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Astron. Astrophys. 323, 177-182 (1997)

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A spectral analysis of the hydrogen-deficient star HD144941

P.M. Harrison and C.S. Jeffery

School of Physics and Astronomy, University of St Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, Scotland

Received 2 April 1996 / Accepted 2 July 1996

Abstract

HD144941 is a B type hydrogen-deficient star. Previous analysis has suggested that its effective temperature and surface gravity are similar to the nitrogen rich H-deficient star V652 Her. However, its H/He ratio puts it between the classifications of an extreme and an intermediate helium star, and its low C and N abundances make it unique amongst known H-deficient stars.

High-resolution, high-S/N, optical spectra have been obtained using the AAT. A grid of model atmospheres has been constructed for varying [FORMULA], [FORMULA] and H/He abundance. Ionisation equilibria for available metal ions, fitted He I line profiles, and UV/visual flux distributions have been used to determine [FORMULA], [FORMULA] and H/He.

With optimal values of [FORMULA] and [FORMULA] the abundances by number of the principal species are: [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA].

HD144941 lies at the high [FORMULA], high [FORMULA] end of the group of EHe stars, but its [FORMULA] ratio of 0.055 is above average for the group. The surface composition is also remarkable in having a considerable metal deficiency (Z=0.0003), probably of primordial origin.

The low metallicity explains why substantial radial pulsations are not observed for a star with these surface properties and is a vindication of modern helium star pulsation models and opacities.

Key words: stars: helium stars – individual stars (HD144941) – atmospheres – abundances – oscillations – evolution

Send offprint requests to: P.M. Harrison

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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