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Mon. Not. R. Astron. Soc. 000, 1{7 (0000) Printed 5 February 1999 (MN L A T E X style le v1.4) Nonadiabatic linear pulsation models for low-mass helium
 

Summary: Mon. Not. R. Astron. Soc. 000, 1{7 (0000) Printed 5 February 1999 (MN L A T E X style le v1.4)
Nonadiabatic linear pulsation models for low-mass helium
stars
C. Simon Je ery 1 and Hideyuki Saio 2
1 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
2 Astronomical Institute, Scool of Science, University of Tohoku, Sendai 980, Japan
Accepted . Received ;
ABSTRACT
Nonadiabatic linear pulsation models have been calculated for low-mass stars with
e ective temperatures between 16 000 and 35 000 K, and with surface gravities in the
range 3 < log g < 5. The models for radial pulsation analysis assume a homogeneous
stellar envelope which is de cient 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 by either a reduction in
metallicity Z or by a selective enhancement of the carbon abundance. An unexpected
result was 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 models in the instability range of parameters

  

Source: Armagh Observatory

 

Collections: Physics