A dedicated polarimeter for the MuSiCoS echelle spectrograph

We present in this paper the technical characteristics of a new polarimetri c unit dedicated to the MuSiCoS echelle spectrograph. The first test runs i ndicate that our instrument is very good at measuring polarisation or depol arisation structures in line profiles. It is therefore one of the very few facilities worldwide for studying magnetic topologies of active and chemica lly peculiar stars through rotational modulation of linearly and circularly polarised Zeeman signatures in line profiles. It is also a very interestin g tool for investigating geometries of non-axisymmetric circumstellar envir onments through depolarisation of spectral lines formed within the scatteri ng envelope.