The nebular remnant and quiescent spectrum of Nova GK Persei

Abstract

CCD images of the nebular shell of the old nova GK Per in [N II] and [O III] emission lines, and also the quiescent spectrum in the optical region, are presented. Proper motion measurements of the knots in [N II] over the baseline 1984–90 give a mean expansion rate of 0.31 ± 0.07 arcsec yr^-1. This value agrees with models of the expansion of the ejecta into the ambient circumstellar medium. A correction for projection effects indicates that the ratio of the mass of the shell to the density of the circumstellar medium is a factor of 2 – 3 higher than estimated previously. The optical spectrum is decomposed into those of the secondary and the accretion disc. The estimate of M_V = + 4.9 for the accretion disc implies a mass transfer rate of 3.5 × 10^-9 M☉ yr^-1 in the steady state. The H and He emission-line fluxes are used to infer that (i) the line-emitting region has a high density, (ii) the He/H abundance is near-solar, and (iii) the ionizing source has a Zanstra temperature of 1.3 × 10⁵ K and an effective radius of 0.01 R☉, which are consistent with its being a white dwarf.