Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS1 at the VLT

摘要

To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have a measuredmagnetic field is an important diagnostic. Previous results based on a smalland possibly biased sample suggest that the distribution of magnetic stars withmass below 3 M_sun in the H-R diagram differs from that of normal stars in thesame mass range (Hubrig et al. 2000). In contrast, higher mass magnetic Bpstars may well occupy the whole main-sequence width (Hubrig, Schoeller & North2005). In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bp stars withaccurate Hipparcos parallaxes and reliably determined longitudinal magneticfields. We used FORS1 at the VLT in its spectropolarimetric mode to measure themagnetic field in chemically peculiar stars where it was unknown or poorlyknown as yet. In this first paper we present our results of the meanlongitudinal magnetic field measurements in 136 stars. Our sample consists of105 Ap and Bp stars, two PGa stars, 17 HgMn stars, three normal stars, and nineSPB stars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and four SPBstars.