Research

I received my PhD in 2018 working with Prof. Robert Mathieu at UW Madison. The bulk of my PhD was spent analyzing the non-standard stellar population of the star cluster M67, a well-studied 4 Gyr open cluster. Here is a color-magnitude diagram of the cluster that uses high quality astrometric and spectroscopic information from Gaia and the WIYN Open Cluster Study (WOCS) to provide high quality memberships. More than 30 years of radial velocity data from WOCS allows us to identify binaries in this cluster out to 10,000 day orbital periods.

M67 Color-magnitude diagram showing members of the cluster down to the WOCS limiting magnitude of V= 16.5. Populations of non-standard stars including blue stragglers, yellow stragglers, and sub-subgiant stars are all present. These stars are not simply field contaminants in the CMD. They are  cluster members whose existence cannot be explained using standard single-star evolutionary models. Head here for an interactive version of this CMD.

Thanks to the long time baseline of  our radial-velocity observations, we know that 80% of the blue stragglers yellow stragglers, and sub-subgiants in this cluster are binary systems. Their origins likely lie in episodes of mass transfer, stellar collision, binary mergers, and tidal interactions; all are types of interactions commonly experienced by binary stars.

Broadly, I am interested in using a variety of observational and modeling approaches to understand these types of binary interactions, particularly the physics of mass transfer. I use the stellar evolution code MESA to model the detailed binary evolution, as well as data from ground and space based observatories including Hubble, Gaia, Kepler, TESS, and the WIYN 3.5 meter at Kitt Peak, and MMT Observatory. I apply a broad range of techniques to analyze this  data including asteroseismology, gyrochronology, and spectroscopy.  Recently, I have been very interested in understanding the impact of magnetic fields on the evolution of binary stars; sub-subgiant stars may be a particularly dramatic example of how magnetic fields impact stellar evolution by creating unusually cool, underluminous subgiant and giant stars. I recently assembled the first sample of sub-subgiants in the galactic field using Gaia data. The plot below shows a color-magnitude diagram of a sample of magnetically active giants. About a quarter of these active giants are so cool and faint that they fall below a metal-rich 14 Gyr isochrone (black line), meaning there is no standard stellar evolution model that can explain them. Most sub-subgiants have rotation periods less than 20 days (purple, blue, and green points; rotation periods are indicated by the color bar).