Model Atmospheres for Irradiated Stars in pre-Cataclysmic Variables

Model atmospheres have been computed for M dwarfs that are strongly irradiated by nearby hot companions. A variety of primary and secondary spectral types are explored in addition to models specific to four known systems: GD 245, NN Ser, AA Dor, and UU Sge. This work demonstrates that a dramatic temperature inversion is possible on at least one hemisphere of an irradiated M dwarf and the emergent spectrum will be significantly different from an isolated M dwarf or a black body flux distribution. For the first time, synthetic spectra suitable for direct comparison to high-resolution observations of irradiated M dwarfs in non-mass transferring post-common envelope binaries are presented. The effects of departures from local thermodynamic equilibrium on the Balmer line profiles are also discussed.Comment: Accepted for publication in ApJ; 12 pages, 10 figure

THE EFFECT OF CHEMICAL ABUNDANCE OSCILLATIONS ON THE PULSATIONAL PROPERTIES OF A 5 M-CIRCLE-DOT HYDROGEN-HELIUM STAR

A model of a first generation intermediate star of 5 M., with Z = 0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell

Radial and nonradial oscillations of 44 Tauri

Evolutionary stellar models of 44 Tauri, a multiperiodic delta Scuti star, have been developed theoretically and compared with earlier observational reports. The models depict 44 Tau at the hydrogen-shell-burning stage, when it is in radiative equilibrium with a very thin surface convective layer. Using the models, we performed calculations to obtain radial and nonradial adiabatic oscillation frequencies, and the equations were treated linearly. The results showed that the radial fundamental (6.899 cycles day(-1)) and first-overtone (8.961 cycles day(-1)) frequencies and the five nonradial modes of low harmonic degree that had been determined theoretically were in agreement with the observed values of previous authors to an accuracy of a few parts in 10(3). However, a difference emerged in the nonradial frequencies, which we classified as g-modes of low harmonic degree, whereas the observational reports had classified them as p-modes. In addition, even though 44 Tau has a rotation v sin i = 6.8 km s(-1) (according to Solano and Fernley), which we considered negligible, we analyzed the effect of rotation. Our findings revealed that rotation modulated the oscillation frequencies of the nonrotating model on the order of 10(-2)

Asteroseismic investigation of 44 Tau, a slowly rotating delta Scuti star

Evolutionary model calculations of 44 Tau, a delta-Scuti star, have been carried out. The star in question is a slow rotator (vsini = 6.8 kms(-1)). However small it may be, the effect of rotation on the oscillation properties of the star was thought to be worth of studying. Models were evolved with uniform rotation. Radial and non-radial adiabatic oscillation frequencies were calculated. In determining oscillation frequencies rotation has been treated as a perturbation. First order effect has been considered. The possible rotational splittings, due to two rotation speeds, have been calculated

A new oscillating model suggestion for FG Vir

Evolutionary stellar models of FG Vir have been developed theoretically and are compared with earlier observational results. Using the models, we performed calculations to obtain radial and non-radial adiabatic oscillation frequencies. The results show that, if the observational splitting was considered and the observational mode identifications were followed, 1.85M(circle dot) star models with the rotational velocities in the range from 32 to 66 kms(-1) seem to be representative models of FG Vir

Second order rotational effect on the oscillation frequencies of V1162 Ori

V1162 is a delta-Scuti type variable star for which a rotational velocity of V sini=46 +/- 4 km s(-1) has been observed. The star has been modelled according to its observed parameters and oscillation frequencies. The results obtained by approximating rotation to the first order have been compared with the ones provided by new calculations that include rotation up to the second order. We found that second order rotation term should be included in frequency calculations for comparatively high rotation speeds

THE EVOLUTION OF A 20M(CIRCLE-DOT) ROTATING STAR - ABUNDANCE ANOMALIES IN OBN STARS IN THE LMC

Evolutionary study of a rotating 20M. star with a chemical composition appropriate for the Large Magellanic Cloud (LMC) has been carried out starting from the threshold of stability through the gravitational contraction phase, approach to the main-sequence, on the hydrogen burning phase, upto the point at which 61% of hydrogen was consumed in the central region of the star. During evolution mixing due to diffusion has been taken into account. As a consequence of such a mixing it has been shown that the atmosphere of the star was enriched the most conspicuously in helium and nitrogen. Thus it was concluded that rotational mixing helps the star to expose processed matter at its surface. When compared with the observations of nitrogen rich early type stars, our results agree well with the observed chemical composition of the OBN stars, if not quantitatively but at least qualitatively