We present results from a spectro-interferometric study of the Miras o Cet, R Leo and W Hya obtained with the Keck Aperture Masking Experiment from 1998 Sep to 2002 Jul. The spectrally dispersed visibility data permit fitting with circularly symmetric brightness profiles such as a simple uniform disk. The stellar angular diameter obtained over up to ∼ 450 spectral channels spaning the region 1....

We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar d...

Results of stellar evolution calculations and results of non-adiabatic stellar pulsation calculations can be used to construct theoretical , composition-dependent, short period boundaries (or \blue edges") of the instability strip in the period-luminosity plane for Cepheids pulsating in the fundamental and rst overtone radial modes. The slopes of these blue edges are very similar to the slopes ...

We report new determinations of the radius and mass of the pulsating helium-rich, hydrogen-deecient star LSS 3184 (BX Cir) using measurements of radial velocity and angular radius throughout its pulsation cycle. Measurements of radial velocity, and thus changes in stellar radius ((R ?), were made using Anglo-Australian Telescope echelle spectra. Hubble Space Telescope ultraviolet spectra and gr...

We suggest a mechanism for enhancing magnetic activity in tidally interacting binaries. We suppose that the deviation of the primary star from spherical symmetry due to the tidal influence of the companion leads to stellar pulsation in its fundamental mode. It is shown that stellar radial pulsation amplifies torsional Alfvén waves in a dipole-like magnetic field, buried in the interior, accordi...

We briefly describe a method of obtaining relative intrinsic stellar parameters, such as absolute magnitudes and colors from the light curves of fundamental mode RR Lyrae (RRab) stars. Absolute stellar parameters of double-mode variables (Cepheids and RR Lyrae stars) can be computed from their periods and intrinsic colors combined with stellar atmosphere and pulsation models. By using these two...