Poster Abstracts

Name/Affiliation:  Lisa Rosén (Uppsala University )

Title:  First Zeeman Doppler imaging of a cool active star using all four Stokes parameters

Magnetic fields in cool stars are ubiquitous but can still be challenging to characterize due to their complexity and relatively low strength. The polarization signatures are proportional to the field strength, and current studies of cool star magnetic fields are using circular polarization only since linear polarization is even weaker. However, circular polarization is only sensitive to the line-of-sight component of the magnetic field, meaning that a lot of structural features are not recovered or misinterpreted when only circular polarization is used for reconstruction of stellar magnetic topologies. Linear polarization, on the other hand, is sensitive to the transverse component of the magnetic field and would provide a more complete picture of the magnetic field topology if combined with circular polarization. We have identified a first suitable cool star, II Peg, for which linear polarization has been systematically detected with current instrumentation at a level sufficient for magnetic mapping. Here we present the very first temperature and magnetic field maps reconstructed for a cool star using all four Stokes parameter spectra.