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The progenitor of Nova Cygni 2006 (=V2362 Cyg)

ATel #795; D. Steeghs (CfA), R. Greimel (ING), J. Drew (Imperial College London), M. Irwin (IoA), B. Gaensicke (Warwick), P. Groot (Nijmegen), C. Knigge (Southampton) and the IPHAS collaboration
on 15 Apr 2006; 00:54 UT
Credential Certification: Danny Steeghs (dsteeghs@cfa.harvard.edu)

Subjects: Optical, Binary, Cataclysmic Variable, Nova, Transient

Referred to by ATel #: 1226

We report on the detection of the likely progenitor to Nova Cygni 2006 = V2362 Cyg (IAUC # 8697 , # 8698 , ATel #792) using images from the INT Photometric H-Alpha Survey (IPHAS; http://www.iphas.org ).

The field containing the classical nova was observed as part of our galactic plane survey on Aug. 3rd 2004 between 02:58-3:42UT using the Isaac Newton Telescope at La Palma Observatory. No clouds were present and seeing was stable, delivering a 1" image-quality sampled with 0.33" per CCD pixel. The images were calibrated using photometric standard star observations.

A single point source was detected at the position reported in IAUC # 8702 with broad-band magnitudes of r'=20.3 +/- 0.05, i'=19.76 +/- 0.07. Our two narrow-band Halpha exposures suggest a r'-Halpha color index of 0.6-0.8 on the Vega scale. Comparing its r'-i' and r'-Halpha colors with the main-sequence locus defined by the large number of field stars in our images places it well above the main-sequence, implying line emission in the Halpha passband. A r'=14.8 star sits 5" west, but has completely different colors such that the apparent Halpha emission cannot be caused by contamination from this nearby star.

The total galactic extinction along the line of sight amounts to E(B-V)=0.8 (from Schlegel et al. (1998) dust-maps as well as our own field star photometry), while outburst spectroscopy indicates E(B-V)=0.56 (IAUC # 8702 ). Our IPHAS colors are consistent with an optically thick accretion disk spectrum reddened to E(B-V)=0.65 +/-0.05, corresponding to an Halpha EW of 40 +/- 15 (see also Drew et al. 2005, MNRAS 362, 752). These properties all fit well with a classical nova progenitor identification and we thus propose this to be the quiescent counterpart to V2362 Cyg.

Our quiescent colors imply an outburst amplitude of ~12 magnitudes, and assuming a typical M(V)=3-5 for a pre-nova cataclysmic variable accreting at high rates would place the system at 5-12 kpc.

IPHAS finding charts containing V2362 Cyg progenitor (PDF)