Open AccessNon‐adiabatic linear pulsation models for low‐mass helium stars
Author(s) -
Jeffery C. Simon,
Saio Hideyuki
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02727.x
Subject(s) - physics , astrophysics , stars , instability , metallicity , helium , adiabatic process , radial velocity , subdwarf , low mass , envelope (radar) , excited state , instability strip , atomic physics , white dwarf , cepheid variable , mechanics , thermodynamics , telecommunications , radar , computer science
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<log g <5. The radial pulsation models assume a homogeneous stellar envelope which is deficient in hydrogen and display the well‐known Z ‐bump instability to radial pulsations. The aim of this paper has been to explore the behaviour of the Z ‐bump instability as a function of mass and composition around a reference model with M =0.5 M ⊙ , 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.