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Pre-outburst photometry of PNV J06483343+0656236

ATel #6751; B. T. Gaensicke, J. E. Drew, G. Barentsen, R. Greimel on behalf of the IPHAS consortium
on 25 Nov 2014; 16:13 UT
Credential Certification: Boris Gaensicke (Boris.Gaensicke@warwick.ac.uk)

Subjects: Infra-Red, Optical, Cataclysmic Variable

PNV J06483343+0656236 has been identified as an optical transient in the galactic plane with an V~18th mag optical counterpart (CBAT). The transient is detected in quiescence in the IPHAS survey of the galactic plane (Drew et al. 2005, MNRAS 362, 753). The IPHAS observations were obtained on November 22, 2007, and Data Release 2 of the survey (Barentsen et al. 2014, MNRAS 444, 3230) identifies the object as IPHAS2 J064833.47+065623.2, a point source with r=18.4+-0.02, i=17.31+-0.02, and Halpha=17.02+-0.01 (in the VEGA system). The system stands out as a strong Halpha emitter in the (r-i, r-Halpha) colour-colour diagram, corroborating the suggested classification as a dwarf nova. Assuming negligible reddening towards the source (the total galactic column is only E(B-V)=0.42, Schlafly & Finkbeiner 2011, ApJ 737, 103), the r-i colour suggests an ~M2 spectral type. However, the r-i colour is subject to contamination with blue light from the white dwarf and the accretion disc, as well as the contribution of the Halpha emission line, and therefore the true spectral type of the companion star is likely somewhat later. The 2MASS (Skrutskie et al. 2006, AJ 131, 1163) observations of PNV J06483343+0656236 (J=15.892+-0.077, H=15.431+-0.117, K_s=15.013+-0.143) suggest a spectral type of M5 to M4, and imply a distance of 200-350pc. Time-series photometry reported in VSNET-outburst 17678 indicates the presence of superhumps in the optical outburst light curve, with a period of 0.105d, placing the system in the 2-3h period gap. The expected spectral type of the donor is ~M4 (Knigge et al. 2011, ApJS 194, 28), in agreement with our estimate based on the 2MASS colours. Assuming that the object was detected near its peak brightness, with a visual magnitude of 11.6, and adopting the absolute magnitude-orbital period relation for dwarf novae in outburst (Warner 1987, MNRAS 227, 23) implies a distance of ~200pc, consistent with the estimate made above.