Author name code: mihalas ADS astronomy entries on 2022-09-14 author:"Mihalas, Dimitri" ------------------------------------------------------------------------ Title: Theory of Stellar Atmospheres Authors: Hubeny, Ivan; Mihalas, Dimitri Bibcode: 2014tsa..book.....H Altcode: No abstract at ADS Title: VizieR Online Data Catalog: Ca II H and K Measurements Made at MWO (Duncan+ 1991) Authors: Duncan, D. K.; Vaughan, A. H.; Wilson, O. C.; Preston, G. W.; Frazer, J.; Lanning, H. H.; Misch, A.; Mueller, J.; Soyumer, D.; Woodard, L.; Baliunas, S. L.; Noyes, R. W.; Hartmann, L. W.; Porter, A.; Zwaan, K.; Middelkoop, F.; Rutter, R.; Mihalas, D. Bibcode: 2005yCat.3159....0D Altcode: Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index "S" are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported.

These observations were obtained with two instruments, HKP-1 and HKP-2. The HKP-2 instrument is a four-channel chopping spectrometer which records counts in 1.09{AA} FWHM triangular bandpasses centered in the H and K lines as well as in two 20{AA} reference bandpasses centered on 3901.067 and 4001.067{AA}. The stellar activity is expressed by the index S defined as

S = {alpha} (Nh+Nk)/(Nr+Nv)

where Nh and Nk are the counts (corrected from background) in the H and K lines, Nr and Nv those in the reference continuum bandpasses, and {alpha} is a constant of proportionality used to correct for night-to-night instrumental variations. Higher values of S generally correspond to higher levels of chromospehric activities.

Factors which effect the ability to detect stellar activity variations and accurately measure their amplitudes such as the accuracy of the H and K measurements and scattered light contamination are discussed. Relations are given which facilitate intercomparison of "S" values with residual intensities from ordinary spectrophotometry, and for converting measurements to absolute fluxes.

(1 data file). Title: Quantitative Spectroscopy of Supernovae for Dark Energy Studies Authors: Baron, E.; Branch, David; Jeffery, David; Nugent, Peter; Thomas, Rollin; Bongard, Sebastien; Hauschildt, Peter H.; Kasen, Daniel; Mihalas, Dimitri Bibcode: 2005astro.ph.10166B Altcode: Detailed quantitative spectroscopy of Type Ia supernovae (SNe~Ia) provides crucial information needed to minimize systematic effects in both ongoing SNe Ia observational programs such as the Nearby Supernova Factory, ESSENCE, and the SuperNova Legacy Survey (SNLS) and in proposed JDEM missions such as SNAP, JEDI, and DESTINY. Quantitative spectroscopy is mandatory to quantify and understand the observational strategy of comparing ``like versus like''. It allows us to explore evolutionary effects, from variations in progenitor metallicity to variations in progenitor age, to variations in dust with cosmological epoch. It also allows us to interpret and quantify the effects of asphericity, as well as different amounts of mixing in the thermonuclear explosion. Title: Cepheid Atmospheres Authors: Mihalas, D. Bibcode: 2003ASPC..288..471M Altcode: 2003sam..conf..471M No abstract at ADS Title: Stellar Atmosphere Modeling Authors: Hubeny, Ivan; Mihalas, Dimitri; Werner, Klaus Bibcode: 2003ASPC..288.....H Altcode: 2003sam..conf.....H No abstract at ADS Title: Laboratory and Astrophysical Radiation Hydrodynamics: An Introduction Authors: Mihalas, D. Bibcode: 2003ASPC..288..459M Altcode: 2003sam..conf..459M The radiation received from stars provides the diagnostic tool to infer temperatures, densities, hydrodynamic motions, and chemical compositions in their atmospheres. For most stars it appears to be an adequate first approximation to assume that there are no large-scale hydrodynamic motions. However, in the most luminous stars the intense radiation field deposits sufficient photon momentum in the outermost layers to drive them off in a supersonic hydrodynamic flow. Likewise, in exploding stars such as novae and supernovae, the dominant form of energy and momentum content and transfer may reside not in the material flow, but in the radiation field. Further, pulsating stars are driven by an internal ``radiation engine'' in which the variation of the opacity of the material with temperature and density acts as a thermodynamic valve. In all these objects, and adequate analysis of the physics of the atmosphere requires application of the discipline of Radiation Hydrodynamics, where one considers the dynamics of a two-component (at least!) radiating fluid. This talk will illustrate some aspects of the radiation-material interaction that produce large-scale motions in stellar atmospheres and envelopes, and make some connections between stellar and laboratory radiation-driven phenomena. Title: Summary/Prognosis of the Workshop Authors: Mihalas, D. Bibcode: 2003ASPC..288..677M Altcode: 2003sam..conf..677M No abstract at ADS Title: Fifty Years of Research on Stellar Atmospheres Authors: Mihalas, Dimitri Bibcode: 2001PASA...18..311M Altcode: I would like to begin by saying what a pleasure it is for me to be here. For my entire adult life I have wanted to come to Australia. Actually, I have been invited to visit here twice before, but each time I was thwarted by circumstances beyond my control. But this time I was determined to (a) prove that the third time is indeed the charm, and (b) pay homage to Walter Stibbs, who in my mind is the epitome of a scholar and a gentleman. I have known Walter as colleague, teacher, and friend, not to mention as an inspiration, both professional and personal. So I am here today to try to give some sense of progress in the study of stellar atmospheres, a field that Walter has graced with his virtuosic touch. I will follow an unabashedly personal path, describing the development as I experienced it. I will focus almost entirely on early-type stars, where we may reasonably expect the atmospheric layers to be homogeneous, and in radiative equilibrium. Only at the end will I mention our nearest stellar neighbor, the Sun, which, because we can study it in so much detail, offers counterexamples to almost all of the the theory that works so well for early-type stars. I offer apologies in advance to anyone this approach may offend. Title: VizieR Online Data Catalog: Radiative forces for stellar envelopes (Seaton, 1997) Authors: Seaton, M. J.; Yan, Y.; Mihalas, D.; Pradhan, A. K. Bibcode: 2000yCat.6089....0S Altcode: (1) Primary data files, stages.zz These files give data for the calculation of radiative accelerations, GRAD, for elements with nuclear charge zz. Data are available for zz=06, 07, 08, 10, 11, 12, 13, 14, 16, 18, 20, 24, 25, 26 and 28. Calculations are made using data from the Opacity Project (see papers SYMP and IXZ). The data are given for each ionisation stage, j. They are tabulated on a mesh of (T, Ne, CHI) where T is temperature, Ne electron density and CHI is abundance multiplier. The files include data for ionisation fractions, for each (T, Ne). The file contents are described in the paper ACC and as comments in the code add.f (2) Code add.f This reads a file stages.zz and creates a file acc.zz giving radiative accelerations averaged over ionisation stages. The code prompts for names of input and output files. The code, as provided, gives equal weights (as defined in the paper ACC) to all stages. Th weights are set in SUBROUTINE WEIGHTS, which could be changed to give any weights preferred by the user. The dependence of diffusion coefficients on ionisation stage is given by a function ZET, which is defined in SUBROUTINE ZETA. The expressions used for ZET are as given in the paper. The user can change that subroutine if other expressions are preferred. The output file contains values, ZETBAR, of ZET, averaged over ionisation stages. (3) Files acc.zz Radiative accelerations computed using add.f as provided. The user will need to run the code add.f only if it is required to change the subroutines WEIGHTS or ZETA. The contents of the files acc.zz are described in the paper ACC and in comments contained in the code add.f. (4) Code accfit.f This code gives gives radiative accelerations, and some related data, for a stellar model. Methods used to interpolate data to the values of (T, RHO) for the stellar model are based on those used in the code opfit.for (see the paper OPF). The executable file accfit.com runs accfit.f. It uses a list of files given in accfit.files (see that file for further description). The mesh used for the abundance-multiplier CHI on the output file will generally be finer than that used in the input files acc.zz. The mesh to be used is specified on a file chi.dat. For a test run, the stellar model used is given in the file 10000_4.2 (Teff=10000 K, LOG10(g)=4.2) The output file from that test run is acc100004.2. The contents of the output file are described in the paper ACC and as comments in the code accfit.f. (5) The code diff.f This code reads the output file (e.g. acc1000004.2) created by accfit.f. For any specified depth point in the model and value of CHI, it gives values of radiative accelerations, the quantity ZETBAR required for calculation of diffusion coefficients, and Rosseland-mean opacities. The code prompts for input data. It creates a file recording all data calculated. The code diff.f is intended for incorporation, as a set of subroutines, in codes for diffusion calculations. (1 data file). Title: The MHD Equation of State with Post-Holtsmark Microfield Distributions Authors: Nayfonov, Alan; Däppen, Werner; Hummer, David G.; Mihalas, Dimitri Bibcode: 1999ApJ...526..451N Altcode: 1999astro.ph..1360N The Mihalas-Hummer-Däppen (MHD) equation of state is a part of the Opacity Project (OP), where it mainly provides ionization equilibria and level populations of a large number of astrophysically relevant species. Its basic concept is the idea of perturbed atomic and ionic states. At high densities, when many-body effects become dominant, the concept of perturbed atoms loses its sense. For that reason, the MHD equation of state was originally restricted to the plasma of stellar envelopes, that is, to relatively moderate densities, which should not exceed ρ<10-2 g cm-3. However, helioseismological analysis has demonstrated that this restriction is much too conservative. The principal feature of the original Hummer & Mihalas paper is an expression for the destruction probability of a bound state (ground state or excited) of a species (atomic or ionic), linked to the mean electric microfield of the plasma. Hummer & Mihalas assumed, for convenience, a simplified form of the Holtsmark microfield for randomly distributed ions. An improved MHD equation of state (Q-MHD) is introduced. It is based on a more realistic microfield distribution that includes plasma correlations. Comparison with an alternative post-Holtsmark formalism (APEX) is made, and good agreement is shown. There is a clear signature of the choice of the microfield distribution in the adiabatic index γ1, which makes it accessible to present-day helioseismological analysis. However, since these thermodynamic effects of the microfield distribution are quite small, it also follows that the approximations chosen in the original MHD equation of state were reasonable. A particular feature of the original MHD papers was an explicit list of the adopted free energy and its first- and second-order analytical derivatives. The corresponding Q-MHD quantities are given in the Appendix. Title: Shuster's Radiative Transfer Model of a Stellar Atmosphere Authors: Mihalas, Dimitri Bibcode: 1999ApJ...525C..25M Altcode: 1999ApJC..525...25M No abstract at ADS Title: Baade's Resolution of M32, NGC 205, and M31 Authors: Mihalas, Dimitri Bibcode: 1999ApJ...525C.359M Altcode: 1999ApJC..525..359M No abstract at ADS Title: Book Review: Computational methods for astrophysical fluid flow / Springer Verlag, 1998 Authors: Leveque, R. J.; Mihalas, D.; Dorfi, E. A.; Müller, E. Bibcode: 1999IrAJ...26...73L Altcode: No abstract at ADS Title: Radiation Hydrodynamics Authors: Mihalas, Dimitri Bibcode: 1998cmaf.conf..161M Altcode: 1998SAAS...27..161M Basic Radiation Theory Specific Intensity Photon Number Density Photon Distribution Function Mean Intensity Radiation Energy Density Radiation Energy Flux Radiation Momentum Density Radiation Stress Tensor (Radiation Pressure Tensor) Thermal Radiation Thermodynamics of Thermal Radiation and a Perfect Gas The Transfer Equation Absorption, Emission, and Scattering The Equation of Transfer Moments of the Transfer Equation Lorentz Transformation of the Transfer Equation Lorentz Transformation of the Photon 4-Momentum Lorentz Transformation of the Specific Intensity, Opacity, and - Emissivity Lorentz Transformation of the Radiation Stress Energy Tensor The Radiation 4-Force Density Vector Covariant Form of the Transfer Equation Inertial-Frame Equations of Radiation Hydrodynamics Inertial-Frame Radiation Equations Inertial-Frame Equations of Radiation Hydrodynamics Comoving-Frame Equation of Transfer Special Relativistic Derivation (D. Mihalas) Consistency Between Comoving-Frame and Inertial-Frame Equations Noninertial Frame Derivation (J. I. Castor) Analysis of O (v/c) Terms Lagrangian Equations of Radiation Hydrodynamics Momentum Equation Gas Energy Equation First Law of Thermodynamics for the Radiation Field First Law of Thermodynamics for the Radiating Fluid Mechanical Energy Equation Total Energy Equation Consistency of Different Forms of the Radiating-Fluid Energy - and Momentum Equations Consistency of Inertial-Frame and Comoving-Frame Radiation Energy - and Momentum Equations Radiation Diffusion Radiation Diffusion Nonequilibrium Diffusion The Problem of Flux Limiting Shock Propagation: Numerical Methods Acoustic Waves Numerical Stability Systems of Equations Implications of Shock Development Implications of Diffusive Energy Transport Illustrative Example Numerical Radiation Hydrodynamics Radiating Fluid Energy and Momentum Equations Computational Strategy Energy Conservation Formal Solution Multigroup Equations An Astrophysical Example Adaptive-Grid Radiation Hydrodynamics Front Fitting Artificial Dissipation The Adaptive Grid The TITAN Code References Title: The Quasi-stationary Structure of Radiating Shock Waves I. The One-temperature Fluid Authors: Sincell, M. W.; Gehmeyr, M.; Mihalas, D. Bibcode: 1997astro.ph.10097S Altcode: We calculate the quasi-stationary structure of a radiating shock wave propagating through a spherically symmetric shell of cold gas by solving the time-dependent equations of radiation hydrodynamics on an adaptive grid. We show that this code successfully resolves the shock wave in both the subcritical and supercritical cases and, for the first time, we have reproduced all the expected features -- including the optically thin temperature spike at a supercritical shock front -- without invoking analytic jump conditions at the discontinuity. We solve the full moment equations for the radiation flux and energy density, but the shock wave structure can also be reproduced if the radiation flux is assumed to be proportional to the gradient of the energy density (the diffusion approximation), as long as the radiation energy density is determined by the appropriate radiative transfer moment equation. We find that Zel'dovich and Raizer's analytic solution for the shock wave structure accurately describes a subcritical shock but it underestimates the gas temperature, pressure, and the radiation flux in the gas ahead of a supercritical shock. We argue that this discrepancy is a consequence of neglecting terms which are second order in the minimum shock compression ratio [$\eta_1 = (\gamma-1)/(\gamma+1)$, where $\gamma$ is the adiabatic index] and the inaccurate treatment of radiative transfer near the discontinuity. In addition, we verify that the maximum temperature of the gas immediately behind the shock is given by $T_{+} = 4 T_1/(\gamma+1)$, where $T_1$ is the gas temperature far behind the shock. Title: The Quasi-stationary Structure of Radiating Shock Waves II. The Two-temperature Fluid Authors: Sincell, M W; Gehmeyr, M; Mihalas, D Bibcode: 1997astro.ph.10095S Altcode: We solve the equations of radiation hydrodynamics in the two-temperature fluid approximation on an adaptive grid. The temperature structure depends upon the electron-ion energy exchange length, $l_{ei}$, and the electron conduction length, $l_{ec}$. Three types of radiating shock structure are observed: subcritical, where preheating of the unshocked gas is negligible; electron supercritical, where radiation preheating raises the temperature of the unshocked electron fluid to be equal to the final electron temperature; supercritical, where preheating and electron-ion energy exchange raise the preshock $T_{e,i}$ to their final post shock values. No supercritical shock develops when $l_{ei}$ is larger than the photospheric depth of the shocked gas because a negligible amount of the ion energy is transferred to the electrons and the shock is weakly radiating. Electron conduction smooths the $T_e$ profile on a length scale $l_{ec}$, reducing the radiation flux. Title: VizieR Online Data Catalog: Opacities from the Opacity Project (Seaton+, 1995) Authors: Seaton, M. J.; Yan, Y.; Mihalas, D.; Pradhan, A. K. Bibcode: 1997yCat.6080....0S Altcode: 1 CODES. ***** 1.1 Code rop.for ************

This code reads opacity files written in standard OP format. Its main purpose is to provide documentation on the contents of the files.

This code, like the other codes provided, prompts for the name of the file (or files) to be read. The file names read in response to the prompt may have up to 128 characters.

1.2 Code opfit.for **************

This code reads opacity files in standard OP format, and provides for interpolation of opacities to any required values of temperature and mass-density. The method used is described in OPF.

The code prompts for the name of a file giving all required control parameters. As an example, the file opfit.dat is provided (users will need to change directory names and file names).

The use of opfit.for is illustrated using opfit.dat. Most users will probably want to adapt opfit.for for use as a subroutine in other codes.

Timings for DEC 7000 ALPHA: 0.3 sec for data read and initialisations; then 0.0007 sec for each temperature-density point.

Users who like OPAL formats should note that opfit.for has a facility to produce files of OP data in OPAL-type formats.

1.3 Code ixz.for ************

This code provides for interpolations to any required values of X and Z. See IXZ. It prompts for the name of a file giving all required control parameters. An example of such a file if provided, ixz.dat (the user will need to change directory and file names).

The output files have names s92INT.'nnn'. The user specifies the first value of nnn, and the number of files to be produced.

2. DATA FILES **********

2.1 Data files for solar metal-mix ******************************

Data for solar metal-mix s92 as defined in SYMP. These files are from version 2 runs of December 1994 (see IXZ for details on Version 2). There are 213 files with names s92.'nnn', 'nnn'=201 to 413. Each file occupies 83762 bytes.

The file s92.version2 gives values of X (hydrogen mass-faction) and Z (metals mass-fraction) for each value of 'nnn'. The user can get s92.version2, select the values of 'nnn' required, then get the required files s92.'nnn'. The user can see the file in ftp, displayed on the screen, by typing "get s92.version2 -".

The files s92.'nnn' can be used with opfit.for to obtain opacities for any requires value of temperature and mass density.

Files for other metal-mixtures will be added in due course. Send requests to mjs@star.ucl.ac.uk.

2.2 Files for interpolation in X and Z **********************************

The data files have names s92xz.'mmm', where 'mmm'=001 to 096. They differ from the standard OP files (such as s92.'nnn' --- section 2.1 above) in that they contain information giving derivatives of opacities with respect to X and Z. Each file s92xz.'mmm' occupies 148241 bytes.

The interpolations to any required values of X and Z are made using ixz.for.

Timings: on DEC 7000 ALPHA, 2.16 sec for each new-mixture file.

For interpolations to some specified values of X and Z, one requires just 4 files s92xz.'mmm'. Most users will not require the complete set of files s92xz.'mmm'. The file s92xz.index includes a table (starting on line 3) giving values, for each 'mmm' file, of x,y,z (abundances by number-factions) and X,Y,Z (abundances by mass-fractions). Users are advised to get the file s92.index, and select values of 'mmm' for files required, then get those files.

The files produced by ixz.for are in standard OP format and can be used with opfit.for to obtain opacities for any required values of temperature and mass density.

3 RECOMMENDED PROCEDURE FOR USE OF OPACITY FILES **********************************************

(1) Get the file s92.version2.

(2) If the values of X and Z you require are available in the files s92.'nnn' then get those files.

(3) If not, get the file s92xz.index.

(4) Select from s92xz.index the values of 'mmm' which cover the range of X and Z in which your are interested. Get those files and use ixz.for to generate files for your exact required values of X and Z.

(5) Note that the exact abundance mixtures used are specified in each file (see rop.for). Also each run of opfit.for produces a table of abundances.

(6) If you want a metal-mix different from that of s92, contact mjs@star.ucl.ac.uk.

4 FUTURE DEVELOPMENTS *******************

(1) Data for the calculation of radiative forces are provided as the CDS catalog <VI/89> (added August 1997)

(2) Facilities will be added later which will enable the user to make calculations giving files for any required mixtures.

(9 data files). Title: Radiative Transfer in Astrophysics: Past, Present, and Future Authors: Mihalas, D. Bibcode: 1996AAS...188.3201M Altcode: 1996BAAS...28..866M The discipline of radiative transfer has provided the foundation for the interpretation of essentially all astrophysical data. Some of the major developments in the field in the 20th Century are reviewed, and an attempt is made to identify directions for future research, and to assess the likely importance of the discipine in the coming century. Title: First Results From TITAN Authors: Gehmeyr, M.; Mihalas, D. Bibcode: 1994AAS...185.4006G Altcode: 1994BAAS...26Q1370G 1. We present the complete solutions to Noh's constant velocity shock tube problem in planar, cylindrical, and spherical symmetry. 2. We discuss the physical properties of radiating shocks for a completely ionized hydrogen gas and highlight the transition from subcritical to supercritical shocks. 3. We give first results from stellar variability computations. Title: Adaptive grid radiation hydrodynamics with TITAN Authors: Gehmeyr, M.; Mihalas, D. Bibcode: 1994PhyD...77..320G Altcode: We have developed a code which solves the coupled sets of radiation transfer and fluid dynamics equations (time dependent in one spatial dimension) by employing a fully implicit adaptive grid procedure to detect, resolve, and track the relevant physical structures. We have formulated TITAN as a general purpose code, written it in a user friendly manner, and documented it in detail. This code is available to the (astrophysical) community for the application to a broad variety of computational problems both as a research and a teching tool. We demonstrate the code's power and versatility in a series of simple problems. They range from pure hydrodynamics tests (shock tubes and blast waves), via radiation transfer tests (radiative heating and cooling), to radiation hydrodynamics tests (radiative shocks and blast waves). These can be viewed as predecessors to a host of interesting astrophysical problems such as nova and supernova explosions and light curves, accretion onto compact objects, star formation, and stellar variability. Title: Opacities for stellar envelopes Authors: Seaton, M. J.; Yan, Y.; Mihalas, D.; Pradhan, A. K. Bibcode: 1994MNRAS.266..805S Altcode: We define stellar envelopes to be those regions of stellar interiors in which atoms exist and are not markedly perturbed by the plasma environment. Availability of accurate and extensive atomic data is a prime requirement for the calculation of envelope opacities. For envelopes we adopt the criterion of mass density p < 0.01 ρ≥g cm-3.

We present radiative Rosseland mean opacities for envelopes obtained using atomic data calculated in an international collaboration referred to as the Opacity Project, or OP. Equations of state are calculated using an occupation-probability formalism. To a good approximation, ionization equilibria and level populations in envelopes depend only on the temperature T and electron density Ne and are insensitive to chemical mixtures. Monochromatic opacities for all abundant chemical elements are therefore calculated on a grid of (T, Ne) values and are archived. Rosseland mean opacities are then readily calculated for any chemical mixture. Tables of Rosseland means, for any required mixtures and as functions of ρ and T, are available on request in computer-readable form.

The present, op, results are compared with those from another recent study, referred to as OPAL, by C. A. Iglesias and F. A. Rogers at the Lawrence Livermore National Laboratory. The agreement between the OP and OPAL calculations is generally good, although there are some differences. Both calculations give results larger than those obtained in earlier work, by factors of up to 3 or more. Title: Stellar Classification and the Theory of Stellar Atmospheres Authors: Mihalas, D. Bibcode: 1994ASPC...60...41M Altcode: 1994mpyp.conf...41M No abstract at ADS Title: Adaptive Grid Radiation Hydrodynamics with TITAN Authors: Gehmeyr, M.; Mihalas, D. Bibcode: 1993AAS...183.4806G Altcode: 1993BAAS...25.1366G TITAN solves the coupled sets of radiation transfer and fluid dynamics equations (time dependent in one spatial dimension) by employing a fully implicit adaptive grid procedure to detect, resolve, and track the relevant physical structures. TITAN is formulated as a general purpose code, written in a user friendly manner, and documented in detail. We intend to make TITAN available to the astrophysical community for the application to a broad variety of computational problems. We demonstrate TITAN's power and versatility in a series of simple problems. They range from pure hydrodynamics test (shock tubes and blast waves), via radiation transfer test (radiative heating and cooling), to radiation hydrodynamics tests (radiative shocks and blast waves). These can be viewed as predecessors to a host of interesting astrophysical problems such as nova and supernova explosions and light curves, accretion onto compact objects, star formation, and stellar variability. Title: On Cepheids at Maximum and Minimum Light Authors: Simon, Norman R.; Kanbur, Shashi M.; Mihalas, Dimitri Bibcode: 1993ApJ...414..310S Altcode: It has been known for many decades that the spectral type of Cepheids at light maximum is constant with period. We use hydrodynamic pulsation models to explain this result in terms of the outward reach of the hydrogen ionization front. On the other hand, we show that, at minimum light, the Cepheid photospheric temperature is mainly a function of amplitude. A number of observed Cepheids have published temperatures that seem too hot at both maximum and minimum. We attribute this to an overestimation of the reddening for these stars. A list is given. Title: ZEUS-2D: A Radiation Magnetohydrodynamics Code for Astrophysical Flows in Two Space Dimensions. III. The Radiation Hydrodynamic Algorithms and Tests Authors: Stone, James M.; Mihalas, Dimitri; Norman, Michael L. Bibcode: 1992ApJS...80..819S Altcode: The radiation hydrodynamical (RHD) algorithms in ZEUS-2D are described. These algorithms use a tensor variable Eddington factor, computed from a solution of the static transfer equation, to close the system of radiation moment equations. This full transport algorithm, which differs significantly from more commonly used methods based on the diffusion approximation, is applicable in both optically thin and thick media. Results computed by these algorithms on a new collection of RHD test problems are presented. For the transfer equation, very detailed tests are possible which compare the numerical solution for the specific intensity at every point on a given tangent plane to the known analytic solution. It is shown that, while the interpolation inherent in the method of short characteristics makes the solution diffusive, it is not overly so. For certain restricted geometries and physical conditions, these methods reproduce the expected results either identically or qualitatively. Title: The International Opacity Project Authors: Seaton, M. J.; Mihalas, D.; Yan, Y. Bibcode: 1992AAS...180.2203S Altcode: 1992BAAS...24..759S No abstract at ADS Title: The Opacity Project - Equation of State Authors: Mihalas, D. Bibcode: 1992RMxAA..23..127M Altcode: The equation of state used in the opacity calculations of the Opacity Project is described briefly. Title: CA II H and K Measurements Made at Mount Wilson Observatory, 1966--1983 Authors: Duncan, Douglas K.; Vaughan, Arthur H.; Wilson, Olin C.; Preston, George W.; Frazer, James; Lanning, Howard; Misch, Anthony; Mueller, Jean; Soyumer, David; Woodard, L.; Baliunas, Sallie L.; Noyes, Robert W.; Hartmann, Lee W.; Porter, Alain; Zwaan, Cornelis; Middelkoop, Frans; Rutten, Rene G. M.; Mihalas, Dimitri Bibcode: 1991ApJS...76..383D Altcode: Summaries are presented of the photoelectric measurements of stellar Ca II H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index 'S' are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported. Factors which affect the ability to detect stellar activity variations and accurately measure their amplitudes, such as the accuracy of the H and K measurements and scattered light contamination, are discussed. Relations are given which facilitate intercomparison of 'S' values with residual intensities derived from ordinary spectrophotometry, and for converting measurements to absolute fluxes. Title: The Quest for Physical Realism in Stellar Atmospheric Modeling Authors: Mihalas, D. Bibcode: 1991ASIC..341..127M Altcode: 1991sabc.conf..127M No abstract at ADS Title: The UK/US Opacity Project Authors: Mihalas, D. Bibcode: 1990BAAS...22R.847M Altcode: No abstract at ADS Title: The Equation of State for Stellar Envelopes. IV. Thermodynamic Quantities and Selected Ionization Fractions for Six Elemental Mixes Authors: Mihalas, Dimitri; Hummer, D. G.; Mihalas, Barbara Weibel; Daeppen, Werner Bibcode: 1990ApJ...350..300M Altcode: The free-energy minimization technique in the form developed in the preceding papers in this series is employed to evaluate thermodynamic quantities and ionization fractions on a fine temperature and density grid for six astrophysical mixtures of 15 elements. The mixtures range from that appropriate to super-metal-rich stars, through solar abundance, to that for extreme Population II objects. In this paper, the results for solar abundances are summarized in a form that is illustrative and which facilitates comparison with the results from other equation of state calculations. Title: Magnetohydrodynamic Simulations of Mass Outflows from Star Forming Regions Authors: Stone, J. M.; Norman, M. L.; Mihalas, D. Bibcode: 1990IAUS..140..351S Altcode: No abstract at ADS Title: Recent Progress and Future Prospects in the Study of Stellar Atmospheres Authors: Mihalas, Dimitri Bibcode: 1990arpf.symp...51M Altcode: 1990arpf.conf...51M A review of the study of stellar atmospheres is presented, with particular emphasis on the development of the basic theory. Attention is also given to improvements in instrumentation, magnetic field studies, geometrical problems, and spatial resolution. Title: Current Status of the Opacity Project Authors: Mihalas, D. Bibcode: 1990ASPC...11...99M Altcode: 1990cbsp.proc...99M No abstract at ADS Title: Numerical Simulation of Mass Outflows from Star Forming Regions Authors: Stone, James M.; Norman, Michael L.; Mihalas, Dimitri Bibcode: 1989ASSL..156..207S Altcode: 1989admf.proc..207S Observational studies of star forming regions in the Galaxy have demonstrated the ubiquity of mass outflows from objects in the late stages of star formation. The most dramatic examples of these flows are molecular bipolar outflows and optical jets. This paper summarizes the results from observational studies of these two classes of objects, and outlines the major theoretical problems in understanding how such flows are generated. Then, a project currently underway to address these problems in detail is described. This project centers on increasingly sophisticated numerical simulations of mass outflows from star-forming regions using a multiphysics hydrocode being developed at the NCSA. Title: Progress Toward an Improved Equation of State and Opacity for Stellar Envelopes Authors: Mihalas, Dimitri Bibcode: 1989upsf.conf...59M Altcode: 1989IAUCo.111...59M This paper describes an international project for computing new stellar envelope opacities and equation of state data, together with the progress achieved in the 5 years since its initiation. Attention is given to the computations of the wave functions and energy levels, and the calculations for the equation of state and the opacity code. The methods used in these computations are described. Title: Book Review: Numerical radiative transfer. / Cambridge U Press, 1988 Authors: Mihalas, D. Bibcode: 1988Obs...108..243M Altcode: No abstract at ADS Title: The HAO/Lowell/AFGL Solar-Stellar Spectrophotometer Authors: Fisher, R. R.; Ramsey, L. W.; Gilliland, R. L.; Radick, R.; Lockwood, G. W.; Mihalas, D. Bibcode: 1988BAAS...20..994F Altcode: No abstract at ADS Title: Detection of Supergiant Variability with the HAO/Lowell/AFGL Solar Stellar Spectrophotometry Project(S3) Authors: Ramsey, L. W.; Mihalas, D.; Radick, R.; Gilliland, R. L.; Lockwood, G. W.; Fisher, R.; Gallagher, J. Bibcode: 1988BAAS...20.1012R Altcode: No abstract at ADS Title: The Stellar Observing Program of the HAO/Lowell/AFGL Solar-Stellar Spectrophotometry Project (S3) Authors: Gilliland, R. L.; Mihalas, D.; Ramsey, L. W.; Radick, R.; Lockwood, G. W. Bibcode: 1988BAAS...20..994G Altcode: No abstract at ADS Title: The Equation of State for Stellar Envelopes. III. Thermodynamic Quantities Authors: Daeppen, Werner; Mihalas, Dimitri; Hummer, D. G.; Mihalas, Barbara Weibel Bibcode: 1988ApJ...332..261D Altcode: The authors derive general formulae for the computation of the thermodynamic properties of a partially ionized (and/or dissociated) multicomponent gas in terms of second derivatives of the free energy with respect to temperature, volume, and occupation numbers. For the free energy used in previous work the authors give explicit analytical expressions for all derivatives required to construct the thermodynamic quantities. Representative results for several different thermodynamic properties of a hydrogen-helium plasma with N(He)/N(H) = 0.10 are presented as color plots. Title: Towards Self-Consistent Numerical Models of Protostellar Outflows Authors: Stone, J. M.; Norman, M. L.; Mihalas, D. Bibcode: 1988BAAS...20Q1093S Altcode: No abstract at ADS Title: Detection of supergiant variability with the HAO/Lowell/AFGL solar-stellar spectrophotometry project (S3). Authors: Mihalas, D.; Ramsey, L. W.; Radick, R.; Gilliland, R. L.; Lockwood, G. W.; Fisher, R.; Gallagher, J. Bibcode: 1988BAAS...20.1012M Altcode: No abstract at ADS Title: The Solar Observing Program of the HAO/Lowell/AFGL Solar-Stellar Spectrophotometry Project (S3) Authors: Mihalas, D.; Radick, R.; Lockwood, G. W.; Gilliland, R. L.; Ramsey, L. W.; Fisher, R.; Livingston, W.; White, O. R. Bibcode: 1988BAAS...20Q1008M Altcode: No abstract at ADS Title: The Equation of State for Stellar Envelopes. I. an Occupation Probability Formalism for the Truncation of Internal Partition Functions Authors: Hummer, D. G.; Mihalas, Dimitri Bibcode: 1988ApJ...331..794H Altcode: The authors have formulated a new equation of state for material in stellar envelopes, subject to the limits T ⪉ 107K and ρ ⪉ 10-2g cm-3. Under these conditions, the method of free energy minimization can be used to allow for nonideal effects; this method ensures thermodynamic consistency among the material properties. A chemical picture is used in which atomic and molecular particles retain their identities. An occupation probability formalism is used to represent the effects of the plasma in establishing a finite partition function, and attention is paid to representing these effects in a way that is consistent from the point of view of statistical mechanics. The use of the static screened Coulomb potential to calculate level shifts and to estimate the cutoff of the internal partition function is shown by elementary arguments to be invalid. For most of the parameter space relevant to stellar envelopes, perturbations arising from the plasma ions are shown to be dominant in establishing the internal partition functions. Title: The Equation of State for Stellar Envelopes. II. Algorithm and Selected Results Authors: Mihalas, Dimitri; Dappen, Werner; Hummer, D. G. Bibcode: 1988ApJ...331..815M Altcode: A free-energy-minimization method for computing the dissociation and ionization equilibrium of a multicomponent gas is discussed. The adopted free energy includes terms representing the translational free energy of atoms, ions, and molecules; the internal free energy of particles with excited states; the free energy of a partially degenerate electron gas; and the configurational free energy from shielded Coulomb interactions among charged particles. Internal partition functions are truncated using an occupation probability formalism that accounts for perturbations of bound states by both neutral and charged perturbers. The entire theory is analytical and differentiable to all orders, so it is possible to write explicit analytical formulas for all derivatives required in a Newton-Raphson iteration; these are presented to facilitate future work. Some representative results for both Saha and free-energy-minimization equilibria are presented for a hydrogen-helium plasma with N(He)/N(H) = 0.10. These illustrate nicely the phenomena of pressure dissociation and ionization, and also demonstrate vividly the importance of choosing a reliable cutoff procedure for internal partition functions. Title: Atomic processes and radiation transport in stars Authors: Mihalas, Dimitri Bibcode: 1988AIPC..168...42M Altcode: To illustrate the tremendous range in physical conditions encountered in analyses of radiation from various astrophysical sources, we discuss representative physical conditions in several zones of a typical star. Even though these zones do not cover the full range of physical conditions encountered in the most exotic astronomical objects, they nevertheless give a good idea of the kinds of data required in astrophysical work. Moreover they provide a sequence of states progressively farther from equilibrium.

We discuss the physical mechanisms important in determining the internal state (i.e., excitation and ionization degrees) of the material in each of the regimes chosen, and comment on whether one should expect equilibrium or non-equilibrium distribution functions. In parallel, we delineate the major issues affecting the transport of radiation through typical astrophysical media; material properties, equilibrium versus non-equilibrium, velocity fields, and dynamics. We attempt to emphasize the close interplay between the nature of the radiation field and the state of the material. We also try to mention where progress is being slowed by lack of data for atomic processes, and indicate what kinds of data are still needed. Title: Book-Review - Radiation Hydrodynamics in Stars and Compact Objects - I.A.U COLL.89 Authors: Mihalas, D.; Winkler, K. H. A.; King, A. Bibcode: 1987Obs...107..219M Altcode: No abstract at ADS Title: Book Review - Physics of the Sun Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.; Carson, T. R. Bibcode: 1987Obs...107..173S Altcode: No abstract at ADS Title: Statistical Mechanics of Partially Ionized Stellar Plasmas: The Planck-Larkin Partition Function, Polarization Shifts, and Simulations of Optical Spectra Authors: Dappen, Werner; Anderson, Lawrence; Mihalas, Dimitri Bibcode: 1987ApJ...319..195D Altcode: We discuss a recent controversy about the Planck-Larkin partition function, and present optical simulations of high-quality spectra from laboratory hydrogen plasmas (Wiese, Kelleher, and Paquette) using several partition function formalisms. We point out that the controversy has arisen from a misunderstanding about the use of the Planck-Larkin partition function. A Planck-Larkin cancellation may still have its place in equations of state that are based on quantum-statistical many-body theory (i.e., the "physical picture"). However, experimental evidence shows that it is inconsistent to use the Planck-Larkin partition function as the internal partition function in simple models of reacting gases (i.e., the "chemical picture"). Moreover, the more sophisticated equations of state of the physical picture will have to be subjected to the same comparison with experimental data. We also address the question of plasma polarization shifts of bound-state energies. We discuss the static-screened Coulomb potential (SSCP) as an atomic potential: from theoretical considerations and observational constraints we conclude that it should not be used. The only useful result of the SSCP potential its prediction of the number of excited be obtained by alternative means, e.g., by an occupation probability formalism. Title: Book-Review - Radiation Hydrodynamics in Stars and Compact Objects Authors: Mihalas, D.; Winkler, K. H. A. Bibcode: 1987S&T....73Q.395M Altcode: No abstract at ADS Title: Book-Review - Radiation Hydrodynamics in Stars and Compact Objects Authors: Mihalas, D.; Winkler, K. H. A. Bibcode: 1987Sci...235..494M Altcode: No abstract at ADS Title: Book-Review - Physics of the Sun - VOL.1 - the Solar Interior - VOL.2 - the Solar Atmosphere - VOL.3 - Astrophysics and Solar-Terrestrial Relations Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K. Bibcode: 1987ApL....25..267S Altcode: No abstract at ADS Title: Book-Review - Physics of the Sun - V.I - the Solar Interior - V.II - the Solar Atmosphere - V.III - Astrophysics and Solar / Terrestrial Relations Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K.; Parker, E. N. Bibcode: 1986Natur.323..210S Altcode: No abstract at ADS Title: The computation of radiation transport using Feautrier variables. II. Spectrum line formation in moving media. Authors: Mihalas, D.; Kunasz, P. B. Bibcode: 1986JCoPh..64....1M Altcode: The Feautrier symmetric/antisymmetric radiation field averages are presently applied to the solution of line transport problems in moving media. These methods, which have proven to be useful in a variety of astrophysical applications, are suggested to be applicable to other areas of computational physics. Attention is given to algorithms for both observer-frame and comoving-frame approaches, noting their respective advantages and shortcomings. Title: Book-Review - the Life and Death of Stars Authors: Cooke, D. A.; Mihalas, D. Bibcode: 1986S&T....71..362C Altcode: No abstract at ADS Title: Book-Review - the Transfer of Spectral Line Radiation Authors: Cannon, C. J.; Mihalas, D. Bibcode: 1986Obs...106...23C Altcode: No abstract at ADS Title: Book-Review - Foundations of Radiation Hydrodynamics Authors: Mihalas, D.; Mihalas, B. W.; Machado, M. E. Bibcode: 1986SoPh..103..409M Altcode: No abstract at ADS Title: Introduction and Overview Authors: Mihalas, D. Bibcode: 1986LNP...255....1M Altcode: 1986IAUCo..89....1M; 1986rhsc.conf....1M No abstract at ADS Title: Physics of the Sun. Vol. I: The solar interior. Vol. II: The solar atmosphere. Vol. III: Astrophysics and solar-terrestrial relations. Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K. Bibcode: 1986psvi.book.....S Altcode: No abstract at ADS Title: Physics of the sun. Volume 3: Astrophysics and solar-terrestrial relations Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K. Bibcode: 1986psun....3.....S Altcode: No abstract at ADS Title: Physics of the sun. Volume 2: The solar atmosphere Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K. Bibcode: 1986psun....2.....S Altcode: Aspects related to the solar interior are discussed, taking into account thermonuclear reactions in the solar interior, atomic and radiative processes in the solar interior, hydrodynamic and hydromagnetic phenomena in the deep solar interior, rotation and magnetic fields, solar waves and oscillations, and observations and theories of solar convection, global circulation, and magnetic fields. In a discussion of the solar atmosphere, attention is given to the radiation output, the chromospheric fine structure, physical processes in the solar corona, magnetic energy storage and conversion in the solar atmosphere, the acceleration and propagation of solar flare energetic particles, solar radio emission, and structure, dynamics, and heating of the solar atmosphere. Other subjects explored are concerned with astrophysics and solar-terrestrial relations. The formation of the sun and its planets is considered along with the solar neutrino problem, solar and stellar magnetic activity, the effects of solar electromagnetic radiation on the terrestrial environment, and the effect of the solar wind. Title: Radiation Hydrodynamics in Stars and Compact Objects Authors: Mihalas, Dimitri; Winkler, Karl-Heinz A. Bibcode: 1986LNP...255.....M Altcode: 1986IAUCo..89.....M; 1986rhsc.conf.....M No abstract at ADS Title: The Equations of Radiation Hydrodynamics Authors: Mihalas, D. Bibcode: 1986ASIC..188...45M Altcode: 1986arh..conf...45M The purpose of this paper is to give an overview of the role of radiation in the transport of energy and momentum in a combined matter-radiation fluid. The transport equation for a moving radiating fluid is presented in both a fully Eulerian and a fully Lagrangean formulation, along with conservation equations describing the dynamics of the fluid. Special attention is paid to the problem of deriving equations that are mutually consistent in each frame, and between frames, to O(v/c). A detailed analysis is made to show that in situations of broad interest, terms that are formally of O(v/c) actually dominate the solution. Title: Physics of the sun Authors: Sturrock, P. A.; Holzer, T. E.; Mihalas, D. M.; Ulrich, R. K. Bibcode: 1986psun....1.....S Altcode: 1986QB521.P48...... Aspects related to the solar interior are discussed, taking into account thermonuclear reactions in the solar interior, atomic and radiative processes in the solar interior, hydrodynamic and hydromagnetic phenomena in the deep solar interior, rotation and magnetic fields, solar waves and oscillations, and observations and theories of solar convection, global circulation, and magnetic fields. In a discussion of the solar atmosphere, attention is given to the radiation output, the chromospheric fine structure, physical processes in the solar corona, magnetic energy storage and conversion in the solar atmosphere, the acceleration and propagation of solar flare energetic particles, solar radio emission, and structure, dynamics, and heating of the solar atmosphere. Other subjects explored are concerned with astrophysics and solar-terrestrial relations. The formation of the sun and its planets is considered along with the solar neutrino problem, solar and stellar magnetic activity, the effects of solar electromagnetic radiation on the terrestrial environment, and the effect of the solar wind. Title: Book-Review - Foundations of Radiation Hydrodynamics Authors: Mihalas, D.; Mihalas, B. W.; King, A. Bibcode: 1985Obs...105..238M Altcode: No abstract at ADS Title: Book-Review - Foundations of Radiation Hydrodynamics Authors: Mihalas, D.; Mihalas, B. Bibcode: 1985S&T....70..231M Altcode: No abstract at ADS Title: Book-Review - Methods in Radiative Transfer Authors: Kalkofen, W.; Mihalas, D. Bibcode: 1985Obs...105...52K Altcode: No abstract at ADS Title: The computation of radiation transport using Feautrier variables. I - Static media Authors: Mihalas, D. Bibcode: 1985JCoPh..57....1M Altcode: A review is presented of methods for solving the radiation transport equation in terms of the symmetric and antisymmetric averages first introduced by Feautrier (1964). These methods have enjoyed good success and have achieved considerable popularity in astrophysics. Both formulation and algorithms are discussed briefly, and basic references are provided in order to provide easy access to workers in other fields where these methods may prove applicable. Title: Implicit adaptive-grid radiation hydrodynamics. Authors: Winkler, K. -H. A.; Norman, M. L.; Mihalas, D. Bibcode: 1985mts..conf..145W Altcode: Contents: I. Introduction. II. Physical equations. III. Adaptive-mesh equations. IV. Numerical equations. V. The adaptive mesh. VI. Numerical techniques: Tensor artificial viscosity. Artificial mass and heat diffusion. On the use of Δξ, Δm, and (δm/δt). Advection. Solution procedure and control. VII. Ordinary gas dynamics: shock tubes. VIII. Radiation hydrodynamics: a supercritical shock. IX. A "Hilbert program" for nonlinear radiation hydrodynamics. Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thomas, R. N.; Mihalas, D. Bibcode: 1984Obs...104..275T Altcode: No abstract at ADS Title: On the Propagation of Acoustic Waves in a Radiative Fluid Authors: Mihalas, D.; Mihalas, B. W. Bibcode: 1984ApJ...283..469M Altcode: No abstract at ADS Title: The H− equilibrium using coupled rate equations for H−, H, H+, H2, and H2+ Authors: Lites, B. W.; Mihalas, D. Bibcode: 1984SoPh...93...23L Altcode: We formulate rate equations for the reaction network coupling H, H−, H+, H2, and H2+. We attempt to systematize the notation, and to write the equations in a form suitable for modern computational methods of handling the coupled rate equations and radiative transfer equations, for both dynamical and static atmospheres. We have accounted for more processes than are generally considered in most current work; some of these may have an impact on the equilibrium of H− (hence its opacity) and on charge conservation (hence the proton density) in the atmospheres of solar-type stars. Title: Adaptive-mesh radiation hydrodynamics - II. The radiation and fluid equations in relativistic flows. Authors: Mihalas, D.; Winkler, K. -H. A.; Norman, M. L. Bibcode: 1984JQSRT..31..479M Altcode: The authors derive the radiation and fluid equations for relativistic flows in conservative form in a completely adaptive coordinate system. Title: Adaptive-mesh radiation hydrodynamics - I. The radiation transport equation in a completely adaptive coordinate system. Authors: Winkler, K. -H. A.; Norman, M. L.; Mihalas, D. Bibcode: 1984JQSRT..31..473W Altcode: The authors formulate the radiation transport equation in a completely adaptive coordinate system, which they define as a system in which the mesh in spacetime, angles and frequency adapts automatically to the dynamical evolution of the radiation field and fluid flow. Title: Foundations of radiation hydrodynamics Authors: Mihalas, D.; Mihalas, B. W. Bibcode: 1984oup..book.....M Altcode: This book is the result of an attempt, over the past few years, to gather the basic tools required to do research on radiating flows in astrophysics. The microphysics of gases is discussed, taking into account the equation of state of a perfect gas, the first and second law of thermodynamics, the thermal properties of a perfect gas, the distribution function and Boltzmann's equation, the collision integral, the Maxwellian velocity distribution, Boltzmann's H-theorem, the time of relaxation, and aspects of classical statistical mechanics. Other subjects explored are related to the dynamics of ideal fluids, the dynamics of viscous and heat-conducting fluids, relativistic fluid flow, waves, shocks, winds, radiation and radiative transfer, the equations of radiation hydrodynamics, and radiating flows. Attention is given to small-amplitude disturbances, nonlinear flows, the interaction of radiation and matter, the solution of the transfer equation, acoustic waves, acoustic-gravity waves, basic concepts of special relativity, and equations of motion and energy. Title: On the Relevance of the MK System and Process to the Theory of Stellar Atmospheres Authors: Mihalas, D. Bibcode: 1984mpsc.conf....4M Altcode: No abstract at ADS Title: Book-Review - the A-Type Stars - Problems and Perspectives Authors: Wolff, S. C.; Mihalas, D. Bibcode: 1984S&T....67..332W Altcode: No abstract at ADS Title: Book-Review - 100,000,000,000 Suns Authors: Kippenhahn, R.; Mihalas, D. Bibcode: 1984S&T....68..134K Altcode: No abstract at ADS Title: Foundations of radiation hydrodynamics Authors: Mihalas, Dimitri; Weibel Mihalas, Barbara Bibcode: 1984frh..book.....M Altcode: No abstract at ADS Title: Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. II. Detailed analysis of the 1980 observing season data. Authors: Baliunas, S. L.; Hartmann, L.; Noyes, R. W.; Vaughan, H.; Preston, G. W.; Frazer, J.; Lanning, H.; Middelkoop, F.; Mihalas, D. Bibcode: 1983ApJ...275..752B Altcode: For a sample of 47 lower main-sequence stars, including the Sun, and eight evolved stars, the relative strength of the Ca II H and K emission cores has been measured daily over a nearly continuous interval during 1980 July through October at Mount Wilson. From these time series measurements of chromospheric emission, rotation rates have been inferred with quantitative estimates of both the reality and precision of the rotation periods. We find rotation rates easily for the main-sequence stars with strong emission or those later than about spectral type K0. With this technique, rotation rates can be measured precisely for the first time for equatorial velocities as slow as 1 km s-1 and independently of the aspect of the rotation axis. In a limited range of spectral type, a small sample of stars indicates that chromospheric emission decreases smoothly as a function of rotation period. No conclusion can be drawn on the question of the reality of a discontinuity in chromospheric emission as a function of time (the "Vaughan-Preston" gap for stars in the solar neighborhood).

In our sample of giant stars, the G2 III star HD 218658 shows a persistent fluctuation of 4.6 days, a period that is inconsistent with stellar rotation. The G0 III star HD 6903 is a previously unreported FK Comae-type star.

For a few main-sequence stars, measurements continued beyond 1980 October suggest the presence of active longitudes (if not individual active regions) persisting through the observing season 1981. Title: On the propagation of acoustic waves in a radiating fluid Authors: Mihalas, D.; Mihalas, B. W. Bibcode: 1983ApJ...273..355M Altcode: The linearized Lagrangian radiation equations of Castor (1972) are used in order to obtain a virtually complete and physically satisfying view of acoustic wave dynamics in a radiating fluid. It is assumed that the radiation field is quasi-static, all dynamical radiation terms are ignored, and the Eddington approximation is applied. It is noted that it would be useful to proceed with the complementary study of the time evolution of initial disturbances. Title: The photometric variability of solar-type stars. III. Results from 1981-82, including parallel observations of thirty-six Hyades stars. Authors: Radick, R. R.; Mihalas, D.; Lockwood, G. W.; Thompson, D. T.; Warnock, A., III; Hartmann, L. W.; Worden, S. P.; Henry, G. W.; Sherlin, J. M. Bibcode: 1983PASP...95..621R Altcode: A photometric survey of main-sequence stars in the Pleiades, Hyades, and Malmquist Field, to investigate variability among solar-type stars, had been continued at Cloudcroft Observatory for a second season. Possibly six of 40 Pleiades stars, two (possibly six) of 49 Hyades stars and possibly four of 42 stars in the Malmquist Field are found to be variable. Parallel observations of Hyades stars were obtained also at Lowell Observatory. These measurements, which achieved better precision, reveal significiant variations in eleven (possibly 16) of 36 Hyades stars, all of spectral type F7 V-K2 V. Agreement between the two surveys is acceptable. The two seasons of the Cloudcroft survey show that changes in the mean annual brightness of the Hyades stars accompany changes in the amplitude of their short-term variability, in the sense that a star tends to become fainter as its variability increases and vice versa. Color effects are absent. Title: Book-Review - Galactic Astronomy - Structure and Kinematics Authors: Mihalas, D.; Binney, J.; Antonov, V. A. Bibcode: 1983Afz....19..505M Altcode: No abstract at ADS Title: Comments on the dynamical effects of radiative viscosity Authors: Mihalas, D. Bibcode: 1983ApJ...266..242M Altcode: Diffusion limit radiation stress intensity tensor term size and radiating fluid dynamical equation term size estimates are presented, with emphasis on radiative viscosity effects. A complete parallelism is demonstrated between radiation and material terms, and Castor's (1972) comoving frame radiation energy and momentum equations, augmented by Buchler's (1979, 1982) acceleration terms, are shown to provide a completely consistent treatment of all effects associated with both radiation viscosity and the equivalent inertia of radiation enthalpy and radiant energy flux. Questions arising in connection with radiative viscous dissipation are discussed, and it is noted that in certain physically reasonable situations, the radiative viscous dissipation function may be only O(v-squared/c-squared) relative to the dominant radiative term in the radiating fluid gas-energy equation. Title: The photometric variability of solar-type stars. I. Preliminary results for the Pleiades, Hyades and the Malmquist field. Authors: Radick, R. R.; Hartmann, L.; Mihalas, D.; Worden, S. P.; Africano, J. L.; Klimke, A.; Tyson, E. T. Bibcode: 1982PASP...94..934R Altcode: The young main sequence stars in the Pleiades and Hyades clusters, and old disk stars in the Malmquist Field near the north galactic pole, have been observed by precision photometry in order to determine the prevalance of variability among solar type stars. Significant variations have been found in at least five, and possibly ten, of 44 Hyades stars, and possibly one of the 41 stars in the Malmquist Field, all of which are of spectral type F8 V-K2 V. Title: Time-dependent radiative transfer with automatic flux limiting Authors: Mihalas, D.; Weaver, R. Bibcode: 1982JQSRT..28..213M Altcode: A simple method for solving the time-dependent transfer problem is discussed. This scheme is automatically flux-limited and affords physical insight into how flux limitation occurs. A second-order, time-dependent radiation energy equation that is similar in form to the diffusion limit radiation energy equation is then developed. This time-dependent energy equation approaches physically reasonable equations in optically thick and thin regions. Computational aspects of solving this energy equation are discussed. Title: The acceleration and propagation of solar flare energetic particles Authors: Forman, M. A.; Ramaty, R.; Zweibel, E. G.; Holzer, T. E.; Mihalas, D.; Sturrock, P. A.; Ulrich, R. K. Bibcode: 1982STIN...8329162F Altcode: Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energetic particles detected in interplanetary space and in the Earth's atmosphere. The implication of these observations are discussed. Stochastic and shock acceleration as well as acceleration in direct electric fields are considered. Interplanetary particle propagation is discussed and an overview of the highlights of both current and promising future research is presented. Title: On iterative solutions of the LTE model atmosphere problem. Authors: Mihalas, D.; Weaver, R. P.; Sanderson, J. G. Bibcode: 1982JQSRT..28...53M Altcode: We discuss iterative methods for solving the coupled radiative-transfer and energy-balance equations in the LTE model atmospheres problem including isotropic coherent scattering. We show that iterative solution (e.g. by SOR techniques) of the grand matrix encountered in such problems is vastly more efficient than a direct solution, and is easily vectorized. The final computational effort is linear in the number of depths and frequencies considered, and thus this approach opens the door for the computation of both static and dynamic line-blanketed models using large numbers of depth-points and huge numbers of frequencies. The iterative methods discussed here can be applied to line-formation problems with complete redistribution and to certain classes of problems with partial redistribution (e.g. Compton scattering problems in the Fokker-Planck approximation). Title: Book-Review - Galactic Astronomy - Part One - Structure and Kinematics Authors: Mihalas, D.; Binney, J.; Robson, I. Bibcode: 1982JBAA...92..204M Altcode: No abstract at ADS Title: On the solution of the time-dependent inertial-frame equation of radiative transfer in moving media to O(v/c). Authors: Mihalas, D.; Klein, R. I. Bibcode: 1982JCoPh..46...97M Altcode: It is demonstrated that practical schemes can be developed for treating the hybrid time-dependent transfer equation including O(v/c) terms both stably and efficiently, and their coupling into radiation-hydrodynamical calculations is sketched. The mixed-frame equation of transfer and the frequency-dependent and frequency-integrated moment equations are developed. The relative sizes of the terms in the transfer equation and the requirement for keeping all v/c terms in order to obtain exact consistency with the energy equation for the radiating fluid are addressed. The computational approach is discussed in Feautrier variables, including a second-order formulation. Several schemes for the solution method are presented along with test calculations for an unattenuated square wave, attenuated radiation front, irradiated grey atmosphere, and velocity effects in a moving atmosphere. How the transfer equation to O(v/c) can be coupled to the hydrodynamic equations in both an Eulerian and Lagrangian formulation is indicated. Title: Book-Review - Galactic Astronomy - ED.2 Authors: Mihalas, D.; Binney, J.; Barrow, J. D. Bibcode: 1982Natur.295..440M Altcode: No abstract at ADS Title: Book-Review - Galactic Astronomy - Structure and Kinematics Authors: Mihalas, D.; Binney, J.; Jones, D. Bibcode: 1982Obs...102..245M Altcode: No abstract at ADS Title: Book-Review - Galactic Astronomy - Structure and Kinematics Authors: Mihalas, D.; Binney, J.; Schmidt-Kaler, T. Bibcode: 1982SSRv...32..468M Altcode: No abstract at ADS Title: Book-Review - the Sun as a Star Authors: Jordan, S.; Mihalas, D. Bibcode: 1982S&T....63..262J Altcode: No abstract at ADS Title: Stellar atmospheres. Authors: Mihalas, D. M. Bibcode: 1982stat.book.....M Altcode: No abstract at ADS Title: Book-Review - Galactic Astronomy - Structure and Kinematics Authors: Mihalas, D.; Binney, J. Bibcode: 1981Sci...214..829M Altcode: No abstract at ADS Title: A Comment on Radiative Transfer in Spherically Symmetric Flows by Castor, J.I. Authors: Mihalas, D. Bibcode: 1981ApJ...250..373M Altcode: Castor's comoving-frame equation of transfer is re-derived retaining a term omitted from one of the coefficients in his metric. This term is important when the flow changes significantly on time scales Δt ∼ Δr/c, so that the fluid acceleration is comparable with cv/r or c(dv/dr). When the term is retained, terms that depend on the acceleration now appear in the coefficients of Castor's transfer equation, in agreement with independent derivations by Buchler and Mihalas. Title: Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. I. Initial results. Authors: Vaughan, A. H.; Baliunas, S. L.; Middelkoop, F.; Hartmann, L. W.; Mihalas, D.; Noyes, R. W.; Preston, G. W. Bibcode: 1981ApJ...250..276V Altcode: Fluxes at 1 Å bands at the centers of the H and K lines in 46 lower main sequence field stars, and in eight selected subgiants and giant stars, have been measured at nightly intervals in the course of a nearly continuous 14-week observing run. In 19 stars we have found clear evidence of rotational modulation, from which values of the rotational periods can be assigned by inspection. In nine others, periods have been found by an autocorrelation analysis of the flux records. The periods obtained imply rotation velocities that are in good accord with spectroscopically determined values of V sin i in the literature for 13 of the stars we have observed.

Much of the short term scatter in H-K flux observed by Wilson appears to be caused by rotational modulation, although variations on other time scales are also present.

As many as 80% of the chromospherically active (i.e., young) stars display prominent rotational modulation, and in some cases the phase of the modulation remained unchanged for the entire observing period, suggesting that markedly asymmetric and long-lived distributions of active regions are common in such stars.

At a given (B - V) < 1.0, the strength of H-K emission is shown to vary as a function of rate of rotation, suggesting that rotation, rather than initial conditions or age per se, is the chief parameter influencing chromospheric output.

From data on stellar activity cycles available at present, it is suggested that periodic cycles resembling the Sun's are almost exclusively found in stars with rotation periods in excess of about 20 days; and, except for this threshold effect, the cycle periods are uncorrelated with rotation rate. Title: A preliminary interpretation of stellar chromospheric CA II emission variations within the framework of stellar dynamo theory. Authors: Durney, B. R.; Mihalas, D.; Robinson, R. D. Bibcode: 1981PASP...93..537D Altcode: Recent stellar chromospheric Ca II emission data are analyzed and interpreted within the framework of simple concepts of dynamo theory. From an examination of the rotation rates and B-V indexes of 26 stars as presented by Vaughn at el. (1981) and the background flux values derived by Wilson (1978) for 18 reference stars, an empirical relation is derived between dynamo number, calculated from the B-V index and rotation rate, and stellar chromospheric emission flux. The Ca-emission cycle morphology of the sample stars is then examined, and differences between the four morphological classes identified are explained in terms of the correlation of large dynamo numbers with the presence of several interfering magnetic modes of different spatial scales, which do not exhibit a marked cyclic behavior, and small numbers with the excitation of only a single mode. The gap noted by Vaughn and Preston (1980) in the relation between the log of the emission flux with (B-V) is then interpreted as representing a transition from a multiple-mode dynamo to a single-mode dynamo as the dynamo number decreases. Title: On the stimulated emission terms in partial redistribution calculations Authors: Baschek, B.; Oxenius, J.; Mihalas, D. Bibcode: 1981A&A....97...43B Altcode: It is shown that the formulation given by Mihalas (1978) of the stimulated emission term in partial redistribution calculations is incorrect. It is noted that in the solar and stellar computations presented thus far in the literature this error is of no importance because the stimulated emission terms were negligible. However, for computations for lines in which h-nu/kT is not large compared with unity, the error could have serious consequences and the correct formulation should therefore be used. To this end, corrected, albeit approximate, equations are given for the various cases of interest. Title: The Photometric Variability of Main Sequence Stars Authors: Radick, R. R.; Hartmann, L. W.; Mihalas, D. M.; Worden, S. P. Bibcode: 1981BAAS...13R.832R Altcode: No abstract at ADS Title: The Solar Stellar Connection: what Observations are Needed? Authors: Mihalas, D. Bibcode: 1981siwn.conf..193M Altcode: No abstract at ADS Title: Difference-equation methods for the solution of radiative transfer problems in media with discontinuities Authors: Mihalas, D. Bibcode: 1981JQSRT..25..145M Altcode: Difference-equation methods are developed for solving the equation of transfer in media with discontinuities in their physical properties. These should prove useful in calculating the radiation field in dynamical atmospheres having shocks. Two examples with thermal or scattering source functions, for which exact solutions can be obtained, are used to evaluate the accuracy of the techniques, which prove quite satisfactory. Title: The activity cycles of stars. Authors: Wilson, O. C.; Vaughan, A. H.; Mihalas, D. Bibcode: 1981SciAm.244b..82W Altcode: 1981SciAm.244...82W No abstract at ADS Title: The activity cycles of stars Authors: Wilson, O. C.; Vaughan, A. H.; Mihalas, D. Bibcode: 1981SciAm.244b.104W Altcode: 1981SciAm.244..104W The activity cycle of the sun is reviewed with attention to the contributions of Galileo, Schwabe, Wolf, Maunder, Carrington, Hale, Babcock and Parker. The use of the H-K photometer in the observation of the chromospheric variability of 91 sun-like stars at the Mount Wilson Observatory is discussed. It is estimated that more than half of the main-sequence stars less massive than 1.5 solar masses may show cyclic behavior. The chromospheric variations for 12 sunlike stars are given. Title: Book-Review - the Brightest Stars Authors: de Jager, C.; Mihalas, D. Bibcode: 1981S&T....61..432D Altcode: No abstract at ADS Title: Book-Review - Galactic Astronomy - Structure and Kinematics Authors: Mihalas, D. Bibcode: 1981S&T....62..592M Altcode: No abstract at ADS Title: Galactic astronomy. Structure and kinematics Authors: Mihalas, D.; Binney, J. Bibcode: 1981gask.book.....M Altcode: An overview of the Milky Way Galaxy is provided and aspects of astronomical background are considered, taking into account positions and coordinate systems, proper motions, parallax, radial velocities, stellar spectra, magnitudes and colors, absolute energy distributions, and astronomical catalogs and atlases. The physical properties of stars and the interstellar medium are examined, giving attention to stellar distances, stellar masses, stellar radii, an analysis of stellar spectra, spiral arm and disk stars, spheroidal-component stars, stellar structure and evolution, pulsating variable stars, and questions of interstellar absorption. The space distribution of stars and the chemical elements in the Milky Way Galaxy are discussed along with the large-scale structure and stellar content of galaxies, the solar motion, the stellar residual-velocity distribution, and the rotation of galaxies. A description is presented of the large-scale distribution of gas in galaxies, taking into consideration the distribution of neutral hydrogen in the Milky Way Galaxy and in other galaxies, molecular clouds in the Milky Way Galaxy, and the galactic center. Title: A Radiative Transfer Model of Filamentary Prominences Authors: Bornmann, P. L.; Mihalas, D. Bibcode: 1980BAAS...12Q.909B Altcode: No abstract at ADS Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. VII - Angle-dependent partial redistribution Authors: Mihalas, D. Bibcode: 1980ApJ...238.1034M Altcode: A method is presented for treating line scattering with general redistribution in angle and frequency in spherical expanding flows. The scheme employs a solution of the moment equations for the source function coupled with a ray-by-ray formal solution for angular shape factors. In both steps the differencing is straightforward and numerically stable. Title: Radiative transfer in spherical flows with nonmonotonic velocity fields - The observer's frame reconsidered Authors: Mihalas, D. Bibcode: 1980ApJ...238.1042M Altcode: It is shown that for spherically symmetric flows with nonmonotonic velocity fields, the solution of the two-level-atom transfer equation in the observer's frame remains a viable method, even at high flow speeds, on computers with vector-processing capabilities. This result is of importance because for such cases comoving-frame methods are, at best, extremely difficult (no successful calculation having been published to date), and Sobolev-theory methods become both cumbersome to use and inaccurate in many situations of interest. The basic algorithm is described and is illustrated by computations for spherically symmetric decelerating expansions. Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. VI - Relativistic flows Authors: Mihalas, D. Bibcode: 1980ApJ...237..574M Altcode: Within the framework of special relativity, radiative transport equations describing exactly, i.e., to all orders in (v/c), the interaction of radiation and matter in spherically symmetric flows are derived. The full angle- and frequency-dependent transfer equation, frequency-dependent moment equations, and frequency-integrated moment equations are obtained. The frequency-integrated moment equations are shown to be precisely equivalent to the equations obtained from the four-divergence of the radiation stress-energy tensor, and all three sets of equations recover the results obtained earlier by Castor in the limit (v/c) much less than 1. A method of solution of the steady-flow transfer equation is discussed, and two illustrative examples are presented. Title: Physics of the Chromosphere - Corona / Wind Complex and Mass Loss in Stellar Atmospheres Authors: Mihalas, D. H. Bibcode: 1980HiA.....5..521M Altcode: No abstract at ADS Title: Some speculations concerning the significance of Beals's type III P Cygni line profiles. Authors: Mihalas, D.; Conti, P. S. Bibcode: 1980ApJ...235..515M Altcode: It is suggested that Beals's Type III P Cygni profiles, in which additional emission appears blueward of the blueshifted absorption feature, may be produced in stars in which the inner parts of the expanding envelope (stellar wind) are forced into corotation with the star out to a few stellar radii by a weak global magnetic field. Numerical estimates are made for the O4ef star Xi Pup which suggest that the Alfvenic radius (limit of corotation) is about 2.1 stellar radii, and that the required magnetic field at that point is about 70 Gauss. The braking time scale implied by angular momentum loss to the wind is short compared with the main-sequence (hydrogen core-burning) lifetime of the star and the present high mass loss rate. Title: Curves of growth and line profiles in expanding and rotating atmospheres Authors: Mihalas, D. Bibcode: 1979MNRAS.189..671M Altcode: A study of diagnosing velocity fields in expanding and rotating stellar atmospheres is presented. Line profiles are calculated by solving for the source function in the comoving fluid frame, and computing emergent intensities using a formal solution in the observer's frame. Results are presented for equivalent widths, line depth, line shift, line width, and asymmetry parameters, and it is shown that the standard curve of growth cannot yield unique physically meaningful results. Line-shape parameters appear to provide sufficient information to estimate the broad features of the flow, and it is shown that a fundamental assumption upon which all present Fourier methods are based is invalid. Possible approaches for overcoming the problem are suggested. Title: Book-Review - Stellar Atmospheres Authors: Mihalas, D.; Ivanov, V. V. Bibcode: 1979SvA....23..386M Altcode: No abstract at ADS Title: Theory of Stellar Atmospheres Authors: Mihalas, D. Bibcode: 1979IAUTA..17b.193M Altcode: 1979IAUT...17..193M No abstract at ADS Title: Two-dimensional radiative transfer. I. Planar geometry. Authors: Mihalas, D.; Auer, L. H.; Mihalas, B. R. Bibcode: 1978ApJ...220.1001M Altcode: Differential-equation methods for solving the transfer equation in two-dimensional planar geometries are developed. One method, which uses a Hermitian integration formula on ray segments through grid points, proves to be extremely well suited to velocity-dependent problems. An efficient elimination scheme is developed for which the computing time scales linearly with the number of angles and frequencies; problems with large velocity amplitudes can thus be treated accurately. A very accurate and efficient method for performing a formal solution is also presented. A discussion is given of several examples of periodic media and free-standing slabs, both in static cases and with velocity fields. For the free-standing slabs, two-dimensional transport effects are significant near boundaries, but no important effects were found in any of the periodic cases studied. Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. V. Multilevel atoms. Authors: Mihalas, D.; Kunasz, P. B. Bibcode: 1978ApJ...219..635M Altcode: The coupled radiative transfer and statistical equilibrium equations for multilevel ionic structures in the atmospheres of early-type stars are solved. Both lines and continua are treated consistently; the treatment is applicable throughout a transonic wind, and allows for the presence of background continuum sources and sinks in the transfer. An equivalent-two-level-atoms approach provides the solution for the equations. Calculations for simplified He (+)-like model atoms in parameterized isothermal wind models indicate that subordinate line profiles are sensitive to the assumed mass-loss rate, and to the assumed structure of the velocity law in the atmospheres. Title: Stellar atmospheres Authors: Mihalas, Dimitri Bibcode: 1978stat.book.....M Altcode: 1978QB809.M5....... The radiation field is considered along with the equation of transfer, the grey atmosphere, absorption cross-sections, the equations of statistical equilibrium, and the solution of the transfer equation. A description of model atmospheres is presented, taking into account the classical model-atmospheres problem, Local Thermodynamic Equilibrium (LTE) radiative-equilibrium models, convection and models for late-type stars, the results of LTE model-atmosphere calculations for early-type stars, non-LTE radiative-equilibrium models for early-type stars, extended atmospheres, and semiempirical solar models. Attention is given to the line absorption profile, classical treatments of line transfer, non-LTE line transfer in the case of the two-level atom and the multilevel atom, line formation with partial frequency redistribution, radiative transfer in moving atmospheres, the equations of hydrodynamics for an ideal compressible fluid, coronal winds, radiation hydrodynamics, and radiatively driven winds. Title: Boundary conditions with mass loss: the radiatively-driven wind model. Authors: Mihalas, D. Bibcode: 1977saif.conf..175M Altcode: No abstract at ADS Title: Erratum and Addendum: "Solution of the comoving-frame equation of transfer in spherically symmetric flows. IV. Frequency-dependent source functions for scattering by atoms and electrons [Astrophys. J., Vol. 210, p. 419 - 433 (1976)]. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1977ApJ...214..337M Altcode: No abstract at ADS Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. IV. Frequency-dependent source functions for scattering by atoms and electrons. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1976ApJ...210..419M Altcode: A numerical method is presented of solving the radiative transfer equation in the comoving frame of a spherically symmetric expanding atmosphere in which both the line and the electron-scattering source function can depend on frequency (i.e., when there is partial frequency redistribution in the scattering process). This method is used to assess the adequacy of various assumptions regarding frequency redistribution in the comoving frame and to discuss the effects of electron scattering more accurately than previously possible. The methods developed here can be used in realistic model atmospheres to account for the (major) effects of electron scattering upon emergent flux profiles. Title: Solution of the Comoving-Frame Equation of Transfer in Spherically Symmetric Flows. III. Effect of Aberration and Advection Terms Authors: Mihalas, Dimitri; Kunasz, P. B.; Hummer, D. G. Bibcode: 1976ApJ...206..515M Altcode: We investigate the importance of the advection and aberration terms, which are of order V/c, in the comoving-frame transfer equation in spherical geometry. Characteristic trajectories are found which reduce the spatial derivatives to a perfect differential, and a generalization of the numerical procedure developed in the earlier papers of this series that permits the integration of the transfer equation on these characteristics is presented. For cases in which V/c 1, a perturbation solution is developed which reduces the problem to that solved in the first paper in this series. For velocities of the form V(r) r (n = 0, 1, 2), it is shown that the magnitude of the effects arising from the advection and aberration terms is about 5 V/c relative to the solution with these terms omitted. In stellar winds V/c <% 0.01; hence we conclude that aberration and advection terms may safely be ignored, and that consideration of the Doppler-shift term alone is adequate in the computation of spectra from such expanding atmospheres. Subject headings: radiative transfer - stars: atmospheres Title: Structure and spectrum of quiescent prominences: energy balance and hydrogen spectrum. Authors: Heasley, J. N.; Mihalas, D. Bibcode: 1976ApJ...205..273H Altcode: In this paper we present theoretical models of quiescent prominences which satisfy the constraints of radiative, magnetohydrostatic, and statistical equilibrium. We obtain reasonable models only if we assume that the exciting ultraviolet radiation field can penetrate diffusely into the slab, or that there is a source of nonradiative energy input. The computed temperatures in our models are in good agreement with observational estimates. The models reproduce most observed features of these objects quite well, and should provide a good starting point to study further the formation of prominence spectra and the effects of nonradiative energy inputs. Title: Resonance-line transfer with partial redistribution. VIII. Solution in the comoving frame for moving atmospheres. Authors: Mihalas, D.; Shine, R. A.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1976ApJ...205..492M Altcode: The effects of partial frequency redistribution in the scattering process for lines formed in moving atmospheres are analyzed using a general method that allows the transfer equation to be solved in the comoving frame of the gas. The same chromospheric and atomic model studied by Cannon and Vardavas (1974) is employed in the calculations, but a depth scale with logarithmically spaced points is adopted. It is found that in both static and moving atmospheres, the profiles obtained with complete and partial frequency redistribution are virtually identical. The large differences in profiles obtained by Cannon and Vardavas when they used complete and partial redistribution are shown to be spurious (and physically unreal) effects resulting from angle averaging in the observer's frame instead of the comoving frame. Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. II. Picket-fence models. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1976ApJ...203..647M Altcode: To examine the effect of the radial flow of atmospheric material on the temperature distribution in a stellar atmosphere, a picket-fence model with Gaussian lines is formulated and solved numerically in the comoving frame of the gas, which is assumed to move with a prescribed velocity law. Extensive results have been obtained for both static and dynamical models, with planar and moderately extended spherical geometries. For static models, the effect of lines on the temperature distribution is virtually independent of extension. When a large-scale velocity field is imposed, significant surface heating and additional back-warming are found; the magnitude of these effects increases with the extension of the atmosphere. If a significant flow velocity persists to sufficient depth, the enhanced escape probability can lead to a cooling in the deeper layers, which competes with the back-warming. The results obtained here suggest that the deposition of energy arising from the intrusion of line opacity into the continuum, caused by velocity gradients, could influence the dynamics of the flow.- Title: Radiative transfer in expanding atmospheres Authors: Mihalas, D. Bibcode: 1976pmas.conf..347M Altcode: No abstract at ADS Title: Theory of stellar atmospheres (Théorie des atmosphères stellaires). Authors: Cayrel, R.; Mihalas, D. Bibcode: 1976IAUTA..16b.189C Altcode: No abstract at ADS Title: Solution of the comoving-frame equation of transfer in spherically symmetric flows. I. Computational method for equivalent-two-level-atom source functions. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1975ApJ...202..465M Altcode: A method for solving the line-formation problem using the full comoving-frame formulation of the radiative-transfer equation is presented for the case of spherically symmetric atmospheres expanding with arbitrarily large velocities. A stable differencing scheme and a frequency-by-frequency elimination procedure are developed to solve the partial differential equations that describe the radiation field in the comoving frame. It is noted that this method allows computation of the radiation field from a given model atmosphere which must specify the depth dependence of all the relevant physical variables. Numerical results obtained for several models involving line formation by two-level atoms, electron scattering, and continuous absorption are discussed which simulate situations in the stellar winds of hot stars and similar objects. The force exerted by radiation on the gas is examined in a number of situations, and flux profiles are described for very high-velocity flows with very weak or nonexistent continuum and electron-scattering opacities. It is concluded that the mechanism proposed by Noerdlinger and Rybicki (1974) for the destruction of radially driven envelopes in planar geometries becomes inoperative even in the case of slightly extended spherical configurations. Title: An Archetype Hydrogen Atmosphere Problem Authors: Athay, R. G.; Mihalas, D.; Shine, R. A. Bibcode: 1975SoPh...45...15A Altcode: Populations for the first three bound states and the continuum of hydrogen are determined for an isothermal, hydrostatic atmosphere at 20 000 K. The atmosphere is treated as being optically thin in the Balmer and Paschen continua and illuminated by continuum radiation at these wavelengths with prescribed radiation temperatures. The atmosphere is optically thick in the 2-1, 3-1, 3-2 and c-1 transitions. Three stages of approximation are treated: radiative detailed balance in the 2-1, 3-1 and 3-2 transitions, Title: Theory of extended stellar atmospheres. II. A grid of static spherical models for O stars and planetary nebula nuclei. Authors: Kunasz, P. B.; Hummer, D. G.; Mihalas, D. Bibcode: 1975ApJ...202...92K Altcode: Spherical static non-LTE model atmospheres are presented for stars from 30 to 60 solar masses at various points on their evolutionary tracks, and for some nuclei of planetary nebulae at two points of a modified Harman-Seaton sequence. The method of Mihalas and Hummer was employed, which uses a parametrized radiation force multiplier to simulate the force of radiation arising from the entire line spectrum. However, in the present work the density structure computed in the LTE models was held fixed in the calculation of the corresponding non-LTE models; in addition, the opacity of an average light ion was taken into account. The effects of sphericity, as distinct from those arising from a density structure modified by a large radiation force, were investigated by computing a few planar models using the same parametrized radiation force multiplier as for the spherical models. Extensive tables are given of monochromatic magnitudes, continuum jumps and gradients, Stroemgren-system colors, monochromatic extensions, and the profiles and equivalent widths of the hydrogen lines for all models. Title: Resonance-line transfer with partial redistribution. VII. Angle-dependent redistribution. Authors: Milkey, R. W.; Shine, R. A.; Mihalas, D. Bibcode: 1975ApJ...202..250M Altcode: A method is presented for treating radiative transfer in resonance lines, allowing for the full angle and frequency dependence of redistribution in the scattering process, as seen in the laboratory frame. The case of an equivalent-two-level-atom source function is considered; the problem to be treated is then linear in the radiation field. We apply this method to the Ca II lines in the solar atmosphere, using a redistribution function which takes into account a mixture of coherence in the atom's frame, with Doppler redistribution in the laboratory frame (for atoms which have not suffered an elastic collision), and of complete redistribution in the laboratory frame (for atoms that are collisionally perturbed during the emission process). Both the angle-averaged approximation and the full angle-dependent solution were obtained, and were compared to assess, differentially, the effects of angular redistribution upon the computed line profile and its center-to-limb behavior. For the Ca II line in a homogeneous solar chromosphere the angle-dependent effects are found to be negligible, indicating that one may use angle-averaged redistribution functions when studying partial redistribution effects in line profiles. Title: Resonance line transfer with partial redistribution. VI. The Ca II K-line in solar-type stars. Authors: Shine, R. A.; Milkey, R. W.; Mihalas, D. Bibcode: 1975ApJ...201..222S Altcode: Using model atmospheres for solar-type stars based on scaled temperature distributions, we discuss the effects of partial frequency redistribution on the Ca ii K-line profiles. We show that the partial redistribution calculations lead to a significantly lower intensity at K1 than given by calculations based on the assumption of complete redistribution. This implies that fits to observed fluxes with complete redistribution calculations could tend to underestimate systematically the value of the temperature at the chromospheric temperature minimum. Subject headings: chromospheres, stellar - line formation - radiative transfer Title: Resonance line transfer with partial redistribution. IV. A generalized formulation for lines with common upper states. Authors: Milkey, R. W.; Shine, R. A.; Mihalas, D. Bibcode: 1975ApJ...199..718M Altcode: A generalized formulation is given for treating partial redistribution effects in transfer problems in resonance lines with common upper states. The formulation allows explicitly for the possibility that several spectral lines may arise in transitions from a given upper level to several sharp lower levels, including, for example, the ground state and metastable states. Line profiles for the Ca II H and K lines have been calculated, accounting for the partial frequency coherence of scattered photons. These profiles are compared with calculations made with identical atomic and atmospheric models but assuming complete redistribution. Very significant differences between the profiles obtained using these two different physical descriptions of the scattering process are found, and it is now apparent that the assumption of complete redistribution is a serious oversimplification of the actual physical situation. The results question the validity of equating brightness temperatures observed at K1 in stellar spectra with minimum temperatures in stellar chromospheres; it appears likely that such a procedure will systematically underestimate the value of T-min. Title: Resonance Line Transfer with Partial Redistribution. V. The Solar CA II Lines Authors: Shine, R. A.; Milkey, R. W.; Mihalas, Dimitri Bibcode: 1975ApJ...199..724S Altcode: Line profiles for the Ca II H and K lines have been calculated, accounting for the partial frequency coherence of scattered photons. These profiles are compared with calculations made with identical atomic and atmospheric models but assuming complete redistribution. Very significant differences between the profiles obtained using these two different physical descriptions of the scattering process are found, and it is now apparent that the assumption of complete redistribution is a serious oversimplification of the actual physical situation. The partial sredistribution (PRD) results are in substantially better agreement with observation than the complete redistribution (CRD) profiles in describing (a) the center-to-limb behavior of the intensity at K1 and K2, (b) the center-to-limb behavior of the wavelength positions of K1 and K2, and (c) the relative behavior of the H and K profiles, as a function of wavelength, at disk center. Further, we find that we may match the observed absolute intensity at K1 with a minimum chromospheric electron temperature of about 4450 K, and that the HSRA temperature minimum is too low when partial redistribution effects are taken into account. This result raises questions about the validity of equating brightness temperatures observed at K1 in stellar spectra with minimum temperatures in stellar chromospheres; it appears likely that such a procedure will systematically underestimate the value of Tmin. Subject headings: chromosphere, solar - line formation - radiative transfer Title: INVITED - Solar and Stellar Spectroscopy. Authors: Mihalas, D. Bibcode: 1975BAAS....7..448M Altcode: No abstract at ADS Title: Solution of the Co-Moving Frame Equation of Transfer in Spherically Symmetric Flows. II. Picket-Fence Models. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1975BAAS....7..449M Altcode: No abstract at ADS Title: He I lambda 4922 profiles in B stars: calculations with an improved line broadening theory. Authors: Mihalas, D.; Barnard, A. J.; Cooper, J.; Smith, E. W. Bibcode: 1975ApJ...197..139M Altcode: Theoretical profiles for the He I A4922 line in B star spectra have been computed using the improved broadening theory of Barnard, Cooper, and Smith, and the level populations calculated by Auer and Mihalas from a simultaneous self-consistent solution of the coupled transfer and statistical equilibrium equations. The revised broadening theory yields excellent agreement with laboratory measurements of the width and intensity of the forbidden (2p ) transition. The results of this paper show that stellar profiles computed with the new theory are in excellent agreement with observed profiles, and the discrepancies between observation and theory that existed previously have now been removed. Subject headings: early-type stars - line profiles Title: Solution of the Co-moving Frame Equation of Transfer in Spherically Symmetric Flows. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1975BAAS....7R.256M Altcode: No abstract at ADS Title: Solution of the co-moving frame equation of transfer in spherically symmetric flows. Authors: Mihalas, D.; Kunasz, P. B.; Hummer, D. G. Bibcode: 1975BAAS....7..256M Altcode: No abstract at ADS Title: Calculations of Profiles for the CaII H and K Lines Including Partial Redistribution Effects Authors: Shine, R. A.; Milkey, R. W.; Mihalas, D. Bibcode: 1975BAAS....7Q.360S Altcode: No abstract at ADS Title: Effects of Departures from LTE and Atmospheric Extension on Colors and Theoretical Continuum Parameters Authors: Mihalas, Dimitri Bibcode: 1975mpth.conf..241M Altcode: 1975mpth.proc..241M No abstract at ADS Title: Erratum Resonance-Line Transfer with Partial Redistribution: a Preliminary Study of Lyman a in the Solar Chromospherer Authors: Milkey, W.; Mihalas, Dimitri Bibcode: 1975ApJ...195..831M Altcode: No abstract at ADS Title: A non-LTE model stellar atmosphere computer program Authors: Mihalas, D.; Heasley, J. N.; Auer, L. H. Bibcode: 1975STIN...7630128M Altcode: A computer program was developed for calculating model atmospheres of early-type stars subject to the constraints of radiative, hydrostatic, and statistical equilibrium, by means of a complete-linearization technique. This program is available through the NCAR High Altitude Observatory's Radiative Transfer Library. Title: Observations of the C III lambda 8500 (3s1S-3p1P) line in O and Of stars. Authors: Mihalas, D.; Frost, S. A.; Lockwood, G. W. Bibcode: 1975PASP...87..153M Altcode: Measurements from coude infrared image-tube spectra of the equivalent widths of the C iii A8500 (3s1S-3p1P0), Heii x10124 (n = 4- n = 5), and hydrogen P8 lines have been made for several 0 and Of stars, and are presented here. An attempt to measure the C ni xx9701-15 complex (3p3P0-3d3D) was thwarted by interference from telluric H20 absorption. The C iii x8500 line strengths provide useful constraints on possible theoretical models, and suggest, on the basis of the calculations of Nussbaumer (1971), that the C iii x5696 (3p2P0-3d'D) and x8500 lines are formed in relatively extended atmospheres, with a dilution factor 0.1. Key words: Of stars - stellar spectra - stellar atmospheres Title: Progress towards an interpretation of stellar spectra. Authors: Mihalas, D. Bibcode: 1974AJ.....79.1111M Altcode: Review of the changes which occurred over the last 10 to 15 years in the approach to the interpretation of stellar spectra, and discussion of the structure and physical assumptions of the underlying theory. The status of current research is examined, with special attention to the effects of departures from the assumption of LTE in stellar spectra, and to extended and expanding atmospheres. Promising areas of future research are pointed out. Title: Theory of extended stellar atmospheres. I. Computational method and first results for static spherical models. Authors: Mihalas, D.; Hummer, D. G. Bibcode: 1974ApJS...28..343M Altcode: A method is presented that makes possible, for the first time, the calculation of extended spherical non-LTE model stellar atmospheres in hydrostatic and radiative equilibrium. This method is a generalization of the complete-linearization technique of Auer and Mihalas. Models have been obtained for a star with 60 solar masses, 1,000,000 solar luminosities, and 24 solar radii, whose atmosphere is characterized by an effective temperature of 39,500 K and a surface gravity log g = 3.45, i.e., with a spectral type near O6. These models are differentiated by the magnitude and radial dependence of a radiation force multiplier that is inserted into the equation of hydrostatic equilibrium to simulate the effect of radiation force on opacity sources which have not been included explicitly in the calculation. Models have been obtained very close to the limit at which the radiation force and gravity balance; as this condition is approached, the atmospheres become more and more extended. Title: Resonance line transfer with partial redistribution: II. The solar Mg II lines. Authors: Milkey, R. W.; Mihalas, D. Bibcode: 1974ApJ...192..769M Altcode: Line profiles for the Mg II h and k lines have been calculated, accounting for the partial frequency redistribution of photons. These profiles are compared with the complete redistribution calculations under identical assumptions for the atomic and atmospheric models, and the inadequacy of the latter approximation is demonstrated. In particular, the temperature as deduced from the intensities at h1 and k1 under the assumption of complete redistribution appears to be a lower limit for the chromospheric temperature minimum. The partial redistribution profiles are in substantially better agreement with observation than complete redistribution results in describing the wavelength position of h1 and k1, and the relative behavior of the h and k profiles. Title: Theoretical Helium i Emission-Line Intensities for Quiescent Prominences Authors: Heasley, J. N.; Mihalas, Dimitri; Poland, A. I. Bibcode: 1974ApJ...192..181H Altcode: Self-consistent solutions of the combined statistical equilibrium and transfer equations have been carried out for a rather complete multilevel, multi-ion model helium atom in model quiescent prominences. The excitation and ionization of both He I and He ii were considered simultaneously, and detailed calculations of the radiative transfer in the resonance lines and ground-state continua of both these ions were made, allowing for the effects of overlapping hydrogen transitions. A large number of excited states have been included in the computation, so that a fairly comprehensive set of predicted subordinate line intensities are now available for comparison with observation. A preliminary comparison of the predicted values with published singleti triplet ratio observations shows good agreement for all the pairs of lines considered. Subject headings: atomic processes - line formation - prominences, solar Title: He I lambda 4471 profiles in B stars: calculation with an improved line-broadening theory. Authors: Mihalas, D.; Barnard, A. J.; Cooper, J.; Smith, E. W. Bibcode: 1974ApJ...190..315M Altcode: Theoretical profiles for the He I A4471 line in B-star spectra have been computed using an improved broadening theory of Barnard, Cooper, and Smith, together with level populations determined by a self-consistent solution by Auer and Mihalas of the coupled transfer and statistical-equilibrium equations. The broadening theory has been constructed to provide a more accurate description of the intensity and width of the forbidden (2p 3P0-4f 3F ) transition as measured in laboratory experiments. The results presented in this paper show that this revision of the broadening theory leads to computed stellar profiles which are in much better agreement with observed profiles than any previously obtained. Subject headings: early-type stars - line profiles Title: Some Observational Implications of Extended Static O-Star Model Atmospheres Authors: Mihalas, Dimitri; Hummer, David G. Bibcode: 1974ApJ...189L..39M Altcode: Some results and observational implications are presented for the first extended spherical non-LTE model atmospheres in hydrostatic and radiative equilibrium. These models all correspond to a star with = 60 , L = 1.25 X 106 Lo and R = 24 , with an effective temperature Te 39,500 K and surface gravity log g 3.45 (spectral type near 06). They are differentiated by the magnitude and radial dependence of a radiation-force multiplier , inserted into the equation of hydrostatic equilibrium, to simulate the effect of radiation force on opacity sources (e.g., lines) that have not been included in the calculations. It has been possible to obtain models very close to the limit at which the radiation force balances the gravity. Hydrogen and helium (`7= 0.1) constitute the gas; siz hydrogen lines are treated explicitly. These models show La in emission, the lower Balmer lines in absorption, the Balmer jump in absorption, and both infrared and ultraviolet excesses relative to the visual. Continuum jumps and gradients, -system colors, and equlvalent widths of Ha, Hp, and H are tabulated and discussed briefly. Subject headings: atmospheres, stellar - radiative transfer Title: The Effect of Partial Frequency Redistribution on the Formation of the Wings of Lyman-α Authors: Milkey, R. W.; Mihalas, Dimitri Bibcode: 1974BAAS....6U.291M Altcode: No abstract at ADS Title: Theoretical helium I emission line intensities for quiescent prominences. Authors: Heasley, J. N.; Mihalas, D.; Poland, A. I. Bibcode: 1974BAAS....6..219H Altcode: No abstract at ADS Title: Theoretical Helium I Emission Line Intensities for Quiescent Prominences. Authors: Heasley, J. N.; Mihalas, D.; Poland, A. I. Bibcode: 1974BAAS....6..220H Altcode: No abstract at ADS Title: Partial Redistribution Effects in the Solar Magnesium II Resonance Lines. Authors: Milkey, R. W.; Mihalas, D. M. Bibcode: 1974BAAS....6R.221M Altcode: No abstract at ADS Title: The N III Emission Lines in the Of Stars Authors: Mihalas, Dimitri Bibcode: 1973PASP...85..593M Altcode: Recent work has lead to an improved understanding of the physical mechanisms which produce the NIH emission lines in Of stars. The present status of the problem is briefly reviewed in this paper. Key words: Of stars - stellar spectra - emission lines Title: Calculation of the Solar Chromospheric Lα Profile Allowing for Partial Redistribution Effects Authors: Milkey, R. W.; Mihalas, Dimitri Bibcode: 1973SoPh...32..361M Altcode: No abstract at ADS Title: Resonance-Line Transfer with Partial Redistribution: a Preliminary Study of Lyman a in the Solar Chromosphere Authors: Milkey, R. W.; Mihalas, Dimitri Bibcode: 1973ApJ...185..709M Altcode: This paper presents a method for solving resonance-line transfer problems including a detailed treatment of the effects of partial redistribution. Calculations were madefor a schematic representation of La in the solar chromosphere. We find that the usual assumption bf complete redistribution leads to spurious estimates of number densities, the Lyman continuum, and the La profile, and thus we support the conclusions of Vernazza and of Vernazza, Avrett, and Loeser. Although we have made too many simplifications in the current computations to be able to compare with the observed La profile in detail, the differential behavior of our results for several cases supports the suggestion made in the papers cited above that the scattering in the La wing is well described as dominantly coherent. The methods developed here are easily extended to more realistic models and can be applied to many other lines of interest. Subject headings: chromosphere, solar - line formation - radiative transfer Title: On the helium-spectrum variations of 56 Arietis and a Centauri. Authors: Mihalas, D. Bibcode: 1973ApJ...184..851M Altcode: It is shown that the observed helium-line variations in 56 Ari and a Cen can be explained by a surface distribution involving two symmetrically placed helium-rich caps at the poles of an axis inclined at a large angle to the axis of rotation. It is proposed that this axis be identified with the symmetry axis of a magnetic field with both toroidal and poloidal components, similar to that analyzed by Mestel and Takhar, and it is argued that the surface distribution may be a natural consequence of such a field. Subject headings: magnetic stars - spectrum variables - stars, individual Title: Analyses of light-ion spectra in stellar atmospheres. V. Neon I in B stars. Authors: Auer, L. H.; Mihalas, D. Bibcode: 1973ApJ...184..151A Altcode: A detailed calculation, allowing fully for departures from LTE, for stars in the range B2 to B5 shows that the neon abundance deduced from LTE analyses is systematically in error by about a factor of five. The results obtained from the simultaneous self-consistent solution of the transfer and statistical equilibrium equations, for a realistic model neon atom, are in excellent agreement with observed Ne I equivalent widths at an abundance of log N(Ne) = 8.0, on the usual scale with log N(H) = 12.0. Thus the long-standing discrepancy between the stellar neon abundance and that found from solar, nebular, and cosmic-ray estimates is removed. Implications for nucleosynthesis and interior opacities are noted. Subject headings: abundances, stellar - atmospheres, stellar - early-type stars Title: Interpreting Early-Type Stellar Spectra Authors: Mihalas, Dimitri Bibcode: 1973S&T....46...79M Altcode: No abstract at ADS Title: Analyses of Light Ion Spectra in Stellar Atmospheres.IV. H II in the B Stars Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1973ApJS...25..433A Altcode: Results of an extensive set of computations of the He I spectrum in B stars, allowing for departures from LTE, using rather complete model atoms, non-LTE model atmospheres, and somewhat improved broadening theory, are presented and discussed. Among the major conclusions we derive are the following: (1) While departures from LTE alter equivalent widths but little in the blue- violet spectral region, their effects are quite large for lines in the visual-red region (e.g., A6678). (2) Very good agreement is obtained in the comparison of our calculated profiles with observed He iline profiles both in the wings and in the cores (except for some triplets at spectral types B0 and B1). (3) Some of the largest effects of departures from LTE occur at the highest and lowest effective temperatures, where the lines are relatively weak. (4) The usually quoted blue-violet singlet/triplet ratio is unaffected by departures from LTE to within the errors of observation. Other line ratios (e.g., A6678/A5876), however, are strongly affected. (5) The systematic wavelength-effect noted by Norris is explained. Good agreement is obtained with most of the conclusions of Johnson and Poland and Poland, though some significant differences arising from non-LTE effects in the model atmospheres are noted. The present results allow analysis for a much wider range of stellar spectral types and luminosity classes with a much higher level of physical consistency than hitherto possible. Subject headings: atmospheres, stellar - early-type stars - line formation Title: Analyses of light-ion spectra in stellar atmospheres. Authors: Mihalas, D.; Hummer, D. G. Bibcode: 1973ApJ...179..827M Altcode: An analysis of the N iii emission lines in 0 stars has been carried out on the basis of a detailed solution of the coupled statistical-equilibrium and transfer equations for a multiline, multilevel, multi-ion ensemble. Our calculations, using static, plane-parallel models reproduce successfully the observed emission at AA4634, 4640, 4641 (3p 2P -3d 2D) and absorption at AA4097, 4103 (3s 2S-3p 2P ). The multiplet is found to come into emission at the observed temperature for both main-sequence and low-gravity objects. The equivalent widths of the emission lines agree very well with those measured for the class of Of stars thought to have compact atmospheres, i.e., those classified as O((f)) by Walborn. In these stars the basic physical mechanism responsible for this phenomenon is the overpopulation of 3d by means of dielectronic recombinations from the low-lying 2s2p(1P )3d autoionizing states with cascades 3d 3p. The 3p state is drained by the "two-electron jumps" coupling 3p to the 2s2p2 (25, 2p, 2D) states, thus preventing emission in the 3s-3p lines. The possible importance of the Swings mechanism to the fully developed Of stars (in Walborn's sense) is pointed out, and the irrelevance of the Bowen mechanism to all Of stars is firmly demonstrated. The fact that the N iii emission lines can be produced in static nonextended atmospheres in radiative equilibrium has the far-reaching significance that the presence of emission lines in a spectrum is not in itself sufficient evidence for the existence of a stellar chromosphere (i.e., an extended, nonradiatively heated region). Subject headings: atmospheres, stellar - emission-line stars line formation Of-type stars Title: Analyses of light-ion spectra in stellar atmospheres. II. The calcium II K-line in B stars. Authors: Mihalas, D. Bibcode: 1973ApJ...179..209M Altcode: A calculation of the Ca ii K-line strength in the middle B stars has been performed by means of a self-consistent solution of the equations of transfer and steady-state statistical equilibrium. The multilevel model ion, with many explicitly computed bound-bound transitions, is treated as part of a multi-ion system (Ca ii, Ca iii, Ca iv). Results are given for two abundances and microturbulent velocities, and are used to assess systematic errors in LTE diagnostics of these parameters. Near the main sequence for the middle B stars the results show that departures from LTE have a negligibly important effect on the K-line equivalent width, but at higher temperature and lower gravities these departures become ever more important, and in the extreme cases can result in errors in the abundance deduced from LTE of a factor of five, or spurious micro turbulent velocities of up to 3 km 5 - . These effects are less spectacular than those found earlier by the author for Mg ii, but insofar as the K-line is at all typical of a line of comparable strength in these stars, the results may have fartherreaching implications of errors in the usual LTE diagnostics. A discussion of the K-line strengths in L Her and y Peg indicates that they are compatible with a Ca abundance in these stars equal to the solar abundance. Subject headings: abundances, stellar - atmospheres, stellar - early-type stars - line formation Title: The Effects of Departures from LTE in Stellar Spectra Authors: Mihalas, Dimitri; Athay, R. Grant Bibcode: 1973ARA&A..11..187M Altcode: No abstract at ADS Title: Analyses of Light-Ion Spectra in Stellar Atmospheres. I. Magnesium II in B and O Stars Authors: Mihalas, Dimitri Bibcode: 1972ApJ...177..115M Altcode: A calculation of the spectrum of Mg ii in B and 0 stars, using a rather complete model atom allowing for many explicitly calculated transitions in steady-state statistical equilibrium, has been performed. These computations give a good fit to tbe observed equivalent widths of the A4481 line on the entire range from B5 through 06, assuming a solar abundance for magnesium. In contrast, for the earliest spectral types, the LTE predictions fit the data poorly, and are shown to yield abundances systematically in error by an order of magi'itude or more. These results open again serious questions concerning the validity of LTE abundances for at least the 0 and early B stars, and suggest strongly that further analyses are needed to delineate the ions and spectral types for which the LTE assumption fails. Title: Non-Lte Effects on Continuum and Hydrogen-Line Parameters in B and O Stars Authors: Mihalas, Dimitri Bibcode: 1972ApJ...176..139M Altcode: Using a homogeneous set of non-LTE models (which allow for bound-bound transitions) on the range 15 000 < < 55,000 K at several gravities, the effects of departures from LTE upon the continuum and Balmer lines are evaluated. Several observational discriminants of non-LTE effects are discussed; in certain specific examples considered, the available data are well fitted by the non-LTE calculations. Title: Observations of the he II λ10124 Line in O and of Stars Authors: Mihalas, Dimitri; Lockwood, G. W. Bibcode: 1972ApJ...175..757M Altcode: Observed equivalent widths of He ii X10124 in absorption-line 0 stars are found to be in agreement with non-LTE computations assuming no overlap of II and He ii lines, and in disagreement with the predictions of LTE and of non-LTE calculations assuming exact coincidence of even-even He ii lines and the corresponding hydrogen lines. it is therefore inferred that pumping of He ii transitions by H lines does not actually occur in the 0 stars. The discovery of the l0124 line in emission in Pup (0Sf) argues further in this direction; and with the often-cited selectivity of the He ii emission mechanism now much weakened, it is suggested that the causes of the emission must involve chromospheric phenomena. Analysis of source-sink terms in equivalent- two-level-atom source functions suggests trends that are compatible with the observed behavior of various lines. Title: ON THE N III λλ4640, 4097 LINES IN Of STARS Authors: Mihalas, Dimitri; Hummer, D. G.; Conti, Peter S. Bibcode: 1972ApJ...175L..99M Altcode: Detailed calculations based on non-LTE plane-parallel model atmospheres show that the N iii emission lines at XX4634, 4640, 4641 observed in Of stars are produced primarliy by dielectronic recombination to 3d 3D followed by the 3d-3p transition in a compact atmosphere. The 3P state in turn is drained by two-electron transitions to the 2p2 levels. We find that X4640 is in emission for Teff < 37,0000 K for main-sequence objects (55,0000 K for giants), while X4097 remains strongly in absorption, in accordance with observations. The calculated equivalent widths are in substantial agreement with the observed values for those Of stars with He II X4686 in absorption, i.e., for those objects designated by Walborn as O((f)). Title: INVITED PAPER Recent Progress in the Interpretation of Band O Star Spectra. Authors: Mihalas, D. Bibcode: 1972BAAS....4..333M Altcode: No abstract at ADS Title: Non-Lte Model Atmospheres. VII. The Hydrogen and Helium Spectra of the O Stars Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1972ApJS...24..193A Altcode: An extensive series of non-LTE calculations of the H, He I, and He II spectra of 0 stars has been carried out by using relatively complete atomic models, allowing for several levels and lines simultaneously. Results are presented for continuum fluxes and for equivalent widths and profiles of the lines. Detailed comparisons are made with the spectra of eleven 0 and B0 stars. It is found that major departures from LTE play a dominant role in the formation of the H and He spectra of these stars. With the non-LTE models we are able to obtain for the first time a consistent explanation of the observations of both lines and continua. The present results show that an assumed helium/hydrogen ratio of 0.10 reproduces the observations; thus present estimates of abundances in 0 stars helium are consistent with those derived by other methods. Title: Non-LTE model atmospheres for B and O stars. Authors: Mihalas, D. Bibcode: 1972nmab.book.....M Altcode: No abstract at ADS Title: A Comment on the Interpretation of the Broad Component of N III λλ4634-4640 Emission in of Stars Authors: Mihalas, Dimitri Bibcode: 1971ApJ...170..541M Altcode: The stabilizing transition from the N iii autoionizing term 2s2p(1P0)3d 2F to the bound double- excitation term 2s2p(1P0)3p 2D gives rise to a very broadened doublet at the wavelengths 4623 and 4630 A. A study of the rate at which the process occurs suggests that this stabilizing transition may appreciably contribute to the broad emission ("band") component near 4634-4640 as observed by Wilson and Underhill. It further appears that dielectronic recombination to the 2s23d level from 2s2p (LP0)3d via the 2s2p H 2s2 stabilizing transition occurs at a rate sufficiently large to outweigh direct radiative recombinations and at a substantial fraction of the decay rate of 2s23d H 2s23p; this process may therefore play an important role in producing the "line" component of the N iii x4634-4640 emission. Title: Theoretical analysis of stellar spectra. Authors: Mihalas, D. Bibcode: 1971tsa..conf....1M Altcode: No abstract at ADS Title: On the excitation mechanism of M emission in the Of stars Authors: Brucato, Robert J.; Mihalas, Dimitri Bibcode: 1971MNRAS.154..491B Altcode: A simplified statistical equilibrium calculation has been carried out to examine the mechanism of the N iii AA 4634-41 emission in Of stars. It is shown that the Swings mechanism, based on pumping in the ultra-violet AA 374 and 452 transitions is probably correct, while the Bowen mechanism, applicable in nebulae, is almost certainly not operative in the Of stars. The possible importance of dielectronic recombinations to the 3d state is pointed out. Title: Theoretical Analysis of Stellar Spectra Authors: Mihalas, D. Bibcode: 1971tdas.conf....1M Altcode: 1971SAAS....1....1M Basic Concepts and Assumptions The goals of stellar atmospheres analysis The specification of the state of the atmosphere Basic definitions Conservation relations Formulation and Solution of Transfer Problems Formal solution Solution by integral-equation methods Iteration Direct methods Solution by differential-equation methods The eigenvalue approach The Riccatti transformation (Rybicki's method) Difference equation methods (Feautrier's method) Difference equation methods : Rybicki's Variant The Equations of Statistical Equilibrium The microscopic implications of LTE The rate equations Limiting cases Opacity and emissivity Continuum - Formation Problems Solution by iteration Simultaneous solution of the transfer and statistical equilibrium - problem The constraint of radiative equilibrium Line-Formation : the Two - Level Atom Without continuum - thermalization lengths With continuum - collision domination and photoionization domination Line-Formation : the Multi-Level Problem Equivalent two-level-atom approach Multiplets, conversion lengths, source function equality The complete linearization method A Survey of Non-LTE Effects in Early-type Stars Survey of results in the continuum for A,B, and O-stars The hydrogen lines in the B-stars The hydrogen-helium spectrum of the O-stars Title: Theorie des atmospheres stellaires Authors: Mihalas, D.; Pagel, B.; Souffrin, P. Bibcode: 1971tdas.conf.....M Altcode: 1971QB809.M52......; 1971tsat.book.....M; 1971SAAS....1.....M No abstract at ADS Title: Non-Lte Model Atmospheres.VI. Limb Darkening and Rotation Broadening of H&alpha Authors: Mihalas, Dimitri; Auer, L. H. Bibcode: 1970ApJ...161.1129M Altcode: The center-to-limb variation and rotation broadening of Ha are discussed for LTE and non-LTE atmospheres. The center-to-limb variation is quite different in these two cases; these differences should be measurable by observations of certain eclipsing-binary systems, and such observations could provide a sensitive test of the theory. It is also shown that (a) significant differences exist between rotationbroadened profiles in the LTE and non-LTE cases and (b) Ha may serve as a useful indicator of rotation velocity. Title: Erratum: Constant-Flux Convective Model Atmospheres Authors: Mihalas, Dimitri Bibcode: 1970ApJ...161..375M Altcode: No abstract at ADS Title: A Comment on 'Far Ultraviolet Photometry of Orion Stars' by G. R. Carruthers Authors: Mihalas, Dimitri Bibcode: 1970Ap&SS...8...50M Altcode: It is shown that the ultraviolet flux-deficiency, recently discovered by Carruthers, in early-type supergiants compared to dwarfs of the same spectral type can be explained in terms of the effects of differences in surface-gravity and effective temperature between stars of these two luminosity classes. It thus appears that this deficiency does not represent a serious discrepancy between theory and observation. Title: Non-Lte Model Atmospheres. V. Multi-Line Hydrogen-Helium Models for O and Early B Stars Authors: Mihalas, Dimitri; Auer, L. H. Bibcode: 1970ApJ...160.1161M Altcode: Results of calculations of non-LTE model atmospheres including the effects of La, L , L , Ha, Hp, and Pa are presented for models on the range 250000 K < < 50000 K, with log g = 4 and N(He)/ N(H) = 0.10. The non-LTE results suggest a severe breakdown of LTE at T0ff > 350000 K. Substantial changes occur in the far-ultraviolet fluxes; these may be of importance in the interpretation of the excitation of emission nebulae. In the visible, the Balmer jump is significantly increased by non-LTE effects for models with T0ff > 350000 K, which implies large changes in effective temperatures for 0 stars inferred from observations of the Balmer jump. Striking changes occur in the hydrogen-line profiles. Vhen non-LTE effects are included, Ha and Hp are computed to be almost 3 times as strong at 400000 K as in LTE. Pa is found to have an emission core in the highest-temperature models. This result is analogous to the situation at lower temperatures where Ba is computed to go into emission. In both cases the emission core is due to coupling to a rise in surface temperature in the non-LTE models; observations are desirable to test the reality of this predicted effect. Title: Non-Lte Model Atmospheres.IV. Results for Multi-Line Computations Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1970ApJ...160..233A Altcode: Results are presented for model atmospheres in hydrostatic, radiative, and steady-state statistical equilibrium, including bound-bound transitions. These calculations allow for the effects of Ha, HP, H , Pa, PP, and Ba. Stark profiles of Edmonds, Schinter, and Wells are used to compute detailed line profiles. With the full non-LTE calculation we have been able to predict correctly the entire line profile, including the line core. The wings of Ha are found to weaken while those of H remain unaffected by departures from LTE. Non-LTE effects strengthen the Paschen lines so that comparison of Paschen lines with Balmer lines should provide a sensitive observational indicator of departures from LTE. Ba has an emission core, because of a rise in surface temperature, and may be a useful diagnostic tool in the analysis of real stellar atmospheres. The surface-temperature rise found in earlier work persists, the boundary temperature differing little from that obtained by allowing for Ha, HP, and Pa only. The energy distribution in the continuum is little affected by departures from LTE, except at very low gravities and in the unobservable Lyman continuum. Title: Model atmospheres for the central stars of planetary nebulae. Authors: Hummer, D. G.; Mihalas, D. Bibcode: 1970MNRAS.147..339H Altcode: Approximately 70 model atmospheres for the central stars of planetary nebulae have been computed under the assumptions of hydrostatic, radiative and local thermodynamic equilibrium and of stratification. These models have effective temperatures and surface gravities in the range and log . The atmospheres have been taken to consist of hydrogen, helium, oxygen, nitrogen, carbon and neon, and the opacity included contributions from both ground and excited states of each ion. The transfer equation is solved using Feautrier's method and the temperature corrections are calculated by means of the Krook-Avrett procedure. Particular attention is given to the effects of gravity and chemical composition on the surface fluxes. The photon fluxes in the H I, He I and He ii continua and the stellar flux at H have been tabulated for use in the determination of Zanstra temperatures. Title: On the use of variable Eddington factors in non-LTE stellar atmospheres computations Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1970MNRAS.149...65A Altcode: It is shown that by use of variable Eddington factors, the accuracy of differenceequation solutions of transfer problems may be greatly improved with only small additional computational effort. It is found that a direct iterative calculation of the Eddington factors leads to a strongly convergent procedure. The resulting set of equations is of wide applicability to problems involving non-coherent radiative transfer. The method is illustrated by application to the classical grey problem, and to a non-LTE stellar atmospheres computation. Title: Stellar atmospheres Authors: Mihalas, Dimitri Bibcode: 1970stat.book.....M Altcode: 1970QB809.M5....... No abstract at ADS Title: Non-Lte Model Atmospheres. III. a Complete-Linearization Method Authors: Auer, Lawrence H.; Mihalas, Dimitri Bibcode: 1969ApJ...158..641A Altcode: In this paper we present a method of solving transfer prob'ems subject to constraints of radiative, hydrostatic, and statistical equilibrium, by using a complete-linearization technique. This approach de- parts rather markedly from the traditional methods, and yields a computational scheme that is stable and strongly convergent. The form of the equations assures that the coupling among all physical variables is fully accounted for self-consistently to first order at each stage of the calculation; convergence is global and quadratic. The constraint equations are included in a particularly transparent way, which allows easy generalization and elaboration. Sample models of pure-hydrogen atmospheres are presented; among these, one includes Ha, H~3, and Pa self-consistently with the continua. Models that were obtained only with great effort by using earlier techniques have been recomputed with no hint of difficulty by using the method described in this paper Title: The Effects of Line Shifts on the Temperature Distribution in Stellar Atmospheres Authors: Mihalas, Dimitri Bibcode: 1969ApJ...157.1363M Altcode: No abstract at ADS Title: Brackett-Alpha Emission in Non-Lte Model Stellar Atmospheres Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1969ApJ...156L.151A Altcode: Recent computations of non-LTE model stellar atmospheres predict the appearance of Brackett- a (Ba) in emission. This line at 4.05 ~& lies in a window of the absorption spectrum of the terrestrial atmosphere and should be observed as a test of this theoretical prediction Title: A Possible Mechanism for Energization of Stellar Winds in Early-Type Stars Authors: Mihalas, Dimitri Bibcode: 1969ApJ...156L.155M Altcode: Expanding envelopes observed in early-type supergiants (and other related stars) are suggested to be stellar winds energized by the mechanical-energy flux produced in a Rayleigh-Taylor instability zone in the photospheres of these stars Title: Non-Lte Model Atmospheres. II. Effects of Balmer α Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1969ApJ...156..681A Altcode: Four models of pure-hydrogen stellar atmospheres in radiative equilibrium with Teff = 15000 and log g = 4 are presented. Results are given for both the LTE and non-LTE cases, with and without the inclusion of Ha. The calculations show that (a) Ha causes a temperature rise, not a drop, at the surface, (b) the direct effect of cooling in the line is less important than the indirect effects of changing level popu- lations, and (c) the Balmer and Paschen jumps are unaltered by non-LTE effect Title: Non-Lte Model Atmospheres. I. Radiative Equilibrium Models with - Alpha Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1969ApJ...156..157A Altcode: We present models of stellar atmospheres of pure hydrogen in hydrostatic, radiative, and statistical equilibrium, including for the first time Lyman-a as well as continua. Only by the direct inclusion of Ly-a may we properly evaluate the effect of this strong line on the structure of the atmosphere. A new temperature-correction scheme was used. It is of the constraint type, is capable of handling very large opacity variations, and guarantees vanishingly small flux derivatives. The model atom assumed the upper fourteen levels in LTE, but permitted non-LTE deviations in the lower two levels. This model was suffi- cient to show that: (a) non-LTE effects from the continua cause a temperature rise at the surface; (b) this rise is partially offset by the inclusion of Ly-a, which causes a temperature drop, the non-LTE drop being very much smaller than the LTE; (c) Ly-a is so optically thick that it does not affect the formation of even the Lyman continuum; and (d) there is essentially no back-warming due to Ly-a in either the LTE case or the non-LTE case Title: Review of Publications- Galactic Astronomy Authors: Mihalas, Dimitri Bibcode: 1969JRASC..63...48M Altcode: No abstract at ADS Title: Non-LTE Model Atmospheres Authors: Auer, L. H.; Mihalas, D. Bibcode: 1969tons.conf..229A Altcode: No abstract at ADS Title: Line Formation with Non-Coherent Scattering by Electrons. II. Calculations with Model Atmospheres Authors: Auer, Lawrence H.; Mihalas, Dimitri Bibcode: 1968ApJ...153..923A Altcode: The effect of non-coherent scattering by electrons and atoms on line formation in early-type stars has been studied using model atmospheres. Variability of the physical parameters has been fully in- cluded. The effect of the non-coherency of the scattering by electrons is noticeable for a line like He ii X4200 but not for a much stronger one like He ii X4686. The solution in the core is dominated by the degree to which scattering (by atoms) occurs, while the wings are unaffected. The observed profile of He ii X4686 in 10 Lac can be fitted if the core of the line is deepened by scattering and broadened by rotation Title: Statistical Equilibrium Model Atmospheres for Early-Type Stars.IV. Remarks on Observational Tests Authors: Mihalas, Dimitri Bibcode: 1968ApJ...153..317M Altcode: A comparison is made between LTE and non-LTE models and observation following the approach of Strom and Kalkofen. It is found that near the main sequence the two sets of models are nearly indis- tinguishable but that large effects exist at lower gravities. The importance of very accurate values for the absolute-energy calibration of stars is emphasized Title: Line Formation with Non-Coherent Scattering by Electrons. I. Parameterized Models Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1968ApJ...153..245A Altcode: We examine in this paper the effects of the non-coherence of the radiation scattered by electrons upon the formation of spectral lines A flexible numerical approach, making use of the difference-equation meth- od of solving the transfer equation, is developed and applied to simplified models in which the lines are taken to be either in LTE or non-LTE, and allowance is made for electron scattering and continuous absorption. Radiation scattered by the atom is assumed to be completely redistributed, although the method is general enough to account for arbitrary redistribution functions. The present calculation dif- fers from earlier work in that the electrons are assumed to be located in the same layers as the line and continuum opacity sources Compared to the case of coherent electron scattering, measurable changes in the line profile occur if the electron-scattering coefficient outweighs continuum absorption. Emission lines are decreased slightly in intensity and develop extensive emission wings. Absorption lines are widened and deepened, and emission humps are obliterated Title: Solution of Transfer Equations Subject to the Constraint of Radiative Equilibrium Authors: Auer, L. H.; Mihalas, Dimitri Bibcode: 1968ApJ...151..311A Altcode: A method is proposed for solving transfer equations subject to the constraint of radiative equilibrium. The approach uses the differential-equation form of the transfer equation and thus allows easy generaliza- tion. A description is given of the equations and boundary conditions, and results for gray and non-gray cases are discussed. We obtain rapid convergence at all depths It appears that this method should be effective in non-LTE cases, though in practice it may be limited by the size of matrix that can be inverted economically. I. INTRODUCTIO Title: Galactic astronomy Authors: Mihalas, Dimitri; Routly, Paul Mcrae Bibcode: 1968gaas.book.....M Altcode: 1968QB857.7.M53.... No abstract at ADS Title: Statistical Equilibrium Model Atmospheres for Early-Type Stars. III. Hydrogen and Helium Continua Authors: Mihalas, Dimitri; Stone, Michael E. Bibcode: 1968ApJ...151..293M Altcode: Results are presented for model atmospheres allowing for departures from LTE in hydrogen, helium, and ionized helium on the temperature range 100000 K «= Teff «= 360000 K. The essential simplifying assumption we make is that all radiative bound-bound transitions are in detailed balance. While this assumption is valid in certain physical circumstances, it is not everywhere correct, and the results de- rived here should be regarded as oniy exploratory As was the case in earlier results, the departures we find are quite small and have only small effects upon the emergent energy distribution, so that LTE appears to be a fairly adequate approximation in the calculation of the continuous energy distribution. No information concerning line formation can be inferred from the present results Title: Erratum: Statistical-Equilibrium Model Atmospheres for Early-Type Stars. I. Hydrogen Continua Authors: Mihalas, Dimitri Bibcode: 1967ApJ...150.1168M Altcode: No abstract at ADS Title: Statistical-Equilibrium Model Atmospheres for Early-Type Stars. II. Formation of the Lyman Continuum Authors: Mihalas, Dimitri Bibcode: 1967ApJ...150..909M Altcode: Results are presented for model atmospheres which allow for deviations from LTE in the first ten bound states of hydrogen. Particular attention is given to the problem of solving the transfer equation in the Lyman continuum, using the approach of introducing the appropriate statistical equilibrium equation explicitly into the expression for the source function. The solution is carried out using Feautrier's method which treats the transfer equation directly in its differential equation form. Full variation with depth and frequency of all relevant parameters is allowed. The present solutions are not yet fully physically realistic since transfer in the bound-bound transitions is not included. From the present work, however, it appears that use of Feautrier's method will allow the treatment of the complete problem. Title: Line Formation with Non-Coherent Electron Scattering in O and B Stars Authors: Hummer, D. G.; Mihalas, D. Bibcode: 1967ApJ...150L..57H Altcode: No abstract at ADS Title: Statistical-Equilibrium Model Atmospheres for Early-Type Stars. I. Hydrogen Continua Authors: Mihalas, Dimitri Bibcode: 1967ApJ...149..169M Altcode: Model atmospheres have been constructed for selected effective temperatures and gravities appropriate to early-type stars, allowing in an approximate way for deviations from LTE in the first ten bound states of hydrogen The essential approximation involved is the assumption of radiative detailed balance in the lines, which seems valid in the region of continuum formation. The resulting models are thought to be adequate for interpretation of the observed energy distribution of stars but cannot be used for discussions of line profiles We find that the deviations from LTE are quite small and that the predicted fluxes agree closely with those of LTE models. Title: The Calculation of Model Stellar Atmospheres Authors: Mihalas, Dimitri Bibcode: 1967MComP...7....1M Altcode: No abstract at ADS Title: Fine Analysis of the Manganese Star 53 Tauri Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E. Bibcode: 1967mrs..conf..433A Altcode: No abstract at ADS Title: The Manganese Star 53 Tauri. II. Fine Analysis Authors: Auer, L. H.; Mihalas, D.; Aller, L. H.; Ross, J. E. Bibcode: 1966ApJ...145..153A Altcode: An abundance analysis of the manganese star 53 Tauri is carried out making use of a model atmosphere with 0 = 0.413, log g = 3.5, N(He)/N(H) = 0.15. The model reproduces the observed hydrogenline profiles with good accuracy. The abundance analysis shows that all of the metals ligbter than titanium have normal abundance. Helium is found to be underabundant by a factor of 5, so that N(He)/ N(H) = 0.03, and the effective gravity accordingly becomes log g = 3.62. From titanium onward, the elements show large overabundance factors, except for iron and chromium, both of which are normal. Manganese is found to be 120 times overabundant; this value is based on both Mn I and Mn ii lines (the two ions giving good agreement), making use of new laboratoryJ-values for Mn ii. Title: Balmer-Line Model Atmospheres for A-Type Stars Authors: Mihalas, Dimitri Bibcode: 1966ApJS...13....1M Altcode: Results are reported for computations of a grid of model atmospheres for A stars which take into detailed account the effects of blanketing by hydrogen lines. The models are in radiative equilibrium and allow explicitly for Ha through H20. Tables of emergent fluxes are presented which allow detailed comparisons with observations. Colors computed for these models agree very well with those obtained observationally for main-sequence stars after the effects of metal-line blanketing are removed. An effective-temperature scale is derived for main-sequence stars of classes B8 to F2, which is in satisfactory agreement with fundamental interferometer measures and Popper's scale. A detailed comparison is made with the absolute-energy distribution of Vega. From the observed H profile and energy distribution in the visible we obtain log g = 4 and 0, = 0.525 (T, = 9600 K). It is found that the Balmer jump for the model is larger than the value now accepted in Code's and Oke's energy distributions, but is in very good agreement with Bahner's measurement. It is suggested that Bahner's result be seriously considered in future work. Finally we find fairly good agreement between the observed number of Balmer lines visible as a function of spectral class and the computed number, although this result holds only statistically. Title: Studies of the Peculiar a Stars. III. Model-Atmosphere Line-Strength Calculations with Application to the A_{p} Stars Authors: Mihalas, Dimitri; Henshaw, James L. Bibcode: 1966ApJ...144...25M Altcode: Calculations are carried out to obtain accurate curves of growth for selected lines of C ii, Mg ir, 0 1, Si ii, and Si iii using model atmospheres. The results are given for a wide range of effective temperatures and gravities for the models and of assumed abundances for the lines; these results should be applicable to abundance analyses for stars on the range of about B3 to F2. As an example of application we rediscuss the observations of Ap stars published by Sargent and Searle, and find good agreement with their results which were based on less elaborate techniques. We derive new information from X 4200 of Si ii and from the C ii lines. We find that the infrared lines of Mg and 0 are observed too strong according to our calculations, and suggest that turbulent motions may be present in the outer atmospheric layers where these lines are formed. Title: A Model for a BI V Star with Line Blanketing. Authors: Mihalas, Dimitri M.; Morton, Donald C. Bibcode: 1965ApJ...142..253M Altcode: A model in radiative equilibrium has been computed for log g = 40, T = 21914 K (0 = 0.23), taking into account the blanketing by the strongest lines in the ultraviolet where the majority of the flux emerges (911 6 < X < 1600 A) it was found that the visible spectrum closely resembles that of an un- blanketed model with log g = 4 0, T = 24001 K (0 = 0 21) Both models were classified at B1 V on the basis of the Balmer discontinuity. Thus at this spectral type the effective temperature assigned on the basis of the unblanketed model was too high by nearly 2100 K. The bolometric correction was estimated to be -200 mag for the blanketed model as compared with -240 mag for the unbianketed one of the same spectral type Details of the model are given in tabular form and the emergent flux distribution is shown graphically. Title: Model Atmospheres and Line Profiles for Early-Type Stars. Authors: Mihalas, Dimitri Bibcode: 1965ApJS...11..184M Altcode: No abstract at ADS Title: Constant-Flux Convective Model Atmospheres. Authors: Mihalas, Dimitri Bibcode: 1965ApJ...141..564M Altcode: Modtl atmospheres have been constructed using the mixing4ength theory to describe the convective transport of energy. The condition of flux constancy is enforced allowing for the simultaneous energy transport by convection and non-gray radiative processes, using a modification of the temperature-correction procedure proposed by Avrett and Krook. The modified equations allow for the convection terms explicitly and, in a more general sense, show that the Avrett-Krook procedure provides a powerful formalism for enfordng the condition of flux constancy in the presence of non-radiative terms. A grid of models has been constructed on the range 0.5 < 0 < 0.7 and 2 < log g < 444 assuming (1/H) = land (t/H) = 2. It is found that the presence of convection produces substantial changes in the structure of the atmosphere at depth, while the overlying radiative layer is virtually unchanged. The emergent flux distribution in the continuum and line profiles are examined with the view of obtaining a criterion for distinguishing convective models from radiative, and the two assumed mixing lengths from one another It is found that only the emergent flux in the rocket or satellite ultraviolet provides such a measure in the sense that the ultraviolet fluxes are appreciably smaller for the convective models. The profiles of HT computed for the convective models differ from those for the radiative models by less than 1 or 2 per cent in all but a few cases, and thus do not provide a clear criterion for establishing convection On the other hand, it is found that in the convective models lines from certain neutral metals may be strengthened relative to the ionic lines, compared to the radiative models. A more detailed solution of the statistical equilibrium equations should be carried out to confirm this conclusion. Title: An Archetype Non-Gray Stellar Atmosphere. Authors: Gingerich, Owen; Mihalas, Dimitri; Matsushima, Satoshi; Strom, Stephen Bibcode: 1965ApJ...141..316G Altcode: No abstract at ADS Title: Model Atmospheres and Line Profiles for Early-Type Stars. Authors: Mihalas, Dimitri Bibcode: 1965ApJS....9..321M Altcode: Model atmospheres have been constructed over a wide range of temperature and gravities. The condition of radiative equilibrium is enforced using a modification of the temperature-correction scheme devised by Avrett and Krook, thus extending the work of Gingerich to the realm of higher temperatures; flux constancy is attained to within 10.5 per cent to a depth of TSTD = 10 or more, the standard wave- length being either X 400() or X 5050. The source function is determined from the Milne-Eddington equation allowing for coherent scattering in the continuum. The properties of the atmospheres are described and given in detailed tabular form, and data of rather general use is presented. For each model we have computed H and H profiles and equivalent widths, and for the hotter models, profiles and equivalent widths of XX 4686, 4200, 4542, 5412 of He ii, and XX 5876, 4713, 38, and 4121 of He 1. When necessary, allowance has been made in the computation of the hydrogen-line profiles for the overlapping Pickering-series lines of He ii. Complete profiles are given for the hydrogen lines because of their great practical utility, but only equivalent widths are tabulated for the helium lines. Title: A Spectroscopic Estimate of the Atmospheric Properties of O and B Stars. Authors: Mihalas, Dimitri Bibcode: 1964ApJ...140..885M Altcode: Equivalent widths of lines in the spectra of six 0 stars were measured using the coude' scanner of the 100-inch telescope. These data and those in the literature for r Sco are fitted to theoretical line-strength calculations in an attempt to derive the effective temperatures, gravities, and helium abundances of these stars. It is found that the effective temperatures and gravities are well determined, while the helium abundance can be estimated only with fair accuracy; it appears that the best estimate for N(He) /N(H) is about 0 15 or 0.2. Comparisons are made between the computed and observed profiles for X 4686 in Sco and 10 Lac; a good fit with the 10 Lac observations can be obtained only with a turbulent velocity of the order of 20 km/sec. Title: The Abundance of Magnesium in the Atmospheres of O and B Stars. Authors: Henry, Richard C.; Mihalas, Dimitri Bibcode: 1964ApJ...140..873H Altcode: Equivalent widths have been computed for the ionized magnesium line X 4481 using flux-constant models and accurate numerical techniques. Several abundance steps have been taken for each model; the models have temperatures appropriate to stars in the range of O9 V to A2 V. Fits are made to the mean observed line strength as a function of spectral type as obtained from data in the literature. A nearly constant mean value of N(Mg)/N(H) = 2.2 X t0- is derived over the range of spectral types of B1 to A2; a larger value is obtained for B0 and O9 stars, but this is thought to be spurious. This analysis reaffirms the discrepancy between solar and B-star Mg abundance. Title: Photoelectric Equivalent Widths in ρ Leo and π4 ORI. Authors: Mihalas, D. Bibcode: 1964ApJ...139..764M Altcode: No abstract at ADS Title: Model Atmosphere Studies of Early Type Stars. Authors: Mihalas, Dimitri Bibcode: 1964AJ.....69S.144M Altcode: A sequence of model atmospheres has been constructed on the range 0.1<0 < 0.7 using an IBM 7090. The source function is given by the Milne-Eddington equation, which allows for coherent scattering. Flux constancy is enforced to +0.5% or better by use of the Krook-Avrett procedure (Avrett, F. H., and Krook, M., A strophys. J. 137, 874,1963), which has been modified simply to allow for scattering terms; this procedure is stable and quickly convergent. The opacity consists of absorption by H, H-, He I, He ii, and H2+, Thompson scattering by free electrons and Rayleigh scattering by neutral H. We took account of the temperature and pressure dependence of the partition functions in the ionization equilibrium of H and He. Neither the effects of lines nor departures from LTE are accounted for. For 0.45<Oe<0.7, models were made with 1~<log g<4.44 while for 0.1<Oe<0.4 they were made with log g=3.5, 4.0, and 4.5, all assuming N(He)/N(H) = 0.15. At the higher temperatures sequences were made with changes in the assumed helium abundance. H~ and H~ profiles were computed using Griem's Stark broadening theory, and for the hotter models we computed the profiles of HeiX5876, X4438, X4121 and Hell X5412, X4686, X4542, and X4200. The computed line strengths have been fitted to observations of six 0-type stars, made with the photoelectric spectrum scanner at the coudk of the 100-in. telescope, and estimates made of these stars' effective temperatures, gravities, and helium abundances. This work was done during tenure of an NSF Predoctoral Fellowship and the Van Maanen Fellowship administered by the California Institute of Technology. The results were partly revised and extended during tenure of the Higgins Fellowship at Princeton University, making use of computer facilities supported in part by NSF Grant NSF-GP5 79. of Washington, Pasadena, California.-A sequence of model atmospheres has been constructed on the range 0.1<0 < 0.7 using an IBM 7090. The source function is given by the Milne-Eddington equation, which allows for coherent scattering. Flux constancy is enforced to +0.5% or better by use of the Krook-Avrett procedure (Avrett, F. H., and Krook, M., A strophys. J. 137, 874,1963), which has been modified simply to allow for scattering terms; this procedure is stable and quickly convergent. The opacity consists of absorption by H, H-, He I, He ii, and H2+, Thompson scattering by free electrons and Rayleigh scattering by neutral H. We took account of the temperature and pressure dependence of the partition functions in the ionization equilibrium of H and He. Neither the effects of lines nor departures from LTE are accounted for. For 0.45<Oe<0.7, models were made with 1~<log g<4.44 while for 0.1<Oe<0.4 they were made with log g=3.5, 4.0, and 4.5, all assuming N(He)/N(H) = 0.15. At the higher temperatures sequences were made with changes in the assumed helium abundance. H~ and H~ profiles were computed using Griem's Stark broadening theory, and for the hotter models we computed the profiles of HeiX5876, X4438, X4121 and Hell X5412, X4686, X4542, and X4200. The computed line strengths have been fitted to observations of six 0-type stars, made with the photoelectric spectrum scanner at the coudk of the 100-in. telescope, and estimates made of these stars' effective temperatures, gravities, and helium abundances. This work was done during tenure of an NSF Predoctoral Fellowship and the Van Maanen Fellowship administered by the California Institute of Technology. The results were partly revised and extended during tenure of the Higgins Fellowship at Princeton University, making use of computer facilities supported in part by NSF Grant NSF-GP5 79. Title: Model atmosphere studies of early type stars Authors: Mihalas, Dimitri Bibcode: 1964PhDT........92M Altcode: 1964PhDT.........4M Model atmospheres have been constructed over a wide range of temperature and gravities. The condition of radiative equilibrium is enforced using a variation of the temperature correction scheme devised by M. Krook, thus extending the work of Gingerich to the realm of higher temperatures; flux constancy is attained to within [plus or minus]1% to a depth of [tau][subscript STD] = 10 or more, the standard wavelength being either [lamda]4000 or [lamda]5050. The source function is determined from the Milne-Eddington equation allowing for coherent scattering in the continuum. The properties of the atmospheres are described and given in detailed tabular form, and data of rather general use is presented.For each model we have computed H[beta] and H[alpha] profiles and equivalent widths, and for the hotter models, profiles and equivalent widths of [lamda]4686, [lamda]4200, [lamda]4542 [lamda]5412 of He II and [lamda]5876, [lamda]4713, [lamda]4438, and [lamda]4121 of He I. Interpolating formulae are devised to describe the temperature and gravity variations of the line strengths.A fit is carried out between theory and observations made with the 100" coude scanner of six O-type stars, yielding the effective temperature, gravity, and an estimate of the helium abundance for these stars. It is found that the computed hydrogen and ionized helium lines appear consistent with observation whereas the computed neutral helium lines seem to be incorrect for these spectral types.

The results indicate that a typical O9 star has the following properties: [theta][subscript e] = 0.146, log g = 4.2, N(He)/N(H) ~ 0.15 or 0.2, and from an assumed mass-luminosity law we find: R/R[...] = 10, [...] = 60, and L/L [...] = 1.4 x 10 [superscript 5]. The helium abundance derived here is in substantial agreement with that found by the Kiel group but in disagreement with nebular studies. The masses and radii are probably quite doubtful because of the possible incorrectness of the assumed mass-luminosity law. Title: Decay times of Type I supernovae light curves. Authors: Mihalas, D. Bibcode: 1963PASP...75..256M Altcode: No abstract at ADS Title: Light Curve of Humason's Supernova in Virgo. Authors: Mihalas, Dimitri M. Bibcode: 1962AJ.....67S.118M Altcode: The supernova discussed in this paper was discovered by M. L. Humason in a faint anonymous galaxy in Virgo (a=13h08rn51S, a=+3C4025~~, 1950) during the 1959 Palomar Supernova Search under the direction of F. Zwicky. This object is number 64 on Zwicky's list. A large number of photographic observations were subsequently made by several observers with the 48- inch Schmidt telescope, and by Arp, Miller, and Zwicky with the 200" telescope; Arp obtained U,B,V magnitudes of the supernova on 5 nights and the galaxy itself on one night. Spectra were obtained by Greenstein and Zwicky, and will be discussed by them elsewhere. The observations extend over about 275 days. The light curve shows a sharp initial decline of 0.07 TABLE I. Half4ife Supernova (days) a 5N64 4.80 0.81 SN NGC 1003 5.53 0.90 SN IC 4182 5.12 0.89 mag./day in B for roughly 40 days followed by a more gradual linear decline of 0.018 mag./day, which is very similar to the behavior of the type I supernovae in NGC 1003 and IC 4182 discussed by Baade and Zwicky. B-V reddens linearly at 0.04 mag./day followed by a period of roughly constant B - V. The time interval between the (estimated) maximum and the change in slope is about 40 days, again in good agreement with other type I supernovae. It has long been known that the tail of a type I light curve could be explained by an exponential intensity decay with a half-life of 55 days or a decay time of 79.3 days. From the data presently at hand it seems that in addition the initial decline can also be fitted by such a decay formula. If we assume that I=I0[aexp(-t/T1)+,&exp(-t/T2)], where a+fl= 1, and T2> T1, we can calculate T1 assuming the T2 given above. This operation has been carried out for SN 64, SN NGC 1003, and SN IC 4182, the latter two taken frnm the data published by Baade and Zwicky. The results are given in Table I; a good fit was obtained in each case. Note that the table gives the half-life, not T~. Thus the average half-life is 5.15*0.25 days and the ratio of the intensities of the two components is always nearly 9:1. The observed maximum was at B= 14.1; correction for absorption in the Virgo galaxy yields B0 = 13.9. With a distance modulus of 33 mag., obtained from an estimate of the absolute magnitude of the galaxy, (MB)e~-19.1. This work was performed during tenure of an NSF pre-doctoral fellowship. Title: Light Curve of Humason's Supernova in Virgo Authors: Mihalas, Dimitri M. Bibcode: 1962PASP...74..116M Altcode: No abstract at ADS