Rotation and mass loss in early type stars

The effects of rotation on the rate of mass loss for O and B stars has been reviewed, and the causes for conflicting results discussed

On non-LTE H<SUB>2</SUB><SUP>+</SUP> as missing solar opacity

A careful examination has revealed that use of incomplete reaction processes and incorrect rates have led Krishna Swamy and Stecher to overestimate the H2+ opacity by a factor of 104 at &#955; = 2000 &#197;. H2+ is not a significant source of opacity in the solar atmosphere

Some comments on empirical FITS to stellar mass loss rates

Two empirical fits to stellar mass loss rates have been examined and found lacking in physical content

Physical atmospheric parameters for late-type stars

For a gas mixture, the relation between total gas pressure, partial pressure of atomic hydrogen, mean molecular weight, and several other auxiliary quantities has been determined as a function of electron piessure and θ = 5040/T, for three hydrogen-to-helium abundance ratios. The effect of molecular hydrogen has been incorporated

Hydrogen-helium adiabats for late-type stars

For late-type main-sequence stars, the earlier models that consisted of convective cores and radiative envelopes have been superseded by models with radiative cores and convective envelopes, topped by an atmosphere in radiative equilibrium. But in the available models of the latter type, the representation of the convective zone has been rather schematic, in so far as the adiabats used would apply only if the gas were completely ionized. Accordingly, an expression for the adiabatic gradient of hydrogen-helium mixtures has been derived from thermodynamics. This derivation takes account of the interlocking ionization of hydrogen and helium and of its coupling with the association of hydrogen into molecules. Adiabats have been computed with three values of hydrogen to helium ratio (by number), 8/1, 16/1, and ∞. Moreover, an expression for the adiabatic gradient, in which the effect of pressure ionization has been included in an approximate way, has been given for the special case of pure hydrogen

IRAS low resolution spectrograph spectral class and M and S Miras

A large sample of 177 M and S Miras, as revealed by their IRAS LRS spectral class, have been examined to determine the dependence of silicate emission on the visual light curve asymmetry factor, f. It is confirmed that 9.7μm silicate emission feature not only in M but in S Miras also occurs only when f ≦ 0.45. However, not all stars with f ≦ 0.45 show the silicate emission; this non-detection reveals dependence on other parameters like the mean visual light amplitude. Though strong emission feature in M Miras may occur for any value of f, very weak features are absent for small values of f, and the strongest features tend to appear for larger values of f. Infrared excess tends to increase with the strength of the silicate emission as well as with decrease in the value of f. Probability of detection of silicate emission is very high for the visual light curve classes (Ludendorff) α1, α2, and α3, decreases for α4 and γ1, and is negligible for the β class

Molecules and late-type stellar models

A difficulty encountered by Osterbrock, when he tried to identify particular red dwarf stars by interpolating between his models of late-type main-sequence stars, is shown to be alleviated by including the effects produced by hydrogen molecules in the convective zone

Mass loss, long-period variables, and the formation of circumnebular shells

We have found that the rate of mass loss M· increases with an increase in the period of pulsation for Mira-type variables. This result suggests that the rate of mass loss is accelerated with time until a maximum value is reached before the ejection of the outer envelope. The matter from the continuous mass loss during the evolution of the star produces supersonic shock waves that sweep up the interstellar gas upon encountering the interstellar medium, so that a shell is formed. This phenomenon may account for the observations of extended regions of emission that surround planetary nebulae

An equation of state from cool-dense fluids to hot gases for mixed elements

An equation of state for the domain extending from hot gases to cool-dense fluids is formulated for a hydrogen-helium mixture. The physical processes take account of temperature ionization and dissociation, electron degeneracy, Coulomb coupling and pressure ionization. Pressure ionization and Coulomb coupling are studied with simple and comprehensive modeling. A single and complete algorithm is achieved with explicit expressions available for the whole domain from hot gases to cool dense fluids ($T>10^2$). Pressure ionization and Coulomb coupling have been examined for their contributions to the pressure and internal energy. The result reveals that their contributions smooth the variation of the pressure and internal energy in the region of pressure ionization even at very low temperatures.Comment: 10 pages, 8 figures, ApJ, accepted, E-mail: [email protected]

Low Temperature Opacities

Previous computations of low temperature Rosseland and Planck mean opacities from Alexander & Ferguson (1994) are updated and expanded. The new computations include a more complete equation of state with more grain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the equation of state calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high temperature condensates such as Al$_2$O$_3$ and CaTiO$_3$ significantly affects the total opacity over a narrow range of temperatures before the appearance of the first silicate grains. The new opacity tables are tabulated for temperatures ranging from 30000 K to 500 K with gas densities from 10$^{-4}$ g cm$^{-3}$ to 10$^{-19}$ g cm$^{-3}$. Comparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method are shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided.Comment: 39 pages with 12 figures. To be published in ApJ, April 200