Chemically peculiar stars present spectral and photometric variability with
a single period. In the oblique rotator model, the non homogeneous distrib
ution of elements on the stellar surface is at the origin of the observed v
ariations. As to helium weak stars; it has been suggested that photometric
and helium line equivalent width variations are out of phase. To understand
the behaviour of helium in CP stars, we have obtained time resolved spectr
a of the HeI5876 A line for a sample of 16 chemically peculiar stars in the
spectral range B3 - A1 and belonging to different sub-groups.
The HeI5876 Angstrom line is too weak to be measured in the spectra of the
stars HD 24155; HD 41269, and HD 220825. No variation of the equivalent wid
th of the selected He line has been revealed in the stars HD 22920, HD 2458
7, HD 36589, HD 49606, and HD 209515. The equivalent width variation of the
HeI5876 Angstrom line is in phase with the photometric variability for the
stars HD 43819, HD 171247 and HD 176582. On the contrary it is out of phas
e for the stars HD 28843, HD 182255 and HD 223640. No clear relation has be
en found for the stars HD 26571 and HD 177003.