Hydrodynamic Models for Novae with Ejecta Rich in Oxygen, Neon, and Magnesium Sumner Starrfield Group T-6, Los Alamos National Laborator

In this paper we ident i fy and seek to explain the characteristics of a new class of novae. /This class consists of those objects that have been observed to eject material rich in oxygen, neon, magnesium, and aluminum at high velocities. We propose that for this class of novae the outburst is occurring not on a carbon-oxygen white dwarf but on an oxygen-neon-magnesium white dwarf which has evolved from a star which had a main sequence mass of ~8M to ~12M . . e e We have simulated such an outburst by evolving. 1.25M white dwarfs accreting hydrogen rich material at various rates. The effective enrichment of the envelope by ONeMg material from the core is simulated by enhancing oxygen in the accreted layers. The resulting evolutionary sequences are the most as violent that we have yet studied and can eject the entire accreted envelope <i£ plus core material at high velocities. They can also become super-Eddington at maximum bolometric luminosity. The expected frequency of such events ("1/4) is in good agreement with the observed numbers of these novae. 3