A solution to a 100-yr problem -- a connection between the transition phase in classical novae and intermediate polars

Abstract

One hundred years after the eruption of GK Per and the detection of oscillations in its light curve it is still unclear why certain novae show a smooth decline in their optical light curves after outburst while others have oscillations / minimum during the `transition phase'. Two years ago we pointed out a possible connection between this phase in classical novae and intermediate polars (IPs), and predicted that novae that have the transition phase should be IPs. Chandra observations on two recent novae support this prediction. Nova V1494 Aql 99/2, which had oscillations during the transition phase, can be classified as an IP, while X-ray observations on Nova V382 Vel 1999, whose optical decline from outburst was smooth, failed to detect any short-term periodicity. About 10 percent of the CV population are IPs. This figure is consistent with the rarity of the transition phase in novae. We also present a model for this idea: the nova outburst disrupts the accretion disc only in IPs because their discs are less massive than in non-magnetic systems and their inner parts are depleted; the recovery of the disc, a few weeks-months after the eruption, causes the formation of dust.