Stratification of helium in the photopsheres of the helium-weak stars HD 28843 and HD 49333

Details Stratification of helium in the photopsheres of the helium-weak stars HD 28843 and HD 49333 Stratification of helium in the photopsheres of the helium-weak stars HD 28843 and HD 49333

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..919f&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 3, p. 919-927

Astronomy and Astrophysics

Astrophysics

7

Abundance, B Stars, Helium, Photosphere, Stratification, Variable Stars, Atmospheric Models, Line Spectra, Spectrograms, Spectrum Analysis, Stellar Models, Stellar Rotation

Scientific paper

For four helium-weak and variable B stars phase-dependent high-resolution spectrograms have been obtained with the Echelec-spectrograph attached to the 1.5 European Southern Observatory (ESO) telescope, with the aim of testing whether He I 4471A will give evidence of chemical stratification within their photospheres. Of the four candidates, HR 3448 = HD 74196 is a fast rotator (v sin i=300 km/s), however, no variability is detectable, while HR 1100=HD 22470 does not exhibit any helium line (possibly due to incomplete phase coverage). Only HR 1441=HD 28843 and HR 2509=HD 49333 are genuine helium variables. Profile analyses of He I 4471, based on fully line blanketed model atmospheres which are adapted to the relevant helium-content show that HD 28843 can fully be explained by a cap model with two asymmetrically located helium caps of equal radii. For HD 49333 vertical stratification in addition has to be assumed in order to explain the excessively broad wings. This confirms earlier (preliminary) results by Groote et al. (see Hunger 1986). Vertical stratification is infered for both inside and outside the helium-caps of HD 49333.

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