RX J0439.8-6809 and RX J0550.0-7151

P. C. Schmidtke and A. P. Cowley, Arizona State University, communicate: "Using data obtained at Cerro Tololo Interamerican Observatory in November, we report the optical identification of two supersoft x-ray sources in the Large Magellanic Cloud. Within the x-ray error circle (Greiner et al. 1994, A.Ap. 281, L61) for RX J0439.8-6809, we find that Star 8 (R.A. = 4h39m49s.6, Decl. = -68o09'02", equinox 2000.0; mean V about 21.8) varies by over half a magnitude on a timescale of less than a day. The star's exceptionally blue colors of B-V = -0.36 and U-B = -1.22 strongly suggest that it is the optical counterpart of this supersoft x-ray source. If at the distance of the LMC, an absolute magnitude of about +3.5 is indicated. From a ROSAT HRI image, an improved position has been obtained for RX J0550.0-7151, a variable, supersoft x-ray source (R.A. = 5h49m46s.7, Decl. = -71o49'38"; Cowley et al. 1993, Ap.J. 418, L63). The source is nearly coincident with a red star (V = 13.53, B-V = +1.45, U-B = +0.86) at R.A. = 5h49m46s.4, Decl. = -71o49'35". Its colors are consistent with a symbiotic or a composite system containing a cool star plus a white dwarf, but spectra are needed."