Super Soft Sources

Super Soft Sources (SSS) are characterized by radiation with effective temperatures of ∼10 to ∼10 K and luminosities of ∼10 to ∼10 erg s. The first luminous SSS in the Large Magellanic Cloud (LMC) have been discovered around 1980 with the Einstein observatory (Long et al. 1981). Optical identifications for both CAL 83 and CAL 87 established the binary nature of these sources (Cowley et al. 1990; Smale et al. 1988). During the ROSAT all-sky survey in 1990–1991 in soft X-rays (cf. Trümper et al. 1991) and pointed follow-up observations many SSS have been detected. BeppoSAX discovered super-soft X-ray emission from recurrent and classical novae. Deep observations performed with Chandra and XMM-Newton led to the discovery of SSS in nearby spiral and elliptical galaxies. A catalog of SSS is given in Greiner (2000a). Optical identifications exist for SSS in the Galaxy, the LMC, and the SMC (cf. Tab. 11.1). Here binary SSS are considered. For 7 systems orbital periods of ∼9 to ∼4 have been determined, in the range predicted for steadily nuclear burning white dwarfs (WDs) in close-binary systems undergoing unstable mass-transfer on a thermal timescale (close-binary SSS, CBSS, DiStefano and Nelson 1996; van den Heuvel et al. 1992). From binary evolutionary calculations follows that such systems may have evolved companions with masses ∼(1.3−3.0) M⊙ (Rappaport et al. 1994). U Sco is a recurrent nova. A few systems with orbital periods of 1.4 to 3.5 are classical novae (CVtype SSS): V 1974 Cyg (Krautter et al. 1996), GQ Mus (Ögelman et al. 1993), Nova LMC 1995 (Orio and Greiner 1999), and V 382 Vel (Orio et al. 2002). 1E 0035.4-7230 and RX J0537.7−7034 may have a lower mass WD. The recurrent novae RS Oph, T CrB, V394 CrA, and CI Aql 2000 have a subgiant or low-mass giant donor and modeling of the optical outburst light