SCIENCE SEMINAR
The Double Core Common Envelope Scenario
for Type Ia Supernova Progenitors
Eric Blais
Thursday, April 28, 2011
2:00 pm
Johnson 103
We investigate a new model for creating type Ia supernovae (SNIa). Stars that are born with mass ratios close to unity as a result of being part of a “twin population” evolve at similar rates so that when the primary overflows its Roche lobe on the red giant or asymptotic giant branch, the secondary is also a giant. This results in a common envelope phase in which both envelopes are expelled (double core common envelope), creating two white dwarfs in one event. We find that this evolutionary scenario can account for ~20% of SNIa and is a big contributor to the 'prompt' population. To complement the double core scenario, we incorporate another model in our population synthesis. Stars overflow their Roche lobes with a main sequence companion. If the mass ratio of the system is below a critical value, stable mass transfer can strip the primary of its envelope, which is then accreted by the secondary. A normal common envelope phase may then eventually occur. Use of this model to complement the double core scenario results naturally in a delay time distribution (DTD) with two components: a 'prompt' population and a 'tardy' one. We find that we can fit a power law of t-1.23±0.01 to the delay time distribution of the tardy population. We obtain a result which matches the work of Maoz et al. (2010), who observationally determined the relation to be t-1.2±0.3. This is the first time that a population synthesis shows such agreement between a model and observations of delay times. From the distribution of SNIa progenitor masses that we obtain, we also find that the double core model allows for the existence of super-Chandrasekhar events.
