During my time as a Ph.D. student at Georgia State University in Atlanta, GA, I worked with Prof. Todd Henry and Dr. Wei-Chun Jao, joining the Research Consortium On Nearby Stars (RECONS, publications). The main expertise of RECONS is in stars within 25 parsecs, with a goal of characterizing all objects within that distance. My project focused on uniformly and efficiently deriving fundamental parameters, most importantly radii, of an all-sky sample of ~1600 low-mass dwarf stars (M0 to L2.5). With the resulting catalog, I revealed trends in these parameters as a function of spectral type and identified candidate young stars and cool subdwarfs.
Telescopes and Observations
As part of my graduate career, I served as the Small and Moderate Aperture Research Telescope System (SMARTS) Graduate Fellow. SMARTS operates and maintains several small telescopes at the Cerro Tololo Inter-American Observatory (CTIO) in Chile and is currently directed by Prof. Todd Henry. My role as the SMARTS Graduate Fellow was to help run the SMARTS/CTIO 0.9m; the image at the top of the page is the peak of CTIO, with me standing next to the 0.9m.
Throughout my time as a Ph.D. student, I spent 87 nights at the SMARTS/CTIO 0.9m telescope, 77 nights using the ARCSAT 0.5-m telescope at Apache Point Observatory (APO), and 28 nights at the WIYN 0.9-m telescope at Kitt Peak National Observatory (KPNO).
Dissertation Project
My interests lie in characterizing the nearby low-mass star population. Using a spectral energy distribution fitting method based on that of Dieterich et al. 2014, I derived the effective temperature, luminosity, and radius of ~1500 main sequence stars within 25 parsecs and control samples of ~50 young stars and ~30 cool subdwarfs within 50 parsecs. The method requires only optical to mid-IR photometry, a parallax, and the BT-Settl 2011 photospheric models. Because it is observationally based only upon photometry and astrometry, the method is flexible and primed to take advantage of Gaia and large photometric surveys such as WISE, 2MASS, Pan-STARRS, SkyMapper, and SDSS. Because no spectrum is needed, the procedure is possible using data from smaller telescopes and/or for fainter stars. The final method is automated and poised to inexpensively determine radii for an unlimited number of M0-L2.5 stars, with results that are uniform, based upon multiple bandpasses, and accurate to within a mean of 6% compared to results from long-baseline interferometry.
Via this method, I’ve identified a candidate subsample of young stars and subdwarfs which stand out from ordinary main sequence stars due to their relatively large and small radii. I’ve also identified trends in radius versus effective temperature.
Ph.D. Degree Conferred on August 13th, 2019
- Advisor: Todd Henry, Head of the RECONS team, Director of SMARTS
- Institution: Georgia State University
- Dissertation Title: Sizing Up Red Dwarfs in the Solar NeighborhoodÂ
Michele L. Silverstein, Ph.D. 