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

¹ Dipartimento di Fisica della Materia e Tecnologie Fisiche Avanzate, Università di Messina, Salita Sperone 31, I–98166 Messina, Italy
² C.N.R.-G.N.A., UdR di Catania, Città Universitaria, Viale A. Doria 6, I–95125 Catania, Italy
³ Osservatorio Astrofisico di Catania, Città Universitaria, Viale A. Doria 6, I–95125 Catania, Italy
⁴ Istituto di Astronomia, Università di Catania, Città Universitaria, Viale A. Doria 6, I–95125 Catania, Italy

Send offprint request to: G. Catanzaro - Istituto di Astronomia, Università di Catania, Viale A. Doria 6, I–95125 Catania, Italy.

Received: 3 June 1998
Accepted: 3 August 1998

Abstract

Chemically peculiar stars present spectral and photometric variability with a single period. In the oblique rotator model, the non homogeneous distribution of elements 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 variations are out of phase. To understand the behaviour of helium in CP stars, we have obtained time resolved spectra of the Hei5876 Å line for a sample of 16 chemically peculiar stars in the spectral range B3 – A1 and belonging to different sub-groups. The Hei5876 Å 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 Å 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.