Research

My research spans several subfields of Galactic archaeology, interstellar dust, and the cosmic distance scale, among them:

  • The Milky Way’s bulge, its morphology, ages, and nature;

  • The origin and properties of second generations in Galactic globular clusters;

  • Interstellar extinction curve and variations thereof, particularly toward the inner Galaxy;

  • The WFIRST microlensing planet survey, systematics and survey design;

  • The cosmic distance scale, RR Lyrae, Mira variables;

  • Red giant stellar evolution the red giant branch bump, the red clump;

Galactic astronomy is currently undergoing a revolution, due to newly bountiful data from several new facilities and large surveys, and continued implementation of more modern probabalistic inference methods. My motivation lies at the interplay of these two, I would like to resolve some longstanding questions in Galactic astronomy, and to integrate that new knowledge within broader astrophysics.

 
 
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Optical/Near-Infrared Extinction curve variations toward the inner Milky Way

At left, the colour-magnitude diagrams for two sightlines (orange and blue) in two different colours, (V-I) on the left and (J-Ks) on the right. Though the two sightlines show a similar (V-I) colour distribution, they show a distinct (J-Ks) colour distribution, with the ratio differing by 40%. This is indicative of the extinction curve toward the inner Galaxy, which is non-standard in the mean, variable, and has at least two components to its shape. 

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The star-formation history and helium abundance of the Galactic bulge

Shown at left, the disparate star formation histories of the Galactic bulge. They are fully inconsistent, with mean ages ranging from 3 to 13 billion years. I have speculated that this inconsistency may be due to elevated helium enrichment, due to the fact that it specifically solves the low number counts and high brightness of the red giant branch bump, and the the fact that it can exactly resolve the turnoff age discrepancy. Efforts to further constrain the helium abundance with detached red giant eclipsing binary twins are ongoing. 

The nature of multiple populations within globular clusters

Shown at left, the distribution of the Milky Way’s globular clusters in the plane of stellar mass and metallicity, with the aluminum abundance difference between chemically-normal and chemically-peculiar stars colour-coded. In general, the more metal-poor and the more massive clusters have greater aluminum enrichment, which suggests contributions from two non-supernovae chemical polluters that were active in the early universe. The scaling with metallicity is not surprising and likely a consequence of hot-bottom burning in massive asymptotic giant branch stars. However, the scaling with stellar mass is of an unknown origin.