Polarimetry of ST LMi (CW1103+254)

White light simultaneous photometry and linear and circular polarimetry is presented for the AM Her variable ST LMi. Linear polarization evident throughout the faint phase is tentatively attributed to electron scattering from gas in the accretion column at heights greater than 5R _wd above the surface. The values of inclination and magnetic colatitude are revised to take into account the height and extent of the cyclotron emitting region which are also determined. A model of two closely connected emitting regions is proposed to account for the asymmetries observed in the light curve and polarization data for this and other AM Her systems. The cyclotron and hard x-ray emitting regions are found to be coincident, which eliminates the region above the shock as the source of polarized light. The shock height is found to be too low and the soft x-ray flux too large for the standard radiative shock model to apply.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.