Kristen Garofali

Broadly, my research interests are in probing massive star evolution from the X-ray perspective. More specifically, I study objects like high-mass X-ray binaries (HMXBs) and supernova remnants (SNRs) in order to learn more about the life and death cycles of massive stars. For my thesis I am working to identify and characterize HMXB populations in nearby galaxies using both the Chandra and Hubble Space Telescopes. This kind of work can provide better observational constraints on population synthesis models for interacting binary stars.

In particular, I am looking at HMXBs in the nearby star-forming Triangulum Galaxy (M33). Currently there are only 3 HMXBs that have been identified and characterized in M33, all of which are extremely interesting. Through careful astrometric alignment of Hubble and Chandra observations of M33 it is possible to identify over 10 times that number.

GALEX NUV image of M33. The Hubble fields are in black, and the blue circles mark the locations of X-ray sources from the ChASeM33 Survey


Once identified, each HMXB can be assigned an age and type based on the Hubble observations of that particular field. The star formation histories (SFHs) of the field surrounding the HMXB can also be determined. The combination of all this information provides constraints for the mass function of binary companions, the dominant type of HMXB, and the age distribution of HMXBs that must be reproduced by theoretical binary population synthesis models.

Left: Typical Chandra error circle in white (0.5" radius) on a color Hubble image of M33. The blue star makes this an HMXB candidate. Center: The CMD of stars within 50 pc of this candidate (cyan star). For reference isochrones from the Padova group are overlaid for ages (from blue to red) of 6, 10, 20, 50, and 100 Myr. Right: Cumulative age distribution for stars younger than 60 Myr from CMD fitting. The most likely age is 30-40 Myr.