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Astron. Astrophys. 332, 199-203 (1998)

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A BeppoSAX LECS observation of the super-soft X-ray source CAL 83

A.N. Parmar 1, P. Kahabka 2, H.W. Hartmann 3, J. Heise 3 and B.G. Taylor 1

1 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
2 Astronomical Institute and Center for High Energy Astrophysics, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received 24 September 1997 / Accepted 1 December 1997


We report on a BeppoSAX Low-Energy Concentrator Spectrometer (LECS) observation of the super-soft source (SSS) CAL 83. The X-ray emission in SSS is believed to arise from nuclear burning of accreted material on the surface of a white dwarf (WD). The LECS spectrum of CAL 83 can be well fit by both absorbed blackbody and WD atmosphere models. If the absorption is constrained to be equal to the value derived from Hubble Space Telescope measurements, then the best-fit blackbody temperature is [FORMULA]  eV while a Non Local Thermal Equilibrium (NLTE) WD atmosphere model gives a lower temperature of [FORMULA]  eV. In contrast to CAL 87, there are no strong absorption edges visible in the X-ray spectrum with a 68% confidence upper limit of 2.3 to the optical depth of a C VI edge at 0.49 keV predicted by WD atmosphere models. The luminosity and radius derived from the NLTE fit are consistent with the values predicted for stable nuclear burning on the surface of a [FORMULA] 0.9-1.0 [FORMULA] WD.

Key words: accretion, accretion disks – binaries: close – stars: individual: CAL 83 – white dwarfs – X-rays: stars

Send offprint requests to: A.N. Parmar (aparmar@astro.estec.esa.nl)

© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998