Computer Science
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...4e..16s&link_type=abstract
The Ultraviolet Universe: Stars from Birth to Death, 26th meeting of the IAU, Joint Discussion 4, 16-17 August 2006, Prague, Cze
Computer Science
Scientific paper
Super-soft X-ray sources (SSXSs) are unique binary systems with a very high mass transfer rate onto the white dwarf (WD) (dm/dt~10^-7 Mo/yr). Such a high dm/dt gives rise to a steady nuclear burning of accreted hydrogen on the surface of the WD (e.g. model by van den Heuvel et al. 1992), and consequently to an intense soft X-ray emission. Its reprocessing on the disk and donor makes SSXS bright source in the ultraviolet and optical. Most SSXS are observed in the Magellanic Clouds. V Sge is one of a few SSXSs located in our Galaxy and is called the representative of the V Sge-type class. This system is very active in various spectral passbands. Here we concentrate on the long-term optical activity of this system in the context of SSXSs. We show that this activity in V Sge underwent dramatic evolution during the recent decades. We also find that in so-called active segments (usually displaying high/low states) cycles are often apparent but their length undergoes large, often gradual variations. We give the implications for the accretion wind evolution (model by Hachisu and Kato 2003): an increase of the mass outflow rate from the donor is in plausible agreement with the observations. We also analyse the color indices and absolute magnitudes of V Sge and compare them with those of the `classical' (SSXBs), the V Sge-type class, the symbiotic SSXBs, and the classical novae in the soft X-ray phase. This approach helps comparing the properties and configuration of the reprocessing medium in the individual systems. We also show that there is no systematic difference between the classical SSXBs and the V Sge-type class, as regards their V and U band absolute magnitudes. Since soft X-rays are easily absorbed, only a small fraction of SSXSs is identified as such. The activity and properties in the ultraviolet and optical can thus serve as a useful method for identification of SSXSs.
Mattei Janet A.
Simon Veronica
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