[vsnet-alert 15290] MASTER OT J211830.74+752621.9 - reddened CV?

Denis Denisenko d.v.denisenko at gmail.com
Thu Jan 17 15:46:45 JST 2013


Interesting optical transient in Cepheus was detected on MASTER-Amur
images on Jan. 14.474 and 14.506 UT. It was confirmed by
MASTER-Kislovodsk 8 hours later. The discovery was reported in ATel
#4738 <http://www.astronomerstelegram.org/?read=4738>.

MASTER OT J211830.74+752621.9
  20130114.474  161C  MASTER-Amur
  20130114.506  163C  MASTER-Amur
  20130114.826  164C  MASTER-Kislovodsk

The object is identical to SDSS star SDSS J211830.65+752620.7 with the
following magnitudes:
u=23.47(73), g=22.24(12), r=20.94(5), i=20.16(4), z=19.42(7)
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237663230684824475

Values of (g-r)=2.08 and (r-i)=0.78 are very large for dwarf novae. At
least no such objects are found on Fig. 2 of the paper by Kato et al.
"Characterization of Dwarf Novae Using SDSS Colors".

The galactic extinction can partially explain the red color. According
to NED extinction calculator, the reddening in this direction is
E(g-r)=0.54, E(r-i)=0.31 from Schlafly et al., 2011 and E(g-r)=0.56,
E(r-i)=0.35 from Schlegel et al., 1998. Still the object seems to be
too red at quiescence, even if it resides at the very edge of our
galaxy.

Another possibility is that SDSS magnitudes were measured at different
phases of the orbital period, and this CV is an eclipsing variable. In
both cases the object is worth of attention. Photometric time series
are needed right now to search for the orbital period. Spectroscopic
observations with large telescopes will be very interesting when the
object returns to quiescence in order to characterize the secondary
component.

Denis Denisenko


More information about the vsnet-alert mailing list