Magnetic Fields in B, (peculiar) A, and F stars - recent results from MuSiCoS Data

Abstract
Ultra-high precision measurements of Stokes V Zeeman signatures have been obtained using the MuSiCoS spectropolarimeter (Donati et al. 1999) at the Pic du Midi obseravtory, aimed at studying the distribution of weak and tangled magnetic fields in F, A, and late-B type stars. We will discuss recent results obtained from these data, including the complete absence of magnetic fields (with an upper limit of around 25 G) in the non-Ap/Bp sample, and the relatively easy detection of magnetic fields in nearly all of the Ap/Bp stars. In addition polarimetric data in all four Stokes parameters ( I, V, Q, and U) has been obtained for a sample of roAp stars, a pulsating subgroup within the magnetic Cp stars, with the aim to study vertical (stratification) and horizontal (via Zeeman Doppler Imaging) abundance characteristics and their relation to the magnetic field geometry. We will present results of our data analysis, using the Least Squares Deconvolution (LSD) technique (Donati et al. 1997) and with the goal of determining the surface abundance distribution of rare earth elements and the magnetic field geometry of these stars.