1997A&A...323L..33P

We report on a BeppoSAX Concentrator Spectrometer observation of the super-soft source (SSS) CAL87. The X-ray emission in SSS is believed to arise from nuclear burning of accreted material on the surface of a white dwarf (WD). An absorbed blackbody spectral model gives a χ_ν² of 1.18 and a temperature of 42±¹³₁₁eV. However, the derived luminosity and radius are greater than the Eddington limit and radius of a WD. Including an O VIII edge at 0.871keV gives a significantly better fit (at >95% confidence) and results in more realistic values of the source luminosity and radius. We also fit WD atmosphere models to the CAL87 spectrum. These also give reasonable bolometric luminosities and radii in the ranges 2.7-4.8x10³⁶erg/s and 8-20x10⁷cm, respectively. These results support the view that the X-ray emission from CAL87 results from nuclear burning in the atmosphere of a WD.