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 1/yr. 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 optical spectrum is decomposed into those of the secondary and the accretion disc. The estimate of Mv = + 4.9 for the accretion disc implies a mass transfer rate of 3.5 x 10 to the power -9 M? 1/yr 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 x 10 to the power 5K and an effective radius of 0.01 R?, which are consistent with its being a white dwarf.
