explanation      blue bibcodes open ADS page with paths to full text
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.
2019arXiv190305971P    Altcode:
  A tutorial associated with the distribution of 2D non-LTE multilevel
  atom radiative transfer codes.

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Title: Acceleration of Convergence
Authors: Auer, L. H.
2009nrt..book..101A    Altcode:
  No abstract at ADS

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Title: FUSE Observations of HD 5980: The Wind Structure of the Eruptor
Authors: Koenigsberger, Gloria; Fullerton, Alexander W.; Massa, Derck;
   Auer, Lawrence H.
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. <P />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.

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Title: Erratum: “W49A North: Global or Local or No Collapse?” (<A
    href="bib_query?2004ApJS...153..463W">ApJS, 153, 463 [2004]</A>)
Authors: Williams, John A.; Dickel, Hélène R.; Auer, Lawrence H.
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<SUP>-1</SUP> cm<SUP>-2</SUP> Hz<SUP>-1</SUP> sr<SUP>-1</SUP>.

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Title: W49A North: Global or Local or No Collapse?
Authors: Williams, John A.; Dickel, Hélène R.; Auer, Lawrence H.
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<SUP>-1</SUP> for a turbulent velocity of
  about 6 km s<SUP>-1</SUP>. High-resolution observations of the J=1-0
  and 5-4 transitions of CS and C<SUP>34</SUP>S may distinguish between
  these three models. Modeling existing observations of HCO<SUP>+</SUP>
  and C<SUP>18</SUP>O does not allow one to distinguish between the
  three models but does indicate the existence of a bipolar outflow.

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Title: W49A North - Global, Local, or no Collapse?
Authors: Dickel, Helene R.; Williams, John A.; Auer, Lawrence H.
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. <P />Research partially supported by
  the National Science Foundation USA; grants AST90-24503 93-20239 and
  96-13999 to the University of Illinois

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Title: Insight into Multi-Dimensional Transfer
Authors: Auer, L.
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.

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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.
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.

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Title: Formal Solution: EXPLICIT Answers
Authors: Auer, L.
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.

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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.
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.*E<SUP>35</SUP> ergs s<SUP>-1</SUP>
  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<SUP>-1</SUP>, at a distance of ~ 8 {R<SUB>sun</SUB> }\&gt;
  from the O-star's surface, and at Θ =60-70<SUP>o</SUP> 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<SUP>-2</SUP>,
  which together with the He II 4686 Å luminosity, indicates that
  the thickness of the shock lies in the range 2-10 x 10<SUP>10</SUP>
  cm and the total density is 1-6 x 10<SUP>12</SUP> cm<SUP>-3</SUP>.

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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
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 ~1×10<SUP>35</SUP>
  ergs s<SUP>-1</SUP> 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<SUP>-1</SUP>, at a distance of ~8 R<SUB>solar</SUB>
  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<SUP>-2</SUP>, which,
  together with the He II 4686 Å luminosity, indicates that the thickness
  of the shock lies in the range 2-10×10<SUP>10</SUP> cm and the total
  density is 1-6×10<SUP>12</SUP> cm<SUP>-3</SUP>.

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Title: W 49 A North: J=2-1 Lines of CS and C<SUP>18</SUP> 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.
2000ESASP.445..359D    Altcode: 2000sfsl.conf..359D
  No abstract at ADS

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Title: Astronomical Refraction: Computational Method for All Zenith
    Angles
Authors: Auer, Lawrence H.; Standish, E. Myles
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.

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Title: Diffusion, P<SUB>1</SUB>, and other approximate forms of
    radiation transport.
Authors: Olson, G. L.; Auer, L. H.; Hall, M. L.
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 P<SUB>1</SUB>
  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 P<SUB>1</SUB> 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.

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Title: W49 A north: J = 2-1 lines of CS and C<SUP>18</SUP>O.
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.
1999BAAS...31.1242D    Altcode:
  No abstract at ADS

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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.
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.

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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.
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<SUP>-1</SUP> is associated with the nonerupting star,
  while the variable wind with velocities ranging from -500 to -3000 km
  s<SUP>-1</SUP> 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 &gt; 40 M<SUB>⊙</SUB>) and very
  luminous (L &gt; 10<SUP>6</SUP> L<SUB>⊙</SUB>), and that during the
  eruption its radius extended beyond the binary orbit (R<SUB>*</SUB>
  &gt; 100 R<SUB>⊙</SUB>).

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Title: Multidimensional radiative transfer with multilevel
    atoms. II. The non-linear multigrid method.
Authors: Fabiani Bendicho, P.; Trujillo Bueno, J.; Auer, L.
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 (&lt;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 &amp; 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.

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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
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 B1.5I<SUB>a</SUB>(+)
  spectra. Subsequent spectra indicate a photosphere which is gradually
  increasing its T<SUB>eff</SUB>, 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.

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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
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.

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Title: A new approximate operator method for partial frequency
    redistribution problems.
Authors: Paletou, F.; Auer, L. H.
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.

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Title: Modeling Radiative Transfer in Molecular Clouds. I. HCO +
    in the Star-forming Region W49A North
Authors: Dickel, Helene R.; Auer, Lawrence H.
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<SUP>-3/2</SUP> 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.

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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.
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.

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Title: Line Profile Variations from Atmospheric Eclipses: Constraints
    on the Wind Structure in Wolf-Rayet Stars
Authors: Auer, L. H.; Koenigsberger, G.
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.

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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.
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.
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.
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.
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.
1993A&A...274..571P    Altcode:
  Theoretical emergent profiles in the resonance lines of H I Lyman α,
  Mg II h &amp; k and Ca II H &amp; 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.
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.
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.
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
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.
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.
1991IAUS..143..175K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Wind Structure of HD 5980
Authors: Auer, Lawrence
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.
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.
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.
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.
1989RMxAA..18..185K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Wind Structure of the SMC Wolf-Rayet Star HD 5980
Authors: Auer, Lawrence
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
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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 D<SUB>1</SUB>
  and D<SUB>2</SUB>, 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 D<SUB>1</SUB> and D<SUB>2</SUB> 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1975BAAS....7R.552S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Digital Image Centering.
Authors: Auer, L. H.; van Altena, W. F.
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.
1975BAAS....7..349A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Stellar Atmospheres - the Middle Man
Authors: Auer, L.; Newell, E. B.
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.
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
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.
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
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
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.
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) &gt; 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
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
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.
1972CoKit.555.....A    Altcode: 1972QB4.K55n555....
  No abstract at ADS

---------------------------------------------------------
Title: The stellar atmospheres problem.
Authors: Auer, L. H.
1971JQSRT..11..573A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Non-Lte Model Atmospheres.VI. Limb Darkening and Rotation
    Broadening of H&amp;alpha
Authors: Mihalas, Dimitri; Auer, L. H.
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.
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 &lt; &lt; 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
  &gt; 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 &gt; 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
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
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
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
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 ~&amp;
  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
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
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

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Title: Formation of the Solar Lyman Continuum (Discussion includes
    R. N. Thomas on non-LTE solar models)
Authors: Auer, L. H.; van Blerkom, D.
1969tons.conf..201A    Altcode:
  No abstract at ADS

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Title: Non-LTE Model Atmospheres
Authors: Auer, L. H.; Mihalas, D.
1969tons.conf..229A    Altcode:
  No abstract at ADS

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Title: Line Formation with Non-Coherent Scattering by
    Electrons. II. Calculations with Model Atmospheres
Authors: Auer, Lawrence H.; Mihalas, Dimitri
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

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Title: Transfer of Lyman Alpha in Diffuse Nebulae
Authors: Auer, Lawrence H.
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&amp; photons will be absorbed before
  they can escape

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Title: Line Formation with Non-Coherent Scattering by
    Electrons. I. Parameterized Models
Authors: Auer, L. H.; Mihalas, Dimitri
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

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Title: Solution of Transfer Equations Subject to the Constraint of
    Radiative Equilibrium
Authors: Auer, L. H.; Mihalas, Dimitri
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

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Title: Improved Boundary Conditions for the Feautrier Method
Authors: Auer, Lawrence
1967ApJ...150L..53A    Altcode:
  No abstract at ADS

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Title: Fine Analysis of the Manganese Star 53 Tauri
Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E.
1967mrs..conf..433A    Altcode:
  No abstract at ADS

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Title: Transfer of Lyman-Alpha in Diffuse Nebulae.
Authors: Auer, Lawrence Herman
1967PhDT.........2A    Altcode:
  No abstract at ADS

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Title: The Manganese Star 53 Tauri. II. Fine Analysis
Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E.
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.

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Title: Mass Loss and the Formation of White-Dwarf Stars.
Authors: Auer, L. H.; Woolf, N. J.
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.

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Title: A Coarse Analysis of the Atmosphere of 10 Aquilae.
Authors: Auer, Lawrence H.
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.