Unraveling the oldest and faintest recovered nova - CK Vulpeculae (1670)

Abstract

A narrow-band H..cap alpha..+(N II) CCD image of the field of Nova CK Vul (1670) shows nebulosity with a morphology (suggestive of equatorial ejection) with several bright subcondensations, and a central star. The net H..cap alpha.. image also reveals a faint jet leading to an H..cap alpha..-bright knot, suggestive of polar ejection. Spectra of the equatorial and polar ejecta are similar to each other and to spectra of the shell of the recurrent nova T Pyx, but with lower excitation. Nitrogen appears enhanced, and the nebular density is low enough that its recombination time scale equals or exceeds the time since outburst. The reconstructed light curve of CK Vul shows it to have been a very slow nova, with large oscillations near maximum. Constraints on its distance place it at 550 +- 150 pc from the Sun, near the far side of, or perhaps within, an intervening obscuring cloud. The implied nebular expansion velocity is extraordinarily low, v/sub exp/ = 59 +- 16 km s/sup -1/, and may not represent the true extent of the ejecta. The present absolute magnitude of the central star, M/sub R/ = +10.4, is 6 mag fainter than canonical old novae, and requires a verymore » low-mass secondary star (Sp.> or approx. = M3 V), short orbital period ( P< or approx. =3--6), and negligible mass transfer rate (m< or approx. =10/sup -11.5/ M/sub sun/ yr/sup -1/). If CK Vul represents a typical state for novae between outbursts, then published survey-based values of the space density and lifetimes of cataclysmic binaries may be seriously underestimated.« less