1994A&A...291..919F

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 m ESO telescope, with the aim of testing whether HeI 4471A will give evidence of chemical stratification within their photospheres. Of the four candidates, HR 3448=HD 74196 is a fast rotator (vsini=300km/s), however, no variability is detectable, while HR 1100=HD 22470 does not exhibit any helium line (posibly due to incomplete phase coverage). Only HR 1441=HD 28843 and HR 2509=HD 49333 are genuine helium variables. Profile analyses of HeI 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.