F. A. Catalano

Fifth supplement to the catalogue of observed periods of Ap stars

New data on the periods of Ap stars with references are presented (Table 1). 21 further stars are introduced for which a periodic variability has recently been discovered or for which it was known before but it was not reported in previous issues of this catalogue. For many stars also present in previous issues of the catalogue new determinations of the periods are given. Recently attributed variable star names are also quoted. Table 1, notes to this Table and related references are only available in LaTEX form at the CDS via anonymous ftp 130.79.128.5 (filename: DS1178.tex).

Variability of the Hei5876 Å line in early type chemically peculiar stars

Chemically peculiar stars present spectral and photometric variability with a single period. In the oblique rotator model, the non homogeneous distribution of ele- ments on the stellar surface is at the origin of the observed variations. As to helium weak stars, it has been suggested that photometric and helium line equivalent width vari- ations are out of phase. To understand the behaviour of helium in CP stars, we have obtained time resolved spec- tra of the Hei5876 A line for a sample of 16 chemically peculiar stars in the spectral range B3 { A1 and belong- ing to dierent sub-groups. The Hei5876 A 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 width of the selected He line has been revealed in the stars HD 22920, HD 24587, HD 36589, HD 49606, and HD 209515. The equivalent width variation of the Hei5876 A 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 phase for the stars HD 28843, HD 182255 and HD 223640. No clear relation has been found for the stars HD 26571 and HD 177003.