The helium abundances in HgMn and normal stars

Details The helium abundances in HgMn and normal stars The helium abundances in HgMn and normal stars

2004-07-26

arxiv.org/abs/astro-ph/0407528v1

Astronomy and Astrophysics

Astrophysics

7 pages, 6 figures, (poster paper at IAU Symposium 224, The A-Star Puzzle, 7-13 July 2004, Poprad, Slovakia)

Scientific paper

10.1017/S1743921305009658

The parameter-free model of diffusion in the atmospheres of HgMn stars (Michaud 1986; Michaud et al 1979) predicts that helium should sink below the He II ionization zone in order that diffusion of other elements may take place, and that all HgMn stars should have deficits of helium in their photospheres, with a minimum deficit of 0.3 dex. In this study, the Smith & Dworetsky (1993) sample of HgMn stars and normal comparison stars is examined, and the helium abundances determined by spectrum synthesis using echelle spectra taken at Lick Observatory and the AAT. The prediction is confirmed; all HgMn stars are deficient in He by as much as 1.5 dex. Also, two HgMn stars, HR7361 and HR7664, show clear evidence of helium stratification.

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