The shapes of light curves of Mira-type variables

Using a sample of 454 mira light curves from the ASAS survey we study the shape of the light variations in this kind of variable stars. Opposite to earlier studies, we choose a general approach to identify any deviation from a sinusoidal light change. We find that about 30% of the studied light curves show a significant deviation from the sinusoidal reference shape. Among these stars two characteristic light curve shapes of comparable frequency could be identified. Some hint for a connection between atmospheric chemistry and light curve shape was found, but beside that no or only very weak relations between light curve shape and other stellar parameters seem to exist.Comment: 7 pages, 7 figures, accepted for publication in A

Astrophysics : Contributions of Indian Scientists .

A glimpse of astronomy and astrophysics from the earliest times to the end of the nineteenth century is given. This is followed by important contributions to astrophysics in the twentieth century with detailed accounts of the work of MN Saha, DS Kothari and a few others. This review ends with a brief account of the astrophysical activities in which a large number of scientists are presently involved

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

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

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

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late-type main-sequence stars, the earlier models that consisted of convective cores and radiative envelopes have been superseded by models with radiative cores and convective envelopes, topped by an atmosphere in radiative equilibrium.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