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New CV candidate in Kepler field

ATel #6224; D. Denisenko (Sternberg Astronomical Institute of Moscow State University), D. G. Hedges, C. J. Tallon, J. E.F. Baruch (Robotic Telescope Group, University of Bradford)
on 10 Jun 2014; 18:50 UT
Credential Certification: Denis Denisenko (d.v.denisenko@gmail.com)

Subjects: Optical, Cataclysmic Variable

During the routine observations of cataclysmic variables DDE 20 and DDE 21 with the Bradford Robotic Telescope's Galaxy camera (0.36-m f/5.3 reflector + 1kx1k CCD, see http://www.telescope.org for more details) we have found the new large-amplitude variable star at the following position (J2000.0): R.A. = 19h22m57s.15, Decl. = +42o04'30".2 which is 13.5' east of DDE 20. Since the FOV of Galaxy camera is approximately 25'x24' with 1.43"/pixel scale, the new variable was outside the field on most images centered at DDE 20. It only appears on 4 images with the pointing slightly offset. On June 07 discovery image the new variable is located 18 pixels from the camera edge. The following magnitudes were measured from those 4 images (unfiltered with V zero point using V=14.42 for 144 comparison star from AAVSO sequence for DDE 20):

Date, yy-mm-dd    Date, JD   CVmag 
---------------------------------- 
2012-05-20.205  2456067.705  17.37 
2012-06-25.106  2456103.606  17.56 
2014-05-25.199  2456802.699  17.30 
2014-06-07.153  2456815.653 <19.50 
---------------------------------- 
The new variable is identical to the star USNO-B1.0 1320-0391697 (19 22 57.105 +42 04 30.27 B1=19.61 R1=17.60 B2=19.61 R2=17.12 I=16.77) = 2MASS J19225714+4204297 (J=16.51+/-0.10 H=16.15+/-0.19 K=15.74+/-0.23). It has an UV counterpart with three entries in GALEX Data Release 6: GALEX J192257.1+420429 (NUV=19.40+/-0.05), GALEX J192257.1+420430 (NUV=20.02+/-0.10) and GALEX J192257.1+420429 (NUV=19.57+/-0.05). No Far UV images are available for this field. There is nothing at this position in 1RXS, GCVS and AAVSO VSX. This area of sky in Lyra is not covered by SDSS, NEAT and Catalina Sky Survey.

Following the naming scheme used before, the new variable was designated DDE 33. Color-combined DSS finder chart is uploaded to http://master.sai.msu.ru/static/OT/DDE33-BRIR.jpg (10'x10' FOV). The star is showing significant variability on the digitized Palomar plates. There are two 2nd epoch plates in each band (B, R and IR). The star was ~2m brighter on 1988-07-09 blue plate than on 1990-07-18 and 1951-07-09. Comparison of POSS-II blue plates and 2011 GALEX NUV image is uploaded to http://master.sai.msu.ru/static/OT/DDE33-POSS-B-GALEX.jpg (5'x5' FOV).

This star was included into Kepler Input Catalog as KIC 6602671 (g=17.07 r=17.07 i=17.10) and Kepler-INT survey as KIS J192257.13+420429.9 (U=17.25 g=17.11 r=16.92 i=16.73). The blue color and UV magnitudes are telling in favor that the object can be a cataclysmic variable. Follow up observations (spectroscopy and photometric time series) are strongly encouraged to determine the type and orbital period of this CV candidate. Checking the archival data of this field is also requested.

Variable Stars discovered by DDE