My research interests revolve around close double white dwarfs. These systems are known to exist and are believed to be the end-point of most stellar evolution. Some white dwarfs are close enough so that the gravitational wave emission can drive them to a phase of mass transfer within a Hubble time. Such interacting systems are suspected to produce observable objects such as Helium-rich hot subdwarfs, R Corona Borealis stars, neutron stars and, maybe most spectacularly, type Ia supernovae.

I use numerical simulations to study the dynamics of mass transfer and the fate of the systems that merge. To learn more and see some science results and movies, click on the following links:

Prelude to a double degenerate merger

This project focused on constructing accurate initial conditions for double white dwarfs and found them to be of paramount importance for the whole evolution of the system. We found that initial conditions impact on the outcome of essentially every aspect of white dwarf merger simulations. In particular, the mass transfer duration is underestimated by more than an order of magnitude if approximate initial conditionss are used. Such initial conditions were used by the previous studies.

The link above contains the movies that accompany the paper Prelude to a double degenerate merger: the onset of mass transfer and its impact to gravitational waves and surface detonations (SAO/NASA ADS)

How the merger of two white dwarfs depends on their mass ratio

For this work, we performed an extensive parameter space study. We followed the evolution of 225 WD-WD systems covering a large range of WD mass and chemical compositions. We investigated which systems are expected to produce strong thermonuclear events in the lead up to or at the point of merger. We found that many systems with Helium donors may produce explosions, but that systems with Carbon-Oxygen donors are incapable of exploding without the inclusion of a significant Helium layer.

This link above contains more details about the paper How the merger of two white dwarfs depends on their mass ratio: orbital stability and detonations at contact (SAO/NASA ADS)

The structure and fate of white dwarf merger remnants

In this work, we have determined the structure of the white dwarf remnants as a function of the total mass and the mass ratio of the binary. We explore a large range of white dwarf masses and compositions as well as the effect of different initial conditions. Our findings are discussed in the context of several possible observed astrophysical events and stellar systems, such as hot subdwarfs, R Coronae Borealis stars, single massive white dwarfs, supernovae of type Ia and other transient events.

We make available a large database with averaged and SPH-interpolated along different directions profiles of 225 white dwarf merger remnants that accompany the paper The structure and fate of white dwarf merger remnants (arXiv:1308.1667)