kiselman

explanation blue bibcodes open ADS page with paths to full text

Author name code: kiselman
ADS astronomy entries on 2022-09-14
author:"Kiselman, Dan"

---------------------------------------------------------
Title: Physical properties of a fan-shaped jet backlit by an X9.3
flare
Authors: Pietrow, A. G. M.; Druett, M. K.; de la Cruz Rodriguez, J.;
Calvo, F.; Kiselman, D.
2022A&A...659A..58P Altcode: 2021arXiv211010541P
Context. Fan-shaped jets sometimes form above light bridges and are
believed to be driven by the reconnection of the vertical umbral
field with the more horizontal field above the light bridges. Because
these jets are not fully opaque in the wings of most chromospheric
lines, it is not possible to study their spectra without highly
complex considerations of radiative transfer in spectral lines from
the atmosphere behind the fan. Aims: We take advantage of a
unique set of observations of the Hα line along with the Ca II 8542
Å and Ca II K lines obtained with the CRISP and CHROMIS instrument
of the Swedish 1-m Solar Telescope to study the physical properties
of a fan-shaped jet that was backlit by an X9.3 flare. For what we
believe to be the first time, we report an observationally derived
estimate of the mass and density of material in a fan-shaped jet. Methods: The Hα flare ribbon emission profiles from behind the fan
are highly broadened and flattened, allowing us to investigate the fan
with a single slab via Beckers' cloud model, as if it were backlit
by a flat spectral profile of continuum emission. Using this model
we derived the opacity and velocity of the material in the jet. Using
inversions of Ca II 8542 Å emission via the STockholm inversion Code,
we were also able to estimate the temperature and to cross-check the
velocity of the material in the jet. Finally, we used the masses
and the plane-of-sky and line-of-sight velocities as functions of
time to investigate the downward supply of energy and momentum to the
photosphere in the collapse of this jet, and evaluated it as a potential
driver for a sunquake beneath. Results: We find that the physical
properties of the fan material are reasonably chromospheric in nature,
with a temperature of 7050 ± 250 K and a mean density of 2 ± 0.3 ×
10−11 g cm−3. Conclusions: The total
mass observed in Hα was found to be 3.9 ± 0.7 × 1013
g and the kinetic energy delivered to the base of the fan in its
collapse was nearly two orders of magnitude below typical sunquake
energies. We therefore rule out this jet as the sunquake driver,
but cannot completely rule out larger fan jets as potential drivers.

---------------------------------------------------------
Title: Inference of the chromospheric magnetic field configuration
of solar plage using the Ca II 8542 Å line
Authors: Pietrow, A. G. M.; Kiselman, D.; de la Cruz Rodríguez, J.;
Díaz Baso, C. J.; Pastor Yabar, A.; Yadav, R.
2020A&A...644A..43P Altcode: 2020arXiv200614486P
Context. It has so far proven impossible to reproduce all aspects of
the solar plage chromosphere in quasi-realistic numerical models. The
magnetic field configuration in the lower atmosphere is one of the
few free parameters in such simulations. The literature only offers
proxy-based estimates of the field strength, as it is difficult to
obtain observational constraints in this region. Sufficiently sensitive
spectro-polarimetric measurements require a high signal-to-noise
ratio, spectral resolution, and cadence, which are at the limit
of current capabilities. Aims: We use critically sampled
spectro-polarimetric observations of the Ca II 8542 Å line obtained
with the CRISP instrument of the Swedish 1-m Solar Telescope to study
the strength and inclination of the chromospheric magnetic field of
a plage region. This will provide direct physics-based estimates of
these values, which could aid modelers to put constraints on plage
models. Methods: We increased the signal-to-noise ratio of the
data by applying several methods including deep learning and PCA. We
estimated the noise level to be 1 × 10-3 Ic. We
then used STiC, a non-local thermodynamic equilibrium inversion
code to infer the atmospheric structure and magnetic field pixel by
pixel. Results: We are able to infer the magnetic field strength
and inclination for a plage region and for fibrils in the surrounding
canopy. In the plage we report an absolute field strength of |B| = 440
± 90 G, with an inclination of 10° ±16° with respect to the local
vertical. This value for |B| is roughly double of what was reported
previously, while the inclination matches previous studies done in
the photosphere. In the fibrillar region we found |B| = 300 ± 50 G,
with an inclination of 50° ±13°.

---------------------------------------------------------
Title: Solar off-limb emission of the O I 7772 Å line
Authors: Pazira, H.; Kiselman, D.; Leenaarts, J.
2017A&A...604A..49P Altcode: 2017arXiv170506459P
 Aims: The aim of this paper is to understand the formation of
the O I line at 7772 Å in the solar chromosphere. Methods: We
used SST/CRISP observations to observe O I 7772 Å in several places
around the solar limb. We compared the observations with synthetic
spectra calculated with the RH code in the one-dimension spherical
geometry mode. New accurate hydrogen collisional rates were included
for the RH calculations. Results: The observations reveal a
dark gap in the lower chromosphere, which is caused by variations in
the line opacity as shown by our models. The lower level of the 7772
Å transition is populated by a downward cascade from the continuum. We
study the effect of Lyman-β pumping and hydrogen collisions between the
triplet and quintet system in O I. Both have a small but non-negligible
influence on the line intensity.

---------------------------------------------------------
Title: Non-LTE line formation of Fe in late-type stars - IV. Modelling
of the solar centre-to-limb variation in 3D
Authors: Lind, K.; Amarsi, A. M.; Asplund, M.; Barklem, P. S.;
Bautista, M.; Bergemann, M.; Collet, R.; Kiselman, D.; Leenaarts,
J.; Pereira, T. M. D.
2017MNRAS.468.4311L Altcode: 2017arXiv170304027L
Our ability to model the shapes and strengths of iron lines in the solar
spectrum is a critical test of the accuracy of the solar iron abundance,
which sets the absolute zero-point of all stellar metallicities. We use
an extensive 463-level Fe atom with new photoionization cross-sections
for Fe I and quantum mechanical calculations of collisional excitation
and charge transfer with neutral hydrogen; the latter effectively remove
a free parameter that has hampered all previous line formation studies
of Fe in non-local thermodynamic equilibrium (NLTE). For the first
time, we use realistic 3D NLTE calculations of Fe for a quantitative
comparison to solar observations. We confront our theoretical line
profiles with observations taken at different viewing angles across
the solar disc with the Swedish 1-m Solar Telescope. We find that
3D modelling well reproduces the observed centre-to-limb behaviour
of spectral lines overall, but highlight aspects that may require
further work, especially cross-sections for inelastic collisions with
electrons. Our inferred solar iron abundance is log (ɛFe)
= 7.48 ± 0.04 dex.

---------------------------------------------------------
Title: SOLARNET WP50: The SOLARNET data pipeline activity
Authors: Kiselman, Dan
2017psio.confE..95K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: JP3D compression of solar data-cubes: photospheric imaging
and spectropolarimetry
Authors: Del Moro, Dario; Giovannelli, Luca; Berrilli, Francesco;
Pietropaolo, Ermanno; Ermolli, Ilaria; Kiselman, Dan
2017psio.confE.121D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stable umbral chromospheric structures
Authors: Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman,
D.; Gallagher, P. T.; Keenan, F. P.
2015A&A...574A.131H Altcode: 2014arXiv1412.6100H
 Aims: We seek to understand the morphology of the chromosphere in
sunspot umbra. We investigate if the horizontal structures observed
in the spectral core of the Ca II H line are ephemeral visuals
caused by the shock dynamics of more stable structures, and examine
their relationship with observables in the H-alpha line. 
Methods: Filtergrams in the core of the Ca II H and H-alpha lines
as observed with the Swedish 1-m Solar Telescope are employed. We
utilise a technique that creates composite images and tracks the
flash propagation horizontally. Results: We find 0.̋15 wide
horizontal structures, in all of the three target sunspots, for every
flash where the seeing is moderate to good. Discrete dark structures
are identified that are stable for at least two umbral flashes, as well
as systems of structures that live for up to 24 min. We find cases of
extremely extended structures with similar stability, with one such
structure showing an extent of 5”. Some of these structures have a
correspondence in H-alpha, but we were unable to find a one-to-one
correspondence for every occurrence. If the dark streaks are formed at
the same heights as umbral flashes, there are systems of structures
with strong departures from the vertical for all three analysed
sunspots. Conclusions: Long-lived Ca II H filamentary horizontal
structures are a common and likely ever-present feature in the umbra
of sunspots. If the magnetic field in the chromosphere of the umbra
is indeed aligned with the structures, then the present theoretical
understanding of the typical umbra needs to be revisited. Movies
associated to Figs. 3 and 4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424664/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Ca II H sunspot tomography from the photosphere to the
chromosphere
Authors: Henriques, V. M. J.; Kiselman, D.
2013A&A...557A...5H Altcode:
 Aims: We aim at gaining insight into the thermal properties of
different small-scale structures related to sunspots. Methods: We
use filtergrams in the Ca ii H filter at the Swedish 1-m Solar Telescope
to study the relationship between fine structure at different heights
in a sunspot. Results: The methods for destretching and aligning
the different image data work well. The magnetic spine structure in
the outer parts of the sunspot penumbra is found to be associated with
higher intensities in the Ca ii H wing passbands but with less steep
vertical temperature gradients. Dark lanes in a light bridge behave
very similarly to dark cores in penumbral filaments. Fibril structures
are seen in the line-core images over the umbra and penumbra. 
Conclusions: The observations add support to the idea that penumbral
filaments, light bridges, and umbral dots are caused by similar
processes of overturning convection. Observations in the Ca ii H &amp;
K wings are a promising observable, complementing others, for testing
simulation results for sunspots at high spatial resolution.

---------------------------------------------------------
Title: Is the solar spectrum latitude-dependent?. An investigation
with SST/TRIPPEL
Authors: Kiselman, D.; Pereira, T. M. D.; Gustafsson, B.; Asplund,
M.; Meléndez, J.; Langhans, K.
2011A&A...535A..14K Altcode: 2011arXiv1108.4527K
Context. In studies of the solar spectrum compared to spectra of solar
twin stars, it has been found that the chemical composition of the Sun
seems to depart systematically from those of the twins. One possible
explanation could be that the effect is caused by the special aspect
angle of the Sun when observed from Earth compared with the aspect
angles of the twins. This means that a latitude dependence of the
solar spectrum, even with the heliocentric angle constant, could
lead to the observed effects. Aims: We explore a possible
variation in the strength of certain spectral lines that are used
in the comparisons between the composition of the Sun and the twins
at loci on the solar disk with different latitudes but at constant
heliocentric angle. Methods: We use the TRIPPEL spectrograph at
the Swedish 1-m Solar Telescope on La Palma to record spectra in five
spectral regions to compare different locations on the solar disk at
a heliocentric angle of 45°. Equivalent widths and other parameters
are measured for fifteen different lines representing nine atomic
species. Spectra acquired at different times are used in averaging the
line parameters for each line and observing position. Results:
The relative variations in equivalent widths at the equator and at
solar latitude ~45° are found to be less than 1.5% for all spectral
lines studied. Translated into elemental abundances as they would be
measured from a terrestrial and a hypothetical pole-on observer, the
difference is estimated to be within 0.005 dex in all cases. 
Conclusions: It is very unlikely that latitude effects could cause the
reported abundance difference between the Sun and the solar twins. The
accuracy obtainable in measurements of small differences in spectral
line strengths between different solar disk positions is very high,
and can be exploited in studies of, e.g. weak magnetic fields or
effects of solar activity on atmospheric structure.

---------------------------------------------------------
Title: A tilted interference filter in a converging beam
Authors: Löfdahl, M. G.; Henriques, V. M. J.; Kiselman, D.
2011A&A...533A..82L Altcode: 2011arXiv1108.1234L
Context. Narrow-band interference filters can be tuned toward shorter
wavelengths by tilting them from the perpendicular to the optical
axis. This can be used as a cheap alternative to real tunable filters,
such as Fabry-Pérot interferometers and Lyot filters. At the Swedish
1-meter Solar Telescope, such a setup is used to scan through the
blue wing of the Ca ii H line. Because the filter is mounted in a
converging beam, the incident angle varies over the pupil, which
causes a variation of the transmission over the pupil, different for
each wavelength within the passband. This causes broadening of the
filter transmission profile and degradation of the image quality. Aims: We want to characterize the properties of our filter, at
normal incidence as well as at different tilt angles. Knowing the
broadened profile is important for the interpretation of the solar
images. Compensating the images for the degrading effects will improve
the resolution and remove one source of image contrast degradation. In
particular, we need to solve the latter problem for images that are
also compensated for blurring caused by atmospheric turbulence. 
Methods: We simulate the process of image formation through a tilted
interference filter in order to understand the effects. We test the
hypothesis that they are separable from the effects of wavefront
aberrations for the purpose of image deconvolution. We measure the
filter transmission profile and the degrading PSF from calibration
data. Results: We find that the filter transmission profile
differs significantly from the specifications. We demonstrate how to
compensate for the image-degrading effects. Because the filter tilt
effects indeed appear to be separable from wavefront aberrations in a
useful way, this can be done in a final deconvolution, after standard
image restoration with Multi-Frame Blind Deconvolution/Phase Diversity
based methods. We illustrate the technique with real data.

---------------------------------------------------------
Title: Detection of Convective Downflows in a Sunspot Penumbra
Authors: Scharmer, G. B.; Henriques, V. M. J.; Kiselman, D.; de la
Cruz Rodríguez, J.
2011Sci...333..316S Altcode:
The fine structure and dynamics of sunspots and the strong outflow in
their outer filamentary part—the penumbra—have puzzled astronomers
for more than a century. Recent theoretical models and three-dimensional
numerical simulations explain the penumbral filaments and their
radiative energy output as the result of overturning convection. Here,
we describe the detection of ubiquitous, relatively dark downward
flows of up to 1 kilometer per second (km/s) in the interior penumbra,
using imaging spectropolarimetric data from the Swedish 1-meter Solar
Telescope. The dark downflows are omnipresent in the interior penumbra,
distinguishing them from flows in arched flux tubes, and are associated
with strong (3 to 3.5 km/s) radial outflows. They are thus part of a
penumbral convective flow pattern, with the Evershed flow representing
the horizontal component of that convection.

---------------------------------------------------------
Title: Solar velocity references from 3D HD photospheric models
Authors: de la Cruz Rodríguez, J.; Kiselman, D.; Carlsson, M.
2011A&A...528A.113D Altcode: 2011arXiv1101.2671D
Context. The measurement of Doppler velocities in spectroscopic solar
observations requires a reference for the local frame of rest. The
rotational and radial velocities of the Earth and the rotation of
the Sun introduce velocity offsets in the observations. Normally,
good references for velocities are missing (e.g. telluric lines),
especially in filter-based spectropolarimetric observations. 
Aims: We determine an absolute reference for line-of-sight velocities
measured from solar observations for any heliocentric angle, calibrating
the convective line shift of spatially-averaged profiles on quiet sun
from a 3D hydrodynamical simulation. This method works whenever there
is quiet sun in the field-of-view, and it has the advantage of being
relatively insensitive to uncertainties in the atomic data. 
Methods: We carry out radiative transfer computations in LTE for
selected C i and Fe i lines, whereas the Ca ii infrared lines are
synthesized in non-LTE. Radiative transfer calculations are done with
a modified version of Multi, using the snapshots of a non-magnetic
3D hydrodynamical simulation of the photosphere. Results:
The resulting synthetic profiles show the expected C-shaped bisector
at disk center. The degree of asymmetry and the line shifts, however,
show a clear dependence on the heliocentric angle and the properties of
the lines. The profiles at μ = 1 are compared with observed profiles
to prove their reliability, and they are tested against errors induced
by the LTE calculations, inaccuracies in the atomic data and the 3D
simulation. Conclusions: Theoretical quiet-sun profiles of lines
commonly used by solar observers are provided to the community. Those
can be used as absolute references for line-of-sight velocities. The
limb effect is produced by the projection of the 3D atmosphere along the
line of sight. Non-LTE effects on Fe i lines are found to have a small
impact on the convective shifts of the lines, reinforcing the usability
of the LTE approximation in this case. We estimate the precision of the
disk-center line shifts to be approximately 50 m s-1, but
the off-center profiles remain to be tested against observations. The spectral profiles are only available in electronic form 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/528/A113">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A113</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Synthetic lines in the Sun (de
la Cruz Rodríguez+, 2011)
Authors: de la Cruz Rodríguez, J.; Kiselman, D.; Carlsson, M.
2011yCat..35289113D Altcode:
We have computed synthetic spectra from a realistic 3D numerical
simulation of the solar photosphere. We provide the spatially
averaged spectra for selected lines that are commonly used on solar
applications. These data can be used to calibrate Doppler velocity
measurements in the solar photosphere. The calculations are carried
out along the solar disk from heliocentric angle mu=1.0 to mu=0.3. (11 data files).

---------------------------------------------------------
Title: Photospheric Temperatures from Ca IIH
Authors: Henriques, V. M. J.; Kiselman, D.; van Noort, M.
2010ASSP...19..511H Altcode: 2010mcia.conf..511H
The temperature stratification in the upper photosphere can be extracted
from Ca II H&amp;K spectrograms following Shine and Linsky (1974)
by assuming LTE, the Eddington-Barbier approximation, hydrostatic
equilibrium, and that Ca II is mostly in the ground state. Rouppe van
der Voort (2002) confirmed that these assumptions were solid for a wide
range in the Ca IIK wings and further developed the method including
forward computation using MULTI (Carlsson 1986).

---------------------------------------------------------
Title: Oxygen lines in solar granulation. II. Centre-to-limb
variation, NLTE line formation, blends, and the solar oxygen abundance
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
2009A&A...508.1403P Altcode: 2009arXiv0909.2310P
Context: There is a lively debate about the solar oxygen abundance and
the role of 3D models in its recent downward revision. These models
have been tested using high-resolution solar atlases of flux and
disk-centre intensity. Further testing can be done using centre-to-limb
variations. Aims: Using high-resolution and high S/N observations
of neutral oxygen lines across the solar surface, we seek to test
that the 3D and 1D models reproduce their observed centre-to-limb
variation. In particular we seek to assess whether the latest generation
of 3D hydrodynamical solar model atmospheres and NLTE line formation
calculations are appropriate to derive the solar oxygen abundance. 
Methods: We use our recent observations of O i 777 nm, O i 615.81 nm,
[O i] 630.03 nm, and nine lines of other elements for five viewing
angles 0.2≤μ≤ 1 of the quiet solar disk. We compared them with
the predicted line profiles from the 3D and 1D models computed with
the most up-to-date line formation codes and line data and allowing
for departures of LTE. The centre-to-limb variation of the O i 777 nm
lines is also used to obtain an empirical correction for the poorly
known efficiency of the inelastic collisions with H i. Results:
The 3D model generally reproduces the centre-to-limb observations of
the lines very well, particularly the oxygen lines. From the O i 777 nm
lines we find that the classical Drawin recipe slightly overestimates
H i collisions (S_H≈ 0.85 agrees best with the observations). The
limb observations of the O i 615.82 nm line allow us to identify a
previously unknown contribution of molecules for this line, prevalent
at the solar limb. A detailed treatment of the [O i] 630.03 nm line
that includes the recent nickel abundance shows that the 3D modelling
closely agrees with the observations. The derived oxygen abundances
with the 3D model are 8.68 (777 nm lines), 8.66 (630.03 nm line), and
8.62 (615.82 nm line). Conclusions: These additional tests have
reinforced the trustworthiness of the 3D model and line formation for
abundance analyses. SST spectra are 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/cgi-bin/qcat?J/A+A/508/1403

---------------------------------------------------------
Title: Oxygen lines in solar granulation. I. Testing 3D models
against new observations with high spatial and spectral resolution
Authors: Pereira, T. M. D.; Kiselman, D.; Asplund, M.
2009A&A...507..417P Altcode: 2009arXiv0909.2307P
Aims: We seek to provide additional tests of the line formation of
theoretical 3D solar photosphere models. In particular, we set out
to test the spatially-resolved line formation at several viewing
angles, from the solar disk-centre to the limb and focusing on atomic
oxygen lines. The purpose of these tests is to provide additional
information on whether the 3D model is suitable to derive the solar
oxygen abundance. We also aim to empirically constrain the NLTE
recipes for neutral hydrogen collisions, using the spatially-resolved
observations of the O i 777 nm lines. Methods: Using the Swedish
1-m Solar Telescope we obtained high-spatial-resolution observations of
five atomic oxygen lines (as well as several lines for other species,
mainly Fe i) for five positions on the solar disk. These observations
have a high spatial (sub-arcsecond) and spectral resolution, and
a continuum intensity contrast up to 9% at 615 nm. The theoretical
line profiles were computed using the 3D model, with a full 3D NLTE
treatment for oxygen and LTE for the other lines. Results:
At disk-centre we find an excellent agreement between predicted
and observed line shifts, strengths, FWHM and asymmetries. At other
viewing angles the agreement is also good, but the smaller continuum
intensity contrast makes a quantitative comparison harder. We use the
disk-centre observations we constrain SH, the scaling factor
for the efficiency of collisions with neutral hydrogen. We find that
SH=1 provides the best match to the observations, although
this method is not as robust as the centre-to-limb line variations to
constrain SH. Conclusions: Overall there is a very
good agreement between predicted and observed line properties over
the solar granulation. This further reinforces the view that the 3D
model is realistic and a reliable tool to derive the solar oxygen
abundance. 2D spectrograms are 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/cgi-bin/qcat?J/A+A/507/417

---------------------------------------------------------
Title: VizieR Online Data Catalog: Oxygen lines in solar
granulation. II. (Pereira+, 2009)
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
2009yCat..35081403P Altcode:
We obtained solar observations of several lines at several positions
of the solar disk. Data were obtained in May 2007 with the TRIPPEL
spectrograph at the Swedish 1-m Solar Telescope (SST). The spectra
were obtained for three distinct wavelength windows at ~615, 630 and
777nm. Each window covers approx. 1nm. Here we provide the spatially and
temporally averaged spectra. Each spectrum was the average of 50 frames
(mu=1.0) or 25 frames (other positions). The frames were selected by
the highest continuum contrast, and thus are not regularly spaced in
time between the start and end Julian dates. The observations are
given for five positions in the solar disk, ordered by mu, the cosine
of the heliocentric angle. The objective was to study the centre-to-limb
variation of the lines. Active sun regions were avoided. Important
note: the wavelength scales have NOT been corrected for solar rotation
or gravitational redshift. (4 data files).

---------------------------------------------------------
Title: Testing 3D solar models against observations
Authors: Pereira, Tiago M. D.; Asplund, Martin; Kiselman, Dan
2009arXiv0909.4121P Altcode:
We present results from a series of observational tests to 3D and 1D
solar models. In particular, emphasis is given to the line formation
of atomic oxygen lines, used to derive the much debated solar oxygen
photospheric abundance. Using high-quality observations obtained
with the Swedish Solar Telescope (SST) we study the centre-to-limb
variation of the O I lines, testing the models and line formation
(LTE and non-LTE). For the O I 777 nm triplet, the centre-to-limb
variation sets strong constraints in the non-LTE line formation, and
is used to derive an empirical correction factor (S_H) to the classical
Drawin recipe for neutral hydrogen collisions. Taking advantage of the
spatially-resolved character of the SST data, an additional framework
for testing the 3D model and line formation is also studied. From
the tests we confirm that the employed 3D model is realistic and its
predictions agree very well with the observations.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Oxygen lines in solar
granulation. I. (Pereira+, 2009)
Authors: Pereira, T. M. D.; Kiselman, D.; Asplund, M.
2009yCat..35070417P Altcode:
We obtained solar observations of several lines at several positions
of the solar disk. Data were obtained in May 2007 with the TRIPPEL
spectrograph at the Swedish 1-m Solar Telescope (SST). The spectra were
obtained for three distinct wavelength windows at approx 615, 630 and
777nm. Each window covers ~1nm. The spectra are spatially-resolved
in the solar surface, hence are given as 2D spectrograms. One axis
covers the wavelength and the other spatial position. The
observations are given for five positions in the solar disk, ordered
by mu, the cosine of the heliocentric angle. The objective was to
study the centre-to-limb variation of the lines. Active sun regions
were avoided. In total 150 spectrograms are given for each wavelength
window: 50 for the solar disk-centre (mu=1) and 25 for the other four
positions (mu=0.8, 0.6, 0.4, 0.2). The images were selected by continuum
contrast, hence their observed times are not the same for the three
windows. The spectrograms are given as FITS files. Each file
has two Header/Data Units (HDU). The first HDU contains the reduced
spectrogram, a 2D array. The first dimension of the array contains
(FITS NAXIS1) corresponds to wavelength, and the second (FITS NAXIS2)
to spatial coordinate. The second HDU contains the continuum levels
obtained for each spatial point (1D array, length equal to the number
of spatial points in the spectrogram). To obtain the normalized reduced
spectrogram one has to divide each spectrum in the spectrogram by the
corresponding continuum level. The spectrograms have been corrected
for stray light and to minimize noise a Fourier filter has been applied
(details in the paper). Important note: the wavelength scales have
NOT been corrected for solar rotation or gravitational redshift. (3 data files).

---------------------------------------------------------
Title: Neutral oxygen spectral line formation revisited with new
collisional data: large departures from LTE at low metallicity
Authors: Fabbian, D.; Asplund, M.; Barklem, P. S.; Carlsson, M.;
Kiselman, D.
2009A&A...500.1221F Altcode: 2009arXiv0902.4472F
Aims: A detailed study is presented, including estimates of the
impact on elemental abundance analysis, of the non-local thermodynamic
equilibrium (non-LTE) formation of the high-excitation neutral oxygen
777 nm triplet in model atmospheres representative of stars with
spectral types F to K. Methods: We have applied the statistical
equilibrium code MULTI to a number of plane-parallel MARCS atmospheric
models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log
g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed
includes, in particular, recent quantum-mechanical electron collision
data. Results: We confirm that the O i triplet lines form under
non-LTE conditions in late-type stars, suffering negative abundance
corrections with respect to LTE. At solar metallicity, the non-LTE
effect, mainly attributed in previous studies to photon losses in the
triplet itself, is also driven by an additional significant contribution
from line opacity. At low metallicity, the very pronounced departures
from LTE are due to overpopulation of the lower level (3s ^5S^o) of the
transition. Large line opacity stems from triplet-quintet intersystem
electron collisions, a form of coupling previously not considered or
seriously underestimated. The non-LTE effects generally become severe
for models (both giants and dwarfs) with higher T_eff. Interestingly,
in metal-poor turn-off stars, the negative non-LTE abundance corrections
tend to rapidly become more severe towards lower metallicity. When
neglecting H collisions, they amount to as much as |Δlog ɛ_O|
~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H]
= -3.5. Even when such collisions are included, the LTE abundance
remains a serious overestimate, correspondingly by |Δlog ɛ_O| ~ 0.5
dex and ~0.9 dex at such low metallicities. Although the poorly known
inelastic hydrogen collisions thus remain an important uncertainty,
the large metallicity-dependent non-LTE effects seem to point to
a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo
stars. Conclusions: Our results may be important in solving
the long-standing [O/Fe] debate. When applying the derived non-LTE
corrections, the LTE oxygen abundance inferred from the 777 nm permitted
triplet will be decreased substantially at low metallicity. If the
classical Drawin formula is employed for O+H collisions, the derived
[O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement
with recent literature estimates generally obtained from other oxygen
abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be
appropriate, as suggested by standard theoretical models of type II
supernovae nucleosynthetic yields. If neglecting impacts with H atoms
instead, [O/Fe] decreases towards lower [Fe/H], which would open new
questions. Our tests using ATLAS model atmospheres show that, though
non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex
when adopting efficient H collisions) than in the MARCS case, our
main conclusions are preserved, and that the LTE approach tends to
seriously overestimate the O abundance at low metallicity. However,
in order to finally reach consistency between oxygen abundances from
the different available spectral features, it is of high priority to
reduce the large uncertainty regarding H collisions, to undertake a
full investigation of the interplay of non-LTE and 3D effects, and to
clarify the issue of the temperature scale at low metallicity.

---------------------------------------------------------
Title: Temperature stratification in the Sun's photosphere in high
horizontal resolution using Ca II H filtergrams.
Authors: Henriques, V. M. J.; Kiselman, D.
2009MmSAI..80..639H Altcode:
A method to extract the temperature stratification in the Sun's
photosphere using filtergrams is presented along with some high
resolution results. The data was acquired with the Swedish 1-m Solar
Telescope (SST) using a tunable filter in the Ca II H blue wing. Each
full scan is completed in the order of seconds thus allowing for
the full resolution of the SST and reasonable depth sampling to be
obtained simultaneously in a shorter time than that of the evolution
time scale of the photosphere. We test the quality of the method by
applying it to a set of synthetic images (obtained through radiative
transfer on 3D HD and MHD simulation snapshots followed by degradation)
and comparing the output with the known 3D simulated atmosphere. Fine
structure around bright points becomes evident in both the temperature
gradient maps computed from a set of test observations and synthetic
images obtained from MHD simulations.

---------------------------------------------------------
Title: Testing 3D solar models against observations . Center-to-limb
variations of oxygen lines, spatially-resolved line formation and
probing for departures from LTE
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
2009MmSAI..80..650P Altcode:
We present results from a series of observational tests to 3D and 1D
solar models. In particular, emphasis is given to the line formation
of atomic oxygen lines, used to derive the much debated solar oxygen
photospheric abundance. Using high-quality observations obtained
with the Swedish Solar Telescope (SST) we study the center-to-limb
variation of the O I lines, testing the models and line formation
(LTE and non-LTE). For the O I 777 nm triplet, the center-to-limb
variation sets strong constraints in the non-LTE line formation, and
is used to derive an empirical correction factor (SH) to
the classical Drawin recipe for neutral hydrogen collisions. Taking
advantage of the spatially-resolved character of the SST data, an
additional framework for testing the 3D model and line formation is
also studied. From the tests we confirm that the employed 3D model is
realistic and its predictions agree very well with the observations.

---------------------------------------------------------
Title: CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
Authors: Scharmer, G. B.; Narayan, G.; Hillberg, T.; de la Cruz
Rodriguez, J.; Löfdahl, M. G.; Kiselman, D.; Sütterlin, P.; van
Noort, M.; Lagg, A.
2008ApJ...689L..69S Altcode: 2008arXiv0806.1638S
We discuss penumbral fine structure in a small part of a pore,
observed with the CRISP imaging spectropolarimeter at the Swedish
1-m Solar Telescope (SST), close to its diffraction limit of
0.16”. Milne-Eddington inversions applied to these Stokes data
reveal large variations of field strength and inclination angle over
dark-cored penumbral intrusions and a dark-cored light bridge. The
mid-outer part of this penumbra structure shows ~0.3” wide spines,
separated by ~1.6” (1200 km) and associated with 30° inclination
variations. Between these spines, there are no small-scale magnetic
structures that easily can be identified with individual flux tubes. A
structure with nearly 10° more vertical and weaker magnetic field is
seen midway between two spines. This structure is cospatial with the
brightest penumbral filament, possibly indicating the location of a
convective upflow from below.

---------------------------------------------------------
Title: Solar 3D models versus observations—a few comments
Authors: Kiselman, D.
2008PhST..133a4016K Altcode:
Some properties of 3D solar photospheric models and the observations
used to test them are discussed: granulation contrast and spectral
line variation in the granulation pattern and over the solar disc. The
recent use of the techniques of solar physics to tackle abundance
problems is encouraged.

---------------------------------------------------------
Title: Spectropolarimetry of Sunspots at 0.16 ARCSEC resolution
Authors: Scharmer, G.; Henriques, V.; Hillberg, T.; Kiselman, D.;
Löfdahl, M.; Narayan, G.; Sütterlin, P.; van Noort, M.; de la Cruz
Rodríguez, J.
2008ESPM...12..2.5S Altcode:
We present first observations of sunspots with the imaging
spectropolarimeter CRISP, recently installed at the Swedish 1-m
Solar Telescope (SST) on La Palma. This spectropolarimeter is based
on a high-fidelity dual Fabry-Perot filter system. Two liquid
crystals and a polarizing beam splitter are used to reduce seeing
induced I,Q,U,V crosstalk by simultaneously recording images with
two 1kx1k back-illuminated Sarnoff CCD's. A third CCD simultaneously
records broadband images through the pre-filter of the FPI filter
system, allowing image reconstruction and co-alignment of images of
different polarization states and at different wavelengths in Zeeman
sensitive spectral lines. The first data, recorded in April 2008,
demonstrate the capability of this system to record high cadence,
high S/N polarimetric data with a spatial resolution at or close to
the diffraction limit of the SST at 630 nm, 0.16 arcsec. We discuss
the analysis of first spectropolarimetric data for sunspots, based on
Milne-Eddington inversion techniques.

---------------------------------------------------------
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: Recent High Resolution Observations and Interpretations of
Sunspot Fine Structure
Authors: Scharmer, G. B.; Langhans, K.; Kiselman, D.; Löfdahl, M. G.
2007ASPC..369...71S Altcode:
We review analyses made of highly resolved filtergrams, magnetograms
and Dopplergrams of sunspots, recorded with the Swedish 1-meter Solar
Telescope (SSTSST) on La Palma. Dark cores in penumbral filaments are
shown to be directly linked to peripheral umbral dots and to dark
lanes in light bridges, suggesting similar or related underlying
physics. The visibility of dark cores is found to depend strongly
on the azimuth angle already for spots located at small heliocentric
distances. It is shown that dark cores are clearly visible close to the
center of the Ca II H line, formed approximately 150--200~km above the
photosphere. We conclude that the τ = 1 layer of dark-cored filaments
outlines a strongly warped surface, consistent with the finding that
the magnetic field strength is strongly reduced in dark cores. We show
that several properties of dark-cored filaments derived from SSTSST
data are consistent with results of inversions of low-resolution Stokes
spectra, but also find important discrepancies with the interpretation
that penumbral filaments can be identified with flux tubes. Our data
are consistent with the model proposed by Spruit &amp; Scharmer (2006),
explaining dark cores as signatures of field-free convection occurring
just below the visible surface of the penumbra. We discuss recent
simulations of light bridges and umbral dots, providing additional
support to that model.

---------------------------------------------------------
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: Observations of dark-cored filaments in sunspot penumbrae
Authors: Langhans, K.; Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G.
2007A&A...464..763L Altcode:
Context: The recent discovery of dark-cored penumbral filaments suggests
that we are resolving the building blocks of sunspot penumbrae. Their
properties are largely unknown but provide important clues to
understanding penumbral fine structure. Aims: Our observations
provide new constraints for the different scenarios put forward to
explain the structure of sunspot penumbrae. Methods: We present
an analysis of dark-cored penumbral filaments, based on intensity
filtergrams (G-band, continuum and Ca II H line wing), magnetograms
and Dopplergrams, obtained at heliocentric distances between 15° and
55°. Results: In general, the visibility of dark cores degrades
with increasing heliocentric distance. Based on Ca II H wing images we
conclude that this is due to a geometrical 3D-effect and not due to a
simple formation height effect. Only in the center-side penumbra are
dark-cored filaments visible at all observed heliocentric distances. We
observe that dark-cored filaments frequently split in the umbra, forming
a Y-shape that disappears after a few minutes, leaving a shortened
filamentary structure and a bright dot in the umbra. The dark-cored
filaments have life times ≥ 90 min. The dark cores are related to
a much weaker and a more horizontal magnetic field than their lateral
brightenings. Where the dark-cored filaments appear in the umbra, the
magnetic field is inclined by 40° with respect to the solar surface
normal for both the dark core and the bright edges. With increasing
distance from the umbra, the magnetic field inclination in the dark
cores increases rapidly within a few thousand km. Both the magnetic
field strength and inclination in the lateral brightenings show very
small variations with spot-center radial distance. The velocity field
possesses a strong horizontal component within the dark cores. The
absolute line-of-sight (LOS) velocity is larger within the dark cores
than in their lateral brightenings. The Evershed flow apparently is
present primarily in the dark cores.

---------------------------------------------------------
Title: The non-LTE line formation of neutral carbon in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
2006A&A...458..899F Altcode: 2006astro.ph..8284F
Aims.We investigate the non-Local Thermodynamic Equilibrium (non-LTE)
line formation of neutral carbon in late-type stars in order to remove
some of the potential systematic errors in stellar abundance analyses
employing C i features. Methods: .The statistical equilibrium
code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric
models. Results: .Within the parameter space explored, the
high-excitation C i lines studied are stronger in non-LTE due to
the combined effect of line source function drop and increased line
opacity due to overpopulation of the lower level for the transitions
considered; the relative importance of the two effects depends on
the particular combination of T{eff}, log g, [Fe/H] and
[C/Fe] and on the analysed C i line. As a consequence, the non-LTE
abundance corrections are negative and can be substantially so,
for example ∼ -0.4 dex in halo turn-off stars at [Fe/H]∼ -3. The
magnitude of the non-LTE corrections is rather insensitive to whether
inelastic H collisions are included or not. Conclusions: .Our
results have implications on studies of nucleosynthetic processes and
on Galactic chemical evolution models. When applying our calculated
corrections to recent observational data, the upturn in [C/O] at low
metallicity might still be present (thus apparently still necessitating
contributions from massive Pop. III stars for the carbon production),
but at a lower level and possibly with a rather shallow trend of ∼
-0.2 dex/dex below [O/H]∼ -1.

---------------------------------------------------------
Title: Inclination of magnetic fields and flows in sunspot penumbrae
Authors: Langhans, K.; Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G.;
Berger, T. E.
2005A&A...436.1087L Altcode:
An observational study of the inclination of magnetic fields and
flows in sunspot penumbrae at a spatial resolution of 0.2 arcsec is
presented. The analysis is based on longitudinal magnetograms and
Dopplergrams obtained with the Swedish 1-m Solar Telescope on La Palma
using the Lockheed Solar Optical Universal Polarimeter birefringent
filter. Data from two sunspots observed at several heliocentric
angles between 12 ° and 39 ° were analyzed. We find that the
magnetic field at the level of the formation of the Fe i-line wing
(630.25 nm) is in the form of coherent structures that extend radially
over nearly the entire penumbra giving the impression of vertical
sheet-like structures. The inclination of the field varies up to
45 ° over azimuthal distances close to the resolution limit of the
magnetograms. Dark penumbral cores, and their extensions into the outer
penumbra, are prominent features associated with the more horizontal
component of the magnetic field. The inclination of this dark penumbral
component - designated B - increases outwards from approximately 40 °
in the inner penumbra such that the field lines are nearly horizontal
or even return to the solar surface already in the middle penumbra. The
bright component of filaments - designated A - is associated with the
more vertical component of the magnetic field and has an inclination
with respect to the normal of about 35 ° in the inner penumbra,
increasing to about 60 ° towards the outer boundary. The magnetogram
signal is lower in the dark component B regions than in the bright
component A regions of the penumbral filaments. The measured rapid
azimuthal variation of the magnetogram signal is interpreted as being
caused by combined fluctuations of inclination and magnetic field
strength. The Dopplergrams show that the velocity field associated with
penumbral component B is roughly aligned with the magnetic field while
component A flows are more horizontal than the magnetic field. The
observations give general support to fluted and uncombed models of
the penumbra. The long-lived nature of the dark-cored filaments makes
it difficult to interpret these as evidence for convective exchange
of flux tubes. Our observations are in broad agreement with the two
component model of Bellot Rubi et al. (2003), but do not rule out the
embedded flux tube model of Solanki &amp; Montavon (1993).

---------------------------------------------------------
Title: CI non LTE spectral line formation in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
2005IAUS..228..255F Altcode: 2005astro.ph..8063F
We present non-Local Thermodynamic Equilibrium (non-LTE) calculations
for neutral carbon spectral line formation, carried out for a grid
of model atmospheres covering the range of late-type stars. The
results of our detailed calculations suggest that the carbon
non-LTE corrections in these stars are higher than usually adopted,
remaining substantial even at low metallicity. For the most metal-poor
stars in the sample of Akerman et al (2004), the effects are of the
order of ΔlogɛC ≃ -0.35ldots-0.45 (when neglecting H
collisions). Applying our results to those observations, the apparent
[C/O] upturn seen in their LTE analysis is no longer present, thus
revealing no need to invoke contributions from Pop. III stars to the
carbon nucleosynthesis.

---------------------------------------------------------
Title: Line formation in solar granulation. IV. [O I], O I and OH
lines and the photospheric O abundance
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.; Allende Prieto,
C.; Kiselman, D.
2004A&A...417..751A Altcode: 2003astro.ph.12290A
The solar photospheric oxygen abundance has been determined from
[O I], O I, OH vibration-rotation and OH pure rotation lines by
means of a realistic time-dependent, 3D, hydrodynamical model of
the solar atmosphere. In the case of the O I lines, 3D non-LTE
calculations have been performed, revealing significant departures
from LTE as a result of photon losses in the lines. We derive a solar
oxygen abundance of log ɛO = 8.66 ± 0.05. All oxygen
diagnostics yield highly consistent abundances, in sharp contrast
with the results of classical 1D model atmospheres. This low value
is in good agreement with measurements of the local interstellar
medium and nearby B stars. This low abundance is also supported by
the excellent correspondence between lines of very different line
formation sensitivities, and between the observed and predicted line
shapes and center-to-limb variations. Together with the corresponding
down-ward revisions of the solar carbon, nitrogen and neon abundances,
the resulting significant decrease in solar metal mass fraction to Z =
0.0126 can, however, potentially spoil the impressive agreement between
predicted and observed sound speed in the solar interior determined
from helioseismology.

---------------------------------------------------------
Title: Penumbral structure at 0.1 arcsec resolution. I. General
appearance and power spectra
Authors: Rouppe van der Voort, L. H. M.; Löfdahl, M. G.; Kiselman,
D.; Scharmer, G. B.
2004A&A...414..717R Altcode:
We analyse sunspot filtergrams of unprecedented quality obtained by
\citet{scharmer02dark} with the Swedish 1-m Solar Telescope on La
Palma. The observations comprise images in three different wavelength
bands: 488, 436, and 430 nm (G-band). We find that there are still
unresolved penumbral filaments which must have widths smaller than
80 km. The fine structuring along the filaments is limited. Penumbral
grains have internal structure and look like they are split or crossed
by narrow dark structures. We calculate intensity power spectra of the
penumbra from images that are corrected for seeing using the Phase
Diversity technique. The effects of high order aberrations that are
not corrected for are estimated to be too low to be consistent with
a flat power spectrum. The penumbral power spectra do not show any
signs of bumps or peaks that could correspond to a preferred scale
at 0\farcs35 for the width of penumbral filaments. We argue that the
power spectrum is not a very reliable source of information concerning
preferred scales.

---------------------------------------------------------
Title: First Results from the Swedish 1-m Solar Telescope
Authors: Scharmer, G. B.; Kiselman, D.; Löfdahl, M. G.; Rouppe van
der Voort, L. H. M.
2003ASPC..307....3S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Granulation Fingerprints of Spectral Lines
Authors: Kiselman, D.; Asplund, M.
2003IAUS..210P.E62K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dark cores in sunspot penumbral filaments
Authors: Scharmer, Göran B.; Gudiksen, Boris V.; Kiselman, Dan;
Löfdahl, Mats G.; Rouppe van der Voort, Luc H. M.
2002Natur.420..151S Altcode:
Sunspot umbrae-the dark central regions of the spots-are surrounded
by brighter filamentary penumbrae, the existence of which remains
largely inexplicable. The penumbral filaments contain magnetic fields
with varying inclinations and are associated with flowing gas, but
discriminating between theoretical models has been difficult because
the structure of the filaments has not hitherto been resolved. Here
we report observations of penumbral filaments that reveal dark cores
inside them. We cannot determine the nature of these dark cores,
but their very existence provides a crucial test for any model of
penumbrae. Our images also reveal other very small structures, in line
with the view that many of the fundamental physical processes in the
solar photosphere occur on scales smaller than 100km.

---------------------------------------------------------
Title: NLTE effects on oxygen lines
Authors: Kiselman, Dan
2002HiA....12..429K Altcode:
The NLTE effects affecting oxygen-abundance determination of solar-type
stars are discussed. LTE is safe for the forbidden lines. The permitted
triplet at 777 nm is expected to show NLTE effects so that assuming
LTE overestimates the abundance, but the magnitude of the effects is
dependent on the poorly known cross sections of collisional excitation
by collisions with neutral hydrogen atoms. Little is known about the
NLTE effects on molecular line formation.

---------------------------------------------------------
Title: NLTE effects on oxygen lines
Authors: Kiselman, Dan
2001NewAR..45..559K Altcode: 2000astro.ph.10300K
The NLTE effects affecting oxygen-abundance determinations of solar-type
stars are discussed. LTE is perfectly safe for the forbidden lines. The
permitted triplet at 777 nm is expected to show NLTE effects on
the order of a few tenths of a dex (always in the sense that LTE
overestimates the abundance), but the magnitude of the effects is
dependent on the still very uncertain cross sections of collisional
excitation by collisions with neutral hydrogen atoms. Little is known
about the NLTE effects on molecular line formation.

---------------------------------------------------------
Title: Spatially Resolved Solar Lines as Diagnostics of NLTE Effects
(CD-ROM Directory: contribs/kiselman)
Authors: Kiselman, D.; Asplund, M.
2001ASPC..223..684K Altcode: 2001csss...11..684K
No abstract at ADS

---------------------------------------------------------
Title: Departures from LTE in be Line Formation
Authors: García Perez, A. E.; Asplund, M.; Kiselman, D.
2001coev.conf..131G Altcode:
Stellar abundances of Be can be affected by NLTE effects. We have
calculated the NLTE corrections to the LTE abundances obtained
from the Bell doublet at 313.0 and 313.1 nm for a range of stellar
parameters. These lines are not formed in LTE due to over-ionization
and over-excitation but the NLTE corrections are in general small
(~0.1 dex).

---------------------------------------------------------
Title: The formation of G-band bright points I: Standard LTE modelling
Authors: Kiselman, D.; Rutten, R. J.; Plez, B.
2001IAUS..203..287K Altcode:
Assuming LTE, we investigate the formation of the G band in models of
quiet solar photosphere and a semiempirical flux-tube model (Briand
&amp; Solanki 1995). Preliminary results agree with observations of
of G-band bright-point contrast, though this a sensitive function
of the amount of scattered light in the observations. Thus LTE line
modelling in models constructed under the LTE assumptions seems to fit
observations. This does not, however, necessarily imply that LTE is
valid here. We also present LTE synthetic spectra of the same models
for the full wavelength range from UV to IR. This serves to point out
other promising pass bands for the observations of flux-tube structures.

---------------------------------------------------------
Title: Proxy Magnetometry of the Photosphere: Why are G-Band Bright
Points so Bright?
Authors: Rutten, R. J.; Kiselman, D.; Rouppe van der Voort, L.;
Plez, B.
2001ASPC..236..445R Altcode: 2001aspt.conf..445R
No abstract at ADS

---------------------------------------------------------
Title: The formation of G-band bright points. I: Standard LTE
modelling
Authors: Kiselman, D.; Rutten, R. J.; Plez, B.
2000astro.ph.10390K Altcode:
Assuming LTE, we synthesise solar G band spectra from the semiempirical
flux-tube model of Briand Solanki (1995). The results agree with
observed G-band bright-point contrasts within the uncertainty set by the
amount of scattered light. We find that it is the weakening of spectral
lines within the flux tube that makes the bright-point contrast in the
G band exceed the continuum contrast. We also synthesise flux-tube
spectra assuming LTE for the full wavelength range from UV to IR,
and identify other promising passbands for flux-tube observations.

---------------------------------------------------------
Title: NLTE effects on oxygen lines
Authors: Kiselman, Dan
2000IAUJD...8E...5K Altcode:
I will review the problems involved in NLTE modelling of lines used
for oxygen-abundance determinations of cool stars. Where are the most
important uncertainties and what could be done about them? Could a
complete understanding of the NLTE effects on OH, OI, and [OI] lines
solve the reported abundance discrepancies?

---------------------------------------------------------
Title: Oxygen Line Formation in 3D Hydrodynamical Model Atmospheres
Authors: Asplund, M.; Carlsson, M.; Garcia Perez, A. E.; Kiselman, D.
2000IAUJD...8E...8A Altcode: 2000astro.ph.11043A
The new generation of realistic 3-dimensional, time-dependent,
hydrodynamical model atmospheres have been applied to the line
formation of {O}{I}, [{O}{I}] and OH lines. Additionally detailed 3D
non-LTE calculations have been performed for {O}{I} in order to study
the influence of temperature inhomogeneities on the line formation
process. Implications in terms of the evolution of oxygen abundance
with metallicity will be discussed, partly based on new VLT/UVES
observations of metal-poor stars.

---------------------------------------------------------
Title: Scattered Light from Envelopes around N-type Stars
Authors: Gustafsson, Bengt; Eriksson, Kjell; Kiselman, Dan; Olander,
Nils; Olofsson, Hans; Schwarz, Hugo E.
2000IAUS..177..409G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Effects of NLTE and Granulation on LiBeB Abundance
Determinations
Authors: Kiselman, Dan
1999ASPC..171...85K Altcode: 1999astro.ph..2375K; 1999lcrr.conf...85K
NLTE effects - the errors caused by assuming local thermodynamic
equilibrium (LTE) - on LiBeB abundance determinations for cool stars
are discussed. These NLTE effects are significant in many cases for
B I and Li I lines. The Be II 313 nm lines are not formed under LTE
circumstances, but the NLTE effects on equivalent widths seem to be
rather small. Reasons for doing LTE abundance analysis are discussed
and confronted with the reasons for doing NLTE abundance analysis. The
impact of three-dimensional photospheric inhomogeneity on line formation
is discussed - there are not many definite results on this yet, but
there may be soon.

---------------------------------------------------------
Title: Boron in Very Metal Poor Stars
Authors: Garcia Lopez, Ramon J.; Lambert, David L.; Edvardsson, Bengt;
Gustafsson, Bengt; Kiselman, Dan; Rebolo, Rafael
1998ApJ...500..241G Altcode: 1998astro.ph..1167G; 1998astro.ph..1167L
We have observed the B I 2497 A line to derive the boron abundances
of two very metal-poor stars selected to help in tracing the origin
and evolution of this element in the early Galaxy: BD +23 3130 and
HD 84937. The observations were conducted using the Goddard High
Resolution Spectrograph on board the Hubble Space Telescope. A
very detailed abundance analysis via spectral synthesis has been
carried out for these two stars, as well as for two other metal-poor
objects with published spectra, using both Kurucz and OSMARCS model
photospheres, and taking into account consistently the NLTE effects
on the line formation. We have also re-assessed all published boron
abundances of old disk and halo unevolved stars. Our analysis shows
that the combination of high effective temperature (Teff &gt; 6000 K,
for which boron is mainly ionized) and low metallicity ([Fe/H]&lt;-1)
makes it difficult to obtain accurate estimates of boron abundances
from the B I 2497 A line. This is the case of HD 84937 and three other
published objects (including two stars with [Fe/H] ~ -3), for which only
upper limits can be established. BD +23 3130, with [Fe/H] ~ -2.9 and
logN(B)_NLTE=0.05+/-0.30, appears then as the most metal-poor star for
which a firm measurement of the boron abundance presently exists. The
evolution of the boron abundance with metallicity that emerges from
the seven remaining stars with Teff &lt; 6000 K and [Fe/H]&lt;-1,
for which beryllium abundances were derived using the same stellar
parameters, shows a linear increase with a slope ~ 1. Furthermore, the
B/Be ratio found is constant at a value ~ 20 for stars in the range
-3&lt;[Fe/H]&lt;-1. These results point to spallation reactions of
ambient protons and alpha particles with energetic particles enriched
in CNO as the origin of boron and beryllium in halo stars.

---------------------------------------------------------
Title: The 671nm Li I line in solar granulation
Authors: Kiselman, Dan
1998A&A...333..732K Altcode: 1998astro.ph..2049K
The astrophysically very interesting Li I 671nm line has been observed
with high spatial resolution in solar granulation with the intention
to diagnose departures from local thermodynamic equilibrium (LTE)
in the line formation. The spectral feature is very weak, so this
is also a test on the limits of such observations. The observations
of the Li I line and other weak lines nearby are compared with the
results of synthetic line calculations in three-dimensional granulation
simulations. The dependence of line-centre velocities on photospheric
continuum brightness is well described by the simulations. The
observed equivalent width of the Li I line show an approximately flat
dependence on continuum brightness, contrary to the theoretical LTE
results. Detailed modelling of the line radiative transfer, with an
approximate inclusion of three-dimensional effects, gives a better
agreement with observations. The match is not perfect and various
interesting reasons for this are considered. However, the possibility
of systematic errors caused by the sensitivity of the Li I equivalent
width to continuum placement calls for cautiousness in the conclusions.

---------------------------------------------------------
Title: Formation of Li I Lines in Photospheric Granulation
Authors: Kiselman, Dan
1997ApJ...489L.107K Altcode: 1997astro.ph..8198K
The possibility of significant systematic errors due to the use
of one-dimensional homogeneous atmospheres in lithium-abundance
determinations of cool stars motivates a study of non-local
thermodynamic equilibrium (NLTE) effects on Li I line formation in
a three-dimensional solar granulation simulation snapshot. The NLTE
effect on the equivalent width of the 671 nm resonance line is small
in one-dimensional models or in integrated light from the granulation
model. The line-strength variations over the granulation pattern are,
however, markedly different in NLTE compared with LTE--observations
of this may provide diagnostics to NLTE effects. The effects of
horizontal photon exchange found in the granulation model are moderate
and due entirely to bound-bound processes; ultraviolet overionization
is unimportant.

---------------------------------------------------------
Title: (Erratum) Line-blanketed model atmospheres for R Coronae
Borealis stars and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
1997A&A...323..286A Altcode:
Erratum to Astron. Astrophys. 318, 521-534 (1997)

---------------------------------------------------------
Title: KI emission from envelopes around N-type stars. Spectroscopic
observations and interpretations.
Authors: Gustafsson, B.; Eriksson, K.; Kiselman, D.; Olander, N.;
Olofsson, H.
1997A&A...318..535G Altcode:
Circumstellar envelopes around three bright N-type stars, R Scl,
X TrA, and V Aql have been detected in emission in resonance lines
from KI. This radiation, which is most probably scattered photospheric
radiation, was first found spectroscopically, but has later been imaged
with coronographic and polarimetric techniques. In the present paper,
which is the first in a series, the spectroscopic KI observations are
discussed. From the observations of the KI 769.9nm emission we find
systemic and expansion velocities in fair agreement with those obtained
from the CO millimetre lines. We find a decline of the emission with
distance from the star, in rough agreement with the assumption of a
constant expansion velocity, mass-loss rate and KI abundance. Our mass
loss rate estimates from the KI line observations agree rather well with
those obtained from CO (ranging from 1/4 to 1/1 of the CO mass loss),
which suggests that a considerable fraction of the potassium stays
neutral through the envelope. This puts strong upper limits on the
photoionizing chromospheric UV emission from the stars. Some indirect
indications that the envelopes have inhomogeneous structures, clumps,
are discussed.

---------------------------------------------------------
Title: Line-blanketed model atmospheres for R Coronae Borealis stars
and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
1997A&A...318..521A Altcode:
We have constructed line-blanketed model atmospheres for the
hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars,
as well as for the similar hydrogen-deficient carbon (HdC) stars and
the cool extreme helium (EHe) stars. Improved continuum opacities have
been used together with realistic line absorption data for atomic
and molecular transitions. The observed dereddened fluxes of R CrB
are compared with the calculated model fluxes and found to agree best
with a model effective temperature of 6900K, while the infrared flux
method gives between 6600 and 6900K, depending on the nature of the
flux excess in the J and H bands compared to the model fluxes. The
excess may correspond to a recently formed dust cloud close to the
star, with a typical temperature around 2000K and a dust mass of
~10^-11^Msun_. The agreement for the ultraviolet flux
distribution is also very satisfactory as seen from IUE spectra of
RCrB. Theoretical broad band photometry is presented and effective
temperatures of RCrB and HdC stars estimated. The constructed
models show a significantly steeper temperature gradient compared
to previously existing models as a result of the line opacity. Due
to the cool surface and high abundance of carbon, molecular bands of
e.g. C_2_ and CO are visible in the spectra even at as high effective
temperatures as 7000K. Furthermore, the high temperatures encountered
at depth explain the observed Hei and CII lines for T_eff_ down to
~7000K. In the inner layers (τ_Ross_ &gt; 3) the models show density
inversions related to the ionization zone of helium. For certain low
gravity models the luminosity exceeds the local Eddington limit and
hence gas pressure inversions occur as well, which could be related
to the decline events of RCrB stars.

---------------------------------------------------------
Title: The NLTE formation of neutral-boron lines in cool stars.
Authors: Kiselman, D.; Carlsson, M.
1996A&A...311..680K Altcode: 1996astro.ph..1144K
We study the formation of BI lines in a grid of cool stellar model
atmospheres without the assumption of local thermodynamic equilibrium
(LTE). The non-LTE modelling includes the effect of other lines
blending with the BI resonance lines. Except for the cases where the
BI lines are very strong, the departures from LTE relevant for the
resonance lines can be described as an overionisation effect and an
optical-pumping effect. This causes the lines to be weaker than in LTE
so that an abundance analysis assuming LTE will underestimate stellar
boron abundances. We present non-LTE abundance corrections useful to
improve on abundances derived from the Bi250nm and 209nm lines under
the LTE assumption. Application of the results on literature data
indicates that the B/Fe ratio in metal-poor stars is constant.

---------------------------------------------------------
Title: 3D non-LTE line formation in the solar photosphere and the
solar oxygen abundance.
Authors: Kiselman, D.; Nordlund, A.
1995A&A...302..578K Altcode: 1995astro.ph..5037K
We study the formation of OI and OH spectral lines in three-dimensional
hydrodynamic models of the solar photosphere. The line source function
of the OI 777nm triplet is allowed to depart from local thermodynamic
equilibrium (lte), within the two-level-atom approximation. Comparison
with results from 1D models show that the 3D models alleviate, but
do not remove, the discrepancy between the oxygen abundances reported
from non-lte work on the 777nm triplet and from the [OI] 630nm and OH
lines. Results for the latter two could imply that the solar oxygen
abundance is below 8.8. If this is confirmed, the discrepancy between
theory and observation for the 777nm triplet lines might fall within
the range of errors in equivalent-width measurements and f-values. The
line source function of the 777nm triplet in the 1.5D approximation
is shown to differ insignificantly from the full 3D non-lte result.

---------------------------------------------------------
Title: A non-LTE study of Li I lines in AGB stars.
Authors: Kiselman, D.; Plez, B.
1995MmSAI..66..429K Altcode: 1994astro.ph.11074K
We study the formation of Li lines in a case study of an S-type AGB
star in the SMC. AGB stars may be important providers of $^7$Li
to the interstellar medium. Abundance analysis of these stars is
difficult due to the heavy molecular blanketing, uncertainties in the
model atmospheres and possible departures from LTE in the Li atomic
level populations. We address here the latter problem and somewhat
also that of background molecular line formation. We do not find
non-LTE effects big enough to alone rule out the possibility that the
reported super-Li-rich stars exist. There are, however, several other
complications connected to the formation of the Li lines in these stars.

---------------------------------------------------------
Title: Non-LTE Effects on Be and B Abundance Determinations in
Cool Stars
Authors: Kiselman, D.; Carlsson, M.
1995lea..conf..372K Altcode: 1994astro.ph..9064K
We discuss the nature of non-LTE effects affecting abundance analysis
of cool stars. The departures from LTE of importance for the B I
lines in solar-type stars are described and some new results are
presented. Boron abundances derived under the LTE assumption have
significant systematic errors, especially for metal-poor stars. For
beryllium, current results suggest that departures from LTE will not
affect abundance analysis significantly.

---------------------------------------------------------
Title: The impact of granulation on the line formation
Authors: Kiselman, D.
1995IAUS..176P.110K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Boron in the extreme Population II star HD 140283 and the
production of light elements in the Early Galaxy
Authors: Edvardsson, B.; Gustafsson, B.; Johansson, S. G.; Kiselman,
D.; Lambert, D. L.; Nissen, P. E.; Gilmore, G.
1994A&A...290..176E Altcode: 1994astro.ph..3002E
Using observations of the 2496.7A Bi line with the HST GHRS at a
nominal resolving power of 90,000, we have found the abundance of
boron of HD140283 to be logɛ_B_(=12+log(N_B_/N_H_))=0.34+/-0.20. This
result is found when a significant non-LTE effect in the formation of
the Bi line is taken into account. The resulting N_B_/N_Be_ ratio is
about 17 (in the range 9-34), which is in very good agreement with
what is expected from spallation by cosmic rays. We conclude that
this origin of Be and B in the Early Galaxy is the most probable of
recently suggested formation mechanisms.

---------------------------------------------------------
Title: A NLTE study of neutral boron in solar-type stars
Authors: Kiselman, D.
1994A&A...286..169K Altcode: 1994astro.ph..1018K
The formation of the resonance lines of neutral boron in solar-type
stellar atmospheres is investigated taking into account effects of
departures from local thermodynamic equilibrium (NLTE effects). The
latter are due to a combination of overionisation and optical
pumping in resonance lines, both caused by the hot, non-local,
ultraviolet radiation fields in the line-forming regions. They lead
to an underestimation of the boron abundance when analysis methods
assuming local thermodynamic equilibrium (LTE) are used. The abundance
correction, for the 249.7 nm resonance line, amounts to +0.56 dex for
the metal-poor star HD 140283 and +0.4 dex for Procyon. No significant
NLTE effects are predicted for the Sun. Applying the abundance
correction on the results for HD 140283 of Duncan et al. (1992) leads
to a B/Be ratio well above the minimum value required by spallation
production of beryllium. The reliability of the results in view of
atomic and atmospheric uncertainties is discussed. With the possible
exception of photospheric inhomogeneity, it seems unlikely that these
could remove the effect for HD 140283.

---------------------------------------------------------
Title: High-spatial-resolution solar observations of spectral lines
used for abundance analysis
Authors: Kiselman, D.
1994A&AS..104...23K Altcode:
Solar observations of spectral lines that are of importance for
abundance analysis have been obtained with high spatial resolution
in order to study the effect of granulation on these lines. Data
are presented in several plots and tables demonstrating both the
detailed behaviour of the lines over the granulation pattern and
the statistical properties of the variation of the different line
properties. The variation of line equivalent width with continuum
intensity is generally linear and looks similar for different kinds of
lines. Thus no effects have been found that could signal significant
problems for abundance analysis using homogeneous model atmospheres.

---------------------------------------------------------
Title: The 777 NM oxygen triplet in the Sun and solar-type stars,
and its use for abundance analysis
Authors: Kiselman, D.
1993A&A...275..269K Altcode:
The use of the neutral oxygen triplet lines at 777 nm and other
atomic lines for abundance analysis of the Sun and solar-type stars
is investigated and discussed taking into account the effects on
these lines by departures from local thermodynamic equilibrium (NLTE
effects). It is found that the discrepant behaviour of the 777 nm
triplet in the Sun is not possible to explain within the context
of one-dimensional homogeneous model atmospheres. It seems very
likely that the inhomogeneous properties of the solar photosphere
(granulation) must be taken inteo account to reproduce these lines
with the accuracy needed for precision abundance analysis. Experiments
with line calculations in a solar granulation simulation snapshot
are made, leading to one possible mechanism for the suppression of
the NLTE effect that is predicted for the 777 nm triplet lines by
one-dimensional model atmospheres.

---------------------------------------------------------
Title: Reliability of classical abundance analysis: boron and oxygen
Authors: Kiselman, D.
1993fces.conf...35K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Implications of departures from LTE and homogeneity in the
sun and solar-type stars
Authors: Kiselman, Dan
1993PhDT.......224K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE effects on oxygen abundance determinations for
solar-type stars
Authors: Kiselman, Dan
1991A&A...245L...9K Altcode:
Non-LTE effects on oxygen abundance determinations for solar-type
stars have been investigated using a model atom of 15 levels plus
continuum. The computed equivalent widths of the 777 nm triplet lines
in the sun are too large compared to observations, the corresponding
LTE values seem to give a better agreement. There are, however,
several reasons not to believe that the lines are formed in LTE,
and the discrepancy could be due to photospheric inhomogeneities. The
implications of the non-LTE effects for oxygen lines on the shape of
the galactic (O/Fe)-(Fe/H) relation are discussed.

---------------------------------------------------------
Title: A uvby-like photometric system for the WF/PC of the HST.
Authors: Kiselman, D.; Oja, T.; Gustafsson, B.
1990A&A...238..265K Altcode:
The possibility of combining four filters of the Hubble Space Telescope
Wide Field/Planetary Camera into a uvby-like photometric system is
discussed. On the basis of earth-based observations with appropriate
filters, such a system consisting of WF/PC filters F 368M, F 413M, F
492M, and F 547M was calibrated for the determination of fundamental
parameters of F dwarf stars. A good agreement was found between this
empirical calibration and a theoretical one by Bell (1988). Good
estimates of effective temperatures and metallicities can be obtained
with this system, while gravity determinations require a UV filter at
shorter wavelengths.

---------------------------------------------------------
Title: Astrophysical processes and structures in the
universe. Abstracts.
Authors: Kiselman, D.; Lagerkvist, C. -I.
1990UppOR..52.....K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Non-LTE effects on oxygen abundance determinations for
solar-type stars.
Authors: Kiselman, D.
1990apsu.conf...38K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Nordic-Baltic Astronomy Meeting : proceedings of a meeting held
at the Astronomical Observatory of the Uppsala University, June 17-21,
1990, celebrating the 250th anniversary of the Celsius Observatory
Authors: Lagerkvist, C. -I.; Kiselman, D.; Lindgren, M.
1990nba..meet.....L Altcode:
No abstract at ADS