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Session 77 - Binary Stars.
Display session, Wednesday, January 15
Metropolitan Ballroom,
Dozens of Super-Soft Sources (SSS) have been discovered and studied with Einstein and ROSAT. It is generally believed that SSS are binary systems in which soft X-rays are produced through nuclear burning on the accreting white dwarves. The ASCA satellite has observed the two ``hardest'' super-soft sources CAL87 and RXJ0925.7--475, which are practically the only SSS emitting enough number of photons in the ASCA SIS band (> 0.4 keV). CAL87 indicates a strong OVII edge at 0.74 keV and a flat spectrum below the edge. This is as expected from theoretical LTE/NLTE spectral models of white-dwarf atmosphere at T_eff \sim 8 \times 10^5 K. On the other hand, the OVIII and NeIX absorption edges in RXJ0925.7--475, which are expected from the LTE/NLTE models, are much weaker, and instead the NeX edge is observed. We will present the results of detailed energy spectral analysis and discuss possible origin of the difference of the two energy spectra.
