A spectral analysis of the hydrogen-deficient star HD144941
P.M. Harrison and
Received 2 April 1996 / Accepted 2 July 1996
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 , 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 , and H/He.
With optimal values of and the abundances by number of the principal species are: , , , , , , , , .
HD144941 lies at the high , high end of the group of EHe stars, but its 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
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© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998