[vsnet-alert 16981] MASTER OT J190519.41+301524.4 - unusual CV in Lyra

[Denis Denisenko]

We have found new very interesting cataclysmic variable in MASTER
data, see ATel #5953 <http://www.astronomerstelegram.org/?read=5953>.
The discovery was serendipitous, actually in part due to the erroneous
photometric calibration of the reference frame in Kislovodsk database.
In short, the robot has assigned the wrong magnitude to this star on
the old database image from 2010! Otherwise the star wouldn't have
been discovered for a long lime.

The variable is not an SU UMa type dwarf nova, but nevertheless
interesting. Why? It is quite bright (unfiltered mag 15.2-15.8 over
the last three years of systematic observations by MASTER) with what
seems to be the only excursion below 19m on the POSS-II red plate of
1987 June 21. See the magnitudes in USNO-B1.0:

USNO-B1.0 1202-0321874
19 05 19.411 +30 15 24.74 B1=16.32 R1=15.65 B2=17.84 R2=N/A I=16.39

GSC 2.3.2 gives Fmag=19.41 (not mentioned in ATel).

Comparison of 1st and 2nd epoch Palomar red plates:
http://master.sai.msu.ru/static/OT/J190519+301524-POSS-Red.jpg (5'x5'
FOV)
Color-combined (BRIR) finder chart:
http://master.sai.msu.ru/static/OT/J190519+301524-BRIR5x5.jpg (2x
zoom)

There is quite a bright UV counterpart GALEX J190519.4+301525
(FUV=17.66, NUV=17.46), but nothing in 1RXS catalog! ROSAT was easily
detecting CVs down to 18m at quiescence. The non-detection in 1RXS can
be explained by the low state during the ROSAT mission. From the light
curve one can think the object is either a polar (AM Her), anti-nova
(VY Scl type) or deeply eclipsing white dwarf. My experience and
intuition are telling that VY Scl scenario takes place here. Were it a
polar, it would've been detected by ROSAT even in the low state.

Optical spectroscopy and time-resolved photometry are required. Of
course, this area in Lyra will be better observable starting from May.
Currently it has rather short morning visibility. But the object is
already well worth of adding it to the regular monitoring program.

Denis Denisenko
Member of MASTER team at SAI MSU