Galactic Evolution and Star Clusters

My primary research utilizes multi-wavelength observations (UV through mid-infrared) in the investigation of local stellar populations. Of particular interest is the use of star clusters and giant stars to probe the structure and evolution, chemical and dynamical, of the Milky Way and other Local Group galaxies. Related issues such as the role of environment and dark matter content of Milky way satellite galaxies are also currently under study.

Click on the images for more information on my major research areas.

Graduate Student Progress

100% Complete (Grad) Thompson
100% Complete (5rd) O'Connell
60% Complete (3rd) Donor
30% Complete (2nd) Melendez
20% Complete (1st) Ray
5% Complete (1st) Carroll

Other Research Projects

Dark Matter & Dwarf Galaxies

Cosmological Cold Dark Matter (CDM) models predict that a galaxy like the Milky Way should have 100's of satellite galaxies filled with dark matter. The reality is that the Milky Way has tens of satellites and how much dark matter they have is not well determined. A major complication in measuring this is that many of these galaxies are also being torn apart by the Milky Way. The dynamics of dwarf galaxies and stellar streams is the key to understand the evolution of dark matter on small scales. I have worked on exploring the Milky Way dwarf satellites, including Sagittarius, the Magellanic Clouds, GASS, Carina, Leo I and II, Ursa Minor, and Sculptor, as well as, investigating star clusters associated with the Galactic Anticenter Stellar Structure "GASS", also know as the "Ring", that may be associated with the proposed "Argo" or "Canis Major" dwarf galaxy. Much of this work is done in collaboration with research groups at the University of Virginia.

Work on the chemical evolution of the Sagittarius dwarf Spheroidal galaxy is ongoing utilizing data from SDSS-APOGEE and CTIO/Hydra spectroscopy data in conjunction with collaborators at New Mexico State University.

Galactic Structure and the Milly Way Bar

Considering the importance of galactic potentials in shaping the chemodynamical evolution of their stellar populations, it is unfortunate that less is known about the dynamics of the Milky Way than for other galaxies. A fundamental problem with exploring the Galaxy — one that thwarted Herschel, concerned Kapteyn (1909), was discovered by Trumpler (1930), and remains a roadblock in our detailed understanding of the Milky Way is extinction by dust. While the near infrared (NIR) photometry of 2MASS has allowed us to probe the Galaxy to dustier regions, our view of the densest, most prominent parts of our galaxy is still challenged by heavy reddening, which typically makes low latitude field star CMDs uninterpretable. However, the combination of 2MASS and Spitzer IRAC photometry allows a direct and powerful assessment of the line of sight reddening to any particular star — and across wavelengths where the reddening law is universal. At these wavelengths the color effects of reddening and stellar atmospheres are completely separable: The long wave-length spectral energy distributions (SEDs) of stars have the same Rayleigh-Jeans shape. Thus, the observed mid-IR colors contain information on the reddening to a star explicitly, whereas the NIR SEDs contain information on the stellar types. Using this powerful technique to make Spitzer-cleaned (J−Ks,Ks) CMDs of previously obscured regions of the Milky Way, we will investigate the structure and the dynamics of the Galactic bar. We have collected a larger spectroscopic sample of Milky Way M-giants and carbon stars to investigate the structure and the dynamics of the Galactic bar.