ε-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

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

Open Astronomy

De Gruyter Open Ltd

Año: 2017 vol. 26 p. 152 - 159

The mechanism is a self-excitation mechanism of stellar pulsations which acts in regions where nuclear burning takes place. It has been shown that the mechanism can excite pulsations in hot pre-horizontal branch stars before they settle into the stable helium core-burning phase and that the shortest periods of LS IV-14∘116 could be explained that way. We aim to study the mechanism in stellar models appropriate for hot pre-horizontal branch stars to predict their pulsational properties. We perform detailed computations of non-adiabatic non-radial pulsations on such stellar models. We predict a new instability domain of long-period gravity modes in the log g log Teff plane at roughly 22000 K Teff 50000 K and 4.67 log g 6.15, with a period range from ∼ 200 to ∼ 2000 s. Comparison with the three known pulsating He-rich subdwarfs shows that the mechanism can excite pulsations in models with similar surface properties except for modes with the shortest observed periods. Based on simple estimates we expect at least 3 stars in the current samples of hot-subdwarf stars to be pulsating by the mechanism. Our results could constitute a theoretical basis for future searches of pulsators in the Galactic field.