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ROTSE-III discovery of a new Cataclysmic Variable

ATEL # 2126; J. Vinko, University of Texas; F. Yuan, University of Michigan; R. Quimby, California Institute of Technology; Z. Balog, University of Arizona; D. Chamarro, M. D. Sisson, C. Akerlof, S. B. Pandey, University of Michigan; J. C. Wheeler and E. Chatzopoulos, University of Texas, on behalf of the ROTSE collaboration
on 11 Jul 2009; 5:13 UT
Password Certification: Fang Yuan (yuanfang@umich.edu)

Subjects: Optical, Cataclysmic Variables, Transients, Variables

We report the discovery of a transient ROTSE3J203224.8+602837 on unfiltered CCD images taken on Jul. 06.82 UT with the 0.45-m ROTSE-IIId telescope at the TUBITAK National Observatory at Bakirlitepe, Turkey, and confirmed by the 0.45-m ROTSE-IIIb telescope at McDonald Observatory, Texas. The transient was discovered by subtracting a reference image constructed from frames taken in 2008 (limiting mag 18.5). The brightness of the source was 16.05 +/- 0.1 mag (unfiltered, tied to USNO B1.0 R-mag) at the time of discovery. The transient was subsequently detected between Jul. 7 and 10, declining to 16.4 +/- 0.2 mag on Jul. 10.26 UT. A finder chart and the ROTSE light curve is posted at the following website URL
http://rotse.net/rsvp/j203224.8+602837/j203224.8+602837.jpg
http://rotse.net/rsvp/j203224.8+602837/rotse_lc.jpg

At the position of the transient, R.A.=20h32m24s.76, Decl=+60o28'36".8 (equinox 2000.0), a faint stellar-like object is apparent on POSS-II images, with USNO B1.0 magnitudes B=20.81, R=19.71 and I=18.11. If this is the same object, the brightening of the transient was about 4 mag in the R-band. There is also an ultrasoft X-ray source within 4" of this position, listed in the Einstein IPC database, which is likely to be associated with this object. These strongly suggest that the transient is a Cataclysmic Variable (CV).

An optical spectrum obtained on Jul.09.24 UT at McDonald Obs. with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by S. C. Odewahn, shows a smooth blue continuum with weak H-alpha emission. Absorption lines due to H-beta, H-gamma and NaD are also present. A plot of the spectrum can be found at the following URL
http://rotse.net/rsvp/j203224.8+602837/het_spec_0709.jpg
The appearance of the spectrum strengthens the classification that the transient a CV, probably a dwarf nova in outburst.


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