Central Bureau for Astronomical Telegrams

CBAT "Transient Object Followup Reports"

TCP J21222057+4730430

TCP J21222057+4730430   2018 04 12.7414*  21 22 20.57 +47 30 43.0  10.7 U             Cyg       8 9

2018 04 12.741

Discovered by T. Kojima, Gunma-ken, Japan, on six frames with five second exposure using Canon EOS 6D digital camera + 200-mm f/3.2 lens under the limiting mag = 13.8, who writes this star was mag.= 13.4 on 2017 Sept. 16.627 and also on 2018 Mar, 27.777, mag.= 13.2 on Apr. 9.740 UT. There is a star (mag.= 13.5, R= 12.6, B= 15.3) at end figures 20s.75, 44".6.

2018 04 12.88

The star at end figures 20s.75, 44".6 mentioned by Kojima-san is USNO-B1.0 1375-0494413 (APASS magnitudes V= 13.98, B= 15.55, B-V= +1.57); it is a red dwarf (M4.5Ve) and an X-ray source (RX J2122.3+4730). According to the latest available ASAS-SN Sky Patrol observations (Shappee et al. 2014ApJ...788...48S and Kochanek et al. 2017PASP..129j4502K) this star was at V= 14.0 mag on 2018 Apr. 10.629 and 11.624 UT. Since 2014 December it was never observed brighter than V= 13.8 mag by the Sky Patrol - with one exception (outlier?): 2015 Oct. 8.382 UT, V= 13.2 mag; light curve at https://asas-sn.osu.edu/light_curves/951b8d55-6073-49ff-bfd9-2483f8a93df8. Another (probable) flare star like TCP J19083989+1210033? --- Patrick Schmeer (Saarbrücken-Bischmisheim, Germany)

2018 04 12.793

http://k-itagaki.jp/images/cyg.jpg