Astron. Astrophys. 354, L37-L40 (2000)

1. Introduction

Luminous supersoft X-ray sources (SSS) have been established as a new and distinct class of objects which are observationally distinguished by their very soft X-ray spectra with temperatures on the order of 30 eV and luminosities of erg s^-1 (for recent reviews see Kahabka & van den Heuvel 1997; van Teeseling 1998). Several SSS have been identified as accreting close binaries with orbital periods of 1 day or less. The most popular interpretation of these systems involves a white dwarf which accretes matter via Roche-lobe overflow and an accretion disk at a rate of /yr, sufficient to permit stable quasi-steady nuclear shell-burning in the surface layers of the white dwarf, either because of thermal timescale mass transfer from a more massive (slightly evolved) main sequence companion (van den Heuvel et al. 1992) or because of wind-driven mass transfer from a low-mass irradiated companion (van Teeseling & King 1998).

© European Southern Observatory (ESO) 2000

Online publication: January 31, 2000
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