SIMBAD references

Simulating ROSAT PSPC hardness ratios HR1 and HR2 and count rates for NLTE white dwarf atmosphere spectra one finds that the 15 supersoft sources in the spiral galaxy M 31 contain hot ≃3.0-4.5x10⁵K white dwarfs. If they undergo steady nuclear burning and if they are located close to the stability line then they harbor massive white dwarfs M_WD≃0.85-1.0M_☉ in agreement with what has been found for the galactic supersoft sources. The recurrent supersoft transient RX J0045.4+4154 affords a very hot ≃8.4x10⁵K white dwarf. If it is on the stability line then it has a white dwarf mass of ≃1.26M_☉. Taking a mass distribution of steadily nuclear burning white dwarfs into account one expects that there exist at least about 650 supersoft sources in M 31. The spectral parameters of the so far most distant (D∼1.3Mpc) supersoft source found in the galaxy NGC 55 imply a hot (∼6x10⁵K) and massive (M_WD∼1.1M_☉) white dwarf. The number of such sources seen in a galaxy at this distance is derived from a luminosity function of supersoft sources.