Two new CVs and ASASSN-13ak detected by MASTER

ATel #5083; S. Shurpakov, V. Yecheistov, D. Denisenko, V. Lipunov, E. Gorbovskoy, P. Balanutsa, N. Tiurina, V. Kornilov, A. Belinski, N. Shatskiy, V. Chazov, A. Kuznetsov (Moscow State University, SAI), V. Krushinsky, I. Zalozhnih, A. Popov, A. Bourdanov, A. Punanova (Ural Federal University), K. Ivanov, S. Yazev, N. Budnev, E. Konstantinov, O. Chuvalaev, V. Poleshchuk, O. Gress, A. Frolova (Irkutsk State University), A. Parkhomenko, A. Tlatov, D. Dormidontov, V. Senik (Kislovodsk solar station of the Pulkovo observatory RAS), V. Yurkov, Y. Sergienko, D. Varda, E. Sinyakov, A. Gabovich (Blagoveshchensk Educational University), P. Podvorotny, V. Shumkov (MASTER team members), H. Levato, C. Saffe (ICATE), C. Mallamaci, C. Lopez and F. Podest (OAFA)
on 24 May 2013; 16:23 UT
Credential Certification: Vladimir Lipunov (lipunov2007@gmail.com)

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MASTER OT J190121.24+471703.4 - new CV

MASTER-Kislovodsk auto-detection system discovered OT source at (RA, Dec) = 19h 01m 21.24s +47d 17m 03.4s on 2013-05-18.00310 UT. The OT unfiltered magnitude is 16.3m (limit 19.1m). The OT is seen in 2 images. We have reference image without OT on 2013-03-30.96237 UT with unfiltered magnitude limit 18.6m.

The object is not present in any catalogs. This area of sky in Lyra is not covered by SDSS. The faint star (mag ~22) is visible on the sum of digitized Palomar plates. Color-combined image (2xBRIR+OVR) centered at J190121.24+471703.4 is uploaded to http://master.sai.msu.ru/static/OT/J190121+471703-BRIR5x5.jpg

Based on the amplitude of variability (~5m) we suggest that MASTER OT J190121.24+471703.4 is a new cataclysmic variable (dwarf nova in outburst). Follow up observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/190121.24471703.4.png

MASTER OT J165153.86+702525.7 - new CV

MASTER-Kislovodsk auto-detection system discovered OT source at (RA, Dec) = 16h 51m 53.86s +70d 25m 25.7s on 2013-05-23.98875 UT. The OT unfiltered magnitude is 15.9m (limit 18.8m). The OT is seen in 3 images. We have reference image without OT on 2013-04-29.97322 UT with unfiltered magnitude limit 19.6m.

The object was also observed, but not automatically detected as a transient by MASTER-Amur a night before, on 2013-05-22.617 and 2013-05-22.646 UT (15.8m). Another outburst was found post factum in the archival MASTER-Amur images obtained a year ago, on 2012-05-13.603 (16.0m) and 2012-05-13.641 UT (15.7m).

The object at quiescence is identical to the blue star USNO-A2.0 1575-03714897 (16 51 53.82 +70 25 25.1 R=18.7 B=18.7) and USNO-B1.0 1604-0112306 (16 51 53.767 +70 25 25.55 B1=19.11 R1=18.70 B2=20.42). Color-combined (BRIR) DSS finder chart is uploaded to http://master.sai.msu.ru/static/OT/J165153+702525-BRIR5x5.jpg

Nothing is present at this position in 1RXS, 2MASS, GCVS and AAVSO VSX. This area of sky in Draco is not covered by SDSS. The OT has an UV counterpart GALEX J165154.2+702525 (FUV=21.72+/-0.34). We also note another blue star (white dwarf) 26" north-north-west of the OT which is visible as well in the UV as GALEX J165150.7+702546 (FUV=21.37+/-0.31 NUV=20.78+/-0.17).

Based on the amplitude of variability, blue color and previous detection we conclude that MASTER OT J165153.86+702525.7 is a cataclysmic variable (dwarf nova in outburst). Follow up observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/165153.86702525.7.png

MASTER-Amur confirmation of ASASSN-13ak as a CV

Following the discovery of ASASSN-13ak on 2013 May 23.46 (Stanek et al., ATel #5082) we have checked the MASTER database and found this object in the bright outburst a year ago, on 2012 May 12.707 and 12.738 UT. Unfiltered magnitude from MASTER-Amur was 14.4m (limit 17.9) and 14.5m (limit 16.8), correspondingly. Coordinates (average of two measurements) are 17h 48m 27.86s, +50d 50m 39s.2. The object was fainter than 19.0m on 2013 May 15.679 UT, eight days before the detection by ASAS-SN. Comparison of MASTER-Amur images of ASASSN-13ak in outburst (2012-05-12) and at quiescence (2013-05-15) is available at: http://master.sai.msu.ru/static/OT/174827.89505040.0.png

As already noted by T. Kato in [vsnet-alert 15742], the object is related to the faint ROSAT X-ray source 1RXS J174827.1+505053 formally 15" away (error radius 11", flux 0.0109+/-0.0035 cnts/s, hardness ratios HR1=1.00+/-0.27, HR2=0.05+/-0.30). Value of HR1=1.0 is typical for dwarf novae among ROSAT sources.

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