Are Recurrent Novae the Progenitors of Type Ia Supernovae?

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Recurrent novae are compact binaries where Roche lobe overflow is spilling material onto a white dwarf, where the matter accumulates until it is hot enough to start a thermonuclear runaway that creates a nova eruption at least once per century. The recurrence time is so fast due to the white dwarf being near the Chandrasekhar mass and due to a high accretion rate. If recurrent novae have massive white dwarves with material being piled onto them at a fast rate, then they must inevitably collapse when the mass accumulates to the Chandrasekhar limit and then produce a Type Ia supernova. With this logic, recurrent novae are a leading contender as being the progenitor system for Type Ia SNe. Various other types of systems have been proposed as progenitors and this has resulted in a still-unresolved 'Type Ia progenitor problem' that has been prominent for over 40 years. This problem is now critical to large enterprises of broad importance since Type Ia events are being used as standard candles for cosmology to determine the age and fate of the Universe. The solution of the progenitor problem is required to calculate the evolution with red shift of the supernovae peak brightnesses. Here, Dr. Schaefer, along with undergraduates and a high school student, will attempt to answer the fundamental question "Are recurrent novae the progenitors of Type Ia supernovae?" by performing two significant tests. The first is whether or not the white dwarfs in such systems are gaining or losing mass. To answer this, the mass ejected during eruption will be measured for two recurrent novae by timing their orbital period changes across recent eruptions. The rate of accretion for these stars will be derived from UBVRIJHK photometry and light curve modeling. An exhaustive search of archive plates dating back to 1889 will determine the rates of eruption. Thus it will be possible to assess the mass accumulated between eruptions to compare with the mass lost. The second question is whether there are enough recurrent novae in our Galaxy and the Local Group to allow for the observed Type Ia events. This will be accomplished through various tests of the discovery frequency, which will result in a realistic estimate of the total number of recurrent novae in our Galaxy, the LMC, and in M31. The novae lifetimes will be derived using their measured accretion rates and the death rate will be the total number divided by the lifetime. This can then be directly compared with the Type Ia event rate. As part of this project, Dr. Schaefer will continue his active public outreach work. This program will also involve undergraduate students and a high school student in front-edge research as well as make up the bulk of a Ph.D. dissertation for a graduate student at Louisiana State University.