Non-adiabatic linear pulsation models for low-mass helium stars |
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| Authors: | C Simon Jeffery Hideyuki Saio |
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| Institution: | Armagh Observatory, College Hill, Armagh BT61 9DG; Astronomical Institute, School of Science, University of Tohoku, Sendai 980, Japan |
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| Abstract: | Non-adiabatic linear pulsation models have been calculated for low-mass stars with effective temperatures between 16 000 and 35 000 K, and with surface gravities in the range 3⊙, X =0.00, Z =0.02. It is shown that the Z -bump instability persists to low masses ( M ～0.4 M⊙) but is suppressed either by a reduction in metallicity Z or by a selective enhancement of the carbon abundance. An unexpected result is the discovery that Z -bump instability persists at hydrogen abundances X >0.3, although the position of the red edge is sensitive to X . We have found that non-radial pulsations are also excited in the same instability region as radial pulsations.
The implications of these results for individual low-mass helium stars are discussed. It is concluded that Z -bump driven pulsations (radial and/or non-radial) may be excited in some helium-rich subdwarf B stars, representing a possible major extension to the class of variable stars represented by the prototype V652 Her. |
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| Keywords: | stars: oscillations |
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