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T. Lanz (U. Maryland), G. A. Telis, M. Audard, F. Paerels (Columbia U.), I. Hubeny (NOAO)
We present a new NLTE model atmosphere analysis of Chandra HRC-S/LETG and XMM-Newton RGS spectroscopy of the supersoft source CAL 83 in the LMC. The two spectra are very similar, and reveal a very rich absorption line spectrum from the hot white dwarf photosphere. We also report a third X-ray off-state during a later Chandra observation, showing the recurrent nature of CAL 83. Moreover, we found evidence of short-timescale variability in the soft X-ray spectrum. The Chandra and XMM-Newton spectra have been successfully matched with our new NLTE line-blanketed model atmospheres that explicitly include 74 ions of the 11 most abundant species. We derived the basic stellar parameters of the hot white dwarf, obtaining the first direct spectroscopic evidence that the white dwarf is massive. The short timescale of the X-ray off-states is consistent with a high WD mass. Our analysis, therefore, provides direct support for supersoft sources as likely progenitors of SN Ia.
This work was supported by a grant from the NASA Astrophysics Theory Program. The Columbia group acknowledges support from NASA to Columbia University for XMM-Newton mission support and data analysis
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.