Research Note

On the progenitor system of Nova V2491 Cygni

¹ Astrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD, UK
e-mail: M.Darnley@astro.ljmu.ac.uk
² INAF Astronomical Observatory of Padova, via dell’Osservatorio, 36012 Asiago (VI), Italy
³ ANS Collaboration c/o Astronomical Observatory, 36012 Asiago (VI), Italy

Received: 1 November 2010
Accepted: 12 April 2011

Abstract

Nova V2491 Cyg is one of just two detected pre-outburst in X-rays. The light curve of this nova exhibited a rare “re-brightening” which has been attributed by some as the system being a polar, whilst others claim that a magnetic WD is unlikely. By virtue of the nature of X-ray and spectroscopic observations the system has been proposed as a recurrent nova, however the adoption of a 0.1 day orbital period is generally seen as incompatible with such a system. In this research note we address the nature of the progenitor system and the source of the 0.1 day periodicity. Through the combination of Liverpool Telescope observations with published data and archival 2MASS data we show that V2491 Cyg, at a distance of 10.5–14 kpc, is likely to be a recurrent nova of the U Sco-class; containing a sub-giant secondary and an accretion disk, rather than accretion directly onto the poles. We show that there is little evidence, at quiescence, supporting a  ~ 0.1 day periodicity, the variation seen at this stage is likely caused by flickering of a re-established accretion disk. We propose that the periodicity seen shortly after outburst is more likely related to the outburst rather than the – then obscured – binary system. Finally we address the distance to the system, and show that a significantly lower distance (~2 kpc) would result in a severely under-luminous outburst, and as such favour the larger distance and the recurrent nova scenario.