Astron. Astrophys. 323, 393-394 (1997)

1. Introduction

It has been well-established that high-luminosity helium stars are unstable against radial or non-radial pulsations at effective temperatures up to at least 30 000 K (Saio & Jeffery 1988). An explanation for pulsations in the lower-luminosity helium star V652 Her (Hill et al. 1981) was only obtained (Saio 1993) with the publication of new opacities. These opacities (Iglesias et al. 1992) show a peak due to iron-group elements in the region of capable of driving pulsations in low-luminosity helium stars with . The success of the theory was vindicated by the prediction (Saio 1995) and discovery (Kilkenny & Koen 1995) of pulsations in the helium star LSS 3184. A problem was that the helium star HD 144941 shows no evidence for pulsations (Jeffery & Hill 1996, Paper I), although it lies in the same pulsational instability strip (Harrison & Jeffery 1996, Paper II). A possible solution and an important test of the theory lay in the prediction that the extent of the pulsational instability finger to low luminosity is strongly metal-dependent (Saio 1995). Measurements of light elements (C,N,O,Si,S) in V652 Her (Jeffery et al. 1986), LSS 3184 (Drilling et al. 1996) and HD 144941 (Paper II) appeared to confirm this.

However pulsations are driven by iron-group elements and the optical spectra of these stars contain only a few weak lines of Fe III. In particular, the iron abundance in HD 144941 had been measured from only one very weak line (Paper II) and indicated an iron underabundance (relative to solar) roughly 0.5 dex smaller than for lighter elements. Thus it is vital to confirm the iron abundance of HD 144941 in order to interpret the absence of pulsations correctly.

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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