The Schweizer-Middleditch star revisited

We have re-observed and re-analysed the optical spectrum of the Schweizer-M iddleditch star, a hot subdwarf which lies along almost the same line-of-si ght as the centre of the historic SN1006 supernova remnant (SNR). Although this object is itself unlikely to be the remnant of the star which exploded in 1006AD, Wellstein et al. (1999) have demonstrated that it could be the remnant of the donor star in a pre-supernova Type Ia interacting binary, if it possesses an unusually low mass. We show that, if it had a mass of 0.1 -0.2 M-circle dot, the SM star would lie at the same distance (approximate to 800pc) as the SNR as estimated by Willingale et al. (1995). However, mos t distance estimates to SN1006 are much larger than this, and there are oth er convincing arguments to suggest that the SM star lies behind this SNR. A ssuming the canonical subdwarf mass of 0.5 M-circle dot, we constrain the d istance of the SM star as 1050 pc<d<2100 pc. This places the upper limit on the distance of SN 1006 at 2.1 kpc.