Ultraviolet Spectropolarimetry With Polstar: Hot Star Magnetospheres

Polstar is a proposed NASA MIDEX space telescope that will provide high-resolution, simultaneous 1 full-Stokes spectropolarimetry in the far ultraviolet, together with low-resolution linear polarimetry in 2 the near ultraviolet. In this white paper, we describe the unprecedented capabilities this observatory 3 would offer in order to obtain unique information on the magnetic and plasma properties of the mag4 netospheres of hot stars. This would enable a test of the fundamental hypothesis that magnetospheres 5 should act to rapidly drain angular momentum, thereby spinning the star down, whilst simultane6 ously reducing the net mass-loss rate. Both effects are expected to lead to dramatic differences in the 7 evolution of magnetic vs. non-magnetic stars. 8