New CV detected by MASTER

ATel #5255; S. Shurpakov, D. Denisenko, V. Lipunov, E. Gorbovskoy, P. Balanutsa, N. Tiurina, V. Kornilov, A. Belinski, N. Shatskiy, V. Chazov, A. Kuznetsov, V. Yecheistov (Moscow State University, SAI), V. Yurkov, Y. Sergienko, D. Varda, E. Sinyakov, A. Gabovich (Blagoveshchensk Educational University), K. Ivanov, S. Yazev, N. Budnev, E. Konstantinov, O. Chuvalaev, V. Poleshchuk, O. Gress, A. Frolova (Irkutsk State University), V. Krushinsky, I. Zalozhnih, A. Popov, A. Bourdanov (Ural Federal University), A. Parkhomenko, A. Tlatov, D. Dormidontov, V. Senik (Kislovodsk solar station of the Pulkovo observatory RAS), P. Podvorotny, V. Shumkov (MASTER team members), H. Levato, C. Saffe (ICATE), C. Mallamaci, C. Lopez and F. Podest (OAFA)
on 7 Aug 2013; 11:05 UT
Credential Certification: Vladimir Lipunov (lipunov2007@gmail.com)

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MASTER OT J204723.04+072759.1 - new bright CV

MASTER-Amur auto-detection system discovered OT source at (RA, Dec) = 20h 47m 23.04s +07d 27m 59.1s on 2013-08-05.60683 UT. The OT unfiltered magnitude is 15.5m (limit 18.2m). The OT is seen in 6 images. There is no minor planet at this place. We have reference image without OT on 2013-04-21.80722 UT with unfiltered magnitude limit 16.5m.

The OT is located within 1.5" of the faint blue star which is present on digitized Palomar plates, in USNO-B catalogue as USNO-B1.0 0974-0693904 (20 47 22.960 +07 28 00.20 B1=20.56 B2=21.42) and in GSC 2.3.2 with jmag=21.58. There is a ~17.5m star 6" East (in PA~100) of the OT which can contaminate the measured magnitude of the new variable. Color-combined (BRIR) DSS finder chart is uploaded to http://master.sai.msu.ru/static/OT/J204723+072759-BRIR5x5.jpg

The object has an UV counterpart GALEX J204723.0+072800 (FUV=21.17+/-0.34, NUV=21.51+/-0.27). There is nothing at this position in 2MASS, 1RXS, GCVS and AAVSO VSX. The nearest known variable star is NN Del (eclipsing binary with the highly eccentric orbit) 10' away. No previous outbursts were detected by Catalina Sky Survey. This area of sky in Delphinus is not covered by SDSS.

Based on the UV detection by GALEX and outburst amplitude (~5.5m) we conclude that MASTER OT J204723.04+072759.1 is a new cataclysmic variable, most likely a dwarf nova of UGSU (SU UMa) type in superoutburst. Follow up observations, as well as checking the archival observations of this field are encouraged. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/204723.04072759.1.png

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