[vsnet-alert 17186] MASTER OT J175924.12+252031.7 - Possible Nova in Hercules (12.7m)

[Denis Denisenko]

Vladimir Vladimirov has found a bright optical transient in
MASTER-Amur data from the last night. It was published in ATel #6059
<http://www.astronomerstelegram.org/?read=6059>. Outburst amplitude is
about 8m. At mag 12.8 this is the 5th brightest object among ~550
transients discovered by MASTER!

MASTER OT J175924.12+252031.7
  20140316.0243  <180C   MASTER-Kislovodsk (latest non-detection)
  20140409.7542  12.74C  MASTER-Amur
  20140409.7554  12.84C  MASTER-Amur
  20140409.7566  12.73C  MASTER-Amur
  20140409.7881  12.71C  MASTER-Amur
  20140409.7893  12.71C  MASTER-Amur
  20140409.7905  12.78C  MASTER-Amur
  20140409.8162  12.73C  MASTER-Amur
  20140409.8174  12.75C  MASTER-Amur
  20140409.8186  12.75C  MASTER-Amur
Internal errors of photometry are formally 0.01m, but the magnitudes
can be affected by the 15.6m star nearby.

MASTER-Amur discovery and reference images:
http://master.sai.msu.ru/static/OT/175924.12252031.7.png

There are two red stars within 2" of the OT in SDSS. The brighter one
has more reliable magnitudes:
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237666229107819060
g=22.25 r=20.67 i=19.25 z=18.57

Interesting enough, it doesn't look that red on the color-combined DSS
image, suggesting a significant variability between POSS-II blue, red
and infrared plates (B1991-07-12, R1991-05-14 and IR1995-07-19,
respectively): http://master.sai.msu.ru/static/OT/J175924+252031-BRIR5x5.jpg

The star has remained nearly constant on three triplets of images over
1.5 hours. So, the UV Ceti flare can be excluded. WZ Sge scenario
appears to be impossible because of the red color. The only reasonable
possibility that's left is a classical Nova. Spectral confirmation is
requested, as well as cheking the images of this area over the last
three weeks.

Denis Denisenko
Member of MASTER team at SAI MSU