[vsnet-alert 17330] GUVV-2 J104325.0+563258.0 outburst

[Denis Denisenko]

MASTER-Tunka has detected an outburst of this AM CVn dwarf nova in
Ursa Major with unknown period:

GUVV-2 J104325.0+563258.0 = SDSS J104325.07+563258.2
  20140524.617   171C   MASTER-Tunka
  20140524.661   170C   MASTER-Tunka

Negative color indices in SDSS suggest an ultrashort orbital period:
SDSS J104325.07+563258.2
u=20.11(4) g=20.26(2) r=20.39(3) i=20.57(5) z=20.47(15)
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237655106761654565

The star was originally discovered as a CV in the Second GALEX UV
variability catalog (J.M. Wheatley et al., 2008). It has two entries
in GALEX data release 6 with 2.4-mag difference between the two epochs
of observations:

GALEX J104325.0+563257
FUV=18.83+/-0.01 NUV=18.69+/-0.00
2006-01-11

GALEX J104325.1+563257
NUV=16.30+/-0.01
2005-04-20

According to P. J. Carter et al. (2012), there is no sign of hydrogen
in the spectrum at quiescence, and helium lines profile is similar to
that of V406 Hya (P=33.8 min) and SDSS J1240-0159 (P=37.4 min).

The current magnitude is close to the maximum possible brightness of
this star (variability range in AAVSO VSX is 16.9-21.0 CV based on CSS
data). Time series are strongly encouraged - of course, if you can
reach 17m with a decent S/N ratio.

Denis Denisenko
Member of MASTER team at SAI MSU