Inestabilidades pulsacionales en estrellas de la prerrama horizontal azul y extendida

BATTICH, T.; M. MILLER BERTOLAMI; CORSICO, A.; ALTHAUS, L. G.

San Juan

Conferencia; 59ava Reunion de la Asociacion Argentina de Astronomia; 2016

The -mechanism is a self-excitation mechanism of pulsations which acts on the regions inside the star where nuclear burning takes place. Due to the strong dependence of nuclear burning rates on temperature, the temperature perturbations induced by pulsations lead to an increase in the oscillation energy at the expense of the thermal energy of the star. Although the mechanism works wherever nuclear reactions are active, the pulsation amplitudes tend to be small in the high temperature layers where nuclear energy is generated so that the -mechanism is usually very weak. To the date there is not confirmation of -mechanism as the responsible of the excitation of pulsations of any star. However, it has been shown that -mechanism can excite pulsations in stellar models that undergo a hot helium-core flash, and the subsequent subflashes, before the star model settles into the stable helium core-burning phase. Moreover, it has been shown that the pulsations of LS IV-14116 could be explained that way. In the present work we aim to extend the study of the -mechanism effects on stellar models appropriate for stars on the blue and extreme pre-horizontal branch, i.e. before the helium core-burning phase. With this aim we perform detailed computations of non-adiabatic non-radial pulsations on such stellar models, adopting different values of metallicity, initial helium abundances and mass of the hydrogen envelope at the time of the main helium flash.