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Nova V2467 Cyg as possible intermediate polar

ATEL # 1723; E. Swierczynski, E. Ragan, C. Galan, M. Mikolajewski (Uniwersytet Mikolaja Kopernika, Torun, Poland)
on 18 Sep 2008; 14:05 UT
Password Certification: Toma Tomov (tomtom@astri.uni.torun.pl)

Subjects: Optical, Binaries, Cataclysmic Variables, Nova

We report the results of 8 nights of unfiltered and RI band CCD photometry of the fast nova V2467Cyg (Nova Cyg 2007). The observations were carried out from 26 June to 8 July 2008 with the 60cm Cassegrain telescope of the Nicolaus Copernicus University Observatory (Torun, Poland). In total we collected 5683 frames during about 20 hours of observations.

The magnitudes estimated on July 25.94 UT were B=16.10, V=14.71, R=14.19, I=13.67. Our observed V-R and V-I color indices are more blue than those observed a few weeks after the nova outburst in 2007 April of about 2 and 2.5 mag, respectively. At the same time, the B-V color index changed from 1 to 1.4 mag. This is consistent with the entry into the nebular phase with development of strong [OIII] lines, weakening of Balmer emissions and disapearance of the previous abnormally intensive OI 8446 line (Tomov et al. 2007, IBVS 5779). We had already observed such spectral changes on October 15 and December 29, 2007, on the prismatic spectra we obtained with our 60/90cm Schmidt camera.

The most noticeable aspect in the one-night light curves are about half-hourly oscillations with mean full amplitude of ~0.1 mag, but their range varied from night to night from 0.15 mag to total disappearance (as happened, for example, on June, 28). These changes were modulated sinusoidally by another light curve component characterized by longer period and lower amplitude (~0.05 mag). Our Fourier analysis of all the data gives two distinct frequencies: 6.2771 cycles/day and 41.5646 cycles/day, corresponding to periods of 3.82h and 34.64 min, respectively.

Similar longer periods, 3.57h and 3.85h, were noticed already in 2007, several weeks after maximum (Tomov et al., 2007, IBVS 5779). Most of our one-night light curves (for example see the link below) show significant variability similar to the 'royal light curves' of FO Aqr, the so-called 'king of intermediate polars' (Patterson 1994, PASP 106, 209). Moreover, about one month after the outburst, V2467 Cyg started its transient phase in the form of a series of 6-7 oscillations with quasi-period of 20-22 days and 0.5-1.1 mag amplitude (Henden 2008, Observations from AAVSO International Database). Retter (2002, ASP Conf. Ser. 637,279) proposed a possible connection between such type of transient phase and intermediate polars.

Assuming that V2467 Cyg is most probably an intermediate polar we extracted 22 maxima and 15 minima of shorter variability, and we found the ephemeris of its spin period using the O-C diagram: HJD(MaxSpin)=2454673.485+0.024063*E. We also applied the timing method to the longer period of 3.82h. We found its phases during five particular nights by means of sinus fitting, and we obtained the orbital ephemeris: HJD(MaxOrb)=2454678.475+0.1596*E.

light curve


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