Rachel R. Strickler

I am currently working on a project to numerically model the interactin wind region of WR 20a, a binary consisting of two 80 solar mass Wolf-Rayet stars. I am creating both a semi-analytic model, and a full hydrodynamical model using FLASH, an adaptive mesh refinement (AMR) parallel simulation code running on Pleiades.

I hope to extend this code to model the agglomeration of winds in OB associations and young star clusters, with particular application to WR 20a's host cluster, Westerlund 2. With the addition of a cosmic ray component, I hope that this will allow us to understand the source of of the extended TeV emission observed in the cluster.

I am also working on a project with Justyn Maund aimed at determining the environments in which extragalactic type Ia (accretion-induced collapse) supernovae (SNe) are found.

Globular clusters (GCs) are hosts to relatively large numbers of close white dwarf binaries. Therefore, we expect that GCs will also be host to large numbers of type Ia SNe. We are examining pre- and post-explosion images of over 30 SNe in the Hubble Space Telescope (HST) archive in order to identify the host cluster, if any, and its properties.

I began my studies of white dwarfs in the nearby globular cluster NGC 6397 while I was at San Francisco State University (SFSU), working with Adrienne Cool. I used the Advanced Camera for Surveys Wide Field Camera (ACS/WFC) on the Hubble Space Telescope (HST) to examine the white dwarf sequence in this cluster. In addition to a large carbon-oxygen (CO) WD sequence, we found a second, smaller population of 20-40 stars that we argue are under-massive WDs. Such helium-core (He) WDs are thought to form when their progenitors' ascent of the red giant branch is interrupted by Roche lobe overflow onto a companion, leaving a star that is no longer massive enough to undergo helium ignition.

We also analyzed the spatial distribution of the two populations of WDs to probe their relative masses. Globular clusters undergo mass segregation, causing more massive objects to become more centrally concentrated. The undermassive He WD candidates are significantly more centrally concentrated than the CO WDs, opposite what one would expect. This suggests that the He WDs may have massive, dark companions, consistent with the binary formation scenario.