The distances to Novae as seen by Gaia

Abstract

The Gaia spacecraft has just released a large set of parallaxes, including 41 novae for which the fractional error is <30%. I have used these to evaluate the accuracy and bias of the many prior methods for getting nova-distances. The best of the prior methods is the geometrical parallaxes from HST for just four novae, although the real error bars are 3× larger than stated. The canonical method for prior nova-distances has been the expansion parallaxes from the nova shells, but this method is found to have real 1-sigma uncertainty of 0.95 mag in the distance modulus, and the prior quoted error bars are on average 3.6× worse than advertised. The many variations on the 'maximum-magnitude-rate-of-decline' (MMRD) relation are all found to be poor, too poor to be useable, and even to be non-applicable for 5-out-of-7 samples of nova, so the MMRD should no longer be used. The prior method of using various measures of the extinction from the interstellar medium have been notoriously bad, but now a new version byÖzdönmez and coworkers has improved this to an unbiased method with 1-sigma uncertainty of 1.14 mag in the distance modulus. For the future, I recommend in order (1) using the Gaia parallax, (2) using the catalog ofÖzdönmez, (3) using M max = -7.0±1.4 mag as an empirical method of poor accuracy, and (4) if none of these methods is available, then to not use the nova for purposes where a distance is needed.

Angular Expansion of Nova Shells

“…The effects of these interactions vary among novae of different speed class (Lloyd et al 1997), which are basically associated to the different time-scales of the slow and fast wind phases, providing an interpretation for the larger asphericities of the remnants of slow novae with respect to those of fast novae (Slavin et al 1995). Finally, the WD rotation may also feed the ejecta with Note-Distances were obtained from Gaia DR2 (Schaefer 2018). References for spectroscopic expansion velocities.-(1) Cohen, & Rosenthal (1983), (2) Duerbeck (1987), (3) Vaytet et al (2007), (4) Gill & O'Brien (2000).…”

ASASSN-16oh: A Nova Outburst with No Mass Ejection—A New Type of Supersoft X-Ray Source in Old Populations

“…There are other common properties between ASASSN-16oh and the dwarf nova V1017 Sgr. The peak V brightness is M V,max ∼ −2.3 in ASASSN-16oh, similar to M V,max ∼ −1.3 in V1017 Sgr (Schaefer 2018). The quiescent brightnesses of the both objects are also similar, that is, M V,min ≈ 2.1 for ASASSN-16oh and M V,min ≈ 1.8 for V1017 Sgr (Schaefer 2018).…”

On a century of extragalactic novae and the rise of the rapid recurrent novae

“…Our privileged location within the spiral structure of the Milky Way (and the irregular nature of the LMC and SMC) severely limits the ability to undertake unbiased studies of the population(s) of Galactic or similarly nearby novae. While the second data release (DR2) from the Gaia mission (Gaia Collaboration et al, 2016, 2018 may have removed some ambiguity from Galactic distance estimates (see the discussions in Schaefer 2018 and Selvelli & Gilmozzi 2019), we must wait for at least the fourth release (DR4) until the potential systematics (in part due to the orbital motion of the unresolved nova binaries; see, for e.g., Lindegren et al, 2018) can be investigated.…”