[vsnet-alert 15560] BY Aur outburst

[Denis Denisenko]

Bradford Robotic Telescope has detected BY Aur in outburst on the 60-sec
unfiltered image taken at 00:01:24 UT on Mar. 31. This is the first
outburst detected after the identification of this variable by MASTER team
on 2012 Sep. 27 (ATel #4428). Before 2012 MASTER detection this variable
was considered to be a Mira for 75 years. The light curve below definitely
shows it is a dwarf nova.

BY Aur
  20121022.250  17.95CV  BRT
  20121106.714   173CR   MASTER-Amur
  20121122.707   181CR   MASTER-Amur
  20121214.170  18.06CV  BRT
  20121223.071  17.82CV  BRT
  20130105.111  17.81CV  BRT
  20130111.135  17.71CV  BRT
  20130115.138  17.77CV  BRT
  20130204.588   175CR   MASTER-Amur
  20130212.029  17.77CV  BRT
  20130224.619   174CR   MASTER-Amur
  20130328.994  17.19CV  BRT
  20130331.001  15.88CV  BRT  outburst
  20130331.611   149CR   MASTER-Amur

The period of variability was listed in GCVS as 264: days from the 1937
discovery paper by H. Shapley and C. Boyd. The variable was given the name
HV 7656 with 34 epochs observed on Harvard plates. Current outburst occured
185 days after Sep. 2012 MASTER detection, so the old 264-d period is not
confirmed and may have been a yearly alias. Another outburst detected by
CRTS on JD=2455294 was 903 days before 2012 Sep. 27, also telling in favor
of ~180d cycle.

Observations of the previous outburst by Ian Miller reported by Taichi Kato
in [vsnet-alert 14961] have shown no sign of superhumps. Either it was a
normal outburst, or the star is a dwarf nova of SS Cyg type. This outburst
appears to be still growing, as shown by MASTER-Amur image taken on
14:39:40 UT. During the Sep. 2012 outburst the robotic photometry was
giving 14.5m (unfiltered with red zero point), while now the object is at
14.9m in the same setup.

Denis Denisenko