Program: GN-2015B-Q-56

We propose spectroscopic observations of two persistent supersoft X-ray sources in M31, which we selected as likely symbiotic stars with a hydrogen burning white dwarf. They are interesting for type I supernova progenitor studies and very relevant to understand binary stars' evolution in general. Symbiotics hosting a very hot white dwarf show very characteristic, clearly distinguishable optical spectra with prominent Balmer emission lines and forbidden lines of higly ionized metals. M31 hosts a large population of over a hundred supersoft X-ray sources and of symbiotics (only the 35 most luminous have recently been discovered) and it is important to initiate the statistics of such binaries. The lines' redshift will prove or disprove M31 membership of the optical counterparts.