2003A&A...406..613S

An analysis of the color indices and absolute magnitudes M_V0 of the ``classical'' supersoft X-ray binary sources (SSXBs), the V Sge-type stars (VSs), the symbiotic SSXBs, and the classical novae in the soft X-ray phase is presented. This approach can help comparing the properties and configuration of the reprocessing medium in the individual systems. The range of M_V0 of the individual objects is very large, from M_V0=8.5 to M_V0=-4, most systems having M_V0<2. The objects with the orbital period P_orb<4 days tend to possess brighter M_V0 with the increasing P_orb. The same trend is apparent also for M_U0. There is no systematic difference between the classical SSXBs and the VSs, as regards their M_V0 and M_U0. The soft X-ray phase of the novae V1974 Cyg and V382 Vel occurred at significantly brighter M_V0 than those of most other SSXBs while M_V0 of the recurrent nova U Sco was comparable to the SSXBs of the comparable P_orb. We showed that the luminosity of the reprocessing medium in the symbiotic SSXBs does not increase much with P_orb, when compared with the luminosity of the classical SSXBs and VSs; this speaks against large disks in these symbiotics. The classical SSXBs and the VSs have colors very similar each to other and form closed groups in the color-color diagrams. A Balmer jump occurs frequently in emission as inferred from the colors. The correlation between the bolometric luminosity, determined from the X-ray spectra and M_V0 or M_U0 of all kinds of the SSXBs is rather weak, but resolvable, and is more prominent for M_U0. The implications for the reprocessing medium are discussed.