THE PHYSICAL-PROPERTIES OF A SLOW NOVA IN THE BULGE OF M31

Observations are presented of an extremely slow nova that was discovered in the bulge of M31 in 1986. The evolution of the object was monitored with subsequent yearly spectra until 1990, as part of a general spectroscopic survey of novae in M31 underway at McDonald Observatory. The spectra cover the nova's evolution in the nebular phase, and these observations have made this nova the most extensively observed extragalactic nova to date. This has provided a unique opportunity to make the first detailed comparison of the evolution and properties of an extragalactic nova with those in our own Galaxy. Since the nova is situated in the bulge, it is likely that the object represents an outburst associated with an older population of novae, in contrast with Galactic novae which are almost entirely discovered as old disk objects. Although the evolution of this object was unusually slow, the derived mass of the nebula gas of 5 x 10(-5) M., electron temperature of 13,000 K, and abundances determined from an analysis of the emission line intensities are typical of those seen in Galactic slow novae: with a close to solar helium abundance (He/H = 0.13 +/- 0.02) and roughly solar abundances of oxygen and neon. In a previous study evidence was found for a possible systematic difference in the proportion of the types of observed outbursts between M31 bulge novae and Galactic novae. For individual novae, however, these results indicate that the general disparate properties seen in nova outbursts probably overwhelm the relatively smaller differences that might be expected when comparing novae from different stellar populations. The implications for using extragalactic novae as distance indicators are discussed.