Research
My primary research interest is massive metal-poor stars. Post Big Bang, the universe consisted of H, He and a sprinkle of other elements. All other elements (referred to as metals by Astronomers) are subsequently produced by very massive stars (up to hundreds of times more massive than our Sun). Metals can be formed in the high-pressure center of stars, through supernova explosions at the end of their life, or through neutron star mergers. The first generation of stars in the Universe were massive and nearly metal-free. While critical to the evolution of the very early Universe, these stars are extremely faint, and hard to study even with our most powerful telescopes (e.g., Hubble Space Telescopes, JWST). The solution is to study nearby metal-poor “dwarf” galaxies, which act as analogs to the first galaxies in the Universe. Massive stars in the metal-poor regime are central to our understanding of astrophysics; from the early Universe to black holes to gravitational waves. (See graphic below for a couple more examples). Over the next few years, my goals are to: (1) build a library of massive, metal-poor stars; (2) use machine learning to emulate the complex stellar physics of massive stars; and (3) investigate the stellar physics in this regime.
A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A
I compare HST multi-band photometric and Keck and MMT optical spectroscopy to study massive stars in the nearest low-metallicity star-forming galaxy Leo A (Z~5% Sun; D~1Mpc). The majority of our OB-stars (~65%) are not near any known H II regions or clusters in Leo A. Furthermore a significant fraction (nearly 50%) of our OB stars show measurable signs of stellar (not nebular) emission, which suggests mass loss through winds, accretion, and a putative high degree of binary star interaction. This is in line with previous findings of enhanced binary activity and stellar feedback at sub-SMC metallicities. I discuss how these spectral features may be a source of tension between photometrically and spectroscopically determined parameters (e.g., temperature, surface gravity). I present 6 Be stars, representing the first sub-SMC Be stars to have both photometry and spectroscopy. I postulate that Be stars can contaminate the core helium burning branch in the optical CMD. Our spectroscopic sample comprises a significant fraction of all known massive stars with high-quality optical spectra at sub-SMC metallicities.
ADS Link
Example normalized spectra of massive stars in Leo A shown from 4000–5100 Å with key features labeled.
