Author name code: auer
ADS astronomy entries on 2022-09-14
author:"Auer, Lawrence H." OR author:"Auer, Larry H."
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Title: Toulouse 2D numerical radiative transfer codes
Authors: Paletou, F.; Léger, L.; Chane-Yook, M.; Auer, L. H.
Bibcode: 2019arXiv190305971P
Altcode:
A tutorial associated with the distribution of 2D non-LTE multilevel
atom radiative transfer codes.
Title: Acceleration of Convergence
Authors: Auer, L. H.
Bibcode: 2009nrt..book..101A
Altcode:
No abstract at ADS
Title: FUSE Observations of HD 5980: The Wind Structure of the Eruptor
Authors: Koenigsberger, Gloria; Fullerton, Alexander W.; Massa, Derck;
Auer, Lawrence H.
Bibcode: 2006AJ....132.1527K
Altcode: 2006astro.ph..6705K
HD 5980 is a unique system containing one massive star (star A)
that is apparently entering the luminous blue variable phase and an
eclipsing companion (star B) that may have already evolved beyond
this phase to become a Wolf-Rayet star. In this paper we present
the results from FUSE observations obtained in 1999, 2000, and 2002,
and one far-UV observation obtained by ORFEUS BEFS in 1993 shortly
before the first eruption of HD 5980. The eight phase-resolved spectra
obtained by FUSE in 2002 are analyzed in the context of a wind-eclipse
model. This analysis shows that the wind of the eruptor obeyed a very
fast velocity law in 2002, which is consistent with the line-driving
mechanism. Large-amplitude line-profile variations on the orbital
period are shown to be due to the eclipse of star B by the wind of
star A, although the eclipse due to gas flowing in the direction
of star B is absent. This can only be explained if the wind of star
A is not spherically symmetric or if the eclipsed line radiation is
``filled in'' by emission originating from somewhere else in the system,
e.g., in the wind-wind collision region. Except for a slightly lower
wind speed, the ORFEUS BEFS spectrum is very similar to the spectrum
obtained by FUSE at the same orbital phase; there is no indication of
the impending eruption. However, the trend for decreasing wind velocity
suggests the occurrence of the ``bistability'' mechanism, which in turn
implies that the restructuring of the circumbinary environment caused
by the transition from fast, rarefied wind to slow, dense wind was
observed as the eruptive event. The underlying mechanism responsible
for the long-term decrease in wind velocity that precipitated this
change remains an open issue. 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 NAS5-32985.
Title: Erratum: ``W49A North: Global or Local or No Collapse?'' (ApJS, 153, 463 [2004])
Authors: Williams, John A.; Dickel, Hélène R.; Auer, Lawrence H.
Bibcode: 2005ApJS..161..183W
Altcode:
There is a typographical error in the cgs units of intensity given
just before equation (1) of the original paper. The correct units are
ergs s-1 cm-2 Hz-1 sr-1.
Title: W49A North: Global or Local or No Collapse?
Authors: Williams, John A.; Dickel, Hélène R.; Auer, Lawrence H.
Bibcode: 2004ApJS..153..463W
Altcode: 2004astro.ph..5085W
We attempt to fit observations with 5" resolution of the J=2-1
transition of CS in the directions of H II regions A, B, and G of
W49A North as well as observations with 20" resolution of the J=2-1,
3-2, 5-4, and 7-6 transitions in the directions of H II regions A
and G by using radiative transfer calculations. These calculations
predict the intensity profiles resulting from several spherical clouds
along the line of sight. We consider three models: global collapse
of a very large (5 pc radius) cloud, localized collapse from smaller
(1 pc) clouds around individual H II regions, and multiple, static
clouds. For all three models we can find combinations of parameters
that reproduce the CS profiles reasonably well provided that the
component clouds have a core-envelope structure with a temperature
gradient. Cores with high temperature and high molecular hydrogen
density are needed to match the higher transitions (e.g., J=7-6)
observed toward A and G. The lower temperature, low-density gas
needed to create the inverse P Cygni profile seen in the CS J=2-1 line
(with 5" beam) toward H II region G arises from different components
in the three models. The infalling envelope of cloud G plus cloud
B creates the absorption in global collapse, cloud B is responsible
in local collapse, and a separate cloud, G', is needed in the case
of many static clouds. The exact nature of the velocity field in the
envelopes for the case of local collapse is not important as long as it
is in the range of 1-5 km s-1 for a turbulent velocity of
about 6 km s-1. High-resolution observations of the J=1-0
and 5-4 transitions of CS and C34S may distinguish between
these three models. Modeling existing observations of HCO+
and C18O does not allow one to distinguish between the
three models but does indicate the existence of a bipolar outflow.
Title: W49A North - Global, Local, or no Collapse?
Authors: Dickel, Helene R.; Williams, John A.; Auer, Lawrence H.
Bibcode: 2003IAUS..221P..32D
Altcode:
Radiative transfer calculations have been performed in an attempt to
fit profiles of several CS transitions (J=2-1 3-2 5-4 7-6) observed
towards HII regions A B G in the star-forming complex W49A North. Three
models were considered: global collapse of a very large (5 pc radius)
cloud localized collapse of smaller (1 pc) clouds and multiple static
clouds. For all three models it was possible to find combinations of
parameters that reproduce the CS profiles reasonably well provided that
the component clouds have a core/ envelope structure with a temperature
gradient. Cores with high temperature and high molecular hydrogen
density are needed to match the higher transitions (e.g. J=7-6 with
20"" beam). The low density gas needed to create the inverse P-Cygni
profile seen in the CS J=2-1 line (with 5"" beam) towards HII G arises
from different components in the 3 models. The infalling envelop of
G plus cloud B creates the absorption in global collapse cloud B is
responsible in local collapse and a separate cloud G' is needed in
the case of many static clouds. Research partially supported by
the National Science Foundation USA; grants AST90-24503 93-20239 and
96-13999 to the University of Illinois
Title: Insight into Multi-Dimensional Transfer
Authors: Auer, L.
Bibcode: 2003ASPC..288..405A
Altcode: 2003sam..conf..405A
Although computers are becoming ever more powerful, modelers must
be aware of potential computational dangers. Resolution of optical
boundaries and interfaces is necessary in order to predict correctly
the radiation field. For regular objects this is accomplished simply
by using "logarithmic gridding" on the outside edges. For irregular
objects, like prominences or loops, resolution of all the interior
interfaces is a nearly insurmountable problem. Monte Carlo is a
powerful and robust tool for validating deterministic results. It is
particularly appropriate in this era of multi-processor computing. It
automatically resolves all boundaries, avoids the "ray effects" inherent
in the use of distinct rays, can easily treat even fractal structures,
and should become a first-look tool for the investigation of the effect
of geometrical structure on the radiation field.
Title: Ultraviolet Spectroscopy of the Massive LMC Multiple Systems
Sk-67^0m#circ;18 (Br 5) and HD 36402 (Br 31)
Authors: Koenigsberger, G.; Moffat, A. F. J.; Auer, L. H.
Bibcode: 2003RMxAA..39..213K
Altcode:
Following previous IUE-based spectroscopic studies of WR+O binaries
in the Galaxy and in the SMC, we present a similar study of the two
systems, Br 5 [O3 If^*(+O) + O8-B0 I(+OB?)] and Br 31 [WC4(+O?) +
O8 I:] in the Large Magellanic Cloud. We detect wind eclipse effects
in the WC4+O (P = 3.033 d) pair in Br 31 similar to, but weaker than
those observed in the Small Magellanic Cloud system Sk 188 (WO4+O4
V). A low-amplitude ( ~ 0 km s-1) variation in the radial velocity
of UV photospheric absorption lines and the O V 1371 emission with
the 3 day period is detected. The radial velocity variations of the
photospheric lines may be due to the superposition of the stationary
set of absorption lines belonging to the O8 I: star and a broader
set of lines belonging to the O-type companion in the close binary
pair. The UV continuum energy distribution of Br 31 also supports the
optical results that the system contains at least 3 bright stars,
one of which is a late O-type supergiant. Contrasting with Br 31,
the absence of significant Si IV 1400 Å emission in the UV spectrum
of Br 5 contradicts the results from optical spectroscopy that imply
that it is triple, with the presence of a late O-type supergiant in
the system. Orbital phase-coverage of the IUE observations does not
allow the detection of possible atmospheric eclipse effects in Br 5,
with P = 2.001 d, but radial velocity variations attributable to
orbital motion of the O3 If^* star are detected.
Title: Formal Solution: EXPLICIT Answers
Authors: Auer, L.
Bibcode: 2003ASPC..288....3A
Altcode: 2003sam..conf....3A
Evaluation of the radiation field arising from a specified set of
thermodynamic and kinetic material conditions is known as the Formal
Solution. The ability to find such solutions efficiently is critical to
the iterative solution of the implicit coupled matter plus radiation
problem. It is first shown how the exact relativistic radiation
transport along a ray may be reduced to a set of easily evaluated
integrals. The short characteristic approach is then used to find the
formal solution of multi-dimensional radiation problems.
Title: The Wind-Wind Collision Region of the Wolf-Rayet Binary V444
Cyg: How much optical line emission does it produce ?
Authors: Flores, A.; Auer, L. H.; Koenigsberger, G.; Cardona, O.
Bibcode: 2001AAS...19915506F
Altcode: 2002BAAS...34..562F
We model the emission line profile variations that are expected to be
produced by physical and wind eclipses in the Wolf-Rayet (WR+O) binary
system V444 Cyg. A comparison of the theoretical profiles with the He
II 4686 Å line observed in V444 Cyg allows us to isolate the effects
that are likely to be due to the wind-wind collision region, in this
particular line. We estimate that the WWC region contributes no more
than ~ 12% of the equivalent width of the emission line, with smaller
values during elongations, when part of the shock cone is being eclipsed
by the O-star. The upper limit implies a maximum contribution from the
wind-wind collision region of ~ 1.*E35 ergs s-1
to the total luminosity of He II 4686 Å line. Using the analytical
solution of Cantó et al. (1996), we find that the bulk of this emission
seems to be arising along the shock cone walls where the flow velocity
is ~ 800 km s-1, at a distance of ~ 8 {Rsun }\>
from the O-star's surface, and at Θ =60-70o from the line
joining the centers of the two stars, with origin in the O-star. The
derived surface density of this region is σ =0.22 gr cm-2,
which together with the He II 4686 Å luminosity, indicates that
the thickness of the shock lies in the range 2-10 x 1010
cm and the total density is 1-6 x 1012 cm-3.
Title: The Wind-Wind Collision Region of the Wolf-Rayet Binary V444
Cygni: How Much Optical Line Emission Does It Produce?
Authors: Flores, Aaron; Auer, Lawrence H.; Koenigsberger, Gloria;
Cardona, Octavio
Bibcode: 2001ApJ...563..341F
Altcode:
We model the emission-line profile variations that are expected to
be produced by physical and wind eclipses in the Wolf-Rayet (W-R+O)
binary system V444 Cyg. A comparison of the theoretical profiles with
the He II 4686 Å line observed in V444 Cyg allows us to isolate the
effects that are likely to be due to the wind-wind collision region in
this particular line. We estimate that the wind-wind collision region
contributes no more than ~12% of the equivalent width of the emission
line, with smaller values during elongations, when part of the shock
cone is being eclipsed by the O star. The upper limit implies a maximum
contribution from the wind-wind collision region of ~1×1035
ergs s-1 to the total luminosity of He II 4686 Å line. Using
the analytical solution of Cantó et al., we find that the bulk of this
emission arises along the shock cone walls where the flow velocity
is ~800 km s-1, at a distance of ~8 Rsolar
from the O star's surface, and at θ=65°-75° from the line joining
the centers of the two stars, with origin in the O star. The derived
surface density of this region is σ=0.22 g cm-2, which,
together with the He II 4686 Å luminosity, indicates that the thickness
of the shock lies in the range 2-10×1010 cm and the total
density is 1-6×1012 cm-3.
Title: W 49 A North: J=2-1 Lines of CS and C18 O -
Collapse Colliding Clouds, or ?
Authors: Dickel, H. R.; Williams, J. A.; Upham, D. E.; Welch, W. J.;
Wright, M. C. H.; Wilson, T. L.; Mauersberger, R.; Auer, L. H.
Bibcode: 2000ESASP.445..359D
Altcode: 2000sfsl.conf..359D
No abstract at ADS
Title: Astronomical Refraction: Computational Method for All Zenith
Angles
Authors: Auer, Lawrence H.; Standish, E. Myles
Bibcode: 2000AJ....119.2472A
Altcode:
It is shown that the problem of computing astronomical refraction for
any value of the zenith angle may be reduced to a simple, nonsingular,
numerical quadrature when the proper choice is made for the independent
variable of integration. The angle between the radius vector and
the light ray is such a choice. The implementation of the quadrature
method is discussed in its general form and illustrated by means of
an application to a piecewise polytropic atmosphere. The flexibility,
simplicity, and computational efficiency of the method are evident.
Title: Diffusion, P1, and other approximate forms of
radiation transport.
Authors: Olson, G. L.; Auer, L. H.; Hall, M. L.
Bibcode: 2000JQSRT..64..619O
Altcode:
Full transport solutions of time-dependent problems can be
computationally very expensive. Therefore, considerable effort has been
devoted to developing approximate solution techniques that are much
faster computationally and yet are accurate enough for a particular
application. Many of these approximate solutions have been used in
isolated problems and have not been compared to each other. This paper
presents two test problems that test and compare several approximate
transport techniques. In addition to the diffusion and P1
approximations, the authors test several different flux-limited
diffusion theories and variable Eddington factor closures. For
completeness, they show some variations that have not yet appeared in
the literature that have some interesting consequences. For example, the
authors have found a trivial way to modify the P1 equations
to get the correct propagation velocity of a radiation front in the
optically thin limit without modifying the accuracy of the solution in
the optically thick limit. Also, the authors demonstrate nonphysical
behavior in some published techniques.
Title: W49 A north: J = 2-1 lines of CS and C18O.
Authors: Dickel, H. R.; Williams, J. A.; Upham, D. E.; Welch, W. J.;
Wright, M. C. H.; Wilson, T. L.; Mauersberger, R.; Auer, L. H.
Bibcode: 1999BAAS...31.1242D
Altcode:
No abstract at ADS
Title: W 49 A North: J=2-1 Lines of CS and C(18) O
Authors: Dickel, H. R.; Williams, J. A.; Upham, D. E.; Welch, Wm. J.;
Wright, M. C. H.; Wilson, T. L.; Mauersberger, R.; Auer, L. H.
Bibcode: 1999AAS...19410902D
Altcode:
Observations of the W 49 A North star forming region in the J=2-1 line
of CS have been made with the BIMA array with an angular resolution
of 4.6'' x 3.8''; complementary observations in the J=2-1 line of
C(18) O and J=3-2 line of C(34) S were made with the IRAM 30 meter
telescope with angular resolutions of 12'' and 17'' respectively. The
molecular complex is elongated along a diagonal from northeast to
southwest. The position-velocity diagrams for CS convolved to 12''
resemble those of C(18) O and the J=5-4 line of C(34) S (from Serabyn
et al. 1993). There is a change in velocity along the major axis of
the molecular complex. At the higher resolution of ~ 4'', absorption of
the continuum emission at 3 mm by CS is clearly observed. The apparent
velocity gradient is seen to be part of a``C''-shaped distribution
of the CS emission. Furthermore, as is found in the J=1-0 HCO(+)
data by Welch et al. (1987), the optically thick J=2-1 CS line
exhibits an inverse P-Cygni profile towards HII region G. These two
characteristics of the CS data lend support to the global collapse model
(Welch et al. 1987). The high resolution CS profiles in the central
region all show varying degrees of absorption. At lower resolution
the surrounding CS emission fills in much of the absorption and the
inverse P-Cygni shape disappears. Most spectra towards W 49 A North
show two main velocity components whose relative intensities vary with
position along the major axis of the molecular complex. It is not clear
whether this behavior can also be explained using the global collapse
model of Welch et al. together with self-absorption effects; it may be
necessary to include some additional cloud components as proposed by
Serabyn et al. (1993). Radiative transfer modeling of these and other
scenarios is nearing completion and is the subject of a separate paper
(Williams and Dickel, in preparation 1999). Research was partially
supported by NSF grants to UIL and UCB.
Title: Wind Velocity Variations in the Luminous Blue Variable-Type
Erupting Star of the Wolf-Rayet Binary HD 5980
Authors: Koenigsberger, G.; Auer, L. H.; Georgiev, L.; Guinan, E.
Bibcode: 1998ApJ...496..934K
Altcode:
We present the wind velocity and UV luminosity variations in the
Wolf-Rayet system HD 5980 obtained over a time span during which
one of the stars of the system was transformed into a luminous blue
variable and underwent an eruption. We are able to separate the velocity
components of the two stars in the system: a stable velocity component
at -1700 km s-1 is associated with the nonerupting star,
while the variable wind with velocities ranging from -500 to -3000 km
s-1 corresponds to the eruptor. The development of a fast
wind following the slow wind eruptive phase is observed. Under the
assumption of radiatively driven winds, these changing velocities
indicate that the radius of the photosphere gradually increased
during at least 12 years prior to the 1994 eruption, decreasing
rapidly thereafter. An estimate of the stellar parameters indicates
that the erupting star is massive (M > 40 M⊙) and very
luminous (L > 106 L⊙), and that during the
eruption its radius extended beyond the binary orbit (R*
> 100 R⊙).
Title: Multidimensional radiative transfer with multilevel
atoms. II. The non-linear multigrid method.
Authors: Fabiani Bendicho, P.; Trujillo Bueno, J.; Auer, L.
Bibcode: 1997A&A...324..161F
Altcode:
A new iterative method for solving non-LTE multilevel radiative
transfer (RT) problems in 1D, 2D or 3D geometries is presented. The
scheme obtains the self-consistent solution of the kinetic and
RT equations at the cost of only a few (<10) formal solutions
of the RT equation. It combines, for the first time, non-linear
multigrid iteration (Brandt, 1977, Math. Comp. 31, 333; Hackbush,
1985, Multi-Grid Methods and Applications, springer-Verlag, Berlin),
an efficient multilevel RT scheme based on Gauss-Seidel iterations
(cf. Trujillo Bueno & Fabiani Bendicho, 1995ApJ...455..646T),
and accurate short-characteristics formal solution techniques. By
combining a valid stopping criterion with a nested-grid strategy
a converged solution with the desired true error is automatically
guaranteed. Contrary to the current operator splitting methods the very
high convergence speed of the new RT method does not deteriorate when
the grid spatial resolution is increased. With this non-linear multigrid
method non-LTE problems discretized on N grid points are solved in O(N)
operations. The nested multigrid RT method presented here is, thus,
particularly attractive in complicated multilevel transfer problems
where small grid-sizes are required. The properties of the method are
analyzed both analytically and with illustrative multilevel calculations
for Ca II in 1D and 2D schematic model atmospheres.
Title: The erupting Wolf-Rayet binary HD 5980 in the Small Magellanic
Cloud: spectral transition from B1.5Ia+ to WN6 and the accompanying
light curve.
Authors: Koenigsberger, Gloria; Shore, Steve; Guinan, Ed; Auer,
Lawrence
Bibcode: 1996RMxAC...5...92K
Altcode:
In this paper we analyze the high dispersion IUE spectra of the erupting
Wolf-Rayet system HD 5980 obtained shortly after the maximum in the
optical light curve and one year later. We show that the earliest
spectrum has features which are characteristic of B1.5Ia(+)
spectra. Subsequent spectra indicate a photosphere which is gradually
increasing its Teff, containing Fe IV and Fe V absorption
features, and becoming finally a WN6. We also present a UV light curve
at two wavelength bands (1300A and 1850A) covering a year after maximum
in the eruption, where both eclipses of the 19.3 day orbit are evident.
Title: Ultraviolet Observations of the Eruption in the Small
Magellanic Cloud Wolf-Rayet System HD 5980
Authors: Koenigsberger, Gloria; Guinan, Ed; Auer, Lawrence; Georgiev,
Leonid
Bibcode: 1995ApJ...452L.107K
Altcode:
We present results of IUE observations ( lambda lambda 1200--3200) of
the erupting system HD 5980 obtained in 1994 November and December. The
1994 spectrum presents emission lines from ions such as N III, Si
II--III and Al III which were absent in 1991. There is a systematic
tendency towards higher degrees of ionization over the 44 days covered
by the present observations. At the start of the observations on HJD
2449674 the UV continuum flux at 1850 A is a factor of ~2 larger than in
1991, declining by 30% in 18 days, followed by a tendency to once again
increase. FES magnitudes indicate a rapid decline in visual brightness
after maximum in the eruption. Wind speeds as high as ~1700 km s-1 are
measured although the P Cygni absorption components are highly peculiar,
containing several emission-like "bumps," the most prominent of which
lies at 920 km s-1. We conclude that the eruption occurred in the
primary star of the 19.3 day orbital pair, the one classified as WN4
by Breysacher et al. and which now is displaying an LBV-type event. The
phenomena in HD 5980 provide evidence supporting evolutionary scenarios
in which pulsationally unstable, H-rich WN stars precede the LBV phase.
Title: A new approximate operator method for partial frequency
redistribution problems.
Authors: Paletou, F.; Auer, L. H.
Bibcode: 1995A&A...297..771P
Altcode:
Methods for the solution of non-lte partial frequency redistribution
(prd) radiative transfer problems are presented. By explicitly
treating the partial frequency coherence, convergence difficulties
caused by using a Complete Redistribution Approximation are completely
overcome. A new core-wing treatment of the redistribution both avoids
the explicit solution of the frequency coupled system, and permits
the use of simple Approximate Operator Iteration to solve prd problems
extremely efficiently.
Title: Modeling Radiative Transfer in Molecular Clouds. I. HCO +
in the Star-forming Region W49A North
Authors: Dickel, Helene R.; Auer, Lawrence H.
Bibcode: 1994ApJ...437..222D
Altcode:
A new general multilevel, non-Local Thermodynamic Equilibrium (LTE)
radiative transfer code, valid for any velocity field, is applied to
HCO(+) observations of W49A North. Three classes of collapse models are
considered: free-fall collapse (v proportional to 1/sq. root of r),
rho proportional to r-3/2 throughout the molecular cloud,
successfully reproduces the features of the observations and gives the
best fit to the J = 1-0 and J = 3-2 profiles both toward the prominent
H II component G of W49A North and off the center. In addition to a
slow radial fall-off of density, the theoretical modeling implies the
following for the molecular cloud: the large line widths result from
motions occurring within the inner 1 pc, and there are probably one
or more fragments with peculiar velocities within this same region.
Title: Multidimensional radiative transfer with multilevel
atoms. I. ALI method with preconditioning of the rate equations.
Authors: Auer, L.; Bendicho, P. Fabiani; Trujillo Bueno, J.
Bibcode: 1994A&A...292..599A
Altcode:
We combine a number of powerful mathematical techniques to produce
an effective method for treating multidimensional radiative transfer
problems in complex atomic models without assuming LTE. The approach
is so efficient that multilevel two-dimensional (2D) modeling can now
be performed with no more than a workstation. We employ Accelerated
Lambda Iteration (ALI) methods: accurate short characteristics for
the formal solution of the transfer equation with an efficient new
strategy for horizontal periodic boundary conditions, local approximate
{LAMBDA}-operators given by the diagonal of the exact operator,
methods to accelerate the convergence, and preconditioning of the rate
equations. Of particular interest is a simple grid-doubling strategy
which both rapidly finds the converged solution in very fine meshes
and also estimates the true error of that solution. The properties of
the method are described in detail with the help of 2D line-transfer
calculations with multilevel model atoms for Ca II and H. These
illustrative multilevel calculations in schematic inhomogeneous
atmospheres demonstrate the importance of properly including the
effects of horizontal radiative transfer and realistic atomic models.
Title: Line Profile Variations from Atmospheric Eclipses: Constraints
on the Wind Structure in Wolf-Rayet Stars
Authors: Auer, L. H.; Koenigsberger, G.
Bibcode: 1994ApJ...436..859A
Altcode:
Binary systems in which one of the components has a stellar wind
may present a phenomenon known as 'wind' or 'atmospheric eclipse',
in which that wind occults the luminous disk of the companion. The
enhanced absorption profile, relative to the spectrum at uneclipsed
orbital phases, can be be modeled to yield constraints on the spatial
structure of the eclipsing wind. A new, very efficient approach to the
radiative transfer problem, which makes no requirements with respect
to monotonicity of the velocity gradient or size of that gradient, is
presented. The technique recovers both the comoving frame calculation
and the Sobolev approximation in the appropiate limits. Sample computer
simulations of the line profile variations induced by wind eclipses are
presented. It is shown that the location of the wind absorption features
in frequency is a diagnostic tool for identifying the size of the wind
acceleration region. Comparison of the model profile variations with
the observed variations in the Wolf-Rayet (W-R)+6 binary system V444
Cyg illustrate how the method can be used to derive information on
the structure of the wind of the W-R star constrain the size of the
W-R core radius.
Title: Remarkable Long-Term Changes in the Small Magellanic Cloud
Wolf-Rayet System HD 5980
Authors: Koenigsberger, G.; Moffat, A. F. J.; St-Louis, N.; Auer,
L. H.; Drissen, L.; Seggewiss, W.
Bibcode: 1994ApJ...436..301K
Altcode:
In this paper we report the remarkable changes which occurred in
the Small Magellanic Cloud W-R system HD5980 = AB5 between 1978 and
1991. Within this timescale, there has been a systematic enhancement
(by factors of 2-10 depending on the line) in the equivalent widths of
all emission lines, and a change in the relative strengths of N III,
N IV, and N V lines. Currently, the W-R spectrum is more typical of
a WN6 star than a WN3 or WN4, as it was originally classified. The
terminal speed of the wind has diminished by ~600 km s^-1^, while
the system has brightened in the visual by 0.45 mag. The UV (1850 A)
continuum changed by less than 0.13 mag. The change from WN3 or WN4
to WN6 is unprecedented. The system appears to he composed of at
least three stars: two WNs in mutual 19.266 day orbit and an O-type
supergiant. We propose that the changes observed in HD 5980 are
related to an increase in wind density of one (or both?) of the W-R
components, where the brighter WN6 component will dominate the W-R
spectrum after the change, and we speculate that this modification of
the wind structure is driven by tidal interaction induced by a possible
current periastron passage of the third component in the system.
Title: Two-dimensional radiative transfer with partial frequency
redistribution I. General method
Authors: Auer, L. H.; Paletou, F.
Bibcode: 1994A&A...285..675A
Altcode:
We present a new method for the solution of non-LTE scattering
problems in two dimensions. It is based on Accelerated Lambda
Iteration and an improved short characteristic method. It is more
than an order of magnitude faster than a direct approach for Complete
Redistribution. We, further, have extended the method to the solution of
Partial Redistribution problems. The computational cost of treating PRD
with the new method is only a small factor larger than CRD. Results with
the new iterative approach are in complete agreement with previously
published results.
Title: Radiative Transfer Modeling of Molecular Clouds: HCO+ in the
Star-Forming Region W 49 A North
Authors: Dickel, H. R.; Auer, L. H.; Wilner, D. J.
Bibcode: 1994ASPC...59..253D
Altcode: 1994amsw.conf..253D; 1994IAUCo.140..253D
No abstract at ADS
Title: Multi-dimensional radiative transfer with multi-level atoms
and the diagnostic problem of small-scale structures
Authors: Trujillo Bueno, J.; Fabiani, P.; Auer, L.
Bibcode: 1994smf..conf..328T
Altcode:
No abstract at ADS
Title: Two-dimensional radiative transfer with partial frequency
redistribution. II. Application to resonance lines in quiescent
prominences
Authors: Paletou, F.; Vial, J. -C.; Auer, L. H.
Bibcode: 1993A&A...274..571P
Altcode:
Theoretical emergent profiles in the resonance lines of H I Lyman α,
Mg II h & k and Ca II H & K formed in quiescent prominences
are presented. Both partial frequency redistribution effects and
two-dimensional structure have been included in the calculations. The
prominence model consists of a static, isobaric and isothermal
freestanding slab irradiated by realistic chromospheric profiles
(080-8 observations). We compare the differences between complete (CRD)
and partial frequency redistribution (PRD). Vertical variations in the
emergent profiles are displayed, and the importance of the geometrical
effects is discussed. In addition, we have evaluated both emergent
profiles for a filament as seen over the disk, and the back-scattered
radiation towards the chromosphere.
Title: Is the W-R System HD 5980 in the SMC Undergoing Outburst?
Authors: Koeningsberger, G.; Auer, L. H.; Cardona, O.; Drissen, L.;
Moffatt, A. F. J.; St. Louis, N.; Seggewiss, W.
Bibcode: 1993ASPC...35..249K
Altcode: 1993msli.conf..249K
No abstract at ADS
Title: Radiative modeling of solar prominences, two-dimensional
transfer plus partial frequency redistribution.
Authors: Paletou, F.; Vial, Jean-Claude; Auer, L. H.
Bibcode: 1992ESASP.348..225P
Altcode: 1992cscl.work..225P
The two-dimensional, PRD radiative transfer code of Auer and
Paletou (1992) has been used to compute the resonance lines of H
I, Mg II and Ca II in quiescent prominences, which are modeled as
isothermal freestanding slabs illuminated from the sides as well as
from below. Partial redistribution (PRD) and 2D effects are evidenced
and compared to complete redistribution computations for both 1D and
2D geometries. Important edge variations are fround at the bottom
and the top that should be observed with a spatial resolution of one
arcsecond. As in 1D, PRD effects allow for greater penetration of the
incident radiation into the layer. The 2D code computes both the radial
emergent intensity and the amount of radiation backscattered into the
chromosphere. It can, accordingly, be used to estimate the visibility of
filaments. It will be of special interest to build non-isothermal models
and compare e.g. the Lyα profiles with the SUMER/SOHO observations.
Title: Intrinsic vs. Binary-Induced Profile Variability: Can we Tell
the Difference? (Invited Paper)
Authors: Koenigsberger, C.; Auer, L. H.
Bibcode: 1992ASPC...22..239K
Altcode: 1992nvos.work..239K
No abstract at ADS
Title: Variability of the Discrete Absorption Components in the
Wolf-Rayet Star HD 193077
Authors: Auer, Lawrence
Bibcode: 1992iue..prop.4198A
Altcode:
HD 193077 is the only well-docurnented example of a Wolf-Rayet star in
which narrow absorption components are consistently present at close to
terminal speed (in the unsaturated resonance lines of both Si IV and C
IV). We propose to obtain high- dispersion time series spectroscopy of
this object in order to investigate, for the first time, the temporal
evolution of discrete components in a WR star. These observations will
show if the behaviour of the discrete components matches that seen in
OB stars, and, therefore, indicates that the dynamics of WR winds at
intermediate velocities are controlled by lineradiation pressure as
they are in OB winds. Moreover, photospheric absorption lines indicate
a projected rotation velocity of ve sin(i) ~500 km/s for HD 193077,
very close to break-up, so this star also offers a unique opportunity
to investigate the correlation between very large ve sin(i) and DAC
development.
Title: Ultraviolet Variability of the Massive W-R Binary System HDE
311884 = WR 47
Authors: Koenigsberger, Gloria; Moffat, Anthony F. J.; Auer,
Lawrence H.
Bibcode: 1991ApJ...376..272K
Altcode:
IUE observations and their analysis of the massive WN6 + O binary
system HDE 311884 are presented. The phase-dependent variations are like
those of WN4-6 binaries studied previously, with atmospheric eclipses
evident in the N IV 1718 A and C IV 1550 A lines, and in the Fe V +
VI pseudocontinuum at wavelengths below 1480 A. The considerable
variability longward of 1700 A is due mostly to Fe II and Fe III lines.
Title: Modelling the Wind Eclipses in WR+O Binaries: the Qualitative
Picture
Authors: Koenigsberger, G.; Auer, L. H.
Bibcode: 1991IAUS..143..175K
Altcode:
No abstract at ADS
Title: The Wind Structure of HD 5980
Authors: Auer, Lawrence
Bibcode: 1991iue..prop.3923A
Altcode:
We propose to observe the Wolf-Rayet + O star binary system HD 5980,
the brightest WR in the Small Magellanic Cloud, at orbital phases in
which the O component undergoes eclipse by the WR wind. Our previous
observations show strong variations occur in the lines of N IV 1718,
C IV and He II and N V. Profile variations am consistent with the
wind eclipse interpretation. Additional high dispersion data are now
necessary in order to obtain sufficient orbital phase coverage to
deduce the wind velocity and opacity laws by detailed modeling of the
profile variations. The same modeling techniques will be applied to
archival high resolution data of V444 Cyg, a Galactic counterpart of
HD 5980, so as to determine the role that the heavy metal abundances
play in the wind structure. Our previous IUE research on HD 5890, under
WRLLA, has shown a major difference between it and Galactic WR+O binary
systems is the absence of a detectable Fe V and Fe VI pseudo-continuum,
which is consistent with lower metal abundances. If radiation pressure
is the driving mechanism for the wind, the detailed wind structure
should likewise differ, as appears to be the case from our preliminary
results. The data already suggest that the physical acceleration zone
in HD 5980 is not as extended as in V444 Cyg, but additional phase
coverage is needed in order to perform a more detailed analysis of
the wind structure.
Title: Acceleration of Convergence
Authors: Auer, L.
Bibcode: 1991ASIC..341....9A
Altcode: 1991sabc.conf....9A
No abstract at ADS
Title: A Source of Observational Constraints on the Structure of
Wolf-Rayet Winds
Authors: Auer, L. H.; Koenigsberger, G.
Bibcode: 1990ASPC....7..291A
Altcode: 1990phls.work..291A
No abstract at ADS
Title: IUE Observations of Wolf-Rayet Binary Systems in the Small
Magellanic Cloud
Authors: Moffat, Anthony F. J.; Koenigsberger, Gloria; Auer,
Lawrence H.
Bibcode: 1989ApJ...344..734M
Altcode:
The results of IUE observations of three SMC W-R binary systems at
various orbital phases are presented. Selective atmospheric eclipse
effects are evident in HD 5980 (WN 4 + O7 I:) and Sk 188 (W04 +
O4 V), and are very weak or absent in Sk 108 (WN 3 + O6.5 I:). The
difference in heavy-metal content between the SMC and Galactic objects
is especially manifest in the lack of atmospheric eclipse effects
due to a clustering of Fe V and Fe VI lines in the wavelength range
1360-1470 A in HD 5980.
Title: IUE Observations of Wolf-Rayet Binaries in the Galaxy, the
LMC and the SMC
Authors: Koenigsberger, G.; Auer, L. H.; Moffat, A. F. J.
Bibcode: 1989RMxAA..18..185K
Altcode:
No abstract at ADS
Title: The Wind Structure of the SMC Wolf-Rayet Star HD 5980
Authors: Auer, Lawrence
Bibcode: 1989iue..prop.3365A
Altcode:
No abstract at ADS
Title: A source of observational constraints on the structure of
Wolf-Rayet winds
Authors: Auer, Larry H.; Koenigsberger, Gloria
Bibcode: 1989STIN...9015023A
Altcode:
In some WR + O-star binary systems the Wolf-Rayet (WR) wind eclipses the
O star. The profile changes as a function of impact are reproduced with
a simple model which gives information on both the radial dependence
of the velocity and opacity.
Title: Atmospheric eclipse effects in Wolf-Rayet binaries in the
small Magellanic cloud
Authors: Koenigsberger, Gloria; Moffat, Anthony F. J.; Auer,
Lawrence H.
Bibcode: 1988ESASP.281a.197K
Altcode: 1988uvai....1..197K; 1988IUES....1..197K; 1988IUE88...1..197K
Results of IUE observations of three SMC W-R binary systems are
presented. Selective atmospheric eclipse effects are evident in HD5980
(WN4+06I) and Sk 188 (W04+04V), and are very weak, or absent in Sk 108
(WN3+06I). The difference in heavy-metal content between the SMC and
Galactic objects is clearly manifest in the lack of atmospheric eclipse
effects in the wavelength range 1360 to 1470 A in HD5980 and Sk 188.
Title: Observations of galactic WC + O binary systems: HD 97152 and
HD 152270
Authors: Auer, L. H.; Colome, C.; Koenigsberger, G.
Bibcode: 1988ESASP.281a.193A
Altcode: 1988IUE88...1..193A; 1988uvai....1..193A
The IUE observations of the Wolf-Rayet binary systems HD 97152 and HD
152270 are presented. Both systems contain a WC7 component, and both
have relatively small orbital inclinations. Weak atmospheric eclipses
at emission line wavelengths are detected in HD 97152, the system for
which a more suitable phase coverage is available.
Title: Radiative Transfer Through Molecular Clouds: P-Cygni Profiles
Authors: Auer, Lawrence H.; Dickel, Hélène R.
Bibcode: 1988inma.conf..165A
Altcode:
A code has been developed to solve the transfer of radiation through
molecular clouds with non-monotonic velocity fields and embedded H
II regions. P-Cygni-like profiles are common for models with an H
II region.
Title: Radiative transfer through molecular clouds: P-Cygni profiles.
Authors: Auer, L. H.; Dickel, H. R.
Bibcode: 1988imgh.conf..165A
Altcode:
A code has been developed to solve the transfer of radiation through
molecular clouds with non-monotonic velocity fields and embedded H
II regions. P-Cygni-like profiles are common for models with an H
II region.
Title: Wolf-Rayet Stellar Wind Instability: Very Rapid Variability
of the Line Spectrum of HD 90657
Authors: Auer, Lawrence
Bibcode: 1988iue..prop.3044A
Altcode:
In our IUE observation of the WN+O6 binary system, HD 90657, changes
in the spectrum were detected with a time scale shorter than 90 minutes
(Koenigsberger and Auer 1987). The variation requires the existence of
significant changes in the small scale structure of the wind. We propose
to augment this result by observation of the system at four distinct
orbital phases, using absorption of the O-star flux as a direct probe
of the small scale wind structure. The data obtained will both give
general information on the growth of wind instabilities and determine
if they are periodio-an important constraint on their origin. We will
also inspect the IUE archives for other evidence of short time scale
variations in WR targets.
Title: Short characteristic integration of radiative transfer
problems: formal solution in two-dimensional slabs.
Authors: Kunasz, Paul; Auer, Lawrence H.
Bibcode: 1988JQSRT..39...67K
Altcode:
A short characteristic method based on parabolic approximation of
the source function is developed and applied to the solution of the
two-dimensional radiative transfer problem on Cartesian meshes. The
method is significantly faster for the evaluation of multidimensional
radiation fields than those currently in use. Convergence as a
functional of the grid resolution is discussed and linear and parabolic
upwind interpolation are compared.
Title: Atmospheric Eclipses in the SMC Wolf-Rayet Eclipsing Binary
HD 5980: The Heavy versus the Light Metal Abundance
Authors: Koenigsberger, G.; Moffat, A. F. J.; Auer, L. H.
Bibcode: 1987ApJ...322L..41K
Altcode:
Phase-dependent variations in the IUE spectra of the SMC 19.6-day
eclipsing binary system HD 5980 (WN4 + 07I) are discussed. The effects
of selective atmospheric eclipses in the N, C, and He lines of HD 5980
are found to be similar to those observed in its Galactic counterpart,
while the variations in the 1350-1490 A continuum region are virtually
undetectable. It is suggested that this observation is a consequence
of the lower initial abundance, particularly of the heavier elements
in the SMC with respect to the Galaxy, combined with subsequent nuclear
processing in the WR star interior.
Title: Rapid emission-line variations in the UV spectrum of the
Wolf-Rayet system HD 90657.
Authors: Koenigsberger, G.; Auer, L. H.
Bibcode: 1987PASP...99.1080K
Altcode:
The authors report IUE observations of the Wolf-Rayet binary system HD
90657 which indicate that a major change in the properties of the W-R
wind occurred on time scales of less than 90 minutes. These are very
rapid variations when compared to those resulting from atmospheric
eclipse effects, which are also observed in this system. The rapid
change is attributed to wind instabilities, possibly induced by
pulsations of the underlying helium-burning core.
Title: Identifying lines in the IUE spectrum of the Wolf-Rayet star
HD 193077.
Authors: Koenigsberger, G.; Auer, L. H.
Bibcode: 1987RMxAA..14..277K
Altcode:
The IUE spectrum of HD 193077 (WN6+O+?) is rich in lines. The authors
present probable identifications for all emission lines which are
evident in the 1240 - 1800 Å wavelength range, and they discuss
several aspects of an intriguing narrow absorption line spectrum.
Title: UV line profile variations in Wolf-Rayet stars.
Authors: Koenigsberger, G.; Auer, L. H.
Bibcode: 1987RMxAA..14..271K
Altcode:
IUE observations of line-profile variability in Wolf-Rayet stars are
presented. Different mechanisms are discussed which are expected to
produce these variations.
Title: Acceleration of Convergence
Authors: Auer, L. H.
Bibcode: 1987nrt..book..101A
Altcode:
No abstract at ADS
Title: A rapidly convergent iterative solution of the non-LTE
radiation transfer problem.
Authors: Olson, G. L.; Auer, L. H.; Buchler, J. R.
Bibcode: 1986JQSRT..35..431O
Altcode:
An iterative scheme has been developed for the solution of the non-LTE
line radiation transfer problem. The method uses an approximate
operator that is deliberately chosen to be local so that it can be
easily extended to multidimensional geometry. The difference between
the formal and approximate solutions is used as a driving term for the
iterations. In one-dimensional, semi-infinite and free-standing slabs,
the technique is found to be very fast, robust, and applicable to a
large class of problems.
Title: Trigonometric parallaxes determined with the Yerkes Observatory
40 inch refractor. VI. Measurements made with PDS microdensitometers.
Authors: van Altena, W. F.; Auer, L. H.; Mora, C. L.; Vilkki, E. U.
Bibcode: 1986AJ.....91.1451V
Altcode:
Thirteen Yerkes Observatory 40 in. parallax series have been measured
on PDS microdensitometers and reduced using digital image-centering
techniques and more rigorous reduction methods. An approach for
determining a priori plate and star weights is discussed which is
based in part on the measurement uncertainties in each image. New
parallax-reduction programs have been written that solve for the
plate constants and the parallaxes and proper motions iteratively,
and realistic estimates have been derived for the error of the image
positions. The application of these modifications to the abovementioned
Yerkes parallax series yields an average accuracy for the parallaxes
of ± 0."10043 (s.e.) for a 24.5 plate single-exposure-per-plate
series. This figure represents a 30% improvement over our previous
results. We also find from a comparison with U.S. Naval Observatory
parallaxes that our internal and external accuracies are identical.
Title: IUE observations of phase-dependent variatons in WN+O systems.
Authors: Koenigsberger, G.; Auer, L. H.
Bibcode: 1985ApJ...297..255K
Altcode:
IUE observations of six WN + O Wolf-Rayet (W-R) systems are
reported. The periodic variations in five of the systems are shown
to result primarily from selective atmospheric eclipses of the O
star continuum by the W-R wind. An optical depth distribution of
the form tau inversely proportional to radius is suggested for radii
greater than 14 solar radii. Phase-dependent variations in the C IV
1550 absorption components in V444 Cyg, HD 90657, and HD 211853 are
interpreted as wind-wind collision effects.
Title: Influence of Solar Heating and Precipitation Scavenging on
the Simulated Lifetime of Post--Nuclear War Smoke
Authors: Malone, Robert C.; Auer, Lawrence H.; Glatzmaier, Gary A.;
Wood, Michael C.; Toon, Owen B.
Bibcode: 1985Sci...230..317M
Altcode:
The behavior of smoke injected into the atmosphere by massive
fires that might follow a nuclear war was simulated. Studies with
a three-dimensional global atmospheric circulation model showed
that heating of the smoke by sunlight would be important and might
produce several effects that would decrease the efficiency with which
precipitation removes smoke from the atmosphere. The heating gives
rise to vertical motions that carry smoke well above the original
injection height. Heating of the smoke also causes the tropopause,
which is initially above the smoke, to reform below the heated
smoke layer. Smoke above the tropopause is physically isolated from
precipitation below. Consequently, the atmospheric residence time of
the remaining smoke is greatly increased over the prescribed residence
times used in previous models of nuclear winter.
Title: Phase Dependent Variations in Wolf-Rayet Binaries: Wind
Structures
Authors: Auer, Lawrence
Bibcode: 1984iue..prop.1760A
Altcode:
We propose observation of the Wolf-Rayet + O Star binary systems HD
90657, HD 186943, HD 211854, HD 97152, and HD 155270 at orbital phases
in which the O component undergoes selective atmospheric eclipse
by the WR wind. Because these particular systems have nearly zero
orbital inclination, the varying absorption of the O Star spectrum as
a function of impact parameter can be used to derive the optical depth
distribution in the winds of the WR's. Each system will be observed
in the lowdispersion mode during US2 shifts. These observations will
be combined with archival data to achieve adequate phase coverage for
the wind structure analysis. Possible wind-wind collision effects will
also be studied. The work being proposed is an extension of our previous
WRDLA research. We wish, in particular, to make observations at small
impact parameters to gain information on the initial acceleration of
the WR wind, and to make similar observation of several WC stars. One
of the results of our previous work was the striking similarity in the
outer parts of the flows of the five WN systems then observed. We will
determine now if there are, however, observational differences between
the WC and WN flows, and in the inner parts of the WN flows.
Title: The energy relation between hard X-ray and O V emission in
solar flares
Authors: Poland, A. I.; Orwig, L. E.; Mariska, J. T.; Auer, L. H.;
Nakatsuka, R.
Bibcode: 1984ApJ...280..457P
Altcode:
The relationship between energy emitted in hard X-rays and the
ultraviolet during the impulsive phase of solar flares provides
an important diagnostic for understanding the energy flow from
nonthermal to thermal. Many flares were observed from the Solar
Maximum Mission satellite simultaneously in hard X-rays and the O V
line at 1371 A formed at 250,000 K, providing information relevant to
this problem. Previous work has shown that short time scale peaks in
emission of these two types of radiation coincide in time to within 1
s. In this work the energy relation between the two types of emission
is investigated and it is found that for any given flare there is a
definite relation between hard X-ray and O V emissions throughout
the flare, but from one flare to the next this relation varies
markedly. These differences are attributed to the initial conditions in
the flaring loops and some exploratory model calculations are presented
to support this hypothesis.
Title: Difference equations and linearization methods for radiative
transfer.
Authors: Auer, L. H.
Bibcode: 1984mrt..book..237A
Altcode: 1984mrt..conf..237A
Difference equation methods are developed for the treatment of
radiation transport in planar and spherical geometries. Using the
Hermite method equations are derived, which give fourth-order accuracy
for the spatial discretization, yet are no more difficult to solve
than the usual second-order Feautrier system. It is shown that the
angular dependence of the radiation field may be handled by the use
of "variable Eddington factors", which reduce the system to just one
equation per frequency. An efficient iterative method for evaluating
these factors is presented and its convergence discussed. Finally,
the difference equations are linearized in terms of the local state
of the material, and methods are developed for solving the general
transfer problem in which there are additional constraints, e.g.,
hydrostatic, statistical, energy equilibria.
Title: Relation Between Hard X-ray and OV Energy Emitted During
Solar Flares
Authors: Poland, A. I.; Orwing, L. E.; Mariska, J. T.; Auer, L. H.
Bibcode: 1983BAAS...15..713P
Altcode:
No abstract at ADS
Title: The non-LTE analysis of carbon lines in the spectra of hot
stars. I. C III λ 4650 and λ 9710 Å triplet lines in the spectra
of O stars
Authors: Sakhibullin, N. A.; Auer, L. H.; van der Hucht, K.
Bibcode: 1982SvA....26..563S
Altcode:
No abstract at ADS
Title: The non-LTE analysis of carbon lines in the spectra of hot
stars. I - C III lambda 4650 and lambda 9710 A triplet lines in the
spectra of O stars
Authors: Sakhibullin, N. A.; Auer, L. H.; van der Hucht, K.
Bibcode: 1982AZh....59..933S
Altcode:
No abstract at ADS
Title: IUE Observations of Phase-Dependent Spectral Variations in
WR Binaries
Authors: Auer, L. H.; Koenigsberger, G.
Bibcode: 1982BAAS...14..634A
Altcode:
No abstract at ADS
Title: The structure of X-ray illuminated stellar atmospheres
Authors: London, R.; McCray, R.; Auer, L. H.
Bibcode: 1981ApJ...243..970L
Altcode:
The theory of X-ray illuminated stellar atmospheres in binary X-ray
systems is described. Particular attention is directed to the location
of the transition zone between the photosphere and the corona, which
largely determines the mass flux in the evaporative wind caused by
X-ray heating. A controversy in previous work concerning the effect of
emission line cooling on this location is resolved. The lines are found
to be optically thick, and they do not greatly affect the location
of the transition region. Detailed NLTE stellar atmosphere models
are constructed, including continuum radiation only. The pressure at
the transition zone is proportional to the local X-ray heating rate,
and the spectrum emitted by the atmosphere is nearly stellar, but
with reduced continuum jumps. The mass loss in the wind may be enough
to power the X-ray emission in the HZ Her-Her X-1 system if a large
fraction is captured by the neutron star.
Title: Wind-Wind Interactions in Wolf-Rayet Binaries
Authors: Auer, Lawrence
Bibcode: 1981iue..prop..721A
Altcode:
Wolf-Rayet and O stars are known to have large rates of mass loss. We
propose phase dependent observations of eclipsing binaries containing
a WR and an O star. The results should enable one to model the
interactions of the winds. As a side benefit knowing the separation
of the objects, one can comment on the rate of acceleration before
the winds collide.
Title: Two-dimensional radiative transfer. II. The wings of Ca K
and Mg k.
Authors: Owocki, S. P.; Auer, L. H.
Bibcode: 1980ApJ...241..448O
Altcode:
The effect of horizontal radiative transfer on the Ca K and Mg k line
wing intensities in two-component models of the solar atmosphere is
investigated. No significant influence on the spatially unresolved
wing profiles of either line was found, even for models in which the
lateral variation was extreme over distances approaching a vertical
scale height. Horizontal contrast as measured by the spatially resolved
Mg k profile was found to be markedly reduced by lateral transfer over
scales at or below the current resolution limit. Contrast as measured
in the Ca K wing was relatively unaffected and was maintained down to
lateral sizes approaching a vertical scale height. The behavior of
Ca K relative to Mg k is attributed to the larger amount of photon
destruction by incoherent scattering in the Ca K wing, which limits
the distance that photons can diffuse laterally and forces the line
to be formed near LTE. It is therefore concluded that the small-scale
photospheric temperature structure predicted by many models can be
detected in Ca K, and that efforts toward reducing seeing limitations
on the resolution of solar observations should be encouraged.
Title: Resonance-Line Polarization - Part Six - Line Wing Transfer
Calculations Including Excited State Interference
Authors: Auer, L. H.; Rees, D. E.; Stenflo, J. O.
Bibcode: 1980A&A....88..302A
Altcode:
A heuristic theory of polarized radiative transfer is developed for
the wings of solar resonance lines. Magnetic fields are neglected. The
theory includes quantum mechanical interference between j = ½ and
3/2 excited states of line transitions sharing a common j = ½ ground
state. Examples of such lines are Ca II and K, Na I D1
and D2, and Mg II h and k. Calculations are made with the
HSRA solar model for these lines as well as the dipole-type transition
Ca I 4227 which is not affected by interference. The results for Ca I
4227, Ca II H and K and Na I D1 and D2 compare
very well with recent observations, lending support to our theory. The
polarization predicted in the Mg H h and k lines is the largest of all
indicating these lines to be prime candidates for linear polarization
observations in the UV spectrum.
Title: Thermal models for solar hard X-ray bursts
Authors: Smith, D. F.; Auer, L. H.
Bibcode: 1980ApJ...238.1126S
Altcode:
Thermal models for hard X-ray bursts consisting of a one-dimensional
flux tube whose central electrons are heated to about 400 million K are
examined. It is found that the evolution of a thermal X-ray source is a
sensitive function of the electron-ion thermal coupling and the state
of the plasma into which the source expands. When this coupling is
weak, the heated electrons separate into a region of high temperature
of about 400 million K and a region of lower temperature of about 100
million K, a process which leads to a power-law X-ray spectrum. In the
case of strong coupling there is only one dominant temperature, about
200 million K, and the X-ray spectrum resembles a true thermal spectrum.
Title: Atmospheres for hot, high-gravity stars. I. Pure hydrogen
models.
Authors: Wesemael, F.; Auer, L. H.; van Horn, H. M.; Savedoff, M. P.
Bibcode: 1980ApJS...43..159W
Altcode:
An extensive grid of pure hydrogen model atmospheres for hot,
high-gravity stars is presented. The models are intended to aid the
analysis of visual, ultraviolet, and soft X-ray spectra of hot DA white
dwarfs and EUV sources. The grid extends from log g equals 4.0(1.0)9.0
and T(eff) ranges from 20,000 K up to the Eddington limit for most
surface gravities. Most of the models are LTE unblanketed calculations,
but selected NLTE models and blanketed LTE models have also been
computed in order to assess the importance of these effects. For each
model, continuum fluxes are tabulated covering the entire range of
wavelengths for which there is significant flux. Stromgren colors,
UBV colors, and bolometric corrections are also given. Profiles and
equivalent widths of the L-alpha, L-beta, L-gamma, H-alpha, H-beta,
H-gamma, and H-delta lines are given as well.
Title: The Structure of X-ray Illuminated Stellar Atmospheres
Authors: London, R.; McCray, R.; Auer, L. H.
Bibcode: 1980BAAS...12..520L
Altcode:
No abstract at ADS
Title: A non-LTE treatment of beryllium lines: misidentification of
the solar Be I feature at 2650 Å.
Authors: Shipman, H. L.; Auer, L. H.
Bibcode: 1979AJ.....84.1756S
Altcode:
The formation of beryllium lines, with particular reference to the
solar Be spectrum, is investigated in a non-LTE context with a 25-level
model atom in which 15 levels are allowed to depart from LTE. In some
transitions, particularly the Be I 2650-A line, the non-LTE effects
can be quite dramatic, changing the deduced abundances by a factor
of 4. Based on the non-LTE calculations and Copernicus observations
of other stars, it is found that a solar spectral feature at 2650
A, previously identified by numerous investigators as a Be I line,
cannot be produced by Be I. Non-LTE effects on the Be II 3131-A line,
used for most Be abundance determinations in the literature, are small
by comparison.
Title: Erratum: "digital Image Centering. 11" [ASTRON. J. 83, 531
(1978)].
Authors: Auer, L. H.; van Altena, W. F.
Bibcode: 1978AJ.....83.1468A
Altcode:
No abstract at ADS
Title: Hot, High-Gravity, Pure Hydrogen Model Stellar Atmospheres
Authors: Wesemael, F.; Auer, L. H.; van Horn, H. M.; Savedoff, M. P.
Bibcode: 1978BAAS...10..682W
Altcode:
No abstract at ADS
Title: The far-ultraviolet spectrum of Sirius B.
Authors: Savedoff, M. P.; Wesemael, F.; Auer, L. H.; Kerridge, S. J.;
van Horn, H. M.
Bibcode: 1978BAAS...10..637S
Altcode:
No abstract at ADS
Title: The Far-Ultraviolet Spectrum of Sirius B
Authors: Savedoff, M. P.; Wesemael, F.; Auer, L. H.; Kerridge, S. J.;
van Horn, H. M.
Bibcode: 1978BAAS...10..642S
Altcode:
No abstract at ADS
Title: Trigonometric parallaxes for southern hemisphere stars.
Authors: Auer, L. H.; Auer, K.; Hoffleit, E. D.; van Altena, W. F.
Bibcode: 1978AJ.....83..640A
Altcode:
New Yale parallaxes are reported for 11 stars and two companions. Of the
13 stars 12 lie in the Southern Hemisphere. Photoelectric photometry
is available for only three of the stars, and observers are urged to
obtain data for the rest.
Title: Digital image centering. II.
Authors: Auer, L. H.; van Altena, W. F.
Bibcode: 1978AJ.....83..531A
Altcode:
Digital image centering algorithms were compared in a test involving
microdensitometer raster scans of a refractor parallax series consisting
of 22 stars on 26 plates. The highest accuracy in determining stellar
image positions was provided by an algorithm which involved fitting of
a symmetric Gaussian curve and a flat background to the image marginal
density distributions. Algorithms involving transmission marginals
instead of density marginals were found to be less accurate. The
repeatability and computational efficiency of the digital image
centering technique were also studied.
Title: Two-dimensional radiative transfer. I. Planar geometry.
Authors: Mihalas, D.; Auer, L. H.; Mihalas, B. R.
Bibcode: 1978ApJ...220.1001M
Altcode:
Differential-equation methods for solving the transfer equation in
two-dimensional planar geometries are developed. One method, which uses
a Hermitian integration formula on ray segments through grid points,
proves to be extremely well suited to velocity-dependent problems. An
efficient elimination scheme is developed for which the computing time
scales linearly with the number of angles and frequencies; problems
with large velocity amplitudes can thus be treated accurately. A very
accurate and efficient method for performing a formal solution is
also presented. A discussion is given of several examples of periodic
media and free-standing slabs, both in static cases and with velocity
fields. For the free-standing slabs, two-dimensional transport effects
are significant near boundaries, but no important effects were found
in any of the periodic cases studied.
Title: The origin of the broad-band circular polarization in sunspots.
Authors: Auer, L. H.; Heasley, J. N.
Bibcode: 1978A&A....64...67A
Altcode:
An analysis is performed to demonstrate that the net circular
polarization previously discovered in broadband observations of
sunspots cannot be explained by either a net continuum polarization
or Zeeman line splitting in a static atmosphere. It is shown that
a velocity gradient is necessary and sufficient for producing a net
circular polarization and that the observations can be explained if
macroscopic motions comparable to some unspecified thermal motions are
involved. The magnetic-field strength and flow velocities required to
explain the cited sunspot observations are estimated.
Title: The determination of vector magnetic fields from Stokes
profiles.
Authors: Auer, L. H.; Heasley, J. N.; House, L. L.
Bibcode: 1977SoPh...55...47A
Altcode:
The application of Unno's (1956) solution of the transfer equation
for polarized radiation to the determination of thevector magnetic
field is investigated. An analysis procedure utilizing non-linear
least squares techniques is developed that allows one to automate the
reduction of measured spectral profiles of the Stokes parameters to
determine the field angles, strength as well as other parameters. The
method is applied to synthetic spectra generated using a model solar
atmosphere and yields results of remarkably high accuracy. The influence
of additional factors upon determination of the vector field are also
considered. These factors include effects of asymmetric profiles,
magneto-optical effects, magnetic field gradients, unresolved field
elements, scattered light, and instrumental noise.
Title: Non-LTE line formation in the presence of magnetic fields.
Authors: Auer, L. H.; Heasley, J. N.; House, L. L.
Bibcode: 1977ApJ...216..531A
Altcode:
The equations of radiative transfer and statistical equilibrium in
the presence of a magnetic field are presented. A general difference
equation scheme for solving the vector transfer equation in Stokes
parameters, allowing for arbitrary variations of the magnetic field
and other quantities, is described. The solution of the Stokes non-LTE
problem for Ca II by the complete linearization method is described,
and numerical examples of the procedure are presented.
Title: Effects of CNO abundances on the Balmer jump of late-B
horizontal-branch stars.
Authors: Auer, L. H.; Demarque, P.
Bibcode: 1977ApJ...216..791A
Altcode:
Model stellar atmospheres have been constructed to investigate the
effects of the continuous opacity of C 1, N 1, and 0 1 on the Balmer
jump of late-B horizontal-branch stars. The large opacity of C i
and N 1 in the ultraviolet raises the Balmer continuum through back
warming without changing the Paschen continuum. The models provide
a natural explanation for the variations in the Balmer jump which
have been observed from star to star by 0ke near 12,500 K on the
horizontal branch of the globular cluster M92. We conclude that some
stars on the horizontal branch of M92 have an atmospheric C and/or N
content as much as 1000 times the cluster average. Although primordial
chemical inhomogeneities within the cluster cannot be ruled out, the
most plausible interpretation for these objects seems to be one in
which surface enrichment occurs through mixing from a helium-burning
region in the interior during the course of stellar evolution. The
possible connection with Zinn's weak G-band stars on the asymptotic
branch of M92 is discussed. The effects of C 1 and N 1 opacities may
also explain Newell's gap 1 in the (U - B, B - V)diagram for field blue
stars in the halo. Subject headings: opacities - stars: atmospheres -
stars: horizontal branch
Title: A self-consistent model-atmosphere analysis of the EUV white
dwarf HZ 43.
Authors: Auer, L. H.; Shipman, H. L.
Bibcode: 1977ApJ...211L.103A
Altcode:
No abstract at ADS
Title: Possible Large Carbon and Nitrogen Abundance Variations on
the Horizontal Branch of M92
Authors: Auer, L. H.; Demarque, P.
Bibcode: 1977ASSL...67...25A
Altcode: 1977cia..proc...25A
Model stellar atmospheres have been constructed to investigate the
effects of the continuous opacity of C I, N I, and O I on the Balmer
jump of late-B horizontal-branch stars. The large opacity of C I and N
I in the ultraviolet raises the Balmer continuum through back warming
without changing the Paschen continuum, while O I has little effect. The
models provide an explanation for the variations in the Balmer jump
which have been observed from star to star by Oke (1975) near 12,500 K
on the horizontal branch of the globular cluster M92. It is concluded
that some stars in M92 appear to have an atmospheric C and/or N content
between one hundred and one thousand times the cluster average. The same
effect of the opacities of C I and N I may also explain Newell's (1973)
gap N I in the (U-B)-(B-V) diagram for blue stars in the galactic halo.
Title: An Hermitian method for the solution of radiative transfer
problems.
Authors: Auer, L.
Bibcode: 1976JQSRT..16..931A
Altcode:
A differential-equation method for solving the radiative-transfer
equation is developed which is based on a three-point Hermitian
formula and is substantially more accurate than integral-equation
methods. Third-order boundary conditions are derived, and a
generalization to the multifrequency-angle case is outlined. The
accuracy and stability of the present method are compared with those
of other differential- and integral-equation methods currently in use.
Title: The far-ultraviolet spectrum of Sirius B from Copernicus.
Authors: Savedoff, M. P.; van Horn, H. M.; Wesemael, F.; Auer, L. H.;
Snow, T. P.; York, D. G.
Bibcode: 1976ApJ...207L..45S
Altcode:
No abstract at ADS
Title: An alternative formulation of the complete linearization
method for the solution of non-LTE transfer problems.
Authors: Auer, L. H.; Heasley, J. N.
Bibcode: 1976ApJ...205..165A
Altcode:
The complete linearization scheme for solving non-LTE transfer
problems is reformulated so that the procedure requires the same
amount of computation per iteration as the 'equivalent-two-level-atom'
approach. The reformulation involves making the timing linearly
proportional to the number of frequencies; the resulting system
of equations may be solved by a simple block iterative method. It
is noted that this reformulation has the same asymptotic timing
as integral-equation methods but retains the flexibility and
self-consistency of the original complete linearization scheme. The
proposed technique is used to solve a multitransition line-formation
problem for a five-level representation of the Ca II ion in the solar
chromosphere and to solve the resonance-doublet problem for Na I in
the chromosphere.
Title: An Analysis of the Extreme Ultraviolet Source HZ 43 Using
Helium-Poor Model Atmospheres
Authors: Auer, L. H.; Shipman, H. L.
Bibcode: 1976BAAS....8..315A
Altcode:
No abstract at ADS
Title: The geometry of YY Canis Majoris derived from SiO maser lines.
Authors: van Blerkom, D.; Auer, L.
Bibcode: 1976ApJ...204..775V
Altcode:
We find by means of a radiation transfer calculation that the SiO
maser lines observed in the spectrum of VY CMa are formed in a rotating
equatorial disk seen nearly edge-on. Other geometries are considered
and eliminated. It is suggested that the SiO lines of NML Cyg also show
evidence that they are formed in a disk. Subject headings: infrared:
sources - masers - stars: circumstellar shells - stars: individual
Title: Digital Image Centering, I.
Authors: van Altena, W. F.; Auer, L. H.
Bibcode: 1975ASSL...54..411V
Altcode: 1975ipta.proc..411V
A series of parallax plates have been measured on a PDS
microdensitometer to assess the possibility of using the PDS for
precision relative astrometry and to investigate centering algorithms
that might be used to analyze digital images obtained with the Large
Space Telescope. The basic repeatability of the PDS is found to be plus
or minus 0.6 micron, with the potential for reaching plus or minus 0.2
micron. A very efficient centering algorithm has been developed which
fits the marginal density distributions of the image with a Gaussian
profile and a sloping background. The accuracy is comparable with the
best results obtained with a photoelectric image bisector.
Title: The Far Ultraviolet Spectrum of Sirius B from Copernicus
Authors: Savedoff, M. P.; van Horn, H. M.; Wesemael, F.; Auer, L. H.;
Snow, T. P.; York, D. G.
Bibcode: 1975BAAS....7R.552S
Altcode:
No abstract at ADS
Title: Digital Image Centering.
Authors: Auer, L. H.; van Altena, W. F.
Bibcode: 1975BAAS....7..443A
Altcode:
No abstract at ADS
Title: Non-LTE Line Formation in the Presence of a Magnetic Field
Authors: Auer, L. H.; Heasley, J. N.; House, L. L.
Bibcode: 1975BAAS....7..349A
Altcode:
No abstract at ADS
Title: Stellar Atmospheres - the Middle Man
Authors: Auer, L.; Newell, E. B.
Bibcode: 1975mpth.conf....1A
Altcode: 1975mpth.proc....1A
No abstract at ADS
Title: A non-LTE model stellar atmosphere computer program
Authors: Mihalas, D.; Heasley, J. N.; Auer, L. H.
Bibcode: 1975STIN...7630128M
Altcode:
A computer program was developed for calculating model atmospheres of
early-type stars subject to the constraints of radiative, hydrostatic,
and statistical equilibrium, by means of a complete-linearization
technique. This program is available through the NCAR High Altitude
Observatory's Radiative Transfer Library.
Title: Neutral Helium Line Strengths. V11. the Population 11 B Star
Barnard 29 IN M13
Authors: Auer, L. H.; Norris, John
Bibcode: 1974ApJ...194...87A
Altcode:
Using non-LTE model atmospheres and helium-line calculations the
atmospheric parameters have been determined for the Population II
star Barnard 29. We find T = 22,500 + 1200 K, log g = 3.0 I 0.15
(cgs) (on an unblanketed temperature scale) and N(He)IN(H) = 0.115
I 0.03. The Population I star, y Pegasi, was analyzed with identical
techniques. The two stars have the same He abundance within the accuracy
of the determinations. An LTE analysis of the heavy elements shows
that N and Si are enhanced relative to the metal abundance of the
cluster giants. We consider possible causes of this result. Subject
headings: abundances, stellar - early-type stars - globular clusters -
population II stars
Title: Analyses of light-ion spectra in stellar atmospheres. V. Neon
I in B stars.
Authors: Auer, L. H.; Mihalas, D.
Bibcode: 1973ApJ...184..151A
Altcode:
A detailed calculation, allowing fully for departures from LTE, for
stars in the range B2 to B5 shows that the neon abundance deduced from
LTE analyses is systematically in error by about a factor of five. The
results obtained from the simultaneous self-consistent solution of the
transfer and statistical equilibrium equations, for a realistic model
neon atom, are in excellent agreement with observed Ne I equivalent
widths at an abundance of log N(Ne) = 8.0, on the usual scale with log
N(H) = 12.0. Thus the long-standing discrepancy between the stellar neon
abundance and that found from solar, nebular, and cosmic-ray estimates
is removed. Implications for nucleosynthesis and interior opacities are
noted. Subject headings: abundances, stellar - atmospheres, stellar -
early-type stars
Title: Analyses of Light Ion Spectra in Stellar Atmospheres.IV. H
II in the B Stars
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1973ApJS...25..433A
Altcode:
Results of an extensive set of computations of the He I spectrum in B
stars, allowing for departures from LTE, using rather complete model
atoms, non-LTE model atmospheres, and somewhat improved broadening
theory, are presented and discussed. Among the major conclusions we
derive are the following: (1) While departures from LTE alter equivalent
widths but little in the blue- violet spectral region, their effects
are quite large for lines in the visual-red region (e.g., A6678). (2)
Very good agreement is obtained in the comparison of our calculated
profiles with observed He iline profiles both in the wings and in the
cores (except for some triplets at spectral types B0 and B1). (3) Some
of the largest effects of departures from LTE occur at the highest and
lowest effective temperatures, where the lines are relatively weak. (4)
The usually quoted blue-violet singlet/triplet ratio is unaffected
by departures from LTE to within the errors of observation. Other
line ratios (e.g., A6678/A5876), however, are strongly affected. (5)
The systematic wavelength-effect noted by Norris is explained. Good
agreement is obtained with most of the conclusions of Johnson and Poland
and Poland, though some significant differences arising from non-LTE
effects in the model atmospheres are noted. The present results allow
analysis for a much wider range of stellar spectral types and luminosity
classes with a much higher level of physical consistency than hitherto
possible. Subject headings: atmospheres, stellar - early-type stars -
line formation
Title: Application of the Complete-Linearization Method to the
Problem of Non-Lte Line Formation
Authors: Auer, Lawrence
Bibcode: 1973ApJ...180..469A
Altcode:
it is shown that the equations of statistical equilibrium may be
incorporated directly into the transfer equation, thus reducing the
basic matrix size for the complete-linearization method. Treatment
of weak transitions and development of starting solutions are also
discussed. Subject headings: atmospheres, stellar - radiative transfer
Title: H Fluorescence in the Filaments of M82
Authors: van Blerkom, David; Castor, John I.; Auer, Lawrence H.
Bibcode: 1973ApJ...179...85V
Altcode:
Polarization of Ha radiation from the filaments of M82 has previously
been attributed to scattering off dust of light emitted by a central
source. It is difficult, however, to find a physically plausible
velocity distribution of the scattering material to account for
the observed line displacements in the filaments. The simplest
interpretation, that of matter ejected by a single explosive event,
requires the Ha emission to be intrinsic to the filaments. We
propose that Ha is produced in the filaments by fluorescence. This
eliminates the velocity distribution problem posed by scattering
and gives 29 percent as the degree of polarization, which is very
nearly the observed value. The physical requirements of this process
appear plausible for M82. A possible test of the hypothesis lies in
the predicted Balmer decrement i(Ha)/i(Hfl) > 20. This is much
higher than would be expected if radiative recombination, collisional
excitation, or extinction by dust in a Seyfert-like nucleus controlled
the Balmer-line intensities. Subject headings: galaxies, individual -
nebulae - polarization - radiative transfer
Title: Electron Scattering in Spherically Expanding Envelopes
Authors: Auer, Lawrence H.; van Blerkom, David
Bibcode: 1972ApJ...178..175A
Altcode:
Broad emission4ine profiles from diverse astronomical objects have been
interpreted as due to rapid radial outflows of matter. Estimates of
characteristic electron densities lead to the conclusion that the effect
of electron scattering on the line profiles may be substantial. A Monte
Carlo method is employed to treat the transfer of radiation through
an expanding envelope of comoving electrons and ions. Two models
are considered: one with a constant velocity of outflow, and one in
which the velocity increases linearly with radius. A spectral line
is formed by recombination, and the only opacity is that due to free
electrons. For electron-scattering optical depths of order unity, very
extensive wings to the red of line center are formed in all cases. These
results are applied to models of Woif-Rayet stars and Seyfert galaxies.
Title: Non-Lte Model Atmospheres. VII. The Hydrogen and Helium
Spectra of the O Stars
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1972ApJS...24..193A
Altcode:
An extensive series of non-LTE calculations of the H, He I, and
He II spectra of 0 stars has been carried out by using relatively
complete atomic models, allowing for several levels and lines
simultaneously. Results are presented for continuum fluxes and for
equivalent widths and profiles of the lines. Detailed comparisons
are made with the spectra of eleven 0 and B0 stars. It is found that
major departures from LTE play a dominant role in the formation of
the H and He spectra of these stars. With the non-LTE models we are
able to obtain for the first time a consistent explanation of the
observations of both lines and continua. The present results show that
an assumed helium/hydrogen ratio of 0.10 reproduces the observations;
thus present estimates of abundances in 0 stars helium are consistent
with those derived by other methods.
Title: A computational program for the solution of non-LTE transfer
problems by the complete linearization method
Authors: Auer, L. H.; Heasley, J. N.; Milkey, R. W.
Bibcode: 1972CoKit.555.....A
Altcode: 1972QB4.K55n555....
No abstract at ADS
Title: The stellar atmospheres problem.
Authors: Auer, L. H.
Bibcode: 1971JQSRT..11..573A
Altcode:
No abstract at ADS
Title: Non-Lte Model Atmospheres.VI. Limb Darkening and Rotation
Broadening of H&alpha
Authors: Mihalas, Dimitri; Auer, L. H.
Bibcode: 1970ApJ...161.1129M
Altcode:
The center-to-limb variation and rotation broadening of Ha are discussed
for LTE and non-LTE atmospheres. The center-to-limb variation is quite
different in these two cases; these differences should be measurable by
observations of certain eclipsing-binary systems, and such observations
could provide a sensitive test of the theory. It is also shown that
(a) significant differences exist between rotationbroadened profiles
in the LTE and non-LTE cases and (b) Ha may serve as a useful indicator
of rotation velocity.
Title: Non-Lte Model Atmospheres. V. Multi-Line Hydrogen-Helium
Models for O and Early B Stars
Authors: Mihalas, Dimitri; Auer, L. H.
Bibcode: 1970ApJ...160.1161M
Altcode:
Results of calculations of non-LTE model atmospheres including the
effects of La, L , L , Ha, Hp, and Pa are presented for models on
the range 250000 K < < 50000 K, with log g = 4 and N(He)/ N(H)
= 0.10. The non-LTE results suggest a severe breakdown of LTE at T0ff
> 350000 K. Substantial changes occur in the far-ultraviolet fluxes;
these may be of importance in the interpretation of the excitation
of emission nebulae. In the visible, the Balmer jump is significantly
increased by non-LTE effects for models with T0ff > 350000 K, which
implies large changes in effective temperatures for 0 stars inferred
from observations of the Balmer jump. Striking changes occur in the
hydrogen-line profiles. Vhen non-LTE effects are included, Ha and Hp
are computed to be almost 3 times as strong at 400000 K as in LTE. Pa is
found to have an emission core in the highest-temperature models. This
result is analogous to the situation at lower temperatures where Ba is
computed to go into emission. In both cases the emission core is due
to coupling to a rise in surface temperature in the non-LTE models;
observations are desirable to test the reality of this predicted effect.
Title: Non-Lte Model Atmospheres.IV. Results for Multi-Line
Computations
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1970ApJ...160..233A
Altcode:
Results are presented for model atmospheres in hydrostatic, radiative,
and steady-state statistical equilibrium, including bound-bound
transitions. These calculations allow for the effects of Ha, HP, H ,
Pa, PP, and Ba. Stark profiles of Edmonds, Schinter, and Wells are used
to compute detailed line profiles. With the full non-LTE calculation we
have been able to predict correctly the entire line profile, including
the line core. The wings of Ha are found to weaken while those of H
remain unaffected by departures from LTE. Non-LTE effects strengthen
the Paschen lines so that comparison of Paschen lines with Balmer lines
should provide a sensitive observational indicator of departures from
LTE. Ba has an emission core, because of a rise in surface temperature,
and may be a useful diagnostic tool in the analysis of real stellar
atmospheres. The surface-temperature rise found in earlier work
persists, the boundary temperature differing little from that obtained
by allowing for Ha, HP, and Pa only. The energy distribution in the
continuum is little affected by departures from LTE, except at very
low gravities and in the unobservable Lyman continuum.
Title: On the use of variable Eddington factors in non-LTE stellar
atmospheres computations
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1970MNRAS.149...65A
Altcode:
It is shown that by use of variable Eddington factors, the accuracy
of differenceequation solutions of transfer problems may be greatly
improved with only small additional computational effort. It is found
that a direct iterative calculation of the Eddington factors leads to
a strongly convergent procedure. The resulting set of equations is
of wide applicability to problems involving non-coherent radiative
transfer. The method is illustrated by application to the classical
grey problem, and to a non-LTE stellar atmospheres computation.
Title: Non-Lte Model Atmospheres. III. a Complete-Linearization Method
Authors: Auer, Lawrence H.; Mihalas, Dimitri
Bibcode: 1969ApJ...158..641A
Altcode:
In this paper we present a method of solving transfer prob'ems subject
to constraints of radiative, hydrostatic, and statistical equilibrium,
by using a complete-linearization technique. This approach de-
parts rather markedly from the traditional methods, and yields a
computational scheme that is stable and strongly convergent. The form
of the equations assures that the coupling among all physical variables
is fully accounted for self-consistently to first order at each stage
of the calculation; convergence is global and quadratic. The constraint
equations are included in a particularly transparent way, which allows
easy generalization and elaboration. Sample models of pure-hydrogen
atmospheres are presented; among these, one includes Ha, H~3, and Pa
self-consistently with the continua. Models that were obtained only
with great effort by using earlier techniques have been recomputed
with no hint of difficulty by using the method described in this paper
Title: Brackett-Alpha Emission in Non-Lte Model Stellar Atmospheres
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1969ApJ...156L.151A
Altcode:
Recent computations of non-LTE model stellar atmospheres predict the
appearance of Brackett- a (Ba) in emission. This line at 4.05 ~&
lies in a window of the absorption spectrum of the terrestrial
atmosphere and should be observed as a test of this theoretical
prediction
Title: Non-Lte Model Atmospheres. II. Effects of Balmer α
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1969ApJ...156..681A
Altcode:
Four models of pure-hydrogen stellar atmospheres in radiative
equilibrium with Teff = 15000 and log g = 4 are presented. Results are
given for both the LTE and non-LTE cases, with and without the inclusion
of Ha. The calculations show that (a) Ha causes a temperature rise,
not a drop, at the surface, (b) the direct effect of cooling in the
line is less important than the indirect effects of changing level
popu- lations, and (c) the Balmer and Paschen jumps are unaltered by
non-LTE effect
Title: Non-Lte Model Atmospheres. I. Radiative Equilibrium Models
with - Alpha
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1969ApJ...156..157A
Altcode:
We present models of stellar atmospheres of pure hydrogen in
hydrostatic, radiative, and statistical equilibrium, including
for the first time Lyman-a as well as continua. Only by the direct
inclusion of Ly-a may we properly evaluate the effect of this strong
line on the structure of the atmosphere. A new temperature-correction
scheme was used. It is of the constraint type, is capable of handling
very large opacity variations, and guarantees vanishingly small flux
derivatives. The model atom assumed the upper fourteen levels in LTE,
but permitted non-LTE deviations in the lower two levels. This model
was suffi- cient to show that: (a) non-LTE effects from the continua
cause a temperature rise at the surface; (b) this rise is partially
offset by the inclusion of Ly-a, which causes a temperature drop,
the non-LTE drop being very much smaller than the LTE; (c) Ly-a is
so optically thick that it does not affect the formation of even the
Lyman continuum; and (d) there is essentially no back-warming due to
Ly-a in either the LTE case or the non-LTE case
Title: Formation of the Solar Lyman Continuum (Discussion includes
R. N. Thomas on non-LTE solar models)
Authors: Auer, L. H.; van Blerkom, D.
Bibcode: 1969tons.conf..201A
Altcode:
No abstract at ADS
Title: Non-LTE Model Atmospheres
Authors: Auer, L. H.; Mihalas, D.
Bibcode: 1969tons.conf..229A
Altcode:
No abstract at ADS
Title: Line Formation with Non-Coherent Scattering by
Electrons. II. Calculations with Model Atmospheres
Authors: Auer, Lawrence H.; Mihalas, Dimitri
Bibcode: 1968ApJ...153..923A
Altcode:
The effect of non-coherent scattering by electrons and atoms on
line formation in early-type stars has been studied using model
atmospheres. Variability of the physical parameters has been fully in-
cluded. The effect of the non-coherency of the scattering by electrons
is noticeable for a line like He ii X4200 but not for a much stronger
one like He ii X4686. The solution in the core is dominated by the
degree to which scattering (by atoms) occurs, while the wings are
unaffected. The observed profile of He ii X4686 in 10 Lac can be
fitted if the core of the line is deepened by scattering and broadened
by rotation
Title: Transfer of Lyman Alpha in Diffuse Nebulae
Authors: Auer, Lawrence H.
Bibcode: 1968ApJ...153..783A
Altcode:
The Monte Carlo method is applied to the solution of the transfer
equation for Ly-a radiation in nebulae with optical thicknesses
up to 1O~. Plane-parallel geometry, two-level atoms, and constant
tem- perature are assumed. The correlation between the direction of
scattering and the frequency redistribu- tion is taken into account
exactly. A method is developed for accelerating the solution by treating
the line core analytically and using the Monte Carlo method only in
the wings. It is found that for Doppler broadening the assumption of
complete redistribution is a reasonably satisfactory approximation. The
mean number of scatterings before escape is on the order of ro. For
lines with finite natural width, the presence of Lorentz wings, where
scattering tends to be coherent, reduces the mean number of scatterings
from the case with zero natural width. This effect is seen only after
the optical depth at line center has become great enough that the
nebula is opaque at all frequencies in the core. The emergent flux
has a double-humped frequency distribution. When the ratio of the
natural width to the Doppler width is increased, the width of the
emergent line is also increased. For density-bounded H xi regions with
optical thickness at the line center of 1O~, illuminated by an incident
Lyman-continuum flux, the energy density in Ly-a does not rise to more
than twenty-five times the energy density of the incident continuum
radia- tion. Radiation pressure from Ly-a does not become large enough
to have dynamical effects. Two- photon emission is negligible, but if
the grain density within the H ii region is as high as it is in inter-
stellar space, almost all Ly-c& photons will be absorbed before
they can escape
Title: Line Formation with Non-Coherent Scattering by
Electrons. I. Parameterized Models
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1968ApJ...153..245A
Altcode:
We examine in this paper the effects of the non-coherence of the
radiation scattered by electrons upon the formation of spectral lines
A flexible numerical approach, making use of the difference-equation
meth- od of solving the transfer equation, is developed and applied to
simplified models in which the lines are taken to be either in LTE or
non-LTE, and allowance is made for electron scattering and continuous
absorption. Radiation scattered by the atom is assumed to be completely
redistributed, although the method is general enough to account for
arbitrary redistribution functions. The present calculation dif- fers
from earlier work in that the electrons are assumed to be located in
the same layers as the line and continuum opacity sources Compared to
the case of coherent electron scattering, measurable changes in the
line profile occur if the electron-scattering coefficient outweighs
continuum absorption. Emission lines are decreased slightly in intensity
and develop extensive emission wings. Absorption lines are widened
and deepened, and emission humps are obliterated
Title: Solution of Transfer Equations Subject to the Constraint of
Radiative Equilibrium
Authors: Auer, L. H.; Mihalas, Dimitri
Bibcode: 1968ApJ...151..311A
Altcode:
A method is proposed for solving transfer equations subject to
the constraint of radiative equilibrium. The approach uses the
differential-equation form of the transfer equation and thus allows
easy generaliza- tion. A description is given of the equations and
boundary conditions, and results for gray and non-gray cases are
discussed. We obtain rapid convergence at all depths It appears
that this method should be effective in non-LTE cases, though in
practice it may be limited by the size of matrix that can be inverted
economically. I. INTRODUCTIO
Title: Improved Boundary Conditions for the Feautrier Method
Authors: Auer, Lawrence
Bibcode: 1967ApJ...150L..53A
Altcode:
No abstract at ADS
Title: Fine Analysis of the Manganese Star 53 Tauri
Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E.
Bibcode: 1967mrs..conf..433A
Altcode:
No abstract at ADS
Title: Transfer of Lyman-Alpha in Diffuse Nebulae.
Authors: Auer, Lawrence Herman
Bibcode: 1967PhDT.........2A
Altcode:
No abstract at ADS
Title: The Manganese Star 53 Tauri. II. Fine Analysis
Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E.
Bibcode: 1966ApJ...145..153A
Altcode:
An abundance analysis of the manganese star 53 Tauri is carried
out making use of a model atmosphere with 0 = 0.413, log g = 3.5,
N(He)/N(H) = 0.15. The model reproduces the observed hydrogenline
profiles with good accuracy. The abundance analysis shows that all
of the metals ligbter than titanium have normal abundance. Helium
is found to be underabundant by a factor of 5, so that N(He)/ N(H) =
0.03, and the effective gravity accordingly becomes log g = 3.62. From
titanium onward, the elements show large overabundance factors, except
for iron and chromium, both of which are normal. Manganese is found
to be 120 times overabundant; this value is based on both Mn I and
Mn ii lines (the two ions giving good agreement), making use of new
laboratoryJ-values for Mn ii.
Title: Mass Loss and the Formation of White-Dwarf Stars.
Authors: Auer, L. H.; Woolf, N. J.
Bibcode: 1965ApJ...142..182A
Altcode:
The presence of white dwarfs in the Hyades and a suspected one in
the Pleiades indicate that stars with masses greater than 2 5 Mo,
and possibly 7 Mo, can become white dwarfs Calculations show that
the excess mass cannot be lost merely through rotational shedding if
the star always rotates like a solid body. Consideration of wide pairs
containing a white dwarf indicates that mass is probably lost on a time
scale greater than 10 years. Nuclear fuel must be the major source of
energy for mass ejection, although in the case of too massive stars it
will be insufficient to eject enough mass to permit a stable white-dwarf
configuration. it is noted that the minimum masses for helium and carbon
burning are comparable with the observed mean mass of white dwarfs,
indicating that mass loss continues until nuclear burning ceases.
Title: A Coarse Analysis of the Atmosphere of 10 Aquilae.
Authors: Auer, Lawrence H.
Bibcode: 1964ApJ...139.1148A
Altcode:
Equivalent widths have been measured on Palomar Observatory coud plates
and stellar 170 vak determined for approximately 600 lines in the region
XX 330( 6600. Using the curve of growth meth' spectroscopic values of
the atmospheric parameters were found: 0= = 0.71, log Kp = -0.23, 1 P6 =
1.71, log P0 = 3.80, and log g.00 = 4.18. Overabundances relative to
the sun were found for F Sr, Mg, Mn, and Co, while underabundances
were found for Al, Sc, Zn and Ba. Despite the compositi' anomalies
the atmospheric parameters are in good agreement with the values of
a main-sequence st of this temperature.