On the Cause of the Nova Outburst

Abstract

The observational studies of the old novae have shown that they are close binaries with one of the components a white dwarf accreting hydrogen-rich material from the other component. To determine if the nova outburst could be caused by a thermal runaway in the envelope of the white dwarf, a computer code designed to take short time steps has been used to compute evolutionary sequences for helium-rich white dwarfs with hydrogen-rich envelopes. None of those computed using initial conditions derived from the observations of DQ Her had significant thermal runaways or produced the 10 45 erg observed in the outburst of DQ Her. An evolutionary sequence was then computed which used initial conditions that included the effects of an accretion shock (Starrfield 1970). A thermal runaway resulted which produced the energy observed in the outburst of DQ Her. Two evolutionary sequences were computed with a mass of |$0.5\,{M}_{\odot}$| . A thermal runaway occurred in each sequence and produced more than 10 45 erg. In these models as the peak of the runaway was reached, the shell source compressed and heated the outer layers of the helium core until helium burning was initiated.