A UV and optical study of 18 old novae with Gaia DR2 distances: mass accretion rates, physical parameters, and MMRD

Abstract

We combine the results of our earlier study of the UV characteristics of 18 classical novae (CNe) with data from the literature and with the recent precise distance determinations from the Gaia satellite to investigate the statistical properties of old novae. All final parameters for the sample include a detailed treatment of the errors and their propagation. The physical properties reported here include the absolute magnitudes at maximum and minimum, a new maximum magnitude versus rate of decline (MMRD) relation, and the inclination-corrected 1100-6000-Å accretion disk luminosity. Most importantly, these data have allowed us to derive a homogenous set of accretion rates in quiescence for the 18 novae. All novae in the sample were super-Eddington during outburst, with an average absolute magnitude at maximum of −7.5 ± 1.0. The average absolute magnitude at minimum corrected for inclination is 3.9 ± 1.0. The median mass accretion rate is logṀ 1M = −8.52 (using 1M as WD mass for all novae) or logṀ M WD = −8.48 (using the individual WD masses). These values are lower than those assumed in studies of CNe evolution and appear to attenuate the need for a hibernation hypothesis to interpret the nova phenomenon. We identified a number of correlations among the physical parameters of the quiescent and eruptive phases, some already known but others new and even surprising. Several quantities correlate with the speed class t 3 including, unexpectedly, the mass accretion rate (Ṁ). This rate correlates also with the absolute magnitude at minimum corrected for inclination, and with the outburst amplitude, providing new and simple ways to estimateṀ through its functional dependence on (more) easily observed quantities. There is no correlation betweenṀ and the orbital period.It should be stressed, however, that reliable statements abouṫ M -the non plus ultra of binary evolution according to Patterson (2011) -can be found only for objects with welldetermined distance and reddening, and by observations covering the satellite UV range (hereafter, simply UV) because the bulk of the accretion luminosity is emitted in this spectral region (Wade & Hubeny 1998). The homogeneous UV data on spectral energy distributions (SEDs) in Paper I are therefore of high relevance for this topic, and since old novae are (unlike other CVs, e.g., DNe) nearly stable accretors (Honeycutt et al 1998;Retter & Naylor 2000;Puebla et al 2007) their accretion luminosity anḋ M can be determined with higher precision.We note that throughout this paper accretion rate is used to indicate the mass transfer rate through the disk (the one that we derive from the observed disk luminosity). Other kinds of accretion rates that may be at play in these systems, for example the mass-loss rate from the donor, the accretion rate on to the WD, or the mass loss from the disk (e.g., via a wind or outflow through the boundary layer) cannot be determined from our data, and should not be confused with the accretion through the disk.In Paper I (Selvelli and Gilmozzi, 2013), we stud...

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