[vsnet-alert 16026] ASASSN-13br

[Denis Denisenko]

Kris Stanek wrote:

ASASSN-13br              17:03:43.01    66:07:45.5    2013-07-19.34  14.84

The object seems to be very interesting! At the first glance it seems
to be originating from SDSS J170342.86+660741.1 = USNO-B1.0
1561-0163484, but there are strong doubts after the close inspection
of SDSS data and Palomar images.

1. SDSS J170342.86+660741.1 has very large (u-g) color index for the
cataclysmic variable:
u=18.93 g=17.78 r=17.42 i=17.25 z=17.23
http://skyserver.sdss3.org/dr8/en/tools/explore/obj.asp?id=1237651310532100373
It looks more like a single white dwarf rather than a cataclysmic binary.

2. SDSS J170342.86+660741.1 is more than 4" south from ASASSN-13br.
This is too much a difference even for a wide-field setup like Brutus
with a large image scale.

3. MASTER follow up observations are giving the coordinates 17 03
43.10 +66 07 44.4 which are also 1.5" east and 3" north of SDSS
J170342.86+660741.1. MASTER-II image scale is 1.88"/pixel, errors of
astrometry are less than 1".

4. There is a faint (~21.5m) blue star on SDSS image and
color-combined DSS plates exactly at this position! It is merged with
the brighter 17m star at 11 o'clock direction (that is, in PA~30). And
there seems to be a proper motion between 1953 POSS-I and 1988 POSS-II
blue plates!

5. USNO-B1.0 1561-0163484 (17 03 42.897 +66 07 41.20 B1=17.42 R1=17.36
B2=17.70 R2=17.24 I=16.84) has a zero proper motion in USNO-B1.0! That
is, less than 4 mas/yr and less than 0.25" in 60 years from POSS-I
epoch.

6. Finally, there were no outbursts in 8 years of Catalina Sky Survey
data. Object was constant within the errors at 17.4m.

Thus, ASASSN-13br may be a UGWZ-type dwarf nova with outburst amplitude of ~7m!

Denis Denisenko (back to Moscow after a short vacation in Montenegro)

P.S. Follow-up photometry from MASTER:

ASASSN-13br
  20130720.871  14.61  MASTER-Kislovodsk
  20130720.872  14.57  MASTER-Kislovodsk