[vsnet-outburst 14652] BY Aur (ATEL 4428)

[Taichi Kato]

from ATEL #4428

MASTER OT J063748.27+442910.9 - outburst of BY Aur (dwarf nova, not 
a Mira!)

MASTER-Kislovodsk auto-detection system discovered OT source at (RA, Dec)
= 06h 37m 48.27s +44d 29m 10.9s on 2012-09-27.05770 UT. 
The OT unfiltered magnitude is 14.4m (limit 19.9m). 

The OT is seen in 11 images.  

We have reference image without OT on 2011-11-04.97069 UT with unfiltered
magnitude limit 20.4m. 

This object is identical to the 17-18th mag. star USNO-B1.0 
1344-0174217 (R.A.=06 37 48.330 Dec.=+44 29 11.10 B1=18.56 R1=17.24 
B2=17.94 R2=17.07 I=16.47) and to the infrared object 2MASS 
06374833+4429107 (J=15.95+/-0.08 H=15.29+/-0.09 K=14.95+/-0.11). There

is also an ultraviolet object at the same position GALEX 
J063748.3+442911 (FUV=21.76+/-0.33 NUV=21.63+/-0.28). 

We note that there is a variable star BY Aur (formerly Harvard 
Variable 7656) with GCVS position 21" away from MASTER OT 
J063748.27+442910.9. It is listed in catalogues of variable stars as 
Mira-type variable. Its 1900.0 coordinates from the original paper (H.

Shapley and C. Boyd, 1937) were given with the precision of 1s in R.A.

and 0.1' in Dec.: 6h30m32s, +44o34.0'. Precessed to J2000.0 epoch this

gives 6h37m49s, +44o29.0' (keeping the original precision). This is 
13" (0.2') from USNO-B1.0 1344-0174217. The next star (USNO-B1.0 
1344-0174211) is 19" (0.3') away and is not variable. 

This area was observed by <a 
href="http://skyview.gsfc.nasa.gov/skymorph/skymorph.html">Palomar/NEAT</a>

project with 30 images obtained in 10 different nights from 1997 Oct. 
29 to 2003 Feb. 10. OT J063748.27+442910.9 was found in outburst to 
16.2m on three images taken on 2003 Feb. 10 and at quiescent level 
(17.3-17.5m) on all other images. 

There was also an outburst to 15.1m on JD=2455294 in <a 
href="http://nesssi.cacr.caltech.edu/DataRelease/">CRTS data</a> and 
possible another one to 16.2m on JD=2455679. 

Based on the shape of the archival light curve and detection of 
previous outbursts we conclude that MASTER OT J063748.27+442910.9 is a

dwarf nova identical to the variable BY Aur whose previous 
identification was incorrect. Follow up observations are required. 

The discovery and reference images are available at: 
http://master.sai.msu.ru/static/OT/063748.27442910.9.png