[vsnet-alert 11979] quiescent GALEX detection of OT_J213806.6+261957

[Boris Gaensicke]

Dear Colleagues,

the optical transient in Pegasus, recently reported in CBET 2273 and 
CBET 2275 (currently designated VSX J213806.5+261957 or 
OT_J213806.6+261957) has been detected in the GALEX All-Sky Survey in 
quiescence (MJD=53955.8) at m(fuv)=16.15+-0.03, F(fuv)=1257.58 +/- 33.16 
microJy and m(NUV)=16.15+-0.02, F(nuv)=1260.16 +/- 23.79 microJy. The 
behaviour of this transient resembles an outburst of a WZ Sge star. The 
ultraviolet spectrum of WZ Sge stars is dominated by emission from the 
white dwarf photosphere. The flat ultraviolet spectrum of 
OT_J213806.6+261957 observed by GALEX is compatible with a white dwarf 
temperature of ~15000K, similar to that of WZ Sge itself. Assuming a 
0.6Msun white dwarf mass, the GALEX fluxes imply a distance of ~70pc. 
Such a short distance is consistent with the proper motion of the object 
discussed by Henden in CBET 2275. It appears now most likely that 
OT_J213806.6+261957 is indeed a WZ Sge star, i.e. a short-period 
cataclysmic variable with a low accretion rate and rare but 
large-amplitude outbursts, and it might be among the closest known 
members of this class.

(posted also as ATel 2605)

Best wishes,

Boris

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Dr. Boris Gaensicke                  www.warwick.ac.uk/go/BorisGaensicke
Associate Professor                        Boris.Gaensicke at warwick.ac.uk
Department of Physics
University of Warwick
Coventry CV4 7AL                                Tel: +44 (0)2476 574741
UK                                              Fax: +44 (0)2476 523672
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