[vsnet-alert 18771] New bright CV DDE 35 = 1RXS J105503.5+681208 (13-17m) in UMa

[Denis Denisenko]

Inspired by the recent outburst of V404 Cyg = 1RXS J202405.3+335157
(flux 0.0211+/-0.0064 cnts/s HR1=1.00+/-0.22 HR2=1.00+/-0.36) I have
re-started my old program of variability search around unidentified
X-ray sources and extracted a list of faint 1RXS with the hardness
ratios equal to unity. Of course, the chances to find another twin of
V404 Cyg are very low compared to more abundant cataclysmic variables
(dwarf novae) with the same HR1=HR2=1.0. For example, Var Cam 06 was
an outburst from 1RXS J055722.9+683219 with the hardness of 1.0.

Having checked less than 10 per cent of selected ROSAT sources I have
found two faint suspect CVs and then a surprisingly bright object with
outbursts to 13m from the quiescent mag 17! This is even brighter than
DDE 8 = 1RXS J231935.0+364705 in Andromeda which has ROSAT flux of
0.0545+/-0.0098 cnts/s and variability range of 17.6-13.6 in
USNO-B1.0.

And the new variable is:

1RXS J105503.5+681208 (flux=0.0102+/-0.0048 cnts/s HR1=1.00+/-0.61
HR2=1.00+/-0.50)
GALEX J105459.2+681153 (FUV=16.48+/-0.03 NUV=16.14+/-0.01)
USNO-B1.0 1581-0156449 (10 54 59.417 +68 11 52.87  pmRA=0  pmDE=0
B1=16.84 R1=N/A B2=15.94 R2=15.06 I=14.76)
2MASS J10545932+6811532 (J=15.028: H=14.915+/-0.091 K=14.984+/-0.134)

Color-combined (BRI) finder chart from POSS-II plates:
http://hea.iki.rssi.ru/~denis/J1055+6812-BRIR.jpg (10'x10' FOV).

It has got the number 35 in the list of variables discovered by DDE
(see http://hea.iki.rssi.ru/~denis/VarDDE.html for the latest
version). The list was started eight years ago while I was working at
Space Research Institute (IKI) and still remains there after I have
moved to SAI MSU and changed my E-mail address.

The new variable has an old outburst 62 years ago on the POSS-I blue
and red plates in February-April 1953 fading below the POSS-II level
by 1954. Animation of four blue plates in 1953-1954 is uploaded to
http://hea.iki.rssi.ru/~denis/DDE35-POSS-blue-anim.gif The variable
becomes brighter than its neibour on 1953-03-07 plate! If it was an
outburst, it was lasting at least for two months (object was already
bright on 1953-02-08, still bright on 1953-04-12 and very faint on
1954-02-09 plate where the third fainter component shows about 5"
south of the variable).

There was a possible outburst in May 1999 in NSVS (ROTSE-I) data. The
star is a blend with 13m neighbor for NSVS (and ASAS-SN). Here is the
light curve of NSVS 867733:
http://skydot.lanl.gov/nsvs/star.php?num=867733&mask=32004 Note the
brightening at JD=2451308 which lasted about 10 days. The zoomed
version of possible 1999 outburst:
http://hea.iki.rssi.ru/~denis/DDE35-NSVS-outburst.gif

I have provisionally classified the variable as a dwarf nova, but with
a semicolon UG: for uncertainty. The prolonged high state in 1953
could have been not a dwarf nova outburst, but really a high state of
anti-nova (VY) or a polar (AM). Or, less likely, an LMXB analogous to
V404 Cyg. We won't know until we get an orbital period.

Though the object is best viewed in spring months, it is circumpolar
in mid-northern latitudes. I advise to add it to your CV monitoring
list, if you are interested in 13-mag dwarf nova. I also strongly
recommend checking the archival data of surveys like DASCH, ASAS-SN,
ROTSE, MASTER and Catalina. This field is not covered by Moscow
collection of photographic plates. There are only four Heidelberg
plates with very poor limits.

The new variable has been submitted to AAVSO VSX as DDE 35 at 10 54
59.32 +68 11 53.2 (2MASS position) and is awaiting the approval by VSX
Administrator.

Denis Denisenko
Sternberg Astronomical Institute of Moscow State University