A Nonlinear Pulsation Model for V652 Her

Abstract

Abstract. When compared with observation, stellar pulsation model predictions provide a test of stellar envelope opacities. Of specific interest, is the radially pulsating extreme helium star V652 Her for which luminosity and radial velocity observations are published. Nonlinear pulsation models of V652 Her, calculated using Opacity Project (OP) opacities, predict luminosity and radial velocity variations in close agreement with observation.

The pulsating hydrogen-deficient star LSS 3184 (BX Cir)

“…The obvious similarities between the two stars together with the theoretical work of Saio (1993, 1994) and Fadeyev & Lynas‐Gray (1996) and the observational data presented in this paper, strongly suggest that LSS 3184 is a radial pulsator. We have, therefore, attempted to apply the Balona (1977) method for stellar‐radius determination to our light, colour and velocity data.…”

“…Many of these stars exhibit regular or ‘quasi’ regular variations, which are proven to result from stellar pulsation in some cases and suspected in others. Recent reviews of the subject can be found in the proceedings of the second conference on hydrogen‐deficient stars held in Bamberg in late 1995 (Jeffery & Heber 1996; see particularly Lawson & Kilkenny 1996, Saio 1996, Fadeyev 1996 in the conference proceedings and Fadeyev & Lynas‐Gray 1996).…”

“…The combination of rapid pulsation, change in pulsation period and highly unusual hydrogen abundance ( n H ∼2 per cent) was not known in any other object. New opacity calculations have enabled Saio (1993) to show that the variations in V652 Her are fundamental radial‐mode pulsations driven by the classical κ ‐mechanism and the iron‐opacity bump at a temperature ∼2×10 5 K (see also Fadeyev & Lynas‐Gray 1996). Also on the basis of the new opacities, Saio (1994) predicted that the EHe star LSS 3184, which closely resembles V652 Her in surface temperature and luminosity (but is more hydrogen‐deficient), should similarly pulsate unless it is very metal‐poor.…”

The instability strip and pulsation features of post-AGB star models

“…The cause of variability is known as iron-group bump in the opacity (Saio 1995;Fadeyev & Lynas-Gray 1996), and the stars are definitely related to post-AGB stars.…”