Colloquium: Dr. Geza Kovacs

Department of Physics and Astrophysics, University of North Dakota 

Nonlinear Stellar Pulsation

Friday, Feb 21, 2014 4:01pm-4:50pm

Finite-amplitude stellar pulsation is a natural outcome of the saturation of the excitation mechanism in pulsating stars that are self-excited due to the fortunate location of their partial ionization zones that drive the pulsation via the opacity mechanism. Although classical pulsating stars (Cepheids, RR Lyrae stars, Mira variables) are the simplest examples of nonlinear pulsation, it occurs at any (however small) amplitudes whenever the star is vibrationally unstable against infinitesimal perturbations. Here we review the basics of the numerical and analytical methods employed in this field. In spite of the success in understanding (and modelling) several phenomena (e.g., light curve distortion, Hertzsprung progression), current models are still unable to give satisfactory explanation for double/multi-mode pulsations and completely fail in giving a physically sound (and working) model for the very common phenomenon of amplitude modulation (the so-called Blazhko effect) in RR Lyrae stars.