Pulsational instabilities in hot pre-horizontal branch stars

ALEJANDRO H. CÓRSICO; TIARA BATTICH; MARCELO M. MILLER BERTOLAMI; LEANDRO G. ALTHAUS

San Pedro de Atacama

Congreso; 22 nd Los Alamos Stellar Pulsation Conference Series Meeting "wide-field variability surveys: a 21st century perspective"; 2016

The $epsilon$-mechanism is a self-excitation mechanism of pulsations which acts on the regions where nuclear burning takes place. It has been shown that $epsilon$-mechanism can excite pulsations in models of hot helium-core flash, and that the pulsations of LS IV-14$^{circ}$116, a He-enriched hot subdwarf star, could be explained that way. We aim to study the $epsilon$-mechanism effects on models of hot pre-horizontal branch stars and determine, if possible, a domain of instability in the $log g-log T_{m eff}$ plane. We compute non-adiabatic non-radial pulsations on such stellar models, adopting different values of initial chemical abundances and mass of the hydrogen envelope at the time of the main helium flash. We find an instability domain of long-period ($400,{m s} lesssim P lesssim 2500,{m s}$) $g$-modes for models with $22000,{m K} lesssim T_{m eff}lesssim 50000,$K and $4.67 lesssim log g lesssim 6.15$.