Supersoft X-ray source: Difference between revisions

Revision as of 15:07, 24 August 2017

Revision as of 15:07, 24 August 2017

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===V751 Cyg===

V751 Cyg (BB, MW) is a VY Scl CV, has a bolometric luminosity of 6.5 x 10³⁶ erg/s,<ref name=Greiner/> and emits soft X-rays at quiescence.<ref name=Patterson>{{ cite journal |doi=10.1086/317973 |display-authors=4 |author=Patterson J |author2=Thorstensen JR |author3=Fried R|author4=Skillman DR |author5=Cook LM |author6=Jensen L |title=Superhumps in Cataclysmic Binaries. XX. V751 Cygni |journal=Publ. Astron. Soc. Pac.) |date=Jan 2001 |volume=113 |issue=779 |pages=72–81 |bibcode=2001PASP..113...72P }}</ref> The discovery of a weak soft X-ray source of V751 Cyg at minimum presents a challenge as this is unusual for CVs which commonly display weak hard X-ray emission at quiescence.<ref name=Patterson/>

The high luminosity (6.5 x 10³⁶ erg/s) is particularly hard to understand in the context of VY Scl stars generally, because observations suggest that the binaries become simple red dwarf + white dwarf pairs at quiescence (the disk mostly disappears).<ref name=Patterson/> "A high luminosity in soft X-rays poses an additional problem of understanding why the spectrum is of only modest excitation."<ref name=Patterson/> The ratio He II λ4686/Hβ did not exceed ~0.5 in any of the spectra recorded up to 2001, which is typical for accretion-powered CVs and does not approach the ratio of 2 commonly seen in supersoft binaries (CBSS).<ref name=Patterson/>