Do novae have optically thick winds during outburst with large deviations from spherical symmetry?

UPMC-CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
e-mail: fried@iap.fr

Received: 22 December 2010
Accepted: 10 October 2011

Abstract

Context. The evidence for the presence of optically thick winds that are produced by classical novae after optical maximum has been challenged in recent papers. In addition, signs of orbital phase-dependent photometric variations, sometimes seen quite early in the development of nova outbursts, are hard to interpret in the framework of optically thick envelopes and especially winds.

Aims. A general discussion of the assumption of optically thick winds with increasing ejection velocities during the early stages of novae after their explosion is needed, also to clarify ideas about novae and in particular to contribute to the understanding of the behaviour of novae V1500 Cyg and V1493 Aql, which show phase-dependent variations during the very early decline after the outburst.

Methods. We considered possible ways of overcoming the apparent contradiction of phase-ependent variations through the production of deviations from spherical symmetry of the winds and made order-of-magnitude estimates for different theoretical scenarios that might produce these deviations.

Results. We found that large deviations from the spherical symmetry of the optically thick winds in early phases after the explosion can easily explain the problem of variations. In particular, the presence of a magnetic field might have had a non-negligible effect on the wind of V1500 Cyg, while at the present there is not enough information available concerning V1493 Aql.

Conclusions. Optically thick winds/envelopes are almost certainly present in the early stages after the optical maximum of a nova, while it is difficult to make pure Hubble-flow models fit the observations of those stages. New more detailed observational and theoretical work, in particular including the effects of magnetic fields on the winds, is needed.