Masses of white dwarfs in O-Ne-Mg novae: Observational constraints, galactic Al-26, Na-22 gamma-rays, and M31 novae

Abstract

About 1/3 of recently observed classical novae eject matter highly enriched in neon. This has prompted suggestions that the underlying white dwarfs in these systems are massive, and are composed of oxygen, neon, and magnesium. O-Ne-Mg WDs in novae have been suggested as important sources of 26A, and likely sources of y rays produced in the ß+ decay of 22Na. I examine two observational constraints presently available on the masses of white dwarfs in O-Ne-Mg novae. These are (1) the ejected shell mass, and (2) the time t3 to decline 3 mag from maximum brightness. Both indicators suggest a wide range of white dwarf masses, including low mass degenerates, in O-Ne-Mg novae. This is in contradiction to the hypothesis of massive progenitors and progeny. In an accompanying paper, Shara & Prialnik [AJ, 107, 1542 (1993)] demonstrate how He shell flashes can create an O-Ne-Mg envelope on a nonmassive, C-0 white dwarf. Novae occurring on such white dwarfs will eject copious quantities of neon. Here I point out that such white dwarfs can also produce all the 26A needed to satisfy observations; that the 22Na y-ray flux from neon novae is likely to be most readily observable in slow O-Ne-Mg nova eruptions; and that the recent suggestion of a very small fraction of neon novae in the M31 bulge is readily explainable. 1.