Observations of magnetic Ap stars at the Pic-du-Midi Observatory:From broadband linear polarization measurements with STERENNto spectropolarimetry with MuSiCoS

Abstract

Observations of magnetic Ap stars taken at the 2m Telescope BernardLyot (TBL) of Pic-du-Midi Observatory are of the greatest importancein the study of the stellar magnetism. With the help of the polarimeterSTERENN, in the '90s, Leroy and collaborators performed a vigorouscampaign of observations of broadband linear polarization of Ap stars,virtually disclosing a new window on the transverse components of thestellar magnetic fields. Less than 10 years later, Donati, Landstreet,Wade and other collaborators are routinely using MuSiCoS in polarimetricmode to observe Stokes profiles of Ap and other kinds of magnetic stars.I will review the impact of TBL observations on the study of magneticfields of Ap stars, and the progresses in the modelling that have beenaccomplished in the last ten years.