altcode: 2001gssi.conf..548S
No abstract at ADS

---------------------------------------------------------
Title: Multiwavelength analyses of the extraordinary nova LMC
1991*
Authors: Schwarz, Greg J.; Shore, S. N.; Starrfield, S.; Hauschildt,
Peter H.; Della Valle, M.; Baron, E.
2001MNRAS.320..103S Altcode:
LMC 91 was a very fast, classical nova and the brightest nova ever
observed in the Large Magellanic Cloud. It was extensively observed
during both its early optically thick and its nebular evolution in
the optical and UV wavelength regions. We successfully fit all the
optically thick spectra using a grid of spherically symmetric, non-LTE,
line-blanketed, expanding synthetic spectra created with the model
atmosphere code PHOENIX. The emission lines of the nebular spectra
have been fitted using an optimization technique for the emission-line
luminosities predicted by the photoionization code CLOUDY. Our analyses
show the following: the bolometric luminosity was super-Eddington before
visual maximum and reached LBolmax~6×105Lsolar,
the ejected mass was ~3×10-4Msolar, and
nuclear burning on the white dwarf ceased after ~100 days. The
elemental abundances (by number) with respect to solar of the ejecta
are He/H=0.8+/-0.2, C/H=5-2+2.5, N/H=85-17+22, O/H=6.5-1.5+2.5, and
all other elements ~0.1. These abundances were determined from both
the optically thick and nebular analyses. The extreme luminosity,
high ejected mass, rapid turn-off time, and low metallicity (except
for enhanced CNO) represent the extreme values of observational nova
parameters and thus present interesting challenges for understanding
the nature of the outburst of LMC 91.

---------------------------------------------------------
Title: Pre-Main Sequence Models for Low-Mass Stars and Brown Dwarfs
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P.
2001ASPC..243..571B Altcode: 2000astro.ph..7157B; 2001fdtl.conf..571B
We present evolutionary models for low mass stars and brown dwarfs
($m \le 1.2 \msol$) based on recent improvement of the theory:
equation of state, atmosphere models, ... We concentrate on early
evolutionary phases from the initial deuterium burning phase to the
zero-age Main Sequence. Evolutionary models for young brown dwarfs
are also presented. We discuss the uncertainties of the present
models. We analyse the difficulties arising when comparing models
with observations for very young objects, in particular concerning
the problem of reddening.

---------------------------------------------------------
Title: Pre-Main Sequence Models for Low-Mass Stars and Brown Dwarfs
Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France;
Hauschildt, Peter
2001IAUS..200..483B Altcode:
We present evolutionary models for young low mass stars (m &lt;=1
msol) based on recent improvement of the theory: equation of state,
atmosphere models, etc. We concentrate on early evolutionary
phases from the initial deuterium burning phase to the zero-age
Main Sequence. Evolutionary models for young brown dwarfs are also
presented. We discuss the uncertainties of the present models. We
analyse the difficulties arising when comparing models with observations
for very young objects, in particular concerning the problem of
reddening.

---------------------------------------------------------
Title: Why are G-Band Bright Points Bright?
Authors: Steiner, O.; Bruls, J.; Hauschildt, P. H.
2001ASPC..236..453S Altcode: 2001aspt.conf..453S
No abstract at ADS

---------------------------------------------------------
Title: Stellar Atmospheres
Authors: Hauschildt, P. H.; Allard, F.; Aufdenberg, J.; Barman, T.;
Schweitzer, A.; Baron, E.
2001ASPC..239..175H Altcode: 2001mlap.conf..175H
No abstract at ADS

---------------------------------------------------------
Title: Cool Stellar Atmospheres
Authors: Hauschildt, P.; Allard, France; Barman, Travis; Schweitzer,
Andreas; Baron, E.; Leggett, S. K.
2001ASPC..231..427H Altcode: 2001gssi.conf..427H
No abstract at ADS

---------------------------------------------------------
Title: Analysis of Type IIn SN 1998S: Effects of Circumstellar
Interaction on Observed Spectra
Authors: Lentz, Eric J.; Baron, E.; Lundqvist, Peter; Branch, David;
Hauschildt, Peter H.; Fransson, Claes; Garnavich, Peter; Bastian,
Nate; Filippenko, Alexei V.; Kirshner, R. P.; Challis, P. M.; Jha, S.;
Leibundgut, Bruno; McCray, R.; Michael, E.; Panagia, Nino; Phillips,
M. M.; Pun, C. S. J.; Schmidt, Brian; Sonneborn, George; Suntzeff,
N. B.; Wang, L.; Wheeler, J. C.
2001ApJ...547..406L Altcode: 2000astro.ph.10615L
We present spectral analysis of early observations of the Type IIn
supernova 1998S using the general non-local thermodynamic equilibrium
atmosphere code PHOENIX. We model both the underlying supernova spectrum
and the overlying circumstellar interaction region and produce spectra
in good agreement with observations. The early spectra are well fitted
by lines produced primarily in the circumstellar region itself, and
later spectra are due primarily to the supernova ejecta. Intermediate
spectra are affected by both regions. A mass-loss rate of order
M~0.0001-0.001 Msolar yr-1 is inferred for
a wind speed of 100-1000 km s-1. We discuss how future
self-consistent models will better clarify the underlying progenitor
structure.

---------------------------------------------------------
Title: Irradiated M Dwarfs
Authors: Barman, T. S.; Hauschildt, P. H.
2001ASPC..231..447B Altcode: 2001gssi.conf..447B
No abstract at ADS

---------------------------------------------------------
Title: Parallel Supercomputing In Stellar Atmosphere Simulations
Authors: Hauschildt, Peter H.; Lowenthal, David K.; Baron, E.;
Allard, France
2001ASPC..247..303H Altcode: 2001scpp.conf..303H
No abstract at ADS

---------------------------------------------------------
Title: Optically Thick Winds of Novae
Authors: Aufdenberg, J. P.; Hauschildt, Peter H.; Short, C. Ian;
Starrfield, Sumner G.
2001ASPC..231..539A Altcode: 2001gssi.conf..539A
No abstract at ADS

---------------------------------------------------------
Title: SN 1984A and Delayed-Detonation Models of Type IA Supernovae
Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter H.
2001ApJ...547..402L Altcode: 2000astro.ph..7302L
SN 1984A shows unusually large expansion velocities in lines from
freshly synthesized material, relative to typical Type Ia supernovae
(SNe Ia). SN 1984A is an example of a group of SNe Ia which have
very large blueshifts of the P Cygni features but otherwise normal
spectra. We have modeled several early spectra of SN 1984A with the
multipurpose non-LTE (NLTE) model atmosphere and spectrum synthesis code
PHOENIX. We have used as input two delayed-detonation models: CS15DD3
(Iwamoto et al.) and DD21c (Höflich, Wheeler, &amp; Thielemann). These
models show line-expansion velocities which are larger than that
for a typical deflagration model like W7, which we have previously
shown to fit the spectra of normal SNe Ia quite well. We find these
delayed-detonation models to be reasonable approximations to large
absorption feature blueshift SNe Ia, like SN 1984A. Higher densities
of newly synthesized intermediate-mass elements at higher velocities,
v&gt;15,000 km s-1, are found in delayed-detonation models
than in deflagration models. We find that this increase in density
at high velocities is responsible for the larger blueshifts in the
synthetic spectra. We show that the variations in line width in
observed SNe Ia are likely due to density variations in the outer,
high-velocity layers of their atmospheres.

---------------------------------------------------------
Title: Preliminary Spectral Analysis of the Type II Supernova 1999EM
Authors: Baron, E.; Branch, David; Hauschildt, Peter H.; Filippenko,
Alexei V.; Kirshner, R. P.; Challis, P. M.; Jha, S.; Chevalier, R.;
Fransson, Claes; Lundqvist, Peter; Garnavich, Peter; Leibundgut,
Bruno; McCray, R.; Michael, E.; Panagia, Nino; Phillips, M. M.; Pun,
C. S. J.; Schmidt, Brian; Sonneborn, George; Suntzeff, N. B.; Wang,
L.; Wheeler, J. C.
2000ApJ...545..444B Altcode: 2000astro.ph.10614B
We have calculated fast direct spectral model fits to two early-time
spectra of the Type II plateau SN 1999em, using the SYNOW synthetic
spectrum code. The first is an extremely early blue optical spectrum
and the second a combined Hubble Space Telescope and optical spectrum
obtained one week later. Spectroscopically this supernova appears to
be a normal Type II, and these fits are in excellent agreement with
the observed spectra. Our direct analysis suggests the presence of
enhanced nitrogen. We have further studied these spectra with the
full non-LTE general model atmosphere code PHOENIX. While we do not
find confirmation for enhanced nitrogen (nor do we rule it out),
we do require enhanced helium. An even more intriguing possible
line identification is complicated Balmer and He I lines, which we
show falls naturally out of the detailed calculations with a shallow
density gradient. We also show that very early spectra such as those
presented here combined with sophisticated spectral modeling allow an
independent estimate of the total reddening to the supernova, since when
the spectrum is very blue, dereddening leads to changes in the blue
flux that cannot be reproduced by altering the “temperature” of the
emitted radiation. These results are extremely encouraging since they
imply that detailed modeling of early spectra can shed light on both
the abundances and total extinction of SNe II, the latter improving
their utility and reliability as distance indicators.

---------------------------------------------------------
Title: Irradiated Planets
Authors: Barman, T. S.; Hauschildt, P. H.; Allard, F.
2000AAS...197.1110B Altcode: 2000BAAS...32.1418B
We have used our general atmosphere code PHOENIX (version 10.8) to
generate radiative equilibrium models of irradiated planets located near
a dM6 and a G2 primary. The external radiation, represented by synthetic
spectra from a previous set of PHOENIX model atmospheres, was explicitly
included in the solution of the radiative transfer equation. We do
not use precomputed, ad hoc, temperature-pressure profiles. A cool
({T eff} = 500 K) and a hot ({T eff} = 1000K)
planet were modeled at various orbital separations from both the
dM6 and the G2 primary. In all scenarios, we compared the effects of
the irradiation in two extreme cases: one where dust clouds form and
remain suspended in the atmosphere and another where dust clouds form
but completely settle out of the atmosphere. The atmospheric structure
and emergent spectrum strongly depend on the presence or absence of
dust clouds. Several models have also been computed by solving the
spherically symmetric radiative transfer equation instead of assuming
plane parallel geometry, as is usually done for EGPs. We find that
the plane parallel solution may, in some circumstances, significantly
underestimate the flux near the planetary limb and should, therefore,
be used with caution.

---------------------------------------------------------
Title: Sphericaly extended, massively non-LTE models of standard
red giant stars
Authors: Short, C. I.; Hauschildt, Peter
2000AAS...197.4401S Altcode: 2000BAAS...32.1471S
We present spherically extended atmospheric models of red giant standard
stars with all of the significant atomic opacity treated in direct
multi-level non-local thermodynamic equilibrium (NLTE). We compare
our synthetic flux distributions to the global energy distribution
and to the detailed shape of lines of the CO fundamental band for
several stars.

---------------------------------------------------------
Title: Grains in the Atmospheres of Late Type Stars
Authors: Alexander, D. R.; Ferguson, J. W.; Allard, France; Hauschildt,
P. H.
2000AAS...197.4409A Altcode: 2000BAAS...32.1473A
As part of a larger project to compute accurate model atmospheres for
cool giant stars (Hauschildt et al, ApJ, 525, 871, 1999), we have used
the PHOENIX program to compute models in spherical geometry with a
detailed treatment of both the equation of state and the opacity. The
equation of state includes atoms, molecules, and the condensation of
solid grains in thermodynamic equilibrium. Monochromatic atomic and
molecular opacities are included via the opacity sampling technique at
20,000 frequencies. The opacity of 26 grain species is computed using
the Mie theory. Despite the very low densities found in red giant
atmospheres, we find that models of oxygen-rich stars with effective
temperatures below 3000 K include dust grains. The presence of grains
in an atmosphere has two important consequences that are potentially
observable. First, the temperature of the surface layers of the
star is raised by the increased opacity of the grains, compared to
a model with identical parameters in which grain condensation is not
included. Second, the depletion of TiO molecules from the gas phase,
as titanium condenses into CaTiO3, reduces the strength of the visible
absorption features of TiO in the emergent spectra of the models. Low
temperature astrophysics at Wichita State University is supported by
NASA EPSCoR grant NCC5-168 and NASA LTSA grant NAG5-3435.

---------------------------------------------------------
Title: The use of the NextGen model atmospheres for cool giants in
a light curve synthesis code
Authors: Orosz, J. A.; Hauschildt, P. H.
2000A&A...364..265O Altcode: 2000astro.ph.10114O
We have written a light curve synthesis code that makes direct use of
model atmosphere specific intensities, in particular the NextGen model
atmosphere grid for cool giants (Teff&lt;= 6800 K and log
(g)&lt;= 3.5, Hauschildt et al. \cite{hauschildt99}). We point out
that these models (computed using spherical geometry) predict a limb
darkening behaviour that deviates significantly from a simple linear or
two-parameter law (there is less intensity at the limb of the star). The
presence of a significantly nonlinear limb darkening law has two main
consequences. First, the ellipsoidal light curve computed for a tidally
distorted giant using the NextGen intensities is in general different
from the light curve computed using the same geometry but with the black
body approximation and a one- or two-parameter limb darkening law. In
most cases the light curves computed with the NextGen intensities have
deeper minima than their black body counterparts. Thus the light curve
solutions for binaries with a giant component obtained with models with
near linear limb darkening (either black body or plane-parallel model
atmosphere intensities) are biased. Observations over a wide wavelength
range (i.e. both the optical and infrared) are particularly useful in
discriminating between models with nearly linear limb darkening and
the NextGen models. Second, we show that rotational broadening kernels
for Roche lobe filling (or nearly filling) giants can be significantly
different from analytic kernels due to a combination of the nonspherical
shape of the star and the radical departure from a simple limb darkening
law. As a result, geometrical information inferred from Vrot
sin i measurements of cool giants in binary systems are likewise biased.

---------------------------------------------------------
Title: Cosmological Measurements from Type II Supernovae with SNAP
Authors: Baron, E.; Branch, D.; Thomas, R.; Hauschildt, P.
2000AAS...197.6108B Altcode: 2000BAAS...32Q1505B
We discuss the exciting potential for using Type II supernova
spectra and photometry expected to be obtained with the proposed SNAP
satellite for determining cosmological parameters. Type II supernovae
provide an independent route to obtaining luminosity distances from
that of Type Ia supernovae, using most of the same photometry and
spectroscopy measurements that will be obtained by SNAP for the Type
Ia supernovae. The Type II method will allow us to derive cosmological
parameters based on completely different physics from that of the Type
Ia supernovae. Since the physics of a Type II supernova atmosphere
involves predominantly hydrogen and helium, evolutionary effects (such
as metallicity variations) can in fact be determined from comparison of
detailed models and observed spectra. Recent advances in computational
power allow us to determine the model parameters to higher accuracy
than was previously possible. We contrast the constraints on measurement
systematics using Type II and Type Ia supernovae as cosmological probes
and show that both supernova types should be aggressively pursued. This
research has been supported in part by the NSF, NASA, the U.S. DOE,
the IBM Corporation, and Research Systems Inc.

---------------------------------------------------------
Title: Deuterium Burning in Substellar Objects
Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P.
2000ApJ...542L.119C Altcode: 2000astro.ph..9174C
We consider the depletion of primordial deuterium in the interior of
substellar objects as a function of mass, age, and absolute magnitude in
several photometric passbands. We characterize potential spectroscopic
signatures of deuterium in the lines of deuterated water HDO. These
results will serve as a useful, independent diagnostic to characterize
the mass and/or the age of young substellar objects and to provide an
independent age determination of very young clusters. These results
can serve to identify objects at the deuterium-burning limit and to
confront the theoretical prediction that D burning is a necessary
condition to form starlike objects.

---------------------------------------------------------
Title: Non-LTE Treatment of Molecules in the Photospheres of Cool
Stars
Authors: Schweitzer, Andreas; Hauschildt, Peter H.; Baron, E.
2000ApJ...541.1004S Altcode: 2000astro.ph..6049S
We present a technique to treat systems with very many levels,
such as molecules, in non-LTE. This method is based on a superlevel
formalism coupled with rate operator splitting. Superlevels consist of
many individual levels that are assumed to be in LTE relative to each
other. The usage of superlevels reduces the dimensionality of the rate
equations dramatically and, thereby, makes the problem computationally
more easily treatable. Our superlevel formalism retains maximum accuracy
by using direct opacity sampling (dOS) when calculating the radiative
transitions and the opacities. We developed this method in order to
treat molecules in cool dwarf model calculations in non-LTE. Cool
dwarfs have low electron densities and radiation fields that are
far from blackbody radiation fields; both properties may disqualify
them from the common LTE approximation. Therefore, the most important
opacity sources, the molecules, need to be treated in non-LTE. As a
case study we applied our method to carbon monoxide. We find that our
method gives accurate results since the conditions for the superlevel
method are very well met for molecules. Because of very high collisional
cross sections with hydrogen and the high densities of H2,
the population of CO itself shows no significant deviation from LTE.

---------------------------------------------------------
Title: CHANDRA and HST/STIS Observations of V382 Vel (1999) and
V1494 Aql (1999)
Authors: Starrfield, S.; Shore, S. N.; Butt, Y.; Drake, J.; Bond,
H. E.; Downes, R.; Krautter, J.; Wagner, R. M.; Gehrz, R. D.; Woodward,
C. E.; Della Valle, M.; Hauschildt, P. H.; Truran, J. W.
2000HEAD....5.4103S Altcode: 2000BAAS...32R1253S
V382 Vel was discovered on May 22, 1999 and reached a Vmax
brighter than 3 making it the brightest nova since V1500 Cyg in 1975. We
observed it with HST/STIS three times during Summer 1999 and activated
our CHANDRA Target of Opportunity program in early Fall 1999. Our first
ACIS-I observation was on December 30, 1999 and we obtained an HRC+LETG
spectrum on February 14, 2000. This nova is known to be an ONeMg nova
and the grating spectrum showed lines of O VII and VIII, N VI and VII,
Ne IX and X, and Mg XI plus other lines. We obtained two more ACIS-I
spectra, one in April 2000 and one in August 2000. We shall show the
results of these observations plus our inferences with respect to the
hard component seen in the ROSAT observations of V1974 Cyg (Krautter et
al. ApJ, 456, 788, 1996) and other novae. V1494 Aql was discovered in
outburst on December 1, 1999 and reached a Vmax of ~5. Our
first CHANDRA ACIS - I observation was in April 2000. We obtained 2
more ACIS-I observations in June and August 2000. At this time, an
HRC+LETG spectrum is planned for late September 2000. We will also
present our available data on this nova. We gratefully acknowledge
partial support from NASA, NSF, STScI, CHANDRA, and DOE grants to our
various institutions.

---------------------------------------------------------
Title: Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs
with Dusty Atmospheres
Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P.
2000ApJ...542..464C Altcode: 2000astro.ph..5557C
We present evolutionary calculations for very low-mass stars and
brown dwarfs based on synthetic spectra and nongray atmosphere
models which include dust formation and opacity, i.e., objects
with Teff&lt;~2800 K. The interior of the most massive
brown dwarfs is shown to develop a conductive core after ~2 Gyr
which slows down their cooling. Comparison is made in optical
and infrared color-magnitude diagrams with recent late-M and L
dwarf observations. The saturation in optical colors and the very
red near-infrared colors of these objects are well explained by the
onset of dust formation in the atmosphere. Comparison of the faintest
presently observed L dwarfs with these dusty evolutionary models
suggests that dynamical processes such as turbulent diffusion and
gravitational settling are taking place near the photosphere. As the
effective temperature decreases below Teff~1300-1400 K,
the colors of these objects move to very blue near-infrared colors,
a consequence of the ongoing methane absorption in the infrared. We
suggest the possibility of a brown dwarf dearth in J, H, and K
color-magnitude diagrams around this temperature.

---------------------------------------------------------
Title: TiO and H2O Absorption Lines in Cool Stellar
Atmospheres
Authors: Allard, France; Hauschildt, Peter H.; Schwenke, David
2000ApJ...540.1005A Altcode: 2000astro.ph..8465A
We compare the structures of model atmospheres and synthetic spectra
calculated using different line lists for TiO and water vapor. We
discuss the effects of different line list combinations on the model
structures and spectra for both dwarf and giant stars. It is shown
that recent improvements result in significantly improved spectra,
in particular, in the optical where TiO bands are important. The
water vapor-dominated near-infrared region remains problematic as the
current water line lists do not yet completely reproduce the shapes
of the observed spectra. We find that the AMES TiO list provides more
opacity in most bands and that the new, smaller oscillator strengths
lead to systematically cooler temperatures for early-type M dwarfs than
previous models. These effects combine and will help to significantly
improve the fits of models to observations in the optical as well as
result in improved synthetic photometry of M stars. We show that the
Davis, Littleton, &amp; Phillips fel-values for the δ and
ϕ bands of TiO best reproduce the observed V-I color indices.

---------------------------------------------------------
Title: Nova in the Large Magellanic Cloud 2000
Authors: Shore, S. N.; Starrfield, S.; Bond, H. E.; Downes, R.;
Hauschildt, P. H.; Gehrz, R. D.; Woodward, C. E.; Krautter, J.; Evans,
A. N.
2000IAUC.7486....1S Altcode: 2000IAUC.7486Q...1S; 2000IAUC.7486A...1S
S. N. Shore, Indiana University, South Bend; S. Starrfield, Arizona
State University; H. E. Bond and R. Downes, Space Telescope Science
Institute; P. H. Hauschildt, University of Georgia; R. D. Gehrz and
C. E. Woodward, University of Minnesota; J. Krautter, Landessternwarte,
Heidelberg; and A. N. Evans, Keele University, write: "We observed
this nova (cf. IAUC 7457, 7458) with the Hubble Space Telescope's
Imaging Spectrograph (STIS) on Aug. 19.7 and Aug. 20.9 UT using the
medium-resolution echelle gratings (E140M and E230M). Three spectra
were obtained, centered at 142.5, 197.8, and 270.7 nm with resolutions
of about 45 000 (E140M) and 30 000 (E230M). Weak iron-peak absorption
may still be present, especially from 155.0 to 156.5 nm. The spectrum
strongly resembles that of V382 Vel obtained 2 months after visual
maximum (IAUC 7261) but with much stronger Ly-alpha and Si III]
189.5-nm and C III] 191.0-nm emission, with Si III]/C III] about
2. Strong C IV P-Cyg absorption is seen with a terminal velocity of
2000 km/s, similar to the FWHM velocity for the emission lines. The
following strong emission lines have been detected: C III 107.6-nm,
N V 124.0-nm, N III/O III 126.7-nm, O I 130.4-nm, C II 133.4-nm, Si
IV/O IV] 140.0- nm, C IV 155.0-nm, He II 164.0-nm, O III] 166.7-nm,
N III] 175.0-nm, Si II 181.6-nm, Al III 186.0-nm, Si III] 189.5-nm,
C III] 191.0-nm, N II] 214.5-nm, C II 232.1-nm, Al II 267.2-nm, and Mg
II 280.0-nm. Unusual features of the spectrum are the absence of N IV]
at 148.6 and 171.8 nm and the presence of strong Ly-alpha emission at a
time when He II 164.0-nm is also strong, but the Ly-alpha in this nova
is stronger due to lower interstellar absorption. Most emission profiles
show fine structure consistent with knots of the sort detected in HST
spectra of V1974 Cyg and V382 Vel. A strong interstellar absorption
line spectrum is present, showing Si II/S II 126.0-nm, Si IV 140.0-nm,
C IV 155.0-nm, Al II 167.1-nm, Al III 186.0-nm, and Fe II 260.0-nm with
Galactic and LMC components (+250 km/s) clearly resolved. The integrated
flux from 115.0 to 312.0 nm was 8.6 x 10**-11 erg cm**-2 s**-1 [or 5.6
x 10**-10 erg cm**-2 s**-1, corrected for LMC reddening with E(B-V) =
0.2]. For a distance of 50 kpc, this corresponds to 4.1 x 10**4 solar
luminosities. In view of the similarity of the spectra, these data yield
a probable distance for V382 Vel of 3000 pc, assuming its reddening
is E(B-V) = 0.2. A further STIS observation is planned for mid-Nov.,
and continued groundbased monitoring at all wavelengths is urged."

---------------------------------------------------------
Title: Spherically Symmetric Model Atmospheres for Low-Mass
Pre-Main-Sequence Stars with Effective Temperatures between 2000
and 6800 K
Authors: Allard, France; Hauschildt, Peter H.; Schweitzer, Andreas
2000ApJ...539..366A Altcode: 2000astro.ph..8464A
We present a grid of spherically symmetric model atmospheres
for young pre-MS stars. This grid spans the parameter range 2000
K&lt;=Teff&lt;=6800 K and 2.0&lt;=logg&lt;=3.5 for M=0.1
Msolar, appropriate for low-mass stars and brown dwarfs. A
major improvement is the replacement of TiO and H2O line
lists with the newer line list, calculated by the NASA-Ames group, for
TiO (about 175 million lines of five isotopes) and for H2O
(about 350 million lines in two isotopes). We provide the model
structures, spectra, and broadband colors in standard filters in
electronic form.

---------------------------------------------------------
Title: A Grid of Non-LTE Model Atmospheres for White Dwarfs in
Cataclysmic Variables
Authors: Barman, Travis S.; Hauschildt, Peter H.; Short, C. Ian;
Baron, E.
2000ApJ...537..946B Altcode:
We have calculated a grid of non-LTE (NLTE) line-blanketed model
atmospheres for white dwarfs in cataclysmic variable (CV) systems using
our stellar atmosphere code PHOENIX. The grid covers the temperature
range 20,000-500,000 K for solar abundances and 10-2
and 10-4 solar metal abundance. The effective temperature
resolution is 10,000 K in the range 20,000-200,000 K and is 20,000
K in the range 200,000-500,000 K. The models include a large number
of NLTE levels for light metals such as CNO and heavy metals such as
Ni and Fe. The necessity of using self-consistent NLTE line-blanketed
model atmospheres for the analysis of white dwarfs is well known and
reaffirmed here. We discuss the importance of metal opacity, especially
metals heavier than Ca, in the atmospheres of CV primaries. We also
compare our grid to previously published models and discuss the general
improvements offered by our models. In addition, a specific model
from our grid is compared to a Hubble Space Telescope observation of U
Gem and predictions for Far-Ultraviolet Spectroscopic Explorer (FUSE)
observations are made.

---------------------------------------------------------
Title: An Effective Temperature Scale for Late-M and L Dwarfs,
from Resonance Absorption Lines of Cs I and Rb I
Authors: Basri, Gibor; Mohanty, Subhanjoy; Allard, France; Hauschildt,
Peter H.; Delfosse, Xavier; Martín, Eduardo L.; Forveille, Thierry;
Goldman, Bertrand
2000ApJ...538..363B Altcode: 2000astro.ph..3033B
We present Keck HIRES spectra of six late-M dwarfs and 11 L dwarfs. Our
goal is to assign effective temperatures to the objects using detailed
atmospheric models and fine analysis of the alkali resonance absorption
lines of Cs I and Rb I. These yield mutually consistent results (+/-50
K) when we use “cleared-dust” models, which account for the removal
of refractory species from the molecular states but do not include dust
opacities. We find a tendency for the Rb I line to imply a slightly
higher temperature, which we ascribe to an incomplete treatment of
the overlying molecular opacities. The final Teff we adopt
are based on the Cs I fits alone, though the Rb I fits support the Cs
I temperature sequence. This work, in combination with results from
the infrared, hints that dust in these atmospheres has settled out of
the high atmosphere but is present in the deep photosphere. We also
derive radial and rotational velocities for all the objects, finding
that the previously discovered trend of rapid rotation for very low
mass objects is quite pervasive. To improve on our analysis, there
is a clear need for better molecular line lists and a more detailed
understanding of dust formation and dynamics.

---------------------------------------------------------
Title: Spectral Energy Distributions for Disk and Halo M Dwarfs
Authors: Leggett, S. K.; Allard, F.; Dahn, Conard; Hauschildt, P. H.;
Kerr, T. H.; Rayner, J.
2000ApJ...535..965L Altcode: 2000astro.ph..1100L
We have obtained infrared (1-2.5 μm) spectroscopy for 42 halo and disk
dwarfs with spectral types M1-M6.5. These data are compared to synthetic
spectra generated by the latest model atmospheres of Allard &amp;
Hauschildt. Photospheric parameters metallicity, effective temperature,
and radius are determined for the sample.We find good agreement between
observation and theory except for known problems due to incomplete
molecular data for metal hydrides and H2O. The metal-poor
M subdwarfs are well matched by the models, as oxide opacity sources
are less important in this case. The derived effective temperatures
for the sample range from 3600 to 2600 K; at these temperatures grain
formation and extinction are not significant in the photosphere. The
derived metallicities range from solar to 1/10 solar. The radii and
effective temperatures derived agree well with recent models of low-mass
stars. The spectra are available in electronic form upon request.

---------------------------------------------------------
Title: Diffusion in the Atmospheres of Blue Horizontal-Branch Stars
Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H.
2000ApJ...535L..43H Altcode:
We investigate the effects of diffusion in the atmospheres of hot
horizontal-branch stars using a model atmosphere code including
diffusion self-consistently. Equilibrium stratifications (i.e., for
which the diffusion velocity equals zero in each layer) are computed
for models of effective temperatures between 10,000 and 25,000 K. The
stratified models provide much better agreement with many observational
features [jump in the (u, u-y) color-magnitude diagram, gaps, lower
spectroscopic gravities] in comparison with classical horizontal-branch
models. The observed abundance anomalies are also consistent with the
amounts that can be supported in the atmospheres.

---------------------------------------------------------
Title: Metallicity Effects in Non-LTE Model Atmospheres of Type
IA Supernovae
Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter
H.; Nugent, Peter E.
2000ApJ...530..966L Altcode: 1999astro.ph..6016L
We have calculated a grid of photospheric phase atmospheres of Type Ia
supernovae (SNe Ia) with metallicities from 10 times to 1/30 the solar
metallicity in the C+O layer of the deflagration model, W7. We have
modeled the spectra using the multipurpose non-LTE model atmosphere
and spectrum synthesis code PHOENIX. We show models for the epochs 7,
10, 15, 20, and 35 days after explosion. When compared to observed
spectra obtained at the approximately corresponding epochs, these
synthetic spectra fit reasonably well. The spectra show variation in
the overall level of the UV continuum with lower fluxes for models with
higher metallicity in the unburned C+O layer. This is consistent with
the classical surface cooling and line-blocking effect due to metals
in the outer layers of C+O. The UV features also move consistently to
the blue with higher metallicity, demonstrating that they are forming
at shallower and faster layers in the atmosphere. The potentially
most useful effect is the blueward movement of the Si II feature at
6150 Å with increasing C+O layer metallicity. We also demonstrate
the more complex effects of metallicity variations by modifying
the 54Fe content of the incomplete burning zone in W7 at
maximum light. We briefly address some shortcomings of the W7 model
when compared to observations. Finally, we identify that the split
in the Ca H+K feature produced in W7 and observed in some SNe Ia is
due to a blending effect of Ca II and Si II and does not necessarily
represent a complex abundance or ionization effect in Ca II.

---------------------------------------------------------
Title: Modelling the M-S-C Giants Spectral Sequence
Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.;
Cohen, Martin; Augason, Gordon C.
2000IAUS..177..517A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Theoretical Models for Substellar Objects (Contributed Talk)
Authors: González, J. -F.; Allard, F.; Baraffe, I.; Chabrier, G.;
Hauschildt, P. H.
2000ASPC..219..486G Altcode: 2000dpp..conf..486G
No abstract at ADS

---------------------------------------------------------
Title: High Resolution Spectra of L Type Stars and Brown Dwarfs
Authors: Basri, G.; Allard, F.; Hauschildt, P.; Mohanty, S.
2000vlms.conf..133B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model Atmospheres and Spectra of Brown Dwarfs to Giant Planets
Authors: Allard, F.; Hauschildt, P. H.; Alexander, D. R.; Ferguson,
J. W.; Tamanai, A.
2000ASPC..212..127A Altcode: 2000fgpc.conf..127A
No abstract at ADS

---------------------------------------------------------
Title: Evolution of Low-Mass Stars and Substellar
Objects. Contribution to the Galactic Mass Budget
Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H.
2000fepc.conf..399C Altcode: 1999astro.ph..5210C
We briefly summarize our present knowledge of the theory of low-mass
stars and substellar objects and their contribution to the Galactic
population.

---------------------------------------------------------
Title: Self-consistent model atmospheres including diffusion
Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H.
2000IAUJD...5E..22H Altcode:
We present a new development of the multipurpose model atmosphere
code PHOENIX which includes self-consistently the effects of
diffusion. Following the approach used for the resolution of the
radiative tranfer, the radiative accelerations of each element are
calculated by the opacity sampling method. The mutual influence
of abundance variations among the different elements is therefore
considered. We compute equilibrium stratifications (i. e. those for
which the diffusion velocity equals zero in each layer) for each
element, that is, the amount that can be supported by the radiative
accelerations. We will compare our results with observations of
Chemically Peculiar stars. In particular, we will show that there is
a much better agreement between our models and the photometry of blue
Horizontal-Branch (HB) stars in comparison with canonical HB models.

---------------------------------------------------------
Title: The multiple system LHS 1070: a case study for the onset of
dust formation in the atmospheres of very low mass stars
Authors: Leinert, Christoph; Allard, France; Richichi, Andrea;
Hauschildt, Peter H.
2000A&A...353..691L Altcode:
<ASTROBJ>LHS 1070</ASTROBJ> (other common name: <ASTROBJ>GJ
2005</ASTROBJ>) is a nearby multiple system consisting of very low
mass red dwarfs. We present the results of WFPC2 photometry and FOS
spectroscopy for the three optically resolved components of this system
acquired during HST cycle 5. These show (1) absolute brightnesses
corresponding to theoretical masses of 0.080-0.083 Msun
and 0.079-0.080 Msun for the faint pair, depending mainly on
their age and metallicity; (2) a saturation of the optical TiO and VO
absorption bands typical of the onset of photospheric dust formation,
and (3) emission lines typical of moderate chromospheric activity in
only the two most massive components. Li I lines are not seen. But also
all other lines of the alkali elements are remakably weak or even absent
in the two faint companions B and C. This appears to be an effect of
dust formation. Comparison of the observations with model spectra,
which account for dust formation and for the resulting opacities,
yields good agreement for solar metallicity and effective temperatures
and gravities (in log cm/s2) of 2950 K;5.3, 2400 K;5.5
and 2300 K;5.5 for the three components A,B and C, respectively. The
existence of a fourth component, recently discovered in this system by
HST Fine Guidance Sensor observations (Henry et al. \cite{henry99}),
has already been taken into account in the evaluation of the data
for the main component. An effective temperature and gravity (in log
cm/s2) for the fourth component of 2500 K;5.3 would best
be compatible with our data. Then, based on our analysis the three
components C, B and D of LHS 1070, in this order, are the faintest
stars within 20 pc of the Sun for which dynamical determinations of
mass appear possible within a decade. The system LHS 1070 thus has the
potential to be the most important source of information for probing
the low mass end of the main sequence. Based on observations with the
Hubble Space Telescope, with additional observations obtained on the
ESO-MPIA 2.2 m telescope on La Silla, Chile.

---------------------------------------------------------
Title: Ni56 Mixing in the Early Expansion Phase of SN 1987A
Authors: Mitchell, R. C.; Baron, E.; Branch, D.; Lundqvist, P.;
Blinnikov, S. I.; Hauschildt, P. H.
1999AAS...195.4305M Altcode: 1999BAAS...31.1432M
Supernova 1987A provided excellent broad-band photometry and
spectroscopic coverage over a wide wavelength range. It is particularly
well studied in the very early days of a supernova expansion. It
is only in recent years that models of the expanding envelope of a
supernova have been of sufficient detail to accurately explain the
observed spectra. Good agreements have been found between observed
and synthetic spectra for day one, but by day four, substantial
discrepancies have been observed. Schmutz et al. (1990), using various
hydrodynamic models, noted that observed Balmer lines were much stronger
than predicted, despite the fact that the photospheric temperature had
dropped below the ionization threshold. Takeda (1991), using a pure
H/He steady-state envelope model in non-LTE, also noted the weakness of
the theoretical Balmer lines. We present the results of work based on
a radiation-hydrodynamic model by Blinnikov et al. (1999). Synthetic
non-LTE spectra generated from this model by the general radiation
transfer code PHOENIX strongly support the theory that significant
mixing of Ni56 into the outer envelope is required to
maintain strong Balmer lines through day four. Preliminary results
suggest an average nickel mass of 10-8 to 10-7
solar masses mixed above the line forming region at day four. Once
the entire time series has been successfully modeled, we will be
able to calculate an accurate distance to SN 1987A. This work was
supported in part by NSF grants AST-9731450 and AST-9417102, NASA grant
NAG5-3505, and an IBM SUR grant to the University of Oklahoma. Some of
the calculations presented in this poster were performed at the San
Diego Supercomputer Center (SDSC), supported by the NSF, and at the
National Energy Research Supercomputer Center (NERSC), supported by the
U.S. DOE. We thank both these institutions for a generous allocation
of computer time.

---------------------------------------------------------
Title: Non-LTE Line-blanketed Stellar Wind Atmosphere Models for
the A-supergiant Deneb
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
1999AAS...195.5001A Altcode: 1999BAAS...31.1446A
We present non-LTE metal line-blanketed stellar wind atmosphere
models and synthetic spectra for comparison with the spectral
energy distribution of the A-supergiant Deneb from UV to radio
wavelengths. Deneb is alone among A-supergiants in having both a
precisely measured angular diameter from the Navy Prototype Optical
Interferometer (Nordgren, T. et al., 1999, priv. comm.) and a positive
detection at centimeter wavelengths with the Very Large Array (Howarth,
I., 1999, priv. comm.). These recent measurements together with our
wind atmosphere models considerably improve constraints on Deneb's
fundamental stellar and wind parameters. Using the precise angular
diameter we are able to use the Barnes-Evans relationship to constrain
the reddening toward Deneb independent of any assumptions about its
intrinsic colors. Our models treat the hydrostatic inner atmosphere
and the extended expanding outer atmosphere as a unified structure
and the radiative transfer is solved in the co-moving frame. We
present synthetic radio spectra for the partially ionized winds of
A-supergiants over a range of mass-loss rates and we find that the
standard assumptions regarding the radio spectra of warm supergiants
break down for A-supergiants. By simultaneously fitting the UV,
optical, IR and radio spectrophotometry we are able to constrain the
mass-loss rate and temperature distribution throughout the extended
atmosphere. Stability of the deep hydrostatic layers against outward
acceleration provides a lower limit on gravitational acceleration
in these layers. This work was supported in part by an Arizona State
University NASA Space Grant Fellowship and CNRS, NSF, and NASA grants
to the University of Georgia. Some calculations were performed on the
IBM SP and the SGI Origin 2000 of the UGA UCNS and on the IBM SP at
SDSC and on the Cray T3E of the NERSC.

---------------------------------------------------------
Title: The Binary L-Dwarf DENIS-P J0205-1159
Authors: Leggett, S. K.; Allard, F.; Geballe, T. R.; Hauschildt, P. H.
1999AAS...19510902L Altcode: 1999BAAS...31R1533L
We report the confirmation of another identical-pair small-separation
binary L-dwarf in imaging JHKL' data taken with the TUFTI camera on
UKIRT. We place the system in physical context within a sample of
nine M9-L7 dwarfs using low (R 600) and medium (R 3000) resolution
infrared spectroscopy, obtained with CGS4 on UKIRT, to constrain
the most recent models by Allard and Hauschildt. We derive effective
temperature, gravity and metallicity. The new models include improved
linelists for titanium oxide, iron hydride and water. The effect of
dust condensation and extinction is treated in a detailed way using
models which include clouds. Metallicity effects are also considered.

---------------------------------------------------------
Title: Nova V382 Velorum: first Hubble Space Telescope spectrum and
NLTE atmospheric modeling
Authors: Short, C. I.; Hauschildt, P. H.; Shore, S. N.; Starrfield,
S.; Baron, E.
1999AAS...195.3606S Altcode: 1999BAAS...31.1420S
We present the initial fitting of non-LTE nova models to the first
ultraviolet spectra of Nova V382 Velorum taken with the Hubble Space
Telescope Imaging Spectrograph. We find a best fit T
eff of 19 000 K and that the velocity field is better described by a
radiatively driven wind law rather than that of ballistic expansion. We
find that by the time that the first HST spectrum was taken at May
31.3 UT, which was eight days after visual maximum, the region around
the Mg II hk lines already exhibited strong nebular emission on top of
the optically thick envelope spectrum. However, at shorter wavelengths
the spectrum still corresponds to the optically thick wind phase of
the nova outburst, and we are able to identify the P-Cyg profiles of
the Al III λ 1855 and 1863 lines. This work was supported in part by
NSF grant AST-9720704, NASA ATP grant NAG 5-3018 and LTSA grant NAG
5-3619 to the University of Georgia.

---------------------------------------------------------
Title: Treatment of molecular non--LTE in cool stellar atmospheres
Authors: Schweitzer, A.; Hauschildt, P.
1999AAS...195.5003S Altcode: 1999BAAS...31.1447S
We developed a technique to treat huge systems like molecules
in non--LTE. This technique is based on the superlevel
formalism. Superlevels consist of many individual levels that are
assumed to be in LTE. The usage of superlevels reduces the size
of the rate equations and the number of rates dramatically and,
thereby, makes the problem computationally feasible. Our superlevel
formalism retains maximum accuracy by using direct opacity sampling
(dOS) when calculating the radiative transitions. We implemented
this method in our current model atmospheres for cool dwarfs. Cool
dwarfs have low electron densities and a radiation field that is
far from a black body. Both properties invalidate the conditions for
the common LTE approximation. Therefore, we need to treat the huge
molecular systems in non--LTE. As a case study we applied our method
on carbon monoxide. We find that our method gives accurate results
since the conditions for the superlevel method are very well met for
molecules. The test molecule CO shows significant deviations from LTE
in the outer regions of cool photospheres.

---------------------------------------------------------
Title: Spectral Models of the Type IC Supernova SN 1994I in M51
Authors: Baron, E.; Branch, David; Hauschildt, Peter H.; Filippenko,
Alexei V.; Kirshner, R. P.
1999ApJ...527..739B Altcode: 1999astro.ph..7172B
We present detailed non-LTE (NLTE) synthetic spectra for comparison
with a time series of observed optical spectra of the Type Ic supernova
SN 1994I which occurred in M51. With the exceptions of Si I and S I,
we treat the important species in the formation of the spectrum in
full NLTE. We present results for both a hydrodynamic model that has
been fitted to the light curve and for an illustrative custom-crafted
model that is more massive. Both models give reasonable fits to the
overall observed spectra; however, neither is able to reproduce all the
observed features. Some conspicuous observed features are absent, and
some predicted features are unobserved. No model that we have explored
is able to reproduce satisfactorily the observed infrared feature
near 1 μm on 1994 April 15 (+7 days), which has been attributed to
the triplet He I λ10830 transition. The low-mass hydrodynamic model
produces an infrared feature with a blend of He I, C I, O I, and Si I-Si
II lines, but it predicts a strong unobserved absorption feature near
6100 Å due to Fe III, and the observed feature just blueward of 6000
Å most likely due to Na D is not reproduced. The more massive model
does a better job of reproducing the observed infrared line shape,
but also predicts the unobserved feature near 6100 Å. The early-time
spectrum of the low-mass model is far too blue; thus, a more massive
model may be slightly favored. Since the predicted infrared feature is
produced by a blend of so many elements, and there is no overwhelming
evidence for other helium features such as λ5876, it may be premature
to conclude that SNe Ic unambiguously contain helium. Thus, we conclude
that pure C + O cores are still viable progenitors for SNe Ic.

---------------------------------------------------------
Title: SN 1984A and Delayed Detonation Models of Type Ia Supernovae
Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H.
1999AAS...195.3807L Altcode: 1999BAAS...31.1424L
Supernova SN 1984A shows unusually large expansion velocities in
lines from freshly synthesized material, relative to typical Type Ia
supernovae (SNe Ia). SN 1984A represents an extreme example of SNe
Ia with large expansion velocities, but otherwise normal spectra. We
have modeled several early spectra of SN 1984A with the multi-purpose
NLTE model atmosphere and spectrum synthesis code, PHOENIX. We have
used as input two delayed detonation models, DD21c (Höflich et
al. 1998) and CS15DD3 (Iwamoto et al. 1999). These models show line
expansion velocities which are larger than for typical deflagration
models like W7 (Nomoto et al. 1984, Thielemann et al. 1986), which
we have previously shown to fit normal SNe Ia quite well (Lentz et
al. 2000). Higher densities of newly synthesized material from burning
at higher velocities are found in delayed detonation models than in
deflagration models. We find these delayed detonation models to be
reasonable approximations to high expansion velocity SNe Ia like SN
1984A. Even if the explosion mechanism of the delayed detonation models
is incorrect, the density of synthesized material at high velocities
is of the right magnitude.

---------------------------------------------------------
Title: The NEXTGEN Model Atmosphere Grid. II. Spherically Symmetric
Model Atmospheres for Giant Stars with Effective Temperatures between
3000 and 6800 K
Authors: Hauschildt, Peter H.; Allard, France; Ferguson, Jason; Baron,
E.; Alexander, David R.
1999ApJ...525..871H Altcode: 1999astro.ph..7194H
We present the extension of our NextGen model atmosphere grid to the
regime of giant stars. The input physics of the models presented here
is nearly identical to that of the NextGen dwarf atmosphere models;
however, spherical geometry is used self-consistently in the model
calculations (including the radiative transfer). We revisit the
discussion of the effects of spherical geometry on the structure of
the atmospheres and the emitted spectra and discuss the results of
non-LTE calculations for a few selected models.

---------------------------------------------------------
Title: Massive Multispecies, Multilevel Non-LTE Model Atmospheres
for Novae in Outburst
Authors: Short, C. Ian; Hauschildt, Peter H.; Baron, E.
1999ApJ...525..375S Altcode: 1999astro.ph..6238S
We have used our PHOENIX multipurpose model atmosphere code to
calculate atmospheric models that represent novae in the optically
thick wind phases of their outburst. We have improved the treatment
of non-local thermodynamic equilibrium (NLTE) effects by expanding
the number of elements that are included in the calculations from
15 to 19 and the number of ionization stages from 36 to 87. The code
can now treat a total of 10,713 levels and 102,646 lines in NLTE. Al,
P, K, and Ni are included for the first time in the NLTE treatment,
and most elements now have at least the lowest six ionization stages
included in the NLTE calculation. We have investigated the effects of
expanded NLTE treatment on the chemical concentration of astrophysically
significant species in the atmosphere, the equilibrium structure of the
atmosphere, and the emergent flux distribution. Although we have found
general qualitative agreement with previous, more limited NLTE models,
the expanded NLTE treatment leads to significantly different values
for the size of many of the NLTE deviations. In particular, for the
hottest model presented here (Teff=35,000 K), for which NLTE
effects are largest, we find that the expanded NLTE treatment reduces
the NLTE effects for these important variables: H I concentration,
pressure structure, and emergent far-UV flux. Moreover, we find that
the addition of new NLTE species may greatly affect the concentration
of species that were already treated in NLTE, so that, generally, all
species that contribute significantly to the e- reservoir
or to the total opacity, or whose line spectrum overlaps or interlocks
with that of a species of interest, must be treated in NLTE to ensure
an accurate result for any particular species.

---------------------------------------------------------
Title: Numerical solution of the expanding stellar atmosphere problem.
Authors: Hauschildt, P. H.; Baron, E.
1999JCoAM.109...41H Altcode: 1998astro.ph..8182H
The authors discuss numerical methods and algorithms for the solution
of NLTE stellar atmosphere problems involving expanding atmospheres,
e.g., found in novae, supernovae and stellar winds. They show how a
scheme of nested iterations can be used to reduce the high dimension
of the problem to a number of problems with smaller dimensions. As
examples of these sub-problems, they discuss the numerical solution
of the radiative transfer equation for relativistically expanding
media with spherical symmetry, the solution of the multi-level nonLTE
statistical equilibrium problem for extremely large model atoms, and
their temperature correction procedure. Although modern iteration
schemes are very efficient, parallel algorithms are essential in
making large-scale calculations feasible, therefore they discuss some
parallelization schemes that they have developed.

---------------------------------------------------------
Title: Nova Sagittarii 1994 1 (V4332 Sagittarii): The Discovery and
Evolution of an Unusual Luminous Red Variable Star
Authors: Martini, Paul; Wagner, R. Mark; Tomaney, Austin; Rich,
R. Michael; della Valle, M.; Hauschildt, Peter H.
1999AJ....118.1034M Altcode: 1999astro.ph..5016M
We report photometry and spectroscopy of the evolution of Nova
Sagittarii 1994 1 (V4332 Sagittarii) during outburst. We compare the
photometric and spectral evolution of this outburst with known classes
of outbursts-including classical novae and outbursts occurring on
symbiotic stars-and find this object does not conform to any known class
of outburst. The closest match to the behavior of this unusual object
is M31 RV, an extremely luminous and red variable object discovered in
the bulge of M31 in 1988. However, the temporal behavior and maximum
luminosity of the two events differ by several orders of magnitude,
requiring substantial intrinsic variation if these two events are
members the same type of outburst. Our model of the spectroscopic
evolution of this outburst shows that the effective temperature cooled
from 4400 to 2300 K over the 3 month span of our observations. In
combination with line diagnostics in our later spectra, including
[O I] lambda5577 and the dramatic increase in the Hα-to-Hβ ratio,
we infer the existence of a cool, dense (N_e~10^8-10^9 cm^-3) envelope
that is optically thick in the hydrogen Balmer recombination lines
(case C). We suggest that a nuclear event in a single star, in which
a slow shock drove the photosphere outward, can power the observed
luminosity evolution and the emission spectrum.

---------------------------------------------------------
Title: Barnes-Evans relations for late-type giants and dwarfs
Authors: Beuermann, K.; Baraffe, I.; Hauschildt, P.
1999A&A...348..524B Altcode: 1999astro.ph..6350B
The visual surface brightness of K/M giants and dwarfs with near-solar
metallicity differ slightly in agreement with the gravity effects
predicted by recent theoretical models. We show that M-dwarfs display
also a metallicity dependence of the surface brightness in the infrared
K-band in agreement with theory. Based on these results, we present
improved Barnes-Evans type relations and estimate the radii of 60
single or presumed M and K-dwarfs.

---------------------------------------------------------
Title: High-resolution spectroscopy of ROSAT-discovered weak-line
T Tauri stars near Lupus
Authors: Wichmann, R.; Covino, E.; Alcalá, J. M.; Krautter, J.;
Allain, S.; Hauschildt, P. H.
1999MNRAS.307..909W Altcode:
We present high-resolution optical echelle spectroscopy for a
large fraction of the Li-rich late-type stars recently discovered
in the vicinity of the Lupus dark clouds. Our results confirm
the high Liilambda6708 equivalent widths previously estimated from
medium-resolution spectra, thus adding strength to the conclusion that
the large majority of these stars are still in the pre-main-sequence
phase of their evolution, contrary to claims from other authors
that many of them might be zero-age main-sequence stars. We present
a statistical approach to derive a mean distance for the sample,
and find that it is consistent with, or slightly lower than, the
Hipparcos distance of the Lupus star-forming region. The radial
velocities measured for part of these stars are consistent with
those observed for the Lupus star-forming region, while stars outside
the dark clouds show a mean difference of the order of 3kms^-1. The
projected rotational velocities show a lack of slow rotators, which is
interpreted as a consequence of the X-ray selection of the sample. The
Li-rich stars in Lupus studied in this work yield a fairly `clean'
sample of very young stars, while in other star-forming regions a
larger fraction of older zero-age main-sequence stars has been found
among ROSAT-discovered Li-rich stars. We argue that this fact reflects
the relation of these stars with the Gould Belt.

---------------------------------------------------------
Title: On the abundance of lithium in T Coronae Borealis
Authors: Shahbaz, T.; Hauschildt, P. H.; Naylor, T.; Ringwald, F.
1999MNRAS.306..675S Altcode: 1999astro.ph..2225S
We have obtained high-resolution echelle spectroscopy of the recurrent
nova T CrB. We find that the surface lithium abundance in T CrB
is significantly enhanced compared with the case of field M giants,
where it is not detectable. We offer possible explanations for this in
terms of either a delay in the onset of convection in the giant star,
enhanced coronal activity caused by star-spots or the enhancement of
Li resulting from the nova explosion(s).

---------------------------------------------------------
Title: Model Atmospheres of Hot Luminous Stars with Winds
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
1999AAS...194.1304A Altcode: 1999BAAS...31..845A
We present preliminary atmospheric structures and synthetic spectra
for hot luminous OB stars with winds. We use the latest version of our
multi-purpose stellar atmosphere and radiative transfer code PHOENIX. In
these steady-state expanding model atmospheres, we assume a beta-law
velocity structure for the wind and solve the spherical co-moving frame
radiative transfer equation with full non-LTE metal-line blanketing. In
these models the solution of the radiation transfer equation treats
both the static photosphere and the expanding wind components as a
single structure. The temperature structure is solved for iteratively
by satisfying energy conservation. These models provide predictions
for the ionization structure within the wind and allow us to calculate
synthetic spectra which include the extreme ultraviolet ionizing flux
distribution and detailed line profiles. We acknowledge partial support
from NASA and NSF grants to our respective institutions.

---------------------------------------------------------
Title: Metallicity Effects in NLTE Model Atmospheres of Type IA
Supernovae
Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H.;
Nugent, P. E.
1999AAS...194.8606L Altcode: 1999BAAS...31R.976L
We have calculated a grid of photospheric phase atmospheres of Type
Ia supernovae (SNe Ia) with metallicities from ten times to one
thirtieth the normal metallicity in the C+O layer of the deflagration
model, W7 (Nomoto et al. 1984, Thielemann et al. 1986). We have
modeled the spectra using the multi-purpose NLTE model-atmosphere and
spectrum-synthesis code, PHOENIX. We show models for the epochs 7, 10,
15, 20, and 35 days after explosion. When compared to approximately
corresponding spectra observed at epochs -12, -9, -4, 0, and 15 days
after peak B magnitude, these synthetic spectra fit reasonably well. The
spectra show a consistent variation in the overall level of the UV
`contiunuum' with higher fluxes for models with lower metallicity in the
unburned C+O layer. The models show higher temperatures in the outer
layers of C+O with lower metallicity and less surface cooling from
the metals. The UV features also move consistently to the blue with
higher metallicity demonstrating that they are forming at shallower
and faster layers in the atmosphere. The last, and potentially most
useful, effect is the blueward movement of the Si II feature at 6150
Angstroms with increasing C+O layer metallicity. We also demonstrate
the more complex effects of modifying the (54) Fe content of the
incomplete burning zone in W7 at maximum light. We discuss effects
of the results on the use of SNe Ia for cosmology. We briefly address
some shortcomings of the W7 model when compared to observations.

---------------------------------------------------------
Title: Period-luminosity-color-radius relationships of Cepheids as
a function of metallicity: evolutionary effects
Authors: Alibert, Yann; Baraffe, Isabelle; Hauschildt, Peter; Allard,
France
1999A&A...344..551A Altcode: 1999astro.ph..1294A
Based on consistent evolutionary and pulsation calculations,
we analyse the effect of metallicity and of different convection
treatments in the stellar models on period-magnitude, -color and
-radius relationships. In order to perform an accurate comparison
with observations, we have computed grids of atmosphere models and
synthetic spectra for different metallicities, covering the range
of effective temperatures and gravities relevant for Cepheids. The
models are compared to recent observations of galactic and Magellanic
Clouds Cepheids. Unprecedented level of agreement is found between
models and observations. We show that within the range of metallicity
for the Galaxy and the Magellanic Clouds, a change of slope in the
period-luminosity (PL) relationship is predicted at low periods, due
to the reduction of the blue loop during core He burning. The minimum
mass undergoing a blue loop and consequently the critical period at
which this change of slope occurs depend on the metallicity Z and on
the convection treatment in the stellar models. However, besides this
change of slope, we do not find any significant effect of metallicity on
period-magnitude relationships from V to K bands, and on period-color
relationships in IR colors. We only find a detectable effect of Z on
(B-V) colors. These results are not affected by uncertainties inherent
in current stellar models, mainly due to convection treatment.

---------------------------------------------------------
Title: On the primordial helium abundance and spectroscopic
uncertainties.
Authors: Pistinner, S. L.; Hauschildt, P. H.; Eichler, D.; Baron, E.
1999PhR...311..151P Altcode:
To assess the uncertainties in primordial helium abundance determination
by nebular codes, the authors calculate a grid of OB stellar atmospheres
at low metallicities, including both non-local thermodynamic equilibrium
(NLTE) and metal line blanketing effects. The more sophisticated stellar
atmosphere models one uses can differ from LTE models by as much as 40%
in the ratio of He to H-ionizing photons.

---------------------------------------------------------
Title: ISO observations of XX Oph
Authors: Evans, A.; Eyres, S. P. S.; Hauschildt, P. H.; Allard, F.
1999ESASP.427..305E Altcode: 1999usis.conf..305E
We present ISO SWS and PHOT-P observations of the binary XX Oph. The
UIR features seen in ground-based data are confirmed. The near
infrared is modelled by a 3400 K log g=3.5 giant, which is likely
to be underabundant in carbon. There is an infrared excess at long
wavelengths, corresponding to emission by dust having temperature 336
K and β-index 0.4.

---------------------------------------------------------
Title: The NextGen Model Atmosphere Grid for
3000&lt;=Teff&lt;=10,000 K
Authors: Hauschildt, Peter H.; Allard, France; Baron, E.
1999ApJ...512..377H Altcode: 1998astro.ph..7286H
We present our NextGen Model Atmosphere grid for low-mass stars
for effective temperatures larger than 3000 K. These LTE models are
calculated with the same basic model assumptions and input physics
as the VLMS part of the NextGen grid so that the complete grid can
be used, e.g., for consistent stellar evolution calculations and for
internally consistent analysis of cool star spectra. This grid is also
the starting point for a large grid of detailed NLTE model atmospheres
for dwarfs and giants. The models were calculated from 3000 to 10,000
K (in steps of 200 K) for 3.5&lt;=logg&lt;=5.5 (in steps of 0.5) and
metallicities of -4.0&lt;=[M/H]&lt;=0.0. We discuss the results of
the model calculations and compare our results to the Kurucz grid. Some
comparisons to standard stars like Vega and the Sun are presented and
compared with detailed NLTE calculations.

---------------------------------------------------------
Title: Spectroscopy of low-metallicity giant HII regions: a grid of
low-metallicity stellar atmospheres
Authors: Pistinner, S. L.; Hauschildt, P. H.; Eichler, D.; Baron, E. A.
1999MNRAS.302..684P Altcode: 1998astro.ph.11021P
We calculate a grid of spherically symmetric OB stellar atmospheres at
low metallicities, including both non-local thermodynamic equilibrium
(NLTE) and metal line blanketing effects. This is done to assess the
uncertainties in helium abundance determination by nebular codes due
to input stellar atmosphere models. The more sophisticated stellar
atmosphere models we use can differ from LTE models by as much as 40
per cent in the ratio of He to H ionizing photons.

---------------------------------------------------------
Title: A Grid of White Dwarf NLTE Model Atmospheres
Authors: Barman, T. S.; Hauschildt, P. H.; Baron, E.; Short, C. I.
1999AAS...19312410B Altcode: 1999BAAS...31S.669B
We have calculated a grid of White Dwarf NLTE line blanketed model
atmospheres using the stellar atmosphere code PHOENIX. The grid covers
the temperature range 20,000K to 500,000K and is complete for solar
abundance, 10-2 and 10-4 solar abundance. The
grid has a temperature resolution of 10,000K in the range of 20,000K
to 200,000K and a resolution of 20,000K in the range of 200,000K to
500,000K. The models include a large number of NLTE levels and lines
for H, He, C, N and O as well as Si, S, and Fe. The necessity of using
self-consistent NLTE line blanketed model atmospheres for the analysis
of White Dwarfs is well known. Our new grid makes the most detailed
state-of-the-art calculations available for both reevaluating current
data and for the study of data yet to be acquired(e.g., by AXAF and
FUSE). Our models will be useful, for example, in spectral analysis
of hot PG 1159 type stars, determining metal abundances in hot DA
and DB White Dwarfs, as well as studying the evolution of novae,
and cataclysmic variables.

---------------------------------------------------------
Title: Effective Temperature Scales of Red Giants Stars
Authors: Alexander, D. R.; Ferguson, J. W.; Wing, R. F.; Johnson,
H. R.; Hauschildt, P. H.; Allard, F.
1999IAUS..191...84A Altcode:
We have completed a grid of spherically symmetric AGB star atmospheres
using the state of the art spectral synthesis code PHOENIX. Models
are constructed for stars with masses of 1 Msun and 1.5
Msun, spanning the range 10 to 3,300 Lsun in
luminosity and 2,500 to 5,200 K in effective temperature. We find
that grains of Al2O 3 and CaTiO3
among other species form in atmospheres cooler than Teff
=~ 3,000 K. In the coolest models the grains cause a weakening of
the TiO absorption features in the red and near infrared of up to 30%
through both a depression of the continuum and a depletion of the TiO
number abundance. We use spectrophotometric observations from a number
of catalogs to determine effective temperature - spectral class and
effective temperature - color relationships. We also compare synthetic
colors calculated from our models with observations of M giants on
Wing's 8-color narrow-band system of classification photometry.

---------------------------------------------------------
Title: The Properties of Novae in the LMC and Beyond
Authors: Starrfield, S.; Vanlandingham, K. M.; Schwarz, G. J.;
Hauschildt, P. H.; Shore, S. N.; Sonneborn, G.
1999ASPC..164..131S Altcode: 1999uosa.conf..131S
No abstract at ADS

---------------------------------------------------------
Title: A non-local thermodynamic equilibrium spherical line-blanketed
stellar atmosphere model of the early B giant beta CMa
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
1999MNRAS.302..599A Altcode:
The observed multiwavelength spectrum of the B1II--III star beta CMa
is successfully reproduced, including the extreme ultraviolet (EUV)
continuum observed by Extreme Ultraviolet Explorer (EUVE), with a
non-local thermodynamic equilibrium fully line-blanketed spherical
hydrostatic model atmosphere. The available spectrophotometry of beta
CMa from 500 A to 25 mu m is best fitted with model parameters T_eff
= 24000 K, log g = 3.5 and an angular diameter of theta_LD = 0.565
mas. We find that a neutral interstellar hydrogen column of N(H^0)
~= 2 x 10^18 cm^-2 provides the best agreement between the model EUV
flux and that observed by EUVE. We use model atmosphere fits together
with Hipparcos distances to calculate radii, luminosities and ionizing
fluxes for beta CMa and alpha Vir. An investigation of spherical and
plane-parallel models shows that the Lyman continuum predictions are
quite sensitive to model geometry and surface gravity between effective
temperatures 18 000 and 33 000 K. This result provides an explanation
for the reported excesses between the observed EUV fluxes from beta
CMa and epsilon CMa and plane-parallel model atmosphere predictions.

---------------------------------------------------------
Title: Model Atmospheres for Novae in Outburst: Summary of Research
Authors: Hauschildt, Peter H.
1999STIN...0030685H Altcode:
This paper presents a final report and summary of research on Model
Atmospheres for Novae in Outburst. Some of the topics include: 1)
Detailed NLTE (non-local thermodynamic equilibrium) Model Atmospheres
for Novae during Outburst: II. Modeling optical and ultraviolet
observations of Nova LMC 1988 #1; 2) A Non-LTE Line-Blanketed Stellar
Atmosphere Model of the Early B Giant epsilon CMa; 3) Spectroscopy
of Low Metallicity Stellar atmospheres; 4) Infrared Colors at the
Stellar/Substellar Boundary; 5) On the abundance of Lithium in T CrB;
6) Numerical Solution of the Expanding Stellar Atmosphere Problem;
and 7) The NextGen Model Atmosphere grid for 3000 less than or equal
to T eff less than or equal to 10000K.

---------------------------------------------------------
Title: Analyses of the LMC Novae
Authors: Vanlandingham, K. M.; Schwarz, G. J.; Starrfield, S.;
Hauschildt, P. H.; Shore, S. N.; Sonneborn, G.
1999IAUS..190..391V Altcode: 1998IAUS..190E.141V
In the past 10 years, 6 classical novae have been observed in the
Large Magellanic Cloud (LMC). We have begun a study of these objects
using ultraviolet spectra obtained by IUE and optical spectra from
nova surveys. We are using the results of this study to further our
understanding of novae and stellar evolution. Our study includes
analysis of both the early, optically thick spectra using model
atmospheres, and the later nebular spectra using optimization
of photoionization codes. By analysing of all the LMC novae in a
consistent manner, we can compare their individual results and use
their combined properties to calibrate Galactic novae. In addition,
our studies can be used to determine the elemental abundances of the
nova ejecta, the amount of mass ejected, and the contribution of novae
to the ISM abundances. To date we have analyzed Nova LMC 1988#1 and
Nova LMC 1990#1, and have obtained preliminary results for Nova LMC
1991. The results of this work are presented in this poster. The metal
content of the LMC is known to be sub-solar and varies as a function
of location within the cloud. A detailed abundance analysis of the
ejecta of the LMC novae provides important information concerning
the effect of initial metal abundances on energetics of the nova
outburst. Since the distance to the LMC is well known, many important
parameters of the outburst, such as the luminosity, can be absolutely
determined. Both galactic and extragalactic novae have been proposed
as potential standard candles. Recent work by Della Valle &amp; Livio
(1995) has improved on the standard relations (e.g., Schmidt 1957;
Pfau 1976; Cohen 1985; Livio 1992) by including novae from the LMC and
M31. Unfortunately, the dependence of the nova outburst on metallicity
has not been well-studied. Recent theoretical work by Starrfield et
al. (1998) indicates that the luminosity of the outburst increases with
decreasing metal abundances. If there is a dependence of luminosity
on metallicity, it will have to be determined before novae can be used
as standard candles.

---------------------------------------------------------
Title: Observations of the Polar ST Leonis Minoris during an Extreme
Low State: Identification of the Secondary Star
Authors: Ciardi, David R.; Howell, Steve B.; Dhillon, V. S.; Wagner,
R. Mark; Hauschildt, Peter H.; Allard, France
1999ASPC..157..146C Altcode: 1999mcv..work..146C
We present near-infrared (1.85-2.47 micron) spectroscopic observations
of the polar ST Leonis Minoris (ST LMi) in an extreme low-state. The
near-infrared spectra, showing no emission lines whatsoever, are
produced solely by the secondary star. We have fit the average spectrum
with a series of stellar atmosphere models and found the secondary star
to have an average temperature of 2800 plus or minus 100 K. However,
the phase-resolved spectra show a strong variation in the near-infrared
spectra as a function of orbital phase, corresponding to a variation
in the surface temperature of the star, ranging from about 3100 K to
2700 K.

---------------------------------------------------------
Title: Spectroscopy of L- and M- Dwarfs
Authors: Leggett, S. K.; Allard, F. A.; Dahn, C. C.; Hauschildt,
P. H.; Rayner, J.
1998AAS...193.9805L Altcode: 1998BAAS...30.1394L
We have obtained infrared (1-2.5 microns) spectroscopy for 54 halo
and disk stars around the stellar/substellar boundary. These data are
combined with optical data where available and compared to synthetic
spectra generated by the latest model atmospheres of Allard &amp;
Hauschildt. We find good agreement between observation and theory except
for known problems in the V and H passbands probably due to incomplete
molecular data for TiO, metal hydrides and H_2O. The metal-poor M
subdwarfs are well matched by the models as oxide opacity sources are
less important in this case. A version of the NextGen-Dusty models
which includes homogeneous formation and extinction by dust grains
produces a much improved match to the coolest objects in the sample,
compared to the grainless models. Photospheric parameters - metallicity,
effective temperature, radius - are determined for the sample. We
present relationships between bolometric correction and color, and
effective temperature and color, as a function of metallicity, and
compare the radii and effective temperatures to recent structural
models of low mass stars and brown dwarfs.

---------------------------------------------------------
Title: Infrared Colors at the Stellar/Substellar Boundary
Authors: Leggett, S. K.; Allard, F.; Hauschildt, P. H.
1998ApJ...509..836L Altcode: 1998astro.ph..7255L
We present new infrared JHK photometry for 61 halo and disk stars around
the stellar/substellar boundary. We also present new L' photometry
for 21 of these stars and for 40 low-mass stars taken from the Leggett
photometry compilation. These data are combined with available optical
photometry and astrometric data to produce color-color and absolute
magnitude-color diagrams; the current sample extends the similar
work presented in the 1992 paper into more metal-poor and lower mass
regimes. The disk and halo sequences are compared to the predictions
of the latest model atmospheres and structural models. We find good
agreement between observation and theory except for known problems
in the V and H passbands, probably due to incomplete molecular
data for TiO, metal hydrides, and H2O. The metal-poor M
subdwarfs are well matched by the models since oxide opacity sources
are less important in this case. The known extreme M subdwarfs have
metallicities about one-hundredth solar, and the coolest subdwarfs
have Teff ~ 3000 K with masses ~0.09M/M⊙. The
grainless models are not able to reproduce the flux distributions of
disk objects with Teff &lt; 2500 K; however, a preliminary
version of the NextGen-Dusty models that includes homogeneous formation
and extinction by dust grains is able to match the colors of these
very cool objects. The least luminous objects in this sample are
GD 165B, three DENIS objects--DBD 0205, DBD 1058, and DBD 1228--and
Kelu-1. These have Teff ~ 2000 K and are at or below the
stellar limit with masses &lt;=0.075M/M⊙. Photometry alone
cannot constrain these parameters further since the age is unknown,
but published lithium detections for two of these objects (Kelu-1 and
DBD 1228) imply that they are young (aged about 1 Gyr) and substellar
(mass &lt;= 0.06M/M⊙).

---------------------------------------------------------
Title: The Lyman Continuum of O stars From Hydrostatic Spherical
Non-LTE Line-Blanketed Model Atmospheres
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
1998AAS...193.4408A Altcode: 1998BAAS...30.1316A
We have used the parallelized version of the stellar atmosphere
and radiative transfer code PHOENIX to compute a set of 45 non-local
thermodynamic equilibrium (NLTE) stellar atmosphere models and synthetic
spectra corresponding to O stars. These hydrostatic models are computed
with spherical geometry treating the ~ 5000 levels of H I, He I-II,
C I-IV, N I-VI, O I-VI, Mg II, Ca II, Ne I, S II-III, Si II-III and
Fe I-III in NLTE. In addition, approximately 5 million background
LTE lines are included in the total line-blanketing. For this set of
models, we use a solar metal abundance. We compare the ionizing Lyman
continuum fluxes from this set of models to published values from LTE
plane-parallel static models. We find our non-LTE spherical models
consistently predict larger Lyman continuum fluxes relative to earlier
models. Our models predict up to 20% more hydrogen ionizing flux and up
to 125% more neutral helium ionizing flux compared to earlier models,
particularly for model O stars with Teff &lt; 36,000 K.

---------------------------------------------------------
Title: Multiwavelength observations of nova LMC 1991 during
pre-maximum
Authors: Schwarz, G. J.; Starrfield, S.; Hauschildt, P. H.; Shore,
S. N.
1998AAS...19310108S Altcode: 1998BAAS...30R1400S
Nova LMC 1991 (hereafter LMC 91) was the intrisically most luminous
nova, and one of the fastest (t_3 = 6 +/- 1 days), yet observed. It
was discovered on 18.3 April, 1991 (Liller, IAUC 5244) at m_v = 12,
although UK Schmidt J (4000 - 5400 Angstroms) plates show that LMC 91
steadily increased in brightness from a possible pre-outburst magnitude
of mV ~ 20.5 in early April. It reached m_V(max) ~ 9 on 24
April. The slow rise to maximum was very unusual, showing behavior
more closely resembling a slow nova. The combination of the rapid
discovery announcement and a very slow pre-maximum rise permitted
many IUE and optical observations. The 20.0 April optical spectrum
showed strong hydrogen and iron multiplet P Cygni lines; most other
novae with pre-maximum spectra (with the exception of DQ Her) show
only blue shifted absorption lines. The IUE spectrum on that date, the
earliest UV spectrum ever obtained of a nova in outburst, showed the
bulk of the flux being emitted below 2300 Angstroms. By 22.8 April,
the UV spectral peak had shifted to lambda &gt; 2500 Angstroms and
the spectrum was similar to the pre-maximum spectra seen in Nova Cyg
1992. The best agreement between the observations and the synthetic
spectra (calculated with spherical, NLTE, line-blanketed PHOENIX model
atmospheres) requires a metallicity Z = 0.1Zsun. This is
significantly lower metallicity than the canonical LMC value of 1/3
used to successfully model nova LMC 1988 #1 (Schwarz et al. 1998,
MNRAS, in press). The extreme brightness and low metallicity of LMC
91 may confirm recent hydrodynamic calculations that metallicity
is inversely correlates with luminosity if mixing occurs during the
thermonuclear runaway (Starrfield et al. 1998, MNRAS, 296, 502).

---------------------------------------------------------
Title: Spectral Analysis of Circumstellar Wind Interaction in the
Type IIn Supernova 1998S
Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H.;
Fransson, C.; Lundqvist, P.; Garnavich, P. M.; Kirshner, R. P.;
SINS Team
1998AAS...193.4708L Altcode: 1998BAAS...30.1324L
We analyze the effects of circumstellar interaction on spectra of
the Type IIn supernova 1998S obtained from the ground and with the
HST by the SINS team. The narrow ( ~ 100 - 1000 km s(-1) ) UV and
Balmer lines are assumed to come from a thin circumstellar shell,
and the broad ( ~ 5000 - 10,000 km s(-1) ), shallow features must
have formed in the supernova. We have modeled the spectra using the
general NLTE model-atmosphere and spectrum-synthesis code, PHOENIX. We
find general agreement between observations and the model results,
however, our models fail to reproduce the strong UV excess. The UV
excess can be probably be explained by adding inverse Comptonization
of the photospheric photons in the hot shocked gas in the interaction
region between ejecta and the wind. A large mass loss rate seems to be
needed. We have also explored the effects of external illumination from
the shocks on the ejecta, and we find this to be important. We predict
that SN 1998S will be a strong radio source, and that it should soon
turn on at short radio wavelengths.

---------------------------------------------------------
Title: Massive multi-species, multi-level, non-LTE modeling of
stellar atmospheres
Authors: Short, C. I.; Hauschildt, P. H.
1998AAS...193.4401S Altcode: 1998BAAS...30R1315S
We have incorporated into the phoenix model atmosphere code the ability
to treat Fe, Ni, and Co up to ionization stage vi, Mg, Ca, and Al up
to ionization stage iii, and S and Si up to ionization stage iv, out
of local thermodynamic equilibrium (LTE) using a multi-level direct
method with large model atoms (~ 400 levels and ~ 7500 transitions
in the case of Ni iii). These species are critically important for
modeling the time development of Novae spectra. We have also added
the ability to similarly treat Cs, Rb, and K, which are important
for fitting chromospheric models to M dwarf spectra, and Ba which
is important for modeling SNe supernovae. This is an increase from
40 to 85 in the total number of ionization stages among all species
treated in non-LTE by phoenix, and provides an unprecedented ability
to directly compute multi-species, multi-level non-LTE solutions with a
model atmosphere code. The equation of state, and the chemical, thermal,
and hydrostatic equilibrium equations are all solved consistently with
the non-LTE equilibrium of the species treated in non-LTE. Also, the
addition of many new non-LTE species allows us to compute synthetic
spectra with self-consistent, massive non-LTE line blanketing due to
many atoms and ions.

---------------------------------------------------------
Title: A multiwavelength study of the early evolution of the classical
nova LMC 1988 1
Authors: Schwarz, Greg J.; Hauschildt, Peter H.; Starrfield, S.;
Whitelock, P. A.; Baron, E.; Sonneborn, G.
1998MNRAS.300..931S Altcode:
LMC 1988 1 was a moderately fast, CO, dust-forming classical nova. It
was observed extensively in many different wavelength regions during
its early evolution. The UV, optical and infrared light curves of
LMC 1988 1 are very similar to those of the Galactic Nova V1668 Cyg
1978. As in V1668 Cyg, LMC 1988 1 showed the presence of an optically
thin dust shell ~55 d after visual maximum which lasted for about two
months. We successfully fit the UV and optical spectra of LMC 1988 1
taken within the first two months of its outburst (when the atmosphere
was still optically thick) with synthetic spectra computed using
PHOENIX nova model atmospheres. The synthetic spectra reproduce most
of the features seen in the observations and provide V-band magnitudes
consistent with the observed light curve. From the synthetic spectral
fits to the observed data, we find that the bolometric luminosity was
approximately constant at (3.0+/-0.3)x10^38ergs^-1 (assuming a distance
of 53 kpc to the LMC) during the first 45 d after visual maximum. The
fits are improved by increasing the CNO abundances to ~10 times their
solar values, implying that the ejecta were enriched in CNO elements.

---------------------------------------------------------
Title: Evolutionary models for solar metallicity low-mass stars:
mass-magnitude relationships and color-magnitude diagrams
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H.
1998A&A...337..403B Altcode: 2009A&A...500..551B; 1998astro.ph..5009B
We present evolutionary models for low mass stars from 0.075 to 1 M_sun
for solar-type metallicities [M/H]= 0 and -0.5. The calculations include
the most recent interior physics and the latest generation of non-grey
atmosphere models. We provide mass-age-color-magnitude relationships for
both metallicities. The mass-M_V and mass-M_K relations are in excellent
agreement with the empirical relations derived observationally. The
theoretical color-magnitude diagrams are compared with the sequences
of globular clusters (47 Tucanae) and open clusters (NGC2420 and
NGC2477) observed with the Hubble Space Telescope. Comparison is also
made with field star sequences in M_V-(V-I), M_K-(I-K) and M_K-(J-K)
diagrams. These comparisons show that the most recent improvements
performed in low-mass star atmosphere models yield now reliable stellar
models in the near-infrared. These models can be used for metallicity,
mass, temperature and luminosity calibrations. Uncertainties still
remain, however, in the optical spectral region below T_eff ~ 3700K,
where predicted (V-I) colors are too blue by 0.5 mag for a given
magnitude. The possible origins for such a discrepancy, most likely
a missing source of opacity in the optical and the onset of grain
formation are examined in detail. Tables 1 to 3 are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

---------------------------------------------------------
Title: Observations of the Polar ST Leonis Minoris during an Extreme
Low State: Identification of the Secondary Star
Authors: Ciardi, David R.; Howell, Steve B.; Dhillon, V. S.; Wagner,
R. Mark; Hauschildt, Peter H.; Allard, France
1998PASP..110.1007C Altcode:
We present near-infrared (1.85-2.47 μm) and optical (4300-5800 Å)
spectroscopic observations of the polar ST Leonis Minoris (ST LMi) in
an extreme low state. The near-infrared spectrum, showing no emission
lines whatsoever, is produced solely by the secondary star. We have
fitted the spectrum with a series of stellar atmosphere models and
found the secondary star to have a temperature of 2800+/-200 K. Six
months later, ST LMi was reobserved in the near-infrared, at which
time mass transfer had resumed, and the system was in a high state.

---------------------------------------------------------
Title: The Relative Contributions to the Near-Infrared Emission in
Short-Period Cataclysmic Variables
Authors: Ciardi, David R.; Howell, Steve B.; Hauschildt, Peter H.;
Allard, France
1998ApJ...504..450C Altcode:
We present phase-resolved near-infrared broadband photometry of
four short-period cataclysmic variables (HU Aqr, WZ Sge, TY Psc, and
V592 Cas). Coupled with ultraviolet and optical data obtained from
the literature, we have modeled the spectral energy distributions
of these four cataclysmic variables, as well as that of the twin of
WZ Sge, AL Com. The secondary stars contribute no more than 20%-50%
of the near-infrared flux except for the polar HU Aqr, where the
secondary contributes ~75% of the near-infrared flux. For the systems
located above the orbital period minimum, the temperatures of the
secondary stars match those for the expected main-sequence secondary
stars. However, our modeling places WZ Sge below the orbital period
minimum and shows it containing a secondary star of less than 1700
K--the coldest “star” yet identified.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Low-mass stars evolutionary models
(Baraffe+ 1998)
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P.
1998yCat..33370403B Altcode:
Physical properties and absolute magnitudes of low-mass stars for
different initial metallicity [M/H], helium mass fraction Y and mixing
length parameter Lmix: mass (in solar mass), age (in Gyrs) effective
temperature (in K), log of gravity (in cgs) and absolute magnitudes. The
VRI magnitudes are in the Johnson-Cousins system and the JHK magnitudes
in the CIT system. Note that the bolometric magnitude corresponds to
M_bol(Sun)=4.64. The lowest mass corresponds to the hydrogen-burning
limit. (1 data file).

---------------------------------------------------------
Title: A Spherical Non-LTE Line-blanketed Stellar Atmosphere Model
of the Early B Giant epsilon Canis Majoris
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Shore, S. N.; Baron, E.
1998ApJ...498..837A Altcode: 1998astro.ph..2031A
We use a spherical non-LTE fully line-blanketed model atmosphere to fit
the full multiwavelength spectrum, including the extreme-ultraviolet
(EUV) continuum observed by the Extreme Ultraviolet Explorer, of the
B2 II star ɛ Canis Majoris (CMa). The available spectrophotometry
of ɛ CMa from 350 Å to 25 μm is best fitted with model parameters
Teff = 21,750 K, log g = 3.5, and an angular diameter
of 0.77 mas. Our best-fit model predicts a hydrogen ionizing flux,
q0, of 1.59 × 1021 photons cm-2
s-1 at the star's surface and 2290 photons cm-2
s-1 at the surface of the Local Cloud. The close
agreement between the model and the measured EUV flux from ɛ CMa is
a result of the higher temperatures at the formation depths of the H
I and He I Lyman continua compared with other models. The realistic
model treatment of early B giants with spherical geometry and non-LTE
metal line-blanketing results in the prediction of significantly
larger EUV fluxes compared with plane-parallel models. We find that
our metal line-blanketed spherical models show significantly warmer
temperature structures, 1-3 kK at the formation depth of the Lyman
continua, and predict stronger EUV fluxes, up to a factor of 5 in the
H I Lyman continuum, compared with plane-parallel atmospheres that
have identical model parameters. In contrast, we find that spherical
and plane-parallel models that do not include metal line blanketing
are nearly identical. Our Teff = 21,000 K, log g = 3.2,
spherical non-LTE model predicts more than twice as many hydrogen
ionizing photons and over 200 times more neutral helium ionizing
photons than a standard hydrostatic plane-parallel LTE model with the
same stellar parameters. Our synthetic spectra are in reasonably
good agreement with observed continuum and line fluxes from echelle
spectra obtained with the Goddard High Resolution Spectrograph. While
we find agreement between the absolute UV flux of ɛ CMa as measured
by GHRS and our model atmosphere, these fluxes are ~30% higher in
the UV than those measured by IUE, OAO 2, and TD-1, in excess of the
published errors in the absolute calibration of these data.

---------------------------------------------------------
Title: New Determinations of Abundances for Novae Ejecta
Authors: Starrfield, S.; Vanlandingham, K.; Schwarz, G.; Hauschildt,
P.; Shore, S. N.
1998AAS...192.0602S Altcode: 1998BAAS...30..823S
The nova outburst is a consequence of the accretion of hydrogen rich
material onto a white dwarf in a close binary system and both theory
and observations show that the accreting material mixes with core
material during the outburst. Abundance determinations of nova ejecta
shows that the core material is either carbon and oxygen or oxygen,
neon, and magnesium. We have determined the ejecta abundances for
V838 Her (1991), OS And (1986), V693 CrA (1981), PW Vul (1984), LMC
1988 #1, and LMC 1990 #1 using both optical and ultraviolet data. Our
analysis technique uses CLOUDY (Ferland 1996) in combination with an
optimization method obtained from high energy physics (MINUIT: James
and Roos 1993). Our predicted line fluxes are in excellent agreement
with the observations. We are also analyzing spectra obtained early
in the outburst, when the expanding shell is optically thick, with
stellar atmospheres computed with PHOENIX (Hauschildt et al. 1997,
ApJ, 490,803). We will present the results of our studies using both
these methods. Our re-analyses of V693 CrA and PW Vul resolved the
problems with the previous studies.

---------------------------------------------------------
Title: Parallel Implementation of the PHOENIX Generalized Stellar
Atmosphere Program. II. Wavelength Parallelization
Authors: Baron, E.; Hauschildt, Peter H.
1998ApJ...495..370B Altcode: 1997astro.ph..9238B
We describe an important addition to the parallel implementation of our
generalized nonlocal thermodynamic equilibrium (NLTE) stellar atmosphere
and radiative transfer computer program PHOENIX. In a previous paper
in this series we described data and task parallel algorithms we
have developed for radiative transfer, spectral line opacity, and
NLTE opacity and rate calculations. These algorithms divided the work
spatially or by spectral lines, that is, distributing the radial zones,
individual spectral lines, or characteristic rays among different
processors and employ, in addition, task parallelism for logically
independent functions (such as atomic and molecular line opacities). For
finite, monotonic velocity fields, the radiative transfer equation is
an initial value problem in wavelength, and hence each wavelength point
depends upon the previous one. However, for sophisticated NLTE models
of both static and moving atmospheres needed to accurately describe,
e.g., novae and supernovae, the number of wavelength points is very
large (200,000-300,000) and hence parallelization over wavelength
can lead both to considerable speedup in calculation time and the
ability to make use of the aggregate memory available on massively
parallel supercomputers. Here, we describe an implementation of
a pipelined design for the wavelength parallelization of PHOENIX,
where the necessary data from the processor working on a previous
wavelength point is sent to the processor working on the succeeding
wavelength point as soon as it is known. Our implementation uses a
MIMD design based on a relatively small number of standard message
passing interface (MPI) library calls and is fully portable between
serial and parallel computers.

---------------------------------------------------------
Title: Time-resolved Spectroscopy of AL Comae Berenices
Authors: Howell, Steve B.; Hauschildt, Peter; Dhillon, V. S.
1998ApJ...494L.223H Altcode:
We present time-resolved spectroscopy for AL Com, one of the faintest
known tremendous outburst amplitude dwarf novae (TOADs). Using
newly produced models for a white dwarf and red secondary, we show
that the star AL Com has orbitally phase-resolved broad absorption
features of yet unidentified origin and an optically thin accretion
disk. Radial velocities measured from the few spectra available show
essentially no motion of the white dwarf, leading to a strict upper
limit on the secondary mass of &lt;=0.18 Msolar, with a
likely value of 0.04-0.09 Msolar. This agrees well with
recent theoretical arguments placing the TOADs as post-period minimum
cataclysmic variables.

---------------------------------------------------------
Title: Optical and ultraviolet spectral observations of nova LMC 1991
Authors: Schwarz, C. J.; Starrfield, S.; Hauschildt, P. H.; Shore,
S. N.
1998ASPC..137..473S Altcode: 1998wsow.conf..473S
No abstract at ADS

---------------------------------------------------------
Title: Elemental abundances for nova ejecta
Authors: Starrfield, S.; Vanlandingham, K.; Schwarz, G.; Hauschildt,
P. H.; Shore, S. N.
1998sese.conf..433S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Superlevel Method for Molecular NLTE in Cool Atmospheres
Authors: Schweitzer, A.; Hauschildt, P. H.; Allard, F.
1998ASPC..134..455S Altcode: 1998bdep.conf..455S
No abstract at ADS

---------------------------------------------------------
Title: Spherical Non-LTE Line-Blanketed Stellar-Atmosphere Models
of the Early-B Giants epsilon-CMa, beta-CMa, and alpha-Vir
Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.
1998ASPC..131..127A Altcode: 1998phls.conf..127A
No abstract at ADS

---------------------------------------------------------
Title: Optical and Infrared Spectroscopy of CM Draconis
Authors: Viti, S.; Jones, H. R. A.; Allard, F.; Schweitzer, A.;
Hauschildt, P.
1998HiA....11..441V Altcode:
The authors compare observations of the binary system CM Draconis with
synthetic spectra. Spectroscopic observations from 0.40 to 2.41 μm,
combined with photometry and the accurately known surface gravity
enable to estimate the temperature and metallicity using detailed
spectra synthesis. They find discrepancies between the analysis of
the infrared and optical spectrum while the optical spectral energy
distribution (SED) yields a metal-rich solution with Teff
= 3000K, the infrared SED yields around 3200K and -0.8 ≤ [M/H]
≤ -0.6 compatible with the high space motion of the system. The
low-metallicity characteristics of the infrared SED could be real and
is partly supported by the detailed analysis of the atomic lines in
the optical region. Although, the known incompleteness of the TiO
and H2O line lists in the models may cause substantial
systematic errors.

---------------------------------------------------------
Title: Photospheric Dust Grains Formation in Brown Dwarfs
Authors: Allard, F.; Alexander, D. R.; Tamanai, A.; Hauschildt, P. H.
1998ASPC..134..438A Altcode: 1998bdep.conf..438A
No abstract at ADS

---------------------------------------------------------
Title: The Formation of PAHs in Carbon Star Atmospheres
Authors: Ferguson, Jason W.; Alexander, David R.; Johnson, Hollis R.;
Allard, France; Hauschildt, Peter H.
1998IAUS..191P.304F Altcode:
Polycyclic Aromatic Hydrocarbons (PAHs) have been suggested as the
source of the diffuse interstellar bands, and may serve as a link
in the formation of grains from complex molecules in atmospheres
of carbon-rich stars. If PAHs exist in interstellar clouds, then
where do they form? The most obvious answer would seem to be in the
atmospheres of carbon stars, where the stellar wind may eject them into
the interstellar medium. Cherchneff, Barker &amp; Tielens (1992) and
Helling et al. (1996) computed the fraction of carbon contained within
PAHs for several carbon-rich stellar atmospheres. Both conclude that
PAHs are not significant in stellar photospheres, that they may form in
dynamical atmospheres, but that the resident time of the PAHs in those
atmosphere may be insufficient for a significant amount of PAHs to form
before being ejected. We extend the calculations of Helling et al. to
much lower temperatures and higher densities, and investigate whether
significant amounts of PAHs form in those outer layers. Even though our
models extend to much smaller optical depths than those considered by
Helling et al. we find that PAHs never account for more than 1 ppm
of the elemental carbon in any static model atmosphere in thermal
equilibrium. If it is assumed that grain formation is inhibited by,
for example, the passage of shock waves, then PAHs may account for up
to 30% of the elemental carbon.

---------------------------------------------------------
Title: ROSAT WTTSs near Lupus: Results of Echelle Spectroscopy
Authors: Wichmann, R.; Covino, E.; Krautter, J.; Alcala, J. M.;
Allain, S.; Hauschildt, P.
1998AGAb...14..102W Altcode: 1998AGM....14..P07W
We have obtained high-resolution echelle spectroscopy for a large
fraction of the Li-rich late-type stars recently discovered in and
near the Lupus dark clouds by follow-up observations of ROSAT x-ray
sources (Krautter et al. 1997, A&amp;AS 123, 329). Our data show that
about 90 percent of these stars exhibit Li I \lambda 6708 equivalent
widths in excess of zero-age main sequence stars, thus confirming
their pre-main sequence nature and supporting their classification
as weak-line T Tauri stars (WTTS). Using previously obtained data
on rotational periods (Wichmann et al. 1998, A&amp;A 330, 521), we
present a statistical approach to determine the mean distance of these
stars, and find this distance, within errors, to be consistent with
the HIPPARCOS distance of the Lupus star forming region (Wichmann
et al. 1997, ESA SP-402). Radial velocities of the ROSAT WTTS are
consistent with the radial velocity of the Lupus star forming region,
although a small difference of 2--3 km s^{-1} cannot be ruled out. If
confirmed, this deviation might yield some insight into the velocity
structure of the Gould Belt towards the Lupus star forming region.

---------------------------------------------------------
Title: Optical and ultraviolet spectral observations of nova LMC 1991
Authors: Schwarz, G. J.; Starrfield, S.; Hauschildt, P. H.; Shore,
S. N.
1998sese.conf..463S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Eclipsing Binary System CM Draconis
Authors: Viti, S.; Tennyson, J.; Jones, H. R. A.; Schweitzer, A.;
Allard, F.; Hauschildt, P. H.
1998ASPC..134..475V Altcode: 1998bdep.conf..475V
No abstract at ADS

---------------------------------------------------------
Title: A Comparison of the Infrared Spectra of Two Very Late-type
M Dwarfs with Different Gravities
Authors: Viti, S.; Tennyson, J.; Jones, H. R. A.; Allard, F.;
Hauschildt, P. H.
1998ASPC..134..471V Altcode: 1998bdep.conf..471V
No abstract at ADS

---------------------------------------------------------
Title: Observational and Theoretical Studies of the Nova Outburst
Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Hauschildt,
P. H.; Shore, S. N.; Krautter, J.; Vanlandingham, K.; Schwarz, G.
1998ASPC..137..352S Altcode: 1998wsow.conf..352S
No abstract at ADS

---------------------------------------------------------
Title: Model Atmospheres of Very Low Mass Stars and Brown Dwarfs
Authors: Allard, F.; Alexander, D. R.; Hauschildt, P. H.
1998ASPC..154...63A Altcode: 1998csss...10...63A
We review the current theory of very low mass stars model atmospheres
including the coolest known M dwarfs, M subdwarfs, and brown dwarfs,
i.e., T_eff &lt;= 5,000 K and -2.0 &lt;= [M/H] &lt;= +0.0. We discuss
ongoing efforts to incorporate molecular and grain opacities in
cool stellar spectra, as well as the latest progress in deriving the
effective temperature scale of M dwarfs. We especially present the
latest results of the models related to the search for brown dwarfs.

---------------------------------------------------------
Title: Model Atmospheres for White Dwarfs in Cataclysmic Variables
Authors: Hauschildt, Peter H.; Aufdenberg, J.; Starrfield, S.;
Baron, E.
1998ASPC..137...96H Altcode: 1998wsow.conf...96H
No abstract at ADS

---------------------------------------------------------
Title: The physics of early nova spectra and light curves
Authors: Hauschildt, P. H.; Shore, S. N.; Schwarz, G.; Starrfield,
S.; Baron, E.; Allard, F.
1998sese.conf..453H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Detailed Non-LTE Model Atmospheres for Novae during
Outburst. I. New Theoretical Results
Authors: Hauschildt, Peter H.; Shore, Steven N.; Schwarz, Greg J.;
Baron, E.; Starrfield, S.; Allard, France
1997ApJ...490..803H Altcode: 1997astro.ph..7104H
We present new, detailed non-LTE (NLTE) calculations for model
atmospheres of novae during outburst. This fully self-consistent
NLTE treatment for a number of model atoms includes 3922 NLTE levels
and 47,061 NLTE primary transitions. We discuss the implication
of departures from LTE for the strengths of the lines in nova
spectra. The new results show that our large set of NLTE lines
constitutes the majority of the total line-blanketing opacity in nova
atmospheres. Although we include LTE background lines, their effects
are small on the model structures and on the synthetic spectra. We
demonstrate that the assumption of LTE leads to incorrect synthetic
spectra and that NLTE calculations are required for reliably modeling
nova spectra. In addition, we show that detailed NLTE treatment for
a number of ionization stages of iron changes the results of previous
calculations and improves the fit to observed nova spectra.

---------------------------------------------------------
Title: Spherical Non-LTE Line-Blanketed Stellar Atmosphere Models
of epsilon CMa, beta CMa, and alpha VIR and the Lyman Continuum in
the Early B Giant Stars.
Authors: Aufdenberg, J. P.; Sankrit, R.; Hauschildt, P. H.; Baron, E.
1997AAS...191.1201A Altcode: 1997BAAS...29.1227A
We model the full multi-wavelength spectrum, including the extreme
ultraviolet (EUV) continuum of three early B giants, epsilon CMa, beta
CMa, and alpha Vir with spherical, non-LTE, fully line-blanketed, model
atmospheres. Comparisons of these models to the spectrophotometric data,
along with the HIPPARCOS parallax measurements, provide fundamental
stellar parameters for these stars. We find close agreement between
the model spectra and the measured EUV fluxes from epsilon CMa and
beta CMa. The realistic treatment of early B giant atmospheres, with
models including spherical geometry and NLTE metal line blanketing,
results in the prediction of larger Lyman continuum fluxes, by up
to a factor of two, than existing plane-parallel models for these
stars. We present a grid of PHOENIX NLTE model atmospheres of late
O and early B stars and provide predictions for the hydrogen and
helium ionizing fluxes as a function of effective temperature. The
increased EUV flux predicted for B stars has significant implications
for our understanding of the ionization of the material surrounding
these stars. We present photoionization models of the H II region
around alpha Vir, calculated using CLOUDY, with our model atmosphere
as the input continuum. The distance to this star and its radius are
known and so it is a well constrained system. We find that our model
can reproduce the measured extent of the H II region, the Hα surface
brightness, the {[S II]}lambda 6716/Hα ratio and the temperature of
the region given by Reynolds (1988). We also estimate the amount of
the ionizing radiation escaping from the surroundings and therefore
available to ionize the diffuse ISM.

---------------------------------------------------------
Title: Spatially Resolved Spectra of V1974 Cygni (Nova Cygni 1992)
with the Goddard High Resolution Spectrograph
Authors: Shore, Steven N.; Starrfield, Sumner; Ake, T. B., III;
Hauschildt, Peter H.
1997ApJ...490..393S Altcode:
We report the observation of spatially resolved low-resolution GHRS
spectra of the shell of the bright Galactic ONeMg nova Cygni 1992. The
spectra were obtained in 1995 September, after the X-ray turnoff of
the nova. We have determined the dynamical structure of the ejecta
and show the evolution of the ionization within the ejecta. Abundance
limits have been found to agree with the published analyses based on
earlier IUE data for key species in the ejecta, especially neon. The
knot spectrum, obtained with the 0.25" aperture, shows an enhanced Ne/He
ratio compared with the 2" aperture observation. These data provide
a detailed picture of physical conditions and abundances of the knots
and larger scale ejecta that have not previously been available from UV
spectra, including those taken before the COSTAR installation and IUE
data. The knots were created during the initial stages of the explosion,
and the differential mixing that may have resulted can be studied
using the spatially resolved spectra. The 1995 spectra were compared
with archival Faint Object Spectrograph data from 1994 and previous
GHRS spectra from 1992 and 1993. We also obtained high signal-to-noise
ratio (S/N) observations of the UV continuum of the hot central star
in order to study the physical conditions in the post-thermonuclear
runaway envelope. These show that the white dwarf had relaxed to a
very low effective temperature, about 20,000 K, and a luminosity of
about 30 L⊙, within 2 years after the X-ray turnoff. We
also used reprocessed archival IUE spectra to determine the decay time
for the ultraviolet continuum flux for this nova, which we find to be
about 1.7 years. The current temperature and luminosity do not fall
on the white dwarf cooling tracks for any reasonable stellar mass.

---------------------------------------------------------
Title: The effective temperature and metallicity of CM Draconis
Authors: Viti, Serena; Jones, Hugh R. A.; Schweitzer, Andreas; Allard,
France; Hauschildt, Peter H.; Tennyson, Jonathan; Miller, Steven;
Longmore, Andrew J.
1997MNRAS.291..780V Altcode:
We compare observations of the binary system CM Draconis with
synthetic spectra computed using the stellar atmosphere code
phoenix. Spectroscopic observations from 0.40 to 2.41mum, combined
with photometry and the accurately known surface gravity, enable us
to estimate the temperature and metallicity using detailed spectral
synthesis. We find discrepancies between the analysis of the infrared
and optical spectra: while the optical spectral energy distribution
(SED) yields a metal-rich solution with T_eff=3000K, the infrared SED
yields around 3200K with -0.8&lt;= [M/H]&lt;=-0.6, compatible with the
high space motion of the system. The low-metallicity characteristics of
the infrared SED could be real, and are partly supported by a detailed
analysis of the atomic lines in the optical region. Although the known
incompleteness of the TiO and H_2O line lists in the models used, as
well as problems with the observational data, will cause systematic
errors, we suggest that CM Draconis could be a chemically peculiar
system in that it cannot be modelled with solar abundances.

---------------------------------------------------------
Title: Evolutionary models for metal-poor low-mass stars. Lower main
sequence of globular clusters and halo field stars
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H.
1997A&A...327.1054B Altcode: 1997astro.ph..4144B
We have performed evolutionary calculations of very-low-mass stars
from 0.08 to 0.8 M_sunl for different metallicites from [M/H]= -2.0
to -1.0 and we have tabulated the mechanical, thermal and photometric
characteristics of these models. The calculations include the most
recent interior physics and improved non-grey atmosphere models. The
models reproduce the entire main sequences of the globular clusters
observed with the Hubble Space Telescope over the afore-mentioned
range of metallicity. Comparisons are made in the WFPC2 Flight
system including the F555, F606 and F814 filters, and in the standard
Johnson-Cousins system. We examine the effects of different physical
parameters, mixing-length, alpha -enriched elements, helium fraction,
as well as the accuracy of the photometric transformations of the
HST data into standard systems. We derive mass-effective temperature
and mass-magnitude relationships and we compare the results with
the ones obtained with different grey-like approximations. These
latter are shown to yield inaccurate relations, in particular
near the hydrogen-burning limit. We derive new hydrogen-burning
minimum masses, and the corresponding absolute magnitudes, for the
different metallicities. We predict color-magnitude diagrams in the
infrared NICMOS filters, to be used for the next generation of the HST
observations, providing mass-magnitudes relationships in these colors
down to the brown-dwarf limit. We show that the expected signature
of the stellar to substellar transition in color-magnitude diagrams
is a severe blueshift in the infrared colors, due to the increasing
collision-induced absorption of molecular hydrogen with increasing
density and decreasing temperature. At last, we apply these calculations
to the observed halo field stars, which yields a precise determination
of their metallicity, and thus of their galactic origin. We find no
evidence for significant differences between the halo field stars and
the globular cluster sequences.

---------------------------------------------------------
Title: Non-Local Thermodynamic Equilibrium Effects of Ti I in M
Dwarfs and Giants
Authors: Hauschildt, Peter H.; Allard, France; Alexander, David R.;
Baron, E.
1997ApJ...488..428H Altcode:
We present detailed NLTE Ti I calculations in model atmospheres of cool
dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti
I model atom with 395 levels and 5279 primary bound-bound transitions
is included, and we discuss the implication of departures from LTE
in this atom for the strengths of Ti I lines and TiO molecular bands
in cool star spectra. We show that in the atmospheric parameter range
investigated, LTE is a poor approximation to Ti I line formation, as
expected from the low collisional rates in cool stars. The secondary
effects of Ti I overionization on the TiO number density and the
TiO molecular opacities, however, are found to be negligible in the
molecular line-forming region for the relatively small parameter range
studied in this paper.

---------------------------------------------------------
Title: Abundance analysis of the slow nova PW Vulpeculae 1984
Authors: Schwarz, Greg J.; Starrfield, Sumner; Shore, Steven N.;
Hauschildt, Peter H.
1997MNRAS.290...75S Altcode: 1997astro.ph..5086S
We determine the elemental abundances for the ejecta of the slow nova
PW Vul 1984. Our technique uses a minimization of the emission-line
fits of a photoionization model to available ultraviolet, optical
and infrared spectra. We find the following abundances (by number)
with respect to solar: He/H=1.0+/-0.4, C/H=7.0^+7_-4, N/H=85^+59_-41
and O/H=6^+7_-2. In addition, there is weak evidence for solar Ne
and Mg, and for twice solar Fe. Previous studies of PW Vul by Saizar
et al. and Andrea et al. yielded considerable differences in their
derived elemental abundances for the ejecta. Our abundances fall in
between those found in the previous studies. To explain the discrepant
abundances, we analyse in detail the data and methods used to obtain
the previous results. The abundances found by Saizar et al. are
significantly smaller than our values because of the lower electron
temperature used by them in deriving elemental abundances from ion
abundances. Andrea et al. used an ionization correction method to obtain
their abundances and later verified their results with a photoionization
model. Our analysis of their data shows that the absolute fluxes of
the optical emission lines used by Andrea et al. are underestimated
by 15 per cent, leading to a factor of 2 increase in their derived
abundances. We also find that the photoionization model used by Andrea
et al. predicts twice as much carbon as the photoionization code we
used even when fitting the same data with similar model parameters.

---------------------------------------------------------
Title: Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae
Authors: Nugent, Peter; Baron, E.; Branch, David; Fisher, Adam;
Hauschildt, Peter H.
1997ApJ...485..812N Altcode: 1996astro.ph.12044N
We present detailed non-LTE synthetic spectra of hydrodynamic supernovae
(SNe) Ia models. We make no assumptions about the form of the spectrum
at the inner boundary. We calculate both Chandrasekhar-mass deflagration
models and sub-Chandrasekhar “helium detonators.” Gamma-ray deposition
is handled in a simple, accurate manner. We have parameterized the
storage of energy, which arises from the time-dependent deposition
of radioactive decay energy, in a reasonable manner that spans the
expected range. We find that the Chandrasekhar-mass deflagration
model W7 of Nomoto, Thielemann, &amp; Yokoi shows good agreement
with the observed spectra of SN 1992A and SN 1994D, particularly
in the UV, where our models are expected to be most accurate. The
sub-Chandrasekhar models do not reproduce the UV deficit observed in
normal SNe Ia. They do bear some resemblance to subluminous SNe Ia,
but the shapes of the spectra (i.e., the colors) are opposite that
of the observed ones, and the intermediate-mass element lines (such
as Si II and Ca II) are extremely weak, which seems to be a generic
difficulty of the models. Although the sub-Chandrasekhar models have
a significant helium abundance (unlike Chandrasekhar-mass models),
helium lines are not prominent in the spectra near maximum light and
thus do not act as a spectral signature for the progenitor.

---------------------------------------------------------
Title: Parallel Implementation of the PHOENIX Generalized Stellar
Atmosphere Program
Authors: Hauschildt, Peter H.; Baron, E.; Allard, France
1997ApJ...483..390H Altcode: 1996astro.ph..7087H
We describe the parallel implementation of our generalized stellar
atmosphere and non-LTE (NLTE) radiative transfer computer program
PHOENIX. We discuss the parallel algorithms we have developed for
radiative transfer, spectral line opacity, and NLTE opacity and rate
calculations. Our implementation uses a multiple instruction-multiple
data design based on a relatively small number of MPI library calls. We
report the results of test calculations on a number of different
parallel computers and discuss the results of scalability tests.

---------------------------------------------------------
Title: Grain Formation in Atmospheres of Cool Dwarfs
Authors: Alexander, D. R.; Allard, F.; Tamanai, A.; Hauschildt, P. H.
1997Ap&SS.251..171A Altcode:
We have constructed a grid of model atmospheres for cool dwarf stars
and brown dwarfs with Teff ≤ 3000 K that includes (i)
an equation of state which accounts for over 600 gas phase species
and 1000 liquids and solids, and (ii) the opacities of corundum
(Al2O3), iron, enstatite (MgSiO3)
and forsterite (Mg2SiO4), as well as amorphous
carbon and SiC. We confirm earlier findings of Tsuji, Ohnaka &amp;
Aoki (1996a) that grains are abundant in the outer photospheric layers
of red and brown dwarfs with spectral type later than M8. We identify
high temperature condensates including perovskite (CaTiO3)
that depletes the photospheres of important absorbers including TiO,
and we confirm the disappearance of TiO bands in the observed spectra
of cool dwarfs.

---------------------------------------------------------
Title: NLTE effects of Ti~I in M dwarfs and giants
Authors: Hauschildt, Peter H.; Allard, France; Alexander, David R.;
Baron, E.
1997astro.ph..5063H Altcode:
We present detailed NLTE Ti~I calculations in model atmospheres of cool
dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti~I
model atom with 395 levels and 5279 primary bound-bound transitions
is included, and we discuss the implication of departures from LTE
in this atom for the strengths of Ti~I lines and TiO molecular bands
in cool star spectra. We show that in the atmospheric parameter range
investigated, LTE is a poor approximation to Ti~I line formation, as
expected from the low collisional rates in cool stars. The secondary
effects of Ti~I overionization on the TiO number density and the
TiO molecular opacities, however, are found to be negligible in the
molecular line forming region for the relatively small parameter range
studied in this paper.

---------------------------------------------------------
Title: Brown Dwarfs from the Stellar Perspective
Authors: Allard, France; Hauschildt, Peter H.
1997astro.ph..5071A Altcode:
In this paper, we review the current theory of very low mass stars
model atmospheres including the coolest known M~dwarfs, M~subdwarfs,
and brown dwarfs, i.e. T$_{eff} \leq 5,000 $K and $-2.0 \le [M/H] \le
+0.0$. We discuss ongoing efforts to incorporate molecular and grain
opacities in cool stellar spectra, as well as the latest progress in
deriving the effective temperature scale of M~dwarfs. We also present
the latest results of the models related to the search for brown dwarfs.

---------------------------------------------------------
Title: The Hubble constant, supernova light curves and spectra,
and radiation transport
Authors: Branch, David; Baron, E.; Nugent, Peter; Hauschildt, Peter H.
1997PhPl....4.2016B Altcode:
As luminous events that can be physically modeled, supernovae provide
an attractive route to the value of the Hubble constant. The modeling
involves radiation transport through matter undergoing homologous
expansion with velocity gradient on the order of 10-6
s-1. For supernovae of type Ia, which are thermonuclear
disruptions of mass accreting or coalescing carbon-oxygen white dwarfs,
one wants to be able to calculate the light curve (luminosity in some
optical passband versus time), which is powered by the radioactivity
decay chain 56Ni→56Co→56Fe. For
all kinds of supernovae, including those of types II, Ib,
and Ic, which result from the gravitational collapse of the
cores of massive stars, the goal is to accurately calculate the
emergent ultraviolet-optical-infrared spectra, as a function of
time. Local-thermodynamic-equilibrium (LTE) light-curve calculations
for type Ia supernovae by Höflich and co-workers, and our spectrum
calculations based on a fully relativistic non-LTE radiative transfer
code, are described. The associated radiative transport needs are
discussed.

---------------------------------------------------------
Title: Preliminary results of the ASU/UGA O-star project
Authors: Scowen, P. A.; Hauschildt, P. H.; Aufdenberg, J. P.;
Sankrit, R.
1997AIPC..393..291S Altcode: 1997sfnf.conf..291S
Understanding the physics of the photodissociation regions (PDRs) which
occur between the ionized HII regions and the surrounding molecular
clouds is critical in assessing the role that primary star formation
has on secondary events. It is also pivotal to understanding how HII
regions affect their local environment. Modelling of these interfaces,
and of the photons that escape to ionize the local ISM, has been
hampered by a lack of modern models of the O-star atmospheres. We
present preliminary results from a program intended to better model
the physics of the extended atmospheres of O stars and thus derive
more physically accurate photon fluxes and therefore better estimates
of the actual ionization rates. The models include features such as
winds, spherical symmetry, accurate and up-to-date opacites, and the
effect of metallicity on the extended envelope of material around O
stars and the spectra that emerge from them.

---------------------------------------------------------
Title: Model Atmospheres of Very Low Mass Stars and Brown Dwarfs
Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.;
Starrfield, Sumner
1997ARA&A..35..137A Altcode:
As progressively cooler stellar and substellar objects are
discovered, the presence first of molecules and then of condensed
particulates greatly complicates the understanding of their physical
properties. Accurate model atmospheres that include these processes
are the key to establishing their atmospheric parameters. They play a
crucial role in determining structural characteristics by setting the
surface conditions of model interiors and providing transformations
to the various observational planes. They can reveal the spectroscopic
properties of brown dwarfs and help establish their detectability. In
this paper, we review the current state-of-the-art theory and modeling
of the atmospheres of very low mass stars, including the coolest known
M dwarfs, M subdwarfs, and brown dwarfs, i.e. T_eff {less than or
equal to} 4000 K and -4.0 {less than or equal to} [M/H]} {less than or
equal to} +0.0.} We discuss ongoing efforts to incorporate molecular
and grain opacities in cool stellar spectra, as well as the latest
progress in (a) deriving the effective temperature scale of M dwarfs,
(b) reproducing the lower main sequences of metal-poor subdwarfs in
the halo and globular clusters, and (c}) results of the models related
to the search for brown dwarfs

---------------------------------------------------------
Title: NLTE modeling of SNe Ia near maximum light
Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A.
1997ASIC..486..627B Altcode: 1997thsu.conf..627B
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE model atmosphere analysis of the early ultraviolet
spectra of Nova OS Andromedae 1986
Authors: Schwarz, Greg J.; Hauschildt, Peter H.; Starrfield, S.;
Baron, E.; Allard, France; Shore, Steven N.; Sonneborn, G.
1997MNRAS.284..669S Altcode: 1996astro.ph..8199S
We analyse the early, optically thick, ultraviolet spectra of Nova
OS And 1986 using a grid of spherically symmetric, non-LTE, line-
blanketed, expanding model atmospheres and synthetic spectra with the
following set of parameters: 5000&lt;=T_model&lt;=60000K, solar abundan
ces, rho ~r^-3, v_max=2000 km s^-1, L=6x10^4Lsolar, and a statistical
or microturbulent velocity of 50 km s^-1. We use the synthetic spectra
to estimate the model parameters corresponding to the observed IUE
spectra. The fits to the observations are then iteratively improved
by changing the parameters of the model atmospheres - in particular,
T_model and the abundances - to arrive at the best fits to the optically
thick pseudo-continuum and the features found in the IUE spectra. The
IUE spectra show two different optically thick sub-phases. The
earliest spectra, taken a few days after maximum optical light, show
a pseudo-continuum created by overlapping absorption lines. The later
observations, taken approximately 3 weeks after maximum light, show
the simultaneous presence of allowed, semiforbidden and forbidden
lines in the observed spectra. Analysis of these phases indicates
that OS And 1986 had solar metallicities, except for Mg which showed
evidence of being underabundant by as much as a factor of 10. We
determine a distance of 5.1 kpc to OS And 1986, and derive a peak
bolometric luminosity of ~5x10^4Lsolar. The computed nova parameters
provide insights into the physics of the early outburst and explain the
spectra seen by IUE. Lastly, we find evidence in the later observations
for large non-LTE effects of Fe ii which, when included, lead to much
better agreement with the observations.

---------------------------------------------------------
Title: The Effective Temperature and Metallicity of CM Draconis
Authors: Viti, S.; Jones, H. R. A.; Schweitzer, A.; Allard, F.;
Hauschildt, P.
1997IAUJD..10E..11V Altcode:
We compare observations of the binary system CM Draconis with
synthetic spectra computed using the PHOENIX stellar atmosphere
code. Spectroscopic observations from 0.40 to 2.41 microns, combined
with photometry and the accurately known surface gravity enable us to
derive the temperature and metallicity using detailed spectra synthesis
as well as the spectral energy distribution. This enables us to obtain
the most direct measurement of both metallicity [M/H] and effective
temperature (Teff) so far made for the system. Our results
imply Teff ~3200K and -0.8 &lt;= [M/H] &lt;= -0.6. The
largest uncertainty in this conclusion lies in the lack of reliable
molecular data for cool stars, especially for water.

---------------------------------------------------------
Title: Multiwavelength Modeling of Nova Atmospheres
Authors: Hauschildt, P. H.; Starrfield, S.
1997nasa.reptV....H Altcode:
We have analyzed the early optically thick ultraviolet spectra of
Nova OS And 1986 using a grid of spherically symmetric, non-LTE,
line-blanketed, expanding model atmospheres and synthetic spectra
with the following set of parameters: 5,000 less than or equal to
Tmodel less than or equal to 60,000K, solar abundances,
(rho)(alpha) r-3, vmax = 2000 km/s, L = 6 x
104 solar luminosity, and a statistical or microturbulent
velocity of 50 km/s. We used the synthetic spectra to estimate the
model parameters corresponding to the observed IUE spectra. The fits
to the observations were then iteratively improved by changing the
parameters of the model atmospheres, in particular Tmodel
and the abundances, to arrive at the best fits to the optically thick
pseudo-continuum and the features found in the IUE spectra. The IUE
spectra show two different optically thick subphases. The earliest
spectra, taken a few days after maximum optical light, show a
pseudo-continuum created by overlapping absorption lines. The later
observations, taken approximately 3 weeks after maximum light, show the
simultaneous presence of allowed, semi-forbidden, and forbidden lines
in the observed spectra. Analysis of these phases indicate that OS And
86 had solar metallicities except for Mg which showed evidence of being
underabundant by as much as a factor of 10. We determine a distance
of 5.1 kpc to OS And 86 and derive a peak bolometric luminosity of
approximately 5 x 104 solar luminosity. The computed nova
parameters provide insights into the physics of the early outburst and
explain the spectra seen by IUE. Lastly, we find evidence in the later
observations for large non-LTE effects of Fe II which, when included,
lead to much better agreement with the observations.

---------------------------------------------------------
Title: Analysis of Keck high-resolution spectra of VB 10
Authors: Schweitzer, Andreas; Hauschildt, Peter H.; Allard, France;
Basri, G.
1996MNRAS.283..821S Altcode: 1996astro.ph..6150S
We use a preliminary version of our `NextGen' grid of cool star
model atmospheres to compute synthetic line profiles which fit
high-resolution Keck spectra of the cool M dwarf VB10 satisfactorily
well. We show that the parameters derived from the Keck data are
consistent with the parameters derived from lower resolution spectra
with larger wavelength coverage. We discuss the treatment of van der
Waals broadening in cool stellar atmospheres that are dominated by
molecules (mostly H_2). The line profiles are dominated by van der Waals
pressure broadening and are a sensitive indicator for the gravity and
metallicity. Therefore the high-resolution Keck spectra are useful for
determining the parameters of M dwarfs. There is some ambiguity between
the metallicity and gravity. For VB10, we find from the high-resolution
spectra that 5.0&lt;logg&lt;5.5 and 0&lt;[M/H]&lt;+0.5 for an adopted
fixed effective temperature of 2700 K, which is consistent with recent
interior calculations.

---------------------------------------------------------
Title: Non-local thermodynamic equilibrium effects in modelling of
supernovae near maximum light.
Authors: Baron, E.; Hauschildt, P. H.; Nugent, P.; Branch, D.
1996MNRAS.283..297B Altcode:
Supernovae (SNe), with their diversity of compositions, velocities,
envelope masses, and interactions, are good testing grounds for
probing the importance of non-local thermodynamic equilibrium (NLTE)
in expanding atmospheres. In addition to treating H, He, Li I, O I,
Ne I, Na I, and Mg II in NLTE, we use a very large model atom of
Fe II to test the importance of NLTE processes in both Type Ia and
Type II SNe. Since the total number of potential line transitions
that one has to include is enormous (≍40 million), approximations
and simplifications are required to treat the problem accurately
and in finite computer time. With our large Fe II model atom (617
levels and 13,675 primary NLTE line transitions) we are able to
test several assumptions for treating the background opacity that
are needed to obtain correct UV line blanketing, which determines
the shape of near-maximum light supernova spectra. we find that,
due to interactions within the multiplets, treating the background
lines as pure scattering (thermalization parameter ɛ = 0) is a poor
approximation, and that an overall mean value of ɛ ≡ 0.05-0.10 is
a far better approximation. This is true even in SNe Ia, where the
continuum absorption optical depth at 5000 Å (≡τstd) is
≪1. we also demonstrate that a detailed treatment of NLTE effects is
required to determine properly the ionization states of both abundant
and trace elements.

---------------------------------------------------------
Title: UV Observations of Three LMC Be-Star/X-ray Binaries
Authors: Schmidtke, P. C.; Cowley, A. P.; Hauschildt, P. H.; Ponder,
A. L.; McGrath, T. K.; Frattare, L. M.; Franklin, B. E.
1996PASP..108..668S Altcode:
This paper describes IUE ultraviolet observations of three Be-star/X-ray
binaries in the LMC: CAL 9, CAL E, and RX J0520.5-6932. Because
the optical spectra show evidence of an overlying continuum source,
ultraviolet spectra were obtained to further investigate its properties,
but no UV emission lines are found. The UV spectra have been compared
to models indicating that the stellar temperatures are near 30000 K
(for log g = 4.0). This is in agreement with the temperatures suggested
by the spectral type determined in the optical region. Thus, there is
no clear evidence in either the optical or UV regions of the gas being
accreted by the unseen compact companion which must give rise to the
X-ray emission. Optical photometry shows these systems undergo irregular
variations of up to a few tenths of a magnitude. (SECTION: Stars)

---------------------------------------------------------
Title: Synthetic Spectra and Mass Determination of the Brown Dwarf
GI 229B
Authors: Allard, France; Hauschildt, Peter H.; Baraffe, Isabelle;
Chabrier, Gilles
1996ApJ...465L.123A Altcode:
We present preliminary nongray model atmospheres and interiors for
cool brown dwarfs. The resulting synthetic spectra are compared to
available spectroscopic and photometric observations of the coolest
brown dwarf yet discovered, Gl 229B (Nakajima et al.). Despite the
grainless nature of the present models, we find that the resulting
synthetic spectra provide an excellent fit to most of the spectral
features of the brown dwarf. We confirm the presence of methane
absorption and the substellar nature of Gl 229B. These preliminary
models set an upper limit for the effective temperature of 1000 K. We
also compute the evolution of brown dwarfs with solar composition and
masses from 0.02 to 0.065 Msolar. While uncertainties in the age of
the system yield some indeterminateness for the mass of Gl 229B, the
most likely solution is m ~ 0.04--0.055 Msolar. In any case, we can
set an upper limit m = 0.065 Msolar for a very unlikely age, t = 10 Gyr.

---------------------------------------------------------
Title: Spectral analysis of M dwarfs
Authors: Jones, Hugh R. A.; Longmore, Andrew J.; Allard, France;
Hauschildt, Peter H.
1996MNRAS.280...77J Altcode:
We compare 1.16-1.22 μm spectra of cool low-mass dwarfs with synthetic
spectra calculated with a stellar atmosphere code. The synthetic spectra
give a representation of the overall spectral features which has not
been possible in previous comparisons with cool low-mass dwarf spectra,
although the interpretation of the observed spectra is severely hampered
by the quality of atomic and molecular input data. The observed spectral
region is rich in absorption features of which the strongest are K,
Fe, Mg and FeH. Each observed spectrum is compared with a grid of
synthetic spectra extending well outside the expected parameter space
for M dwarfs. The effective temperatures, metallicities and gravities
derived are compared with expectations based on previous work. For
the cooler objects the parameters show broad agreement; however,
for the hotter objects the poor fit of Fe lines leads to best fits to
models with low gravity and metallicity. All features show a strong
sensitivity to temperature, especially the K and FeH. Metallicity and
gravity effects are relatively smaller. For the hotter stars, Mg and
Fe absorption lines are the most useful discriminators between gravity
and metallicity. For the cooler objects the complicated dependence of
modelled equivalent widths on metallicity and gravity makes it awkward
to separate effects due to a single model parameter. The comparisons
suggest a similar spread in metallicities to that anticipated,
although for our sample neither kinematic motion nor membership of
a particular photometric class is, on its own, a reliable indicator
of metallicity. Comparison of the observed strong K lines in GD 165B
with synthetic spectra indicate that it is relatively metal rich. This
result together with an improved measurements of its distance means that
within the best available constraints it is likely to be a brown dwarf.

---------------------------------------------------------
Title: Model Atmospheres for Novae and Supernovae
Authors: Hauschildt, P. H.; Baron, E.; Allard, F.; Starrfield, Sumner
1996AAS...188.3204H Altcode: 1996BAAS...28..866H
The spectra of novae and supernovae form in an environment that (a)
is optically thick for lines and continua, (b) has a large radial
extension, (c) has very high-speed (and differential) velocity fields,
(d) huge temperature gradients, (e) very low densities, and (f) a
huge number of spectral lines. Analyzing the thousands of observed
spectra of novae and SNe available today in various archives requires
very sophisticated numerical techniques. These methods must include
a detailed treatment of non-LTE effects for a large number of lines,
special relativistic radiative transfer, inclusion of millions of
spectral lines, and an equation of state that is capable of handling
several hundred species of both atoms and molecules. I will describe
how we solve these problems with our general model atmosphere code
PHOENIX and describe a few results of general interest, e.g., the
influence of non-LTE effects on nova spectra.

---------------------------------------------------------
Title: NLTE Effects in Modeling of Supernovae near Maximum Light
Authors: Baron, E.; Hauschildt, P. H.; Nugent, P.; Branch, D.
1996astro.ph..5088B Altcode:
Supernovae, with their diversity of compositions, velocities,
envelope masses, and interactions are good testing grounds for
probing the importance of NLTE in expanding atmospheres. In addition
to treating H, He, Li I, O I, Ne I, Na I, and Mg II in NLTE, we
use a very large model atom of Fe II to test the importance of NLTE
processes in both SNe Ia and II. Since the total number of potential
line transitions that one has to include is enormous ($\approx 40$
million), approximations and simplifications are required to treat the
problem accurately and in finite computer time. With our large Fe II
model atom (617 levels, 13,675 primary NLTE line transitions) we are
able to test several assumptions for treating the background opacity
that are needed to obtain correct UV line blanketing which determines
the shape of near-maximum light supernova spectra. We find that,
due to interactions within the multiplets, treating the background
lines as pure scattering (thermalization parameter $\epsilon = 0$)
is a poor approximation and that an overall mean value of $\epsilon
\sim 0.05 - 0.10 $ is a far better approximation. This is true even
in SNe Ia, where the continuum absorption optical depth at 5000 Å
($\equiv \tau_{\rm std}$) is $&lt;&lt; 1$. We also demonstrate that a
detailed treatment of NLTE effects is required to properly determine
the ionization states of both abundant and trace elements.

---------------------------------------------------------
Title: Infrared Spectra of Low-Mass Stars: Toward a Temperature
Scale for Red Dwarfs
Authors: Leggett, S. K.; Allard, F.; Berriman, Graham; Dahn, Conard
C.; Hauschildt, Peter H.
1996ApJS..104..117L Altcode:
We present new low-resolution (R ∼ 250)1.0-2.4 μm spectra for 13
red dwarf stars. The sample size is increased to 16 by including other
published infrared spectra. New, as well as published, red spectra are
presented for 10 of these 16 stars, and new and published VRIJHKLL'
photometry is also presented. Both halo and disk stars are included
in the sample, which covers a range of spectral type from dM0 to
dM6.5. We derive bolometric luminosities and bolometric corrections
from the observational data, finding good agreement with earlier
results for the disk stars. We fit synthetic spectra generated by
Allard &amp; Hauschildt's state-of-the-art model atmospheres to
the observed spectra. Although some discrepancies remain between
the theoretical and observed spectra, we find that the molecular
features give a consistent value for effective temperature across
the entire observed wavelength range. The Teff values and
radii derived, and their dependency on metallicity, are in agreement
with the most recent structural models of low-mass stars, removing
the long-standing discrepancy between the observed and calculated
locations of such stars in the H-R diagram, at least for stars more
massive than 0.1 Msun.

---------------------------------------------------------
Title: The Effects of Fe II Non-LTE on Nova Atmospheres and Spectra
Authors: Hauschildt, Peter H.; Baron, E.; Starrfield, Sumner; Allard,
France
1996ApJ...462..386H Altcode: 1996astro.ph..1149H
The atmospheres of novae at early times in their outbursts are
very extended, expanding shells with low densities. Models of these
atmospheres show that non-LTE effects are very important and must be
included in realistic calculations. We have, therefore, been improving
our atmospheric studies by increasing the number of ions treated in
non-LTE. One of the most important ions is Fe II, which has a complex
structure and numerous lines in the observable spectrum. In this
paper we investigate non-LTE effects for Fe II for a wide variety of
parameters. We use a detailed Fe II model atom with 617 level and 13,675
primary lines, treated using a rate-operator formalism. We show that
the radiative transfer equation in nova atmospheres must be treated
with sophisticated numerical methods and that simple approximations,
such as the Sobolev method, cannot be used because of the large number
of overlapping lines in the comoving frame. Our results show
that the formation of the Fe II lines is strongly affected by non-LTE
effects. For low effective temperatures, Teff &lt; 20,000 K,
the optical Fe II lines are most influenced by non-LTE effects, while
for higher Teff the UV lines of Fe II are very strongly
affected by non-LTE. The departure coefficients are such that Fe II
tends to be overionized in non-LTE when compared to LTE. Therefore,
Fe II non-LTE must be included with sophisticated radiative transfer
in nova atmosphere models in order to analyze observed nova spectra
reliably. Finally, we show that the number of wavelength points
required for the Fe II non-LTE model atmosphere calculations can be
reduced from 90,000 to about 30,000 without changing the results if
we choose a sufficiently dense UV wavelength grid.

---------------------------------------------------------
Title: Preliminary spectral analysis of SN 1994I
Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Kirshner, R. P.;
Filippenko, A. V.
1996MNRAS.279..799B Altcode: 1995astro.ph.10070B
We present optical spectra of the Type 1c supernova 1994I in M51 and
preliminary non-local thermodynamic equilibrium (non-LTE) analysis of
the spectra. Our models are not inconsistent with the explosions of C+O
cores of massive stars. While we find no direct evidence for helium
in the optical spectra, our models cannot rule out small amounts of
helium. More than 0.1 M_solar of helium seems unlikely.

---------------------------------------------------------
Title: Synthetic Spectra and Mass Determination of the Brown Dwarf
Gl229B
Authors: Allard, France; Hauschildt, Peter H.; Baraffe, Isabelle;
Chabrier, Gilles
1996astro.ph..3019A Altcode:
We present preliminary non-grey model atmospheres and interiors for
cool brown dwarfs. The resulting synthetic spectra are compared to
available spectroscopic and photometric observations of the coolest
brown dwarf yet discovered, Gl229B (Nakajima \etal, 1995). Despite
recognized shortcomings of current methane opacities, we find that the
model spectra provide an excellent fit to most of the spectral features
of the brown dwarf. We confirm the presence of methane absorption
and the substellar nature of Gl229B. These preliminary models set an
upper limit for the effective temperature of 1000~K. We also compute
the evolution of brown dwarfs with solar composition and masses from
0.02 to 0.065 $\msol$. While uncertainties in the age of the system
yield some undetermination for the mass of Gl229B, the most likely
solution is $m\approx 0.04-0.055 \msol$. In any case, we can set an
upper limit $m= 0.065\msol$ for a very unlikely age $t=10$ Gyr.

---------------------------------------------------------
Title: Radiative transfer in the comoving frame
Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A.
1996MNRAS.278..763B Altcode:
We discuss the formulation of the radiative transfer equation in the
comoving frame. For characteristic velocities larger than ~2000 km s^-1,
the effects of advection on the synthetic spectra are non-negligible,
and hence they should be included in model calculations. We show that
the time-independent or quasi-static approximation is adequate for
most astrophysical problems, e.g., hot stars, novae and supernovae. We
examine the use of the Sobolev approximation in modelling moving
atmospheres, and find that the number of overlapping lines in the
comoving frame make the approximation suspect in models that predict
both lines and continua. We also discuss the form of the Rosseland
mean opacity in the comoving frame, and derive a formula that is easy
to implement in radiation hydrodynamics calculations.

---------------------------------------------------------
Title: Spectrum synthesis of type IA SNe
Authors: Hauschildt, P. H.; Baron, E.; Nugent, P.; Branch, D.
1996ASPC...96..175H Altcode: 1996hds..conf..175H
No abstract at ADS

---------------------------------------------------------
Title: Water and titanium oxide in late-type M dwarfs
Authors: Jones, H. R. A.; Viti, S.; Miller, S.; Tennyson, J.; Allard,
F.; Hauschildt, P.
1996ASPC..109..717J Altcode: 1996csss....9..717J
No abstract at ADS

---------------------------------------------------------
Title: Pressure broadening in M dwarfs and VB 10
Authors: Schweitzer, A.; Hauschildt, P. H.; Allard, F.
1996ASPC..109..571S Altcode: 1996csss....9..571S
No abstract at ADS

---------------------------------------------------------
Title: NLTE model atmospheres for M dwarfs and giants
Authors: Hauschildt, P. H.; Allard, F.; Alexander, D. R.; Schweitzer,
A.; Baron, F.
1996IAUS..176..539H Altcode: 1996astro.ph..1155H
The atmospheres of M stars are dominated by a small number of very
strong molecular compounds (H$_2$O, TiO, H$_2$, CO, VO). Most of the
hydrogen is locked in molecular H$_2$, most of the carbon in CO; and
H$_2$O, TiO and VO opacities define a pseudo-continuum covering the
entire flux distribution of these stars. The optical “continuum”
is due to TiO vibrational bands which are often used as temperature
indicators for these stars. These may be the depth of the bands relative
to the troughs in between them; or the depth of the VO bands; or of the
atomic lines relative to the local “continuum”; or even the strength
of the infrared water bands; all of these depend on the strength of the
TiO bands and the amount of flux-redistribution to longer wavelengths
exerted by them. Departures from LTE of the Ti I atom, and thus the
concentration of the important TiO molecule, could, therefore, have
severe and measurable consequences on the atmospheric structure and
spectra of these stars. In this paper we discuss NLTE effects of Ti
I in fully self-consistent models for a few representative M/Brown
dwarf and M giant model atmospheres and spectra.

---------------------------------------------------------
Title: Are novae standard candles?
Authors: Pistinner, S.; Shaviv, G.; Hauschildt, P. H.; Starrfield, S.
1996ASSL..208..295P Altcode: 1996cvro.coll..295P; 1996IAUCo.158..295P
No abstract at ADS

---------------------------------------------------------
Title: The Hot Winds of Novae
Authors: Hauschildt, Peter H.; Starrfield, S.; Baron, E.; Allard, F.
1996aeu..conf..413H Altcode: 1996IAUCo.152..413H
No abstract at ADS

---------------------------------------------------------
Title: Water vapour in cool dwarf stars
Authors: Jones, Hugh R. A.; Longmore, Andrew J.; Allard, France;
Hauschildt, Peter H.; Miller, Steven; Tennyson, Jonathan
1995MNRAS.277..767J Altcode:
We present comparisons which show good agreement between observed
and synthetic spectra for water vapour transitions in a range of M
dwarfs. The observations were made from 2.85 to 3.40 μm where water
vapour transitions are strong in cool stars but relatively weak in the
Earth's atmosphere, allowing reliable observations to be made. The
synthetic spectra were computed using a stellar atmosphere code and
include preliminary ab initio calculations for ro-vibrational bands
up to J=30. Synthetic spectra indicate that changes in metallicity
and gravity have a small effect on the strength of the observed
water bands whereas temperature changes produce large differences in
strength. Formally, we find similar effective temperatures to those
found in previous work. However, since the molecular opacity at the
peak of the flux distribution is not well determined, uncertainties
in the model atmosphere structure and the effective temperature scale
remain. Detailed line profiles can be modelled for atomic lines because
their damping constants are known, but they are not known for molecular
transitions. Atomic lines computed with Voigt profiles and Van der Waals
pressure broadening give an averaged full width half maximum of around
50 km s^-1. For the observed water vapour transitions to match this
generation of synthetic spectra we use Gaussian profiles with a full
width half maximum of 2 km s^-1 to model the pressure broadening of
water vapour transitions. Examination of the model structure indicates
that water vapour lines are formed relatively high in the photosphere
at pressures about an order of magnitude lower than those of atomic
lines. These results strongly suggest that water vapour transitions
are not pressure broadened sufficiently to overlap; as previously
assumed when modelling molecular transitions in cool dwarfs using the
Just Overlapping Line Approximation. The inferred lack of pressure
broadening allows flux to escape between water lines, even within a
region of strong water vapour absorption, and leads to weaker water
band strengths. We demonstrate that this result is likely to explain
much of the past discrepancy between observed and theoretical spectra
energy distributions for M dwarfs.

---------------------------------------------------------
Title: Evidence for a Spectroscopic Sequence among Type 1a Supernovae
Authors: Nugent, Peter; Phillips, Mark; Baron, E.; Branch, David;
Hauschildt, Peter
1995ApJ...455L.147N Altcode: 1995astro.ph.10004N
In this Letter we present evidence for a spectral sequence among Type Ia
supernovae (SN Ia's). The sequence is based on the systematic variation
of several features seen in the near-maximum light spectrum. This
sequence is analogous to the recently noted photometric sequence
among SN Ia's which shows a relationship between the peak brightness
of a SN Ia and the shape of its light curve. In addition to the
observational evidence we present a partial theoretical explanation
for the sequence. This has been achieved by producing a series of
non-LTE synthetic spectra in which only the effective temperature is
varied. The synthetic sequence nicely reproduces most of the differences
seen in the observed one and presumably corresponds to the amount of
56Ni produced in the explosion.

---------------------------------------------------------
Title: An Exploratory Model Atmosphere for the Brown Dwarf Gl229B
Authors: Hauschildt, P. H.; Allard, F.; Alexander, D. R.
1995AAS...18710312H Altcode: 1995BAAS...27.1432H
We present an exploratory convective model atmosphere and synthetic
spectrum for the cool brown dwarf Gl229B recently discovered by Nakajima
et al (1995). The model is computed using the multi-purpose stellar
atmosphere code Phoenix with a special implementation of condensation
rates and grain opacities (Alexander &amp; Ferguson 1994), an H_3(+)
line list by Neale &amp; Tennyson (1995), and the combined HITRAN
(Rothman et al, 1992) and GEISA (Husson et al, 1992) planetary data
bases. The synthetic spectrum is compared to the available spectroscopic
and photometric observations of Gl229B. We investigate in particular the
effects of grain condensation and opacities, and some alternatives to
the incompleteness of the considered CH4 line list. By discussing the
inferred structure and spectrum of Gl229B, we provide some insights
and guidelines for future studies of this brown dwarf in different
spectral ranges. Model atmospheres, synthetic spectra and colors
presented here will be made available upon request. This research
is partially supported by a NASA LTSA grant to ASU and an NSF grant
AST-9217946 to WSU.

---------------------------------------------------------
Title: Hot Water in Cool Stars
Authors: Viti, S.; Jones, H. R. A.; Tennyson, J.; Polyansky, O. L.;
Miller, S.; Hauschildt, P.; Allard, F.
1995AAS...18710314V Altcode: 1995BAAS...27.1432V
We compare high quality data of the infrared water vapour bands for one
of the coolest known M dwarfs, TVLM 513-46546 with synthetic spectra
from the model atmosphere code sc {PHOENIX}. We show how the use
of three different datasets for the water vapour input to the model
produces dramatic changes to the synthetic spectra yet none account
for the observations. These comparisons underline the urgent need for
more accurate data for water vapour. We have calculated a preliminary
water linelist computed with parameters suitable for Sunspots. The
codes employed calculate quantum mechanically the rotation-vibration
energy levels, wavefunctions and associated dipole transition strengths
using the sc {DVR3D} program suite. This water linelist improves on the
previous one because it uses a better potential and the full symmetry
of the water molecule. However, so far the energy levels computed are
limited to the ground vibrational state. Using these calculations we
have compared our results with linestrengths measured in laboratory
experiments performed at a temperature of 1823K and the agreement is
very good. We are calculating a more complete water linelist. It will
include all energy levels up to 30 000 cm(-1) for angular momentum
states up to J=30 and it uses an accurate potential surface. First
results from this production are already available. Progress on these
projects will be reported at the conference.

---------------------------------------------------------
Title: Non-LTE treatment of Fe II in astrophysical plasmas.
Authors: Hauschildt, P. H.; Baron, E.
1995JQSRT..54..987H Altcode: 1996astro.ph..1148H
The authors describe their implementation of an extremely detailed
model atom of singly ionized iron for NLTE computations in static
and moving astrophysical plasmas. The model atom includes 617 levels,
13,675 primary permitted transitions and up to 1.2 million secondary
transitions. The authors' approach guarantees that the total iron
opacity is included at the correct wavelength with reasonable
memory and CPU requirements. They find that the lines saturate the
wavelength space, such that special wavelength points inserted along
the detailed profile functions may be replaced with a statistical
sampling method. The authors describe the results of various test
calculations for novae and supernovae.

---------------------------------------------------------
Title: A New Generation of Evolutionary Sequences for Novae
Authors: Starrfield, S.; Hauschildt, P.; Truran, J.; Sparks, W.;
Wiescher, M.
1995AAS...187.7915S Altcode: 1995BAAS...27.1399S
We report on the results of new calculations of Thermonuclear
Runaways (TNR) on 1.25Msun and 1.35Msun
oxygen-neon-magnesium white dwarfs using an updated version of
NOVA. NOVA is a one-dimensional, fully implicit, hydrodynamic stellar
evolution code that includes a large nuclear reaction network. The
results of our previous studies can be found in Starrfield et al (1992,
ApJ, 391, L71) and Politano et al (1995, ApJ, 448, 807). Since those
calculations were done, we have updated both the nuclear reaction
network and the nuclear reaction rates (see, for example, Van Wormer
et al 1994, ApJ, 432, 326 and Herndl et al 1995, Phys. Rev. C, 52,
1078). We now use opacities from the OPAL carbon rich tables. When we
are outside the range of validity of the OPAL tables, we continue to
use the Iben fit. The new sequences also include boundary layer heating
both from the accretion shock and the internal energy of the infalling
material (Shaviv and Starrfield 1987, ApJ, 321, L51). Finally, in order
to improve the agreement between our theoretical light curves and the
observations, we use bolometric corrections obtained from the latest
generation of spherical, expanding, Non-LTE, stellar atmospheres for
novae (Hauschildt et al 1995a, ApJ, 447, 829; Hauschildt et al 1995b,
ApJ, in press). Our first results show that the changes in the reaction
rates and the opacities cause quantitative changes with respect to our
published studies. For accretion onto the 1.25Msun white
dwarf, for example, we find that less mass is ejected and a smaller
amount of (26) Al is produced. In addition, the abundances of (31) P
and (32) S increase by factors of more than two. The causes are that
(1)the OPAL opacities are larger than those given by the Iben fit,
which results in less mass being accreted on the white dwarf for the
same initial conditions, and (2) the proton-capture reaction rates for
some of the intermediate mass nuclei near (26) Al have increased so
that the evolution to higher mass nuclei is enhanced. We acknowledge
partial support by DOE, NASA, and NSF.

---------------------------------------------------------
Title: M Stars Model Atmospheres: Spectra and Colors
Authors: Allard, F.; Lawlor, T.; Alexander, D. R.; Hauschildt, P. H.
1995AAS...18710311A Altcode: 1995BAAS...27.1432A
In this paper, we present new pressure-dependent line-by-line LTE model
atmospheres for red giants in spherical geometry, computed using the
multi-purpose atmospheric code Phoenix, which constitutes an extension
of the existing cool dwarf grids of Allard &amp; Hauschildt (1995) to
the abundance and gravity regimes of cool M-S-C type giants. Departures
from LTE in the Ti I lines is investigated for some selected models
across the grid, but only modest NLTE effects are found in the abundance
of the important absorber TiO. The combined dwarf and giant grid is
compared to observations in the 8-colors Wing photometric sample of
cool dwarfs and M-S-C giants of the Large Magellanic Clouds. The
Pheonix giant grid is also compared to results obtained with our
version of the Atlas9 code. In particular, we investigate the failure
of Atlas-family models to reproduce the Violet (2700 to 4000 Angstroms)
energy distribution of cool giants. Short &amp; Lester (1994) suggested
this may be due to a lack of molecular photo-dissociation opacities of
hydrides. We find that Phoenix models computed with opacities similar
to our Atlas9 opacities do not show this Violet discrepancy. We explore
remaining opacity differences as well as differences in the treatment
of radiative transfer. Model atmospheres, synthetic spectra and colors
presented here will be made available upon request. This research is
partially supported by a grant AST-9217946 from the National Science
Foundation.

---------------------------------------------------------
Title: NLTE Modeling of SNe Ia Near Maximum Light
Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A.
1995astro.ph.11081B Altcode:
Modeling the atmospheres of SNe~Ia requires the solution of the
NLTE radiative transfer equation. We discuss the formulation of the
radiative transfer equation in the co-moving frame. For characteristic
velocities larger than about 2000 km/s, the effects of advection on the
synthetic spectra are non-negligible, and hence should be included in
model calculations. We show that the time-independent or quasi-static
approximation is adequate for SNe~Ia near maximum light, as well as for
most other astrophysical problems; e.g., hot stars, novae, and other
types of supernovae. We examine the use of the Sobolev approximation
in modeling moving atmospheres and find that the number of overlapping
lines in the co-moving frame make the approximation suspect in models
that predict both lines and continua. We briefly discuss the form of
the Rosseland mean opacity in the co-moving frame, and present a formula
that is easy to implement in radiation hydrodynamics calculations.

---------------------------------------------------------
Title: Some Remarks about Nova Spectroscopy and Photometry
Authors: Pistinner, Shlomi; Shaviv, Giora; Hauschildt, Peter H.;
Starrfield, Sumner
1995ApJ...451..724P Altcode:
In this paper we explore the sensitivity of stellar atmosphere modeling
of early nova spectra to the input parameters. Our results identify
spectral regions where the continuum spectra are insensitive to the
input parameters and certain wave bands where they are sensitive to
the input parameters. Thus, we identify the best spectral region
for determining elemental abundances, effective temperatures, and
luminosities. We find in some cases that nova atmospheres have a
continuum extinction coefficient that is dominated by scattering. The
continuum scattering and the resulting continuum extinction are
for these cases nearly gray. We apply and extend the small parameter
Chandrasekhar expansion and we use the properties of the gray opacity,
to study the effects of small residual absorption in the atmosphere. Two
cases are treated: the case of a static extended atmosphere and the
case of an extended atmosphere in motion. We solve, self-consistently,
the transfer equation for these physical conditions. The assumption
of radiative equilibrium allows us to also obtain a self-consistent
temperature profile which validates our approximation a posteriori. Using these solutions, we (a) derive conditions for the required
signal-to-noise ratio (or the relative accuracy of the observed
fluxes) and the required observed frequency range needed to obtain a
prescribed accuracy for those nova parameters obtained from a comparison
of observed with synthetic spectra; (b) assess and establish the
importance of spectroscopic (in contrast to photometric) measurements;
(c) show that the use of synthetic spectra is an essential part, in the
optically thick phase, of the determination of nova characteristics from
the observations; and (d) define a new property continuum similarity and
show how and when nova spectra possess this property. We find that the
only wavelength region which is not affected by the physical conditions
used to arrive at these conclusions is the ultraviolet. Therefore,
we conclude that the ultraviolet is the most important wavelength
region to use when deriving nova parameters from synthetic spectra.

---------------------------------------------------------
Title: Erratum:“Low Hubble Constant from the Physics of Type Ia
Supernovae” [Phys. Rev. Lett. 75, 394 (1995)]
Authors: Nugent, Peter; Branch, David; Baron, E.; Fisher, Adam;
Vaughan, Thomas; Hauschildt, Peter H.
1995PhRvL..75.1874N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Physics of Early Nova Spectra
Authors: Hauschildt, Peter H.; Starrfield, Sumner; Shore, Steven N.;
Allard, France; Baron, E.
1995ApJ...447..829H Altcode:
We discuss the physical effects that are important for the formation of
the early spectra of novae. Nova atmospheres are optically thick, fast
expanding shells with flat density profiles, leading to geometrically
very extended atmospheres. We show that the properties of early nova
spectra can be understood in terms of this basic model and discuss
some important effects that influence the structure and the emitted
spectrum of nova atmospheres, e.g., line blanketing, non-LTE effects,
and the velocity field. The proper modeling of nova atmospheres is
discussed, and we give some computational details.

---------------------------------------------------------
Title: Low Hubble Constant from the Physics of Type Ia Supernovae
Authors: Nugent, Peter; Branch, David; Baron, E.; Fisher, Adam;
Vaughan, Thomas; Hauschildt, Peter H.
1995PhRvL..75..394N Altcode:
Two physical methods for determining luminosities and distances of type
Ia supernovae, the spectral fitting expanding atmosphere method and the
56Ni radioactivity method, depend on the interval between the
times of explosion and maximum brightness, but in differing ways. By
requiring consistency between the two methods we derive blue and
visual absolute magnitudes MB~=MV~=-19.74+/-0.45
mag which, together with the ridge line of type Ia supernovae in
the magnitude-redshift diagram, constrain the Hubble constant to be
50+12-10 km s-1 Mpc-1.

---------------------------------------------------------
Title: New Evolutionary Tracks for Very Low Mass Stars
Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H.
1995ApJ...446L..35B Altcode:
We present new evolutionary calculations for low-mass and very low
mass M dwarfs, for a metallicity range -2 ≤ [M/H] ≤ 0, down
to the hydrogen-burning minimum mass (0.07 &lt; M/Msun
&lt; 0.6). We use the most recent atmosphere models calculated by
Allard &amp; Hauschildt (1995), based on synthetic spectra at finite
metallicity, and gray atmosphere models based on Alexander &amp;
Ferguson (1994) Rosseland opacities. Comparisons are made with
observational results down to the bottom of the main sequence, for
different metallicities, in magnitude-color and color-color diagrams. We
find excellent agreement between theory and observations over the
whole characteristic temperature/luminosity range. This enables us to
determine the mass of the faintest objects observed, which is found
to be mlim ≍ 0.085 Msun for [M/H] = 0 and
-0.5, and mlim = 0.09 Msun for [M/H] = -1.5,
for an age of 10 Gyr. We also examine the effect of the age,
the metallicity, and the outer boundary conditions on the evolution.

---------------------------------------------------------
Title: Supernova 1993J: one year later.
Authors: Baron, E.; Hauschildt, P. H.; Young, T. R.
1995PhR...256...23B Altcode:
Supernova 1993J, a Type IIpec supernova, was discovered on 1993 March
28 in the nearby galaxy M81. The spectra displayed strong Balmer
lines establishing its classification as a Type II supernova. About
26 days after explosion the Hα profile became anomalous, signaling
the presence of significant amounts of helium. Additionally, the light
curve displayed an anomalous double peak. We review the observations
and interpretation of SN 1993J through the use of light curve fitting
and synthetic spectra.

---------------------------------------------------------
Title: Model Atmospheres for M (Sub)Dwarf Stars. I. The Base
Model Grid
Authors: Allard, France; Hauschildt, Peter H.
1995ApJ...445..433A Altcode: 1996astro.ph..1150A
We have calculated a grid of more than 700 model atmospheres valid for
a wide range of parameters encompassing the coolest known M~dwarfs,
M~subdwarfs and brown dwarf candidates: $1500\le \teff \le 4000\,$K,
$3.5\le \log(g)\le 5.5$, and $-4.0\le { [M/H]}\le +0.5$. Our equation
of state includes 105 molecules and up to 27 ionization stages of 39
elements. In the calculations of the base grid of model atmospheres
presented here, we include over 300 molecular bands of 4 molecules (TiO,
VO, CaH, FeH) in the JOLA approximation, the water opacity of Ludwig
(1971), collision induced opacities, b-f and f-f atomic processes, as
well as about 2 million spectral lines selected from a list with more
than 42 million atomic and 24 million molecular (H$_2$, CH, NH, OH,
MgH, SiH, C$_2$, CN, CO, SiO) lines. High-resolution synthetic spectra
are obtained using an opacity sampling method. The model atmospheres
and spectra are calculated with the generalized stellar atmosphere
code PHOENIX, assuming LTE, plane-parallel geometry, energy (radiative
plus convective) conservation, and hydrostatic equilibrium. The model
spectra give close agreement with observations of M~dwarfs across a
wide spectral range from the blue to the near-IR, with one notable
exception: the fit to the water bands. We discuss several practical
applications of our model grid, e.g., broadband colors derived from
the synthetic spectra. In light of current efforts to identify genuine
brown dwarfs, we also show how low-resolution spectra of cool dwarfs
vary with surface gravity, and how the high-resolution line profile
of the Li~I resonance doublet depends on the Li abundance.

---------------------------------------------------------
Title: Non-LTE Spectral Analysis and Model Constraints on SN 1993J
Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Austin, S.;
Garnavich, P.; Ann, Hong Bae; Wagner, R. M.; Filippenko, A. V.;
Matheson, T.; Liebert, James
1995ApJ...441..170B Altcode:
We present non-LTE synthetic spectra for a time series of observations
of SN 1993J obtained on 1993 March 30-31, April 7, April 13-15,
and June 13 UT. The spectra are dominated by hydrogen Balmer lines;
neutral helium lines, which have been nonthermally excited; and Fe II
features. The density profile evolves from an extremely steep "brick
wall" structure with an equivalent power-law index of about 50 on
March 30 to a more typical SN II profile with a power law index of
about 10. The early spectra are well fitted by a solar composition
of metals, although an enhanced abundance of helium is required in
order to fit the neutral helium lines. By June 13, the photosphere
has receded deep into the helium layer, although there appears to be
a layer of hydrogen at higher velocity. The distance is estimated for
each epoch. While consistent results are found for spectra obtained in
the month of April, the spread in distances from March to June is quite
large. Our value for April is μ = 28.0 +/- 0.3 mag, consistent with
the recent Cepheid distance to the host galaxy M81. We also compare our
results to other implementations of the expanding photosphere method.

---------------------------------------------------------
Title: Spectrum Synthesis of the Type IA Supernovae SN 1992A and
SN 1981B
Authors: Nugent, Peter; Baron, E.; Hauschildt, Peter H.; Branch, David
1995ApJ...441L..33N Altcode:
We present non-LTE synthetic spectra for the Type Ia supernovae SN 1992A
and SN 1981B, near maximum light. At this epoch both supernovae were
observed from the UV through the optical. This wide spectral coverage
is essential for determining the density structure of a SN Ia. Our
fits are in good agreement with observation and provide some insight
as to the differences between these supernovae. We also discuss the
application of the expanding photosphere method to SNe Ia which gives
a distance that is independent of those based on the decay of ^56^Ni
and Cepheid variable stars.

---------------------------------------------------------
Title: Ionization and temperature of nova shells. II. The influence
of realistic photospheric radiation fields.
Authors: Beck, H. K. B.; Hauschildt, P. H.; Gail, H. -P.; Sedlmayr, E.
1995A&A...294..195B Altcode:
In order to determine the physical situation preceding the process
of dust formation in classical novae we calculate the time dependent
ionization and temperature structure of an expanding shell which is
exposed to the ionizing radiation of a hot central source. Additionally
the energy balance between ionizational heating and cooling processes
by electron recombination, gas expansion, collisionally excited
forbidden lines of several atoms and free-free radiation of hydrogen
is solved. The radiation field of the classical nova is given by a
synthetic spectrum calculated on the assumption of spherical symmetry
and a time-independent, expanding, non-LTE atmosphere in radiative
equilibrium. We show that in novae of slow and moderate speed class
complete carbon ionization throughout the nova shell is not possible
before day ~50 after the outburst. In the early phases the degree of
carbon ionization is significantly lower than in the corresponding
blackbody model, thus enabling a complex chemistry to proceed, which
may involve fast ion-neutral reactions.

---------------------------------------------------------
Title: The Physics of Early Nova Spectra
Authors: Hauschildt, P. H.; Starrfield, S.; Shore, S. N.; Allard,
F.; Baron, E.
1995ASSL..205..257H Altcode: 1995cava.conf..257H
No abstract at ADS

---------------------------------------------------------
Title: The Outburst of Nova Cassiopeiae 1993
Authors: Starrfield, S.; Hauschildt, P. H.; Shore, S. N.;
Gonzales-Riestra, R.; Sonneborn, G.; Allard, F.
1995ASSL..205..267S Altcode: 1995cava.conf..267S
No abstract at ADS

---------------------------------------------------------
Title: M (sub) Dwarf Model Atmospheres: The Next Generation
Authors: Allard, F.; Hauschildt, P. H.
1995bmsb.conf...32A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model Atmospheres for the “Most Abnormal” DZ White Dwarf
Authors: Aannestad, P. A.; Hauschildt, P.; Hammond, G. L.; Allard, F.
1994AAS...185.4602A Altcode: 1994BAAS...26.1382A
We present model atmospheres calculations for G165-7, a DZ white
dwarf with the most metal lines in its spectrum. The model spectra
are fitted to existing ground-based observations from 3200 Angstroms
to 10,000 Angstroms , including high resolution MMT data in the region
3700 Angstroms - 4600 Angstroms (Sion et al. ApJS,72,707). We use the
plane-parallel, LTE mode of the general computer code PHOENIX 4.9 to
compute the model atmospheres and synthetic spectra for G165-7. About
10(5) atomic lines and 10(6) molecular lines are included within the
spectral region. The equation of state is solved for 39 elements (with
up to 26 ionization stages per element) and 105 molecules. The models
include, self consistently, line blanketing of the lines selected from
the latest atomic and molecular line list of Kurucz (1993, CD-ROM,
1 and 15) and others.

---------------------------------------------------------
Title: Non-LTE Effects on the Strength of the Lyman Edge in Quasar
Accretion Disks
Authors: Stoerzer, H.; Hauschildt, P. H.; Allard, F.
1994ApJ...437L..91S Altcode:
We have calculated UV/EUV (300 A &lt;= λ &lt;= 1500 A) continuous
energy distributions of accretions disks in the centers of active
galactic nuclei (AGNs) for disk luminosities in the range 0.1L_Edd
&lt;= L_acc_ &lt; 1.0L_Edd_ and central masses ranging from 10^8^
M_sun_ to 10^9^ M_sun_. The vertical gas pressure structure of the
disk and the disk height are obtained analytically; the temperature
stratification and the resulting continuum radiation fields are
calculated numerically. We have included non-LTE effects of both
the ionization equilibrium and the level populations of hydrogen and
helium. We show that these non-LTE effects reduce the strength of the
Lyman edge when compared to the LTE case. In non-LTE we find that the
edge can be weakly in emission or absorption for disks seen face-on,
depending on the disk parameters.

---------------------------------------------------------
Title: Spectrum Synthesis of the Type IA SNe 1992A and 1981B
Authors: Nugent, Peter; Baron, E.; Branch, David; Hauschildt, Peter
1994AAS...185.7902N Altcode: 1994BAAS...26.1444N
We present NLTE synthetic spectra for the Type Ia supernovae SN 1992A
and SN 1981B, near maximum light. At this epoch both supernovae were
observed from the UV through the optical. This wide spectral coverage
is essential for determining the density structure of a SN Ia. Our
fits are in good agreement with observation and provide some insight
as to the differences between these supernovae. We also discuss the
application of the expanding photosphere method to SNe Ia which gives
a distance that is independent of those based on the decay of (56)
Ni and Cepheid variable stars.

---------------------------------------------------------
Title: The early Spectral Evolution of Nova Cassiopeiae 1993
Authors: Hauschildt, Peter H.; Starrfield, Sumner; Shore, Steven N.;
Gonzalez-Riestra, Rosario; Sonneborn, George; Allard, France
1994AJ....108.1008H Altcode:
In this paper we describe the evolution of Nova Cas 1993 over the first
two months of its outburst. We present an ultraviolet light curve that
covers the period from announcement to just after dust began forming in
the ejecta (1994 Feb. 15) and International Ultraviolet Explorer (IUE)
spacecraft constraints forced us to halt our observations. We have used
spherical, expanding, Non-local Thermodynamic Equilibrium (NLTE) stellar
atmospheres to compute synthetic spectra and have compared the results
to combined ultraviolet (low-resolution 1200-3400 A and high-resolution
2400-3300 A) spectra. Our fits show that the effective temperature
of the ejecta increased from approx. 8000 to about approx. 16 000 K
between 1993 Dec. 12 and 1993 Dec. 26. The temperature then increased
more slowly to approx. 24 000 on 1994 Jan. 28. A preliminary abundance
analysis shows evidence for hydrogen depletion, as we also found for
Nova V1974 Cygni; however we find a larger enhancement of carbon,
nitrogen, and oxygen. We also show that the principal mechanism for
mass ejection in this nova is a radiation pressure driven wind and
that mechanical driving is not necessary.

---------------------------------------------------------
Title: EUV energy distributions of accretion disks in active galactic
nuclei.
Authors: Storzer, H.; Hauschildt, P. H.
1994A&A...289...45S Altcode:
We have calculated UV/EUV (300A&lt;=λ&lt;=1500A) continuous
energy distributions of accretion disks in the centers of
active galactic nuclei (AGNs) for disk luminosities in the range
0.1xL_Edd_&lt;=L_acc_&lt; 1.0xL_Edd_ and central masses ranging
from 10^8^Msun_ to 10^10^Msun_. The vertical
gas pressure structure of the disk is obtained analytically, the
temperature stratification and the resulting continuum radiation
fields are calculated numerically. We show that weak Lyman edges are
an intrinsic feature of such disks. The strength of the H I Lyman
edge decreases for increasing accretion rate and fixed mass of the
central black hole. It increases for increasing central mass and fixed
luminosity in terms of the Eddington luminosity.

---------------------------------------------------------
Title: Convergence properties of the accelerated Λ-iteration method
for the solution of radaitive transfer problems.
Authors: Hauschildt, P. H.; Störzer, H.; Baron, E.
1994JQSRT..51..875H Altcode:
The authors investigate the convergence properties and the computational
speed of the accelerated Λ-iteration method for the solution of a
wide variety of radiative transfer problems.

---------------------------------------------------------
Title: Dust formation in Nova Cassiopeiae 1993 seen by ultraviolet
absorption
Authors: Shore, S. N.; Starrfield, S.; Gonzalez-Riestrat, R.;
Hauschildt, P. H.; Sonneborn, G.
1994Natur.369..539S Altcode:
The clouds of gas in interstellar space also contain grains of
dust, whose properties and origins have been the focus of debate for
decades. Some dust formation has been assumed to take place in novae
explosions1-5, as was first implied by the observation of a
steep decrease in the amount of light emitted by the nova1,2
DQ Herculis 1934 about 100 days after outburst, presumed to be due to
extinction by dust. Here we report observations from the International
Ultraviolet Explorer satellite which show directly the onset of dust
formation in Nova Cassiopeiae 1993, a classical nova of the same type
as DQ Her 1934. The dust formed very quickly- about 70 days after the
nova explosion-despite the initially high temperature of the ejecta. Our
results suggest that high-energy photons are absorbed efficiently by
the gas in the ejecta, lowering the temperature in the gas while it
is still dense, and thereby allowing molecules to form and then to
condense into dust.

---------------------------------------------------------
Title: Modeling and Interpretation of the Optical and HST UV Spectrum
of SN 1993J
Authors: Baron, E.; Hauschildt, P. H.; Branch, D.
1994ApJ...426..334B Altcode:
We present spherically symmetric, non-LTE, expanding model atmosphere
synthetic spectra of SN 1993J and compare them to the ultraviolet
and optical spectra obtained simultaneously on 1993 April 15 by the
HST and at Lick Observatory. We are able to fit the optical and HST
near-UV spectra with a variety of compositions, but find that our
best fits are obtained with an enhanced helium abundance (Y = 0.8)
and significant nonthermal ionization due to gamma rays produced by
the decay of ^56^Ni. We find the effects of X-rays produced by thermal
bremsstrahlung in the circumstellar material to have little effect
on the spectrum. Our current models are unable to fit the HST far-UV
region, predicting too little flux and strong, unseen Fe II features.

---------------------------------------------------------
Title: Non-LTE Modeling of Nova Andromedae 1986
Authors: Schwarz, G.; Hauschildt, P.; Starrfield, S.; Allard, F.;
Sonneborn, G.; Shore, S. N.
1994AAS...184.4703S Altcode: 1994BAAS...26..937S
We have analyzed the IUE spectra which covers the early optically thick
phase of Nova OS And 1986. We use spherically symmetric, non-LTE,
line-blanketed, expanding model atmospheres to calculate a grid of
co-moving frame, NLTE atmospheres for this nova with the following set
of parameters: L=2 times 10(5) L_sun, rho ~ r(-3) , statistical velocity
= 50 km s(-1) , 5000 &lt;= T_eff &lt;= 60000K, v_max = 2000 km s(-1)
and solar abundances. We then computed observer frame synthetic spectra
for each of the model atmospheres in the grid and used them to estimate
the model parameters corresponding to the observed IUE spectra. The
fit to the observations was iteratively improved by changing the
parameters of the model atmospheres, in particular T_eff, v_max,
and the abundances. The synthetic spectra give a very good fit to the
pseudo-continuum and many of the features found in the IUE spectra. The
earliest spectra, approximately 4 and 5 days after maximum light in
the optical, are best fit by models with solar abundances for all
elements except for carbon and oxygen which have abundances enhanced
by a factor of about ten. We can not determine nitrogen abundances
due to the lack of strong nitrogen lines in the ultraviolet. The later
spectra, taken 19 and 27 days after maximum light, show, simultaneously,
allowed, semi-forbidden, and forbidden lines. For these epochs, we can
fit the allowed lines and the pseudo-continuum with solar abundances,
except for carbon and oxygen which are still required to be enhanced
by a about a factor of ten. The semi-forbidden and forbidden lines are
formed in the emerging pre-nebula and are not, currently, included in
the model atmospheres. We also find evidence for large non-LTE effects
of Fe II in the later observations.

---------------------------------------------------------
Title: NLTE Synthetic Spectra of Type IA Supernovae
Authors: Nugent, Peter; Baron, E.; Branch, David; Hauschildt, Peter
1994AAS...184.5706N Altcode: 1994BAAS...26..953N
An approximate lambda iteration is used to solve the fully relativistic
radiation transport equation to all orders in v/c. The NLTE rate
equations are solved for MgII, CaII and NaI using an extension of the
method of Rybicki and Hummer 1991, simultaneously with the condition of
radiative equilibrium. The Kurucz list of 3 million lines is used to
select the approximately 300,000 strongest lines with the populations
assumed to be in LTE. The model atmospheres are constructed assuming
that the velocity profile is homologous and that the density profile
follows either a power law or an exponential falloff. Both SNe 1981B
and 1992A are fit from the UV through the optical near maximum light
producing reasonable agreement with observations. We discuss the
application of the expanding photosphere method to SNe Ia which gives
a distance that is independent of those based on radioactive nickel
decay and Cepheids variable stars.

---------------------------------------------------------
Title: An operator splitting method for atmospheres with shocks
Authors: Buchholz, B.; Hauschildt, P. H.; Rammacher, W.; Ulmschneider,
P.
1994A&A...285..987B Altcode:
We develop a fast operator splitting (OS) method to solve spectral line
radiative transfer problems in time-dependent hydrodynamic computations
with shock discontinuities, assuming complete redistribution. The
convergence properties and the results obtained with our method are
compared with results obtained using a modified core-saturation method
and with the {LAMBDA}-iteration. We find that our operator splitting
method is robust, accurate and fast.

---------------------------------------------------------
Title: The Influence of H 2O Line Blanketing on the Spectra of Cool
Dwarf Stars
Authors: Allard, F.; Hauschildt, P. H.; Miller, S.; Tennyson, J.
1994ApJ...426L..39A Altcode:
We present our initial results of model atmosphere calculations for
cool M dwarfs using an opacity sampling method and a new list of H2O
lines. We obtain significantly improved fits to the infrared spectrum
of the M dwarf VB10 when compared to earlier models. H2O is by far the
dominant opacity source in cool stars. To illustrate this, we show the
Rosseland mean of the total extinction under various assumptions. Our
calculations demonstrate the importance of a good treatment of the
water opacities in cool stars and the improvements possible by using
up-to-date data for the water line absorption.

---------------------------------------------------------
Title: Analysis of the Early Spectra and Light Curve of SN 1987A
Authors: Hauschildt, Peter H.; Ensman, Lisa M.
1994ApJ...424..905H Altcode:
Numerical modeling of supernova spectra, light curves, and hydrodynamics
requires physical inputs, numerical techniques, approximations,
and assumptions which must be thoroughly understood in order to
study the details of supernova explosions. Here, we discuss some of
these in the context of the early evolution of supernova 1987A. Gray
radiation-hydrodynamics is used to calculate the bolometric light curve
and the hydrodynamic evolution of the supernova. Synthetic spectra are
then obtained for the resulting density and velocity structure. The
spectrum calculations are performed using a special-relativistic
treatment of the radiative transfer equation in the comoving frame,
line blanketing by about 10^5^ spectral lines, and departures from
LTE for H I, He I, Mg II, and Ca II. We find that we are able to
simultaneously fit the early light curve and spectra reasonably well,
using a progenitor model from Arnett (1991a), without fine-tuning the
free parameters. Temperature structures and radiative equilibrium,
non-LTE effects, homologous expansion, and mean opacities are discussed.

---------------------------------------------------------
Title: Non--LTE Model Atmosphere Analysis of Nova Cygni 1992
Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Wagner, R. M.;
Shore, S. N.; Sonneborn, G.
1994ApJ...422..831H Altcode:
We use spherically symmetric non-local thermodynamic equilibrium
(non-LTE), line-blanketed, expanding model atmospheres to analyze
the International Ultraviolet Explorer (IUE) and optical spectra of
Nova Cygni 1992 during the early phases of its outburst. We find
that the first IUE spectrum obtained just after discovery on 1992
February 20, is best reproduced by a model atmosphere with a steep
density gradient and homologous expansion, whereas the IUE and optical
spectra obtained on February 24 show an extended, optically thick,
wind structure. Therefore, we distinguish two phases of the early
evolution of the nova photosphere: the initial, rapid, 'fireball' phase
and the subsequent, much longer, optically thick 'wind' phase. The
importance of line-blanketing in nova spectra is demonstrated. Our
preliminary abundance analysis implies that hydrogen is depleted in
the ejecta, corresponding to abundance enhancements of Fe by a factor
of approximately 2 and of CNO by more than a factor of 10 when compared
to solar abundances. The synthetic spectra reproduce both the observed
pseudo-continua as well as most of the observed features from the
UV to the optical spectral range and demonstrate the importance of
obtaining nearly simultaneous UV and optical spectra for performing
accurate analyses of expanding stellar atmospheres (for both novae
and supernovae).

---------------------------------------------------------
Title: Nova Cassiopeiae 1993
Authors: Shore, S. N.; Starrfield, S.; Hauschildt, P.;
Gonzalez-Riestra, R.; Sonneborn, G.
1994IAUC.5938....1S Altcode:
S. N. Shore, Indiana University, South Bend; S. Starrfield and
P. Hauschildt, Arizona State University; R. Gonzalez-Riestra,
IUE Observatory, Vilspa; and G. Sonneborn, NASA/Goddard Space
Flight Center, report: "Observations of Nova Cas 1993 with the IUE
Satellite have confirmed the formation of dust (IAUC 5925, 5936) in
the nova ejecta during the deep optical decline that is now underway
(IAUC 5934). Spectra obtained on Feb. 18.1 and 19.5 UT show that
the 120-200-nm portion of the spectrum has declined by more than a
factor of ten since Feb. 11.2 UT with virtually no change in the
absorption line opacity; the entire wavelength interval has been
uniformly depressed. The longer-wavelength portion of the spectrum,
220-340 nm, exhibits depression by more than a factor of 20 in
comparison to Feb. 11.5, with a broad peak in the extinction near
Mg II 280 nm. The Feb. 18.3 long-wavelength spectra now show the C
II 232-nm multiplet in emission, one of the few changes in the line
spectrum during the past two weeks. There is no evidence for either
enhanced absorption near 220 nm or for a steep short-wavelength
rise. Therefore, the observed extinction, from the circumstellar
dust that has just formed in the nova ejecta, does not resemble
typical interstellar dust. The most likely explanation is that these
grains are larger than normal interstellar dust. If the drop in the
emitted radiation in the ultraviolet and optical is compensated by
an increase in the infrared radiation as expected (cf. Gehrz 1988,
Ann. Rev. Astron. Astrophys. 26, 377), the integrated infrared flux
longward of 1 micron should reach of order 8*10**-8 erg cm-2 s-1
(based on the ultraviolet flux depression). We have used E(B-V) = 0.5
to correct for the interstellar (not circumstellar) extinction. Before
the decline began, the 120-340-nm continuum contained the bulk of the
luminosity. The bolometric luminosity of the nova has been constant to
within about 10 percent from 1993 Dec. 15 to 1994 Feb. 11. It likely
still is, except that it is now hidden by the enhanced extinction
produced by the increasingly opaque circumstellar dust."

---------------------------------------------------------
Title: Novae at Maximum Light: They can be Cool!
Authors: Hauschildt, P. H.; Starrfleld, S.; Allard, F.
1994ASPC...64..705H Altcode: 1994csss....8..705H
No abstract at ADS

---------------------------------------------------------
Title: Nova Cassiopeiae 1993
Authors: Shore, S. N.; Starrfield, S.; Hauschildt, P. H.; Sonneborn,
G.; Gonzalez-Riestra, R.; Mikuz, H.; Prudic, J.
1994IAUC.5925....1S Altcode:
S. N. Shore, Indiana University, South Bend; S. Starrfield and
P. H. Hauschildt, Arizona State University; G. Sonneborn, Goddard
Space Flight Center; and R. Gonzalez-Riestra, International Ultraviolet
Explorer (IUE) Observatory, Vilspa, report: "Observations of N Cas 1993
have been obtained with the IUE satellite since shortly after the report
of its discovery (IAUC 5902). The first spectra (1993 Dec. 12.1 UT)
showed the nova at ultraviolet (UV) minimum with most of the opacity
coming from overlapping absorption lines from the iron group elements:
the 'iron curtain'. We have been obtaining IUE spectra at about 4-day
intervals since that time, which reveal that the ejected material has
remained in an extremely optically thick shell stage. The wavelength
region around 280 nm is a blend of both Fe II and Mg II. This blend
displays a pseudo-P-Cyg profile with a broad absorption trough that
extends to a velocity of about -1600 km/s. Interstellar Mg II h and k
absorption lines are superposed on emission from the nova; they have
mean velocities of -35 km/s but extend to nearly -60 km/s. Windows
in the Fe II absorption spectrum have recently begun to appear at
158 nm and longer wavelengths, and changes in the spectral energy
distribution imply a slowly growing temperature for the ejecta. An
ultraviolet rise of a factor of three occurred around Dec. 22, but
after that time the nova has remained at nearly constant integrated
UV flux (through 1994 Jan. 12). A preliminary upper limit of E(B-V)
= 0.6 is derived from the UV-to-optical flux ratio. The interstellar
Mg II and Na I lines suggest a distance of 4-6 kpc. We note that
the optical light curve is similar to that of a DQ Her-type of nova
(Payne-Gaposchkin 1957, The Galactic Novae, p. 13). Such a nova will
form an optically-thick dust shell about 60-90 days after maximum
light in the optical. Our stellar-atmosphere modeling indicates that
the slow spectral evolution is consistent with steady- state ejection
over the past month. The optical light curve, the relatively slow UV
spectral evolution, the steady state mass ejection, and the detection
of CO molecular lines in the infrared (IAUC 5916, 5922) lead us to
expect that this nova will also form optically-thick dust (Shore and
Starrfield 1994, Sky Telesc., in press); infrared observations will be
necessary to confirm this expectation." H. Mikuz, Ljubljana, Slovenia,
reports that a prediscovery photograph, taken by J. Prudic (Ljubljana)
on 1993 Dec. 4.95 UT with a 58-mm f/2 lens and T-Max 400 film, shows
this object at mpv = 8.0 (comparison stars from AAVSO Atlas).

---------------------------------------------------------
Title: On the strength of the Lyman edge in quasar accretion disks.
Authors: Störzer, H.; Hauschildt, P. H.
1994AGAb...10..227S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectral Analysis of SN 1993J
Authors: Baron, E.; Hauschildt, P. H.; Branch, D.
1993AAS...183.3902B Altcode: 1993BAAS...25.1348B
We present results of model calculations of synthetic spectra for a
time series of observations of the Type IIpec supernova SN 1993 in
M81. We find that at very early times the composition was likely to be
roughly solar and the atmosphere was rather extended. The structure
quickly evolved to be extremely steep with equivalent power-law
indices at the “photosphere” of N ~ 20-40 and the composition became
significantly enhanced in helium with Y ~ 0.8. We find the helium is
excited by non-thermal ionization from fast electrons produced by the
Comptonization of gamma rays from the decay of ~ 0.1 M_sun of (56)
Ni. We find a distance to the supernova consistent with that of the
recently determined Cepheid distance. We compare our distance with
other published distance determinations. We also discuss discrepancies
between our models and the observations.

---------------------------------------------------------
Title: Interpretation of the Early Spectra of SN 1993J in M81
Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Wagner, R. M.;
Austin, S. J.; Filippenko, A. V.; Matheson, T.
1993ApJ...416L..21B Altcode:
We present optical spectra obtained on 1993 April 7 and April 13 of the
bright supernova SN 1993J in the nearby galaxy M81. The spectra show
strong hydrogen Balmer lines with pronounced P Cygni profiles, except
for Hα, which is greatly dominated by emission. In order to obtain
diagnostics on the velocities, temperatures, densities, and composition
of the atmosphere, we present non-local thermodynamic equilibrium (NLTE)
synthetic spectrum fits to these observations. For April 7 we find a
photospheric velocity of 10,000-11,000 km s^-1^, with a photospheric
electron temperature of 7500-8000 K and a radius of 10^15^ cm. On April
13 the photospheric velocity is about 11,000 km s^-1^, the photospheric
temperature is about 6500 K, and the radius is ~1.6 x 10^15^ cm. Most
of the features of the spectra are well fitted by model atmospheres
with solar composition. We find a distance for SN 1993J of 4.0 +/-
0.5 Mpc and the explosion epoch to be UT 1993 March 27.5+/-0.5.

---------------------------------------------------------
Title: Multi-level non-LTE radiative transfer in expanding shells.
Authors: Hauschildt, P. H.
1993JQSRT..50..301H Altcode:
The author presents a new and general method for the solution of
complex multi-level non-LTE radiative transfer problems both in static
and moving media. The method is based on the approximate Λ-iteration
method and is a direct extension of the scheme devised by Rybicki
and Hummer (1991). The author demonstrates that this method is able
to treat both active continua and overlapping lines with relatively
small amount of computer resources. Some simplified test cases are
presented and discussed.

---------------------------------------------------------
Title: Non-LTE Model Atmosphere Studies of Nova Cygni 1992
Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Shore, S.;
Wehrse, R.; Shaviv, G.
1993AnIPS..10..109H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Prediction of the 22Na and 26Al
Production and γ-RAY Emission from Nova CYG 1992 and Nova HER 1991
Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Shore, S. N.;
Sonneborn, G.; Wagner, R. M.; Gonzales-Riestra, R.; Hauschildt, P. H.;
Austin, S.; Vanlandingham, K.
1993AnIPS..10..320S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet Studies of Novae in the Large Magellanic Cloud
Authors: Starrfield, Sumner; Hauschildt, Peter H.; Shore, Steven N.;
Sonneborn, George; Gonzales-Riestra, R.; Sparks, Warren M.
1993LNP...416..181S Altcode: 1993namc.meet..181S
We report on the ultraviolet observations of five novae in the Large
Magellanic Cloud (LMC). They are LMC 1988 #1, which was a CO nove
similar to OS And; LMC 1988 #2, which was an ONeMg nova similar to
Nova Her 1991; LNC 1990 #1, which was a very fast ONeMG nova similar
to V693 CrA 1981; LMC 1990 #2, which was a recurrent nova similar to
U Sco; and LMC 1991 which reached V approximately 9.

---------------------------------------------------------
Title: Spherical Expanding NLTE Model Atmosphere Studies of Nova
Cyg 1992
Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Wagner, R. M.;
Shore, S. N.; Wehrse, R.; Shaviv, G.
1992AAS...18110012H Altcode: 1992BAAS...24.1280H
We show synthetic spectra for Nova Cyg 1992 during the early, optically
thick phase of its evolution. The model atmospheres are calulated using
the assumptions of a steady state, spherically symmetric wind model
for the early envelope. We solve the non-gray special relativistic
equations of radiative transfer and radiative equilibrium in the
Lagrangian frame. Non-LTE effects are included self-consistently, as
is the effect of line blanketing of about 100,000 UV metal lines (the
“iron-curtain”). The models assume a radial density gradient (rho ~
r(-3) ) and self-similar expansion. These follow from hydrodynamical
calculation of the nova outburst and from late time observations of
Nova Cyg 1992. We show comparisons between our synthetic spectra and
observed IUE low and high resolution spectra and medium resolution
optical spectra of Nova Cyg 92 and discuss some of the properties
of the spectra and the model atmospheres. An especially important
generalization from our models is that the pseudo-emission features,
resulting from line opacity minima, are sensitive to the velocity
gradient in the ejecta.

---------------------------------------------------------
Title: Radiative Equilibrium in Rapidly Expanding Shells
Authors: Hauschildt, P. H.
1992ApJ...398..224H Altcode:
The equation of radiative equilibrium for rapidly expanding spherical
shells including the special relativistic terms is discussed,
and a temperature-correction procedure for the solution of this
equation is given. The temperature-correction scheme combines a
partial linearization approach with the approximate Lambda-operator
iteration method. For some test problems, the temperature structures
of atmospheres in radiative equilibrium in the Lagrangian frame
are calculated. The effects of the velocity field on the temperature
stratification and the luminosity are also discussed. We find that the
temperature structure of a moving photosphere in radiative equilibrium
in the Lagrangian frame differs significantly from that of a static
photosphere and that, at least, all first-order terms, in particular
the advection and aberration terms, have to be included consistently
both in the radiative transfer and the energy equation in studies of
supernovae atmospheres and other high-speed radiating flows.

---------------------------------------------------------
Title: Prediction of the 22Na and 26Al
Production and γ-Ray Emission from Nova Cyg 1992 and Nova Her 1991
Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Shore, S. N.;
Sonneborn, G.; Wagner, R. M.; Gonzalez-Riestra, R.; Hauschildt, P. H.;
Austin, S.; Vanlandingham, K.
1992AAS...181.4406S Altcode: 1992BAAS...24.1190S
No abstract at ADS

---------------------------------------------------------
Title: Spherically Symmetric, Expanding, Non--LTE Model Atmospheres
for Novae during Their Early Stages
Authors: Hauschildt, P. H.; Wehrse, R.; Starrfield, S.; Shaviv, G.
1992ApJ...393..307H Altcode:
In the continuum and line-blanketed models presented here, nova
atmospheres are characterized by a very slow decrease of density
with increasing radius. This feature leads to very large geometrical
extensions so that there are large temperature differences between the
inner and outer parts of the line-forming regions. The theoretical
spectra show a large IR excess and a small Balmer jump which may be
either in absorption or in emission. For the parameters considered
(effective temperature of about 10 exp 4 K, L = 2 x 10 exp 4 solar
luminosities, outer boundary density of about 3 x 10 exp -15 g cm
exp -3, mass-loss rate of 10 exp -5 solar masses/yr), most lines are
in absorption. The effects of changes in the abundances of the heavy
elements on the emergent spectra are discussed. The strong unidentified
features observed in ultraviolet spectra of novae are found in actuality
to be regions of transparency within the Fe 'forest'. Ultraviolet
spectra obtained from the IUE archives are displayed, and spectral
synthesis of these spectra is done using the theoretical atmospheres.

---------------------------------------------------------
Title: A fast operator perturbation method for the solution of the
special relativistic equation of radiative transfer in spherical
symmetry.
Authors: Hauschildt, P. H.
1992JQSRT..47..433H Altcode:
A fast method for the solution of the radiative transfer equation in
rapidly moving spherical media, based on an approximate Λ-operator
iteration, is described. The method uses the short characteristic
method and a tridiagonal approximate Λ-operator to achieve fast
convergence. The convergence properties and the CPU time requirements
of the method are discussed for the test problem of a two-level atom
with background continuum absorption and Thomson scattering. Details
of the actual implementation for fast vector and parallel computers
are given. The method is accurate and fast enough to be incorporated
in radiation-hydrodynamic calculations.

---------------------------------------------------------
Title: Model Atmospheres for Nova during the Early Stages
Authors: Hauschildt, P. H.; Wehrse, R.; Starrfield, S.; Shaviv, G.
1992ASPC...29..178H Altcode: 1992cvs..work..178H
No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet studies of novae in the large Magellanic cloud
Authors: Starrfield, S.; Hauschildt, P. H.
1992STIN...9316181S Altcode:
We report on the ultraviolet observations of five novae in the LMC. They
are as follows: LMC1988 no. 1, which was a CO nova similar to OS,
and LMC 1988 no. 2, which was an ONeMg nova similar to Nova Her 1991;
LMC 1990 no. 1, which was a very fast ONeMg nova similar to V693 CrA
1981; LMC 1990 no. 2, which was a recurrent nova similar to U Sco;
and LMC 1991 which reached V approximately 9.

---------------------------------------------------------
Title: Solution of the special relativistic equation of radiative
transfer in rapidly expanding spherical shells.
Authors: Hauschildt, P. H.; Wehrse, R.
1991JQSRT..46...81H Altcode:
A new method for the solution of the radiative transfer equation
in expanding spherical media based on the Discrete Ordinate Matrix
Exponential (DOME) method is describe. The effects of advection and
aberration terms on line profiles for scattering dominated shells as
observed, e.g., in supernova photospheres are discussed. It is shown
that these effects have a large influence on the radiation field in
rapidly expanding shells and should therefore be included in model
calculations.

---------------------------------------------------------
Title: Model atmospheres for SNe II during early stages.
Authors: Best, M.; Hauschildt, P. H.; Wehrse, R.; Shaviv, G.
1991AnPCS..16..397B Altcode:
The photospheres of type II supernovae during the coasting phase
are characterized by moderate temperatures, large radii, very low
densities and high expansions velocities. These properties lead to large
geometrical extensions and to electron scattering as the main source
of opacity. Therefore these photospheres are very different from those
of stars in hydrostatic equilibrium. In this review the authors first
describe the input physics for models and essential numerical aspects
of the model construction. In particular they stress the central role
of an adequate treatment of the radiative transfer equation which
should simultaneously take into account the sphericity, a high ratio
of scattering to absorption, and relativistic effects. Subsequently
they discuss details of the emergent spectra and their relevance for
parameter determinations. Finally, model spectra are compared with
observations of the brights supernovae SN 1979c and SN 1980k, which
seem to be more average examples of type II supernovae than SN 1987A,
and possibilities for using these objects for extragalactic distance
determinations are investigated.

---------------------------------------------------------
Title: Relativistic effects in supernova photospheres
Authors: Hauschildt, P. H.; Best, M.; Wehrse, R.
1991A&A...247L..21H Altcode:
The role of relativistic effects in the radiative transfer equation
and the condition of radiative equilibrium is studied for supernova
photospheres. It is found that these effects change significantly
the equilibrium temperature stratification and the emergent spectra
so that in abundance determinations errors up to about one order of
magnitude may occur if they are neglected.

---------------------------------------------------------
Title: Non-LTE-Modellatmosphären für Novae und Supernovae Title:
Non-LTE-Modellatmosphären für Novae und Supernovae

---------------------------------------------------------
Title: Non-LTE
model atmospheres for novae and supernovae;
Authors: Hauschildt, Peter H.
1991PhDT.......290H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Model atmospheres for SNe II during early stages
Authors: Best, Monika; Hauschildt, Peter H.; Wehrse, Rainer; Shaviv,
Giora
1991AnPh...16..397B Altcode:
The photospheres of type II supernovae during the coasting
phase ( ~ 1 week to 1 month after outburst) are characterized by
moderate temperatures (Teff ~ 7...12 Ö- 10^3K) , large radii (R ~
10^13...10^15cm) , very low densities (p ~ 10^-13... 10^-16 gcm-3)
and high expansions velocities (up to ~ 30000 km-1 in the outer
layers). These properties lead to large geometrical extensions
(i.e. the photons can travel a large fraction of the radius without
being absorbed) and to electron scattering as the main source of
opacity. Therefore these photospheres are very different from those
of stars in hydrostatic equilibrium. In this review we first describe
the input physics for models and essential numerical aspects of the
model construction. In particular we stress the central role of an
adequate treatment of the radiative transfer equation which should
simultaneously take into account the sphericity, a high ratio of
scattering to absorption, and relativistic effects. Subsequently
we discuss details of the emergent spectra and their relevance for
parameter determinations. Finally, model spectra are compared with
observations of the bright supernovae SN 1979C and SN 1980 K, which
seem to be more average examples of type II supernovae than SN 1987A,
and possibilities for using these objects for extragalactic distance
determinations are investigated.

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Title: Non-LTE Modellatmosphären für Novae und Supernovae.
Authors: Hauschildt, P.
1991nmfn.book.....H Altcode:
Contents: 1. Einleitung. 2. Die Zustandsgleichung. 3. Die Absorptions-
und Streukoeffizienten. 4. Der Strahlungstransport. 5. Die
Modellberechnung. 6. Ergebnisse für Supernovae. 7. Ergebnisse für
Novae.

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Title: Line Formatio in SN II Photospheres
Authors: Best, M.; Hauschildt, P. H.; Wehrse, R.
1991ESOC...37..415B Altcode: 1991sos..conf..415B
No abstract at ADS

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Title: Model atmospheres for the early stages of novae in outburst
Authors: Wehrse, R.; Hauschildt, P. H.; Shaviv, G.; Starrfield, S.
1990ESASP.310..461W Altcode: 1990eaia.conf..461W
No abstract at ADS

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Title: Model Atmospheres for Novae during the Early Stages
Authors: Wehrse, R.; Hauschildt, P. H.; Shaviv, G.; Starrfield, S.
1990LNP...369..264W Altcode: 1990IAUCo.122..264W; 1990pcn..conf..264W
Continuum and line blanketing models for the photospheres of novae
in the early stages of their outbursts are presented. The expanding
envelopes are characterized by a very slow increase of density with
decreasing radius which leads to very large geometrical extensions and
large temperature differences between the inner and outer parts. The
spectra show a large IR excess and a small Balmer jump which may be
either in absorption or in emission. For the parameters considered
(T eff = 104,1.5 x 104, 2 x
104K, R = 1011 cm, solar composition), most
lines are in absorption. The effects of both modifications in the
temperature structure (e.g. by heating from shock fronts) and changes
in the abundances of the heavy elements on the emergent spectra are
briefly discussed.

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Title: Theoretical models for the continuum and colors of SN 1979C
and SN 1980K.
Authors: Hauschildt, P. H.; Shaviv, G.; Wehrse, R.
1989A&A...210..262H Altcode:
Models for the continuum energy distribution from supernovae of type
II are constructed and compared with the recently observed SN 1979 C
and SN 1980 K for the coasting phase of their evolution. Fairly good
agreement with the observed energy distributions from the UV range
down to the IR as well as with colors is found. Using the colors we
demonstrate how the distance to the SN can be found. The advantage of
this method relative to the classical Baade-Wesselink method is that
it needs data only for a single time.

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Title: An atlas of calculated continuum energy distributions for
supernovae of type II
Authors: Hauschildt, P. H.; Wehrse, R.; Shaviv, G.
1989A&AS...77..115H Altcode:
An atlas of continuum energy distributions in the UV, visible,
and near-IR regions has been compiled for type II supernovae. It
is assumed that the cooling envelope can be approximated with a
sequence of stationary atmospheres, that the level populations follow
a Boltzmann distribution for the local temperature throughout the
photosphere, and that the strongest source of continuum opacity is
electron scattering. Results are presented for models with effective
temperatures of between 7000 and 15,000 K.

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Title: Ultraviolet observations of LMC nova 1988.
Authors: Starrfield, S.; Stryker, L. L.; Sonneborn, G.; Sparks, W. M.;
Sion, E. M.; Wagner, R. M.; Ferland, G.; Gallagher, J. S.; Wade, R.;
Williams, R. E.; Heathcote, S.; Gehrz, R.; Ney, E. P.; Kenyon, S.;
Shav, G., IV; Wehrse, R.; Hauschildt, P.; Truran, J. W.; Wu, C. C.
1988ESASP.281a.175S Altcode: 1988uvai....1..175S; 1988IUE88...1..175S; 1988IUES....1..175S
The IUE obtained ultraviolet spectra of a nova in an external
galaxy. The spectral features do not seem unusual for a nova at maximum
but it is hoped to be able to follow it for a long enough time to be
able to study the high ionization lines that appear when the density
drops to lower values (the nebular stage). A high dispersion spectrum
was also obtained to assist in the line identification and to study
the line of sight to the LMC 1 deg of arc away from SN 1987A.

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Title: The analysis of spectra of novae taken near maximum.
Authors: Stryker, L. L.; Hestand, J.; Starrfield, S.; Wehrse, R.;
Hauschildt, P.; Spies, W.; Baschek, B.; Shaviv, G.
1988ESASP.281a.149S Altcode: 1988IUES....1..149S; 1988IUE88...1..149S; 1988uvai....1..149S
A project to analyze ultraviolet spectra of novae obtained at or near
maximum optical light is presented. These spectra are characterized
by a relatively cool continuum with superimposed permitted emission
lines from ions such as Fe II, Mg II, and Si II. Spectra obtained
late in the outburst show only emission lines from highly ionized
species and in many cases these are forbidden lines. The ultraviolet
data will be used with calculations of spherical, expanding, stellar
atmospheres for novae to determine elemental abundances by spectral
line synthesis. This method is extremely sensitive to the abundances
and completely independent of the nebular analyses usually used to
obtain novae abundances.

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Title: Zur Bestimmung von Elementhäufigkeiten aus Supernova
II-Spektren.
Authors: Hauschildt, P. H.; Wehrse, R.
1988AGAb....1...19H Altcode:
No abstract at ADS

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Title: Calculated Energy Distributions for Type-Ii Supernovae
Authors: Hauschildt, P. H.; Spies, W.; Wehrse, R.; Shaviv, G.
1988LNP...305..412H Altcode: 1988IAUCo.108..412H; 1988adse.conf..412H
The authors have calculated a large grid of hydrogen-rich supernova
photospheres, in which radii, effective temperatures, density profiles,
and expansion velocities have been varied. In the quasi-exact radiative
transfer, the dilution of the radiation field, and scattering as well
as absorption are accurately considered. Good agreement can be obtained
with the UV and IR spectra of supernovae 1979C, 1980K, and 1987A as
observed during the coasting phase. Potential methods of parameter
determinations for SN II are briefly discussed.

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Title: Model Photospheres and Synthetic Spectra for Supernova Type-Ii
Authors: Hauschildt, P.; Spies, W.; Wehrse, R.; Shaviv, G.
1987ESOC...26..433H Altcode: 1987sn...work..433H
The UV spectra of recent type II supernovae were calculated
theoretically and compared with observation. Two phases in the
evolution of SN type II envelopes are distinguished. The first phase
is characterized by a high effective temperature and small effects
of lines. The second phase is characterized by a low effective
temperature and strong line blanketing. Continuum models were fitted
to SN 1980K during its first phase of evolution, and good agreement
was found. Blanketed models were fitted to SN 1987A. It is shown that
blanketed models for the second phase provide good agreement with
observations, and that the UV spectra of SN 1987A can be explained
by metal abundances that are between those found in the LMC and the
sun. The peculiar features in the spectra are due to the combined
effect of a large number of Fe group lines in an expanding atmosphere.

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Title: Synthetic Spectra for Supernovae II
Authors: Spies, W.; Hauschildt, P.; Wehrse, R.; Baschek, B.; Shaviv, G.
1987LNP...287..316S Altcode: 1987nuas.proc..316S
The results of an attempt to study the spectra of supernova photospheres
using detailed photospheric models are reported. The photosphere is
calculated assuming a spherical configuration, a density following
a power law with exponent 10, the existence of LTE and radiative
equilibrium, and expansion velocity increasing proportionally to the
radius. The calculated spectra and effective temperature agree well
with the observed spectrum of SN 1980 K. Interesting correspondences
are found between the UV fluxes of SN 1987 A and the energy distribution
of a blanketed model with T(eff) = 8000 K and v(exp) = 15,000 km/s.