Astronomy and Astrophysics, volume 323, 177-182 (1997/7-1)
A spectral analysis of the hydrogen-deficient star HD 144941.
HARRISON P.M. and JEFFERY C.S.
Abstract (from CDS):
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 Teff, logg and H/He abundance. Ionisation equilibria for available metal ions, fitted Hei line profiles, and UV/visual flux distributions have been used to determine Teff, logg and H/He. With optimal values of Teff=23200K and logg=3.9 the abundances by number of the principal species are: nH=5.21%, nHe=94.79%, nC=0.0017%, nN=0.00079%, nO=0.0024%, nMg=0.00031%, nAl=0.000019%, nSi=0.00027%, nFe=0.00066%. HD144941 lies at the high logg, high Teff end of the group of EHe stars, but its nH/nHe 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.
stars: helium stars - individual stars (HD 144941) - atmospheres - abundances - oscillations - evolution
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