My Name is Jack Warfield and I am a sixth-year PhD candidate in astronomy at the University of Virginia.

I am originally from Fulton County, Ohio, and graduated from The Ohio State University with a B.S. in astronomy and physics. At OSU, I worked with Marc Pinsonneault, Jennifer Johnson, and Joel Zinn studying red giants observed by K2 and APOGEE.

At UVA, I have been working with Nitya Kallivayalil and collaborators in the HSTPROMO Collaboration (among others) investigating the properties of dwarf galaxies in the Local Group. In particular, I am interested in measuring the proper motions of dwarf galaxies using multi-epoch HST and JWST imaging. Because the kinematics of dwarf galaxies is highly correlated with the properties of dark matter halos (such as their masses and density profiles), these measurements are an essential piece of testing and informing cosmological models at "small" scales. In 2023, I published a paper on my software tool HubPUG, which allows you to measure proper motions for resolved stellar systems (e.g., dwarf galaxies, globular clusters, stellar streams) for which there are two epochs of HST imaging by using Gaia as a foreground reference frame. This allows both for improved proper motion measurements for Milky Way satellites versus relying on Gaia alone, as well as enabling us to utilize Gaia for systems with no or very few Gaia stars themselves (e.g., UFDs or the distant satellites of M31).

I am also a member of the JWST Early Release Science (ERS) Program Resolved Stellar Populations team. Our task was/is to develop tools and best practices for reducing, analyzing, and interpreting JWST data for resolved stellar populations using data that we obtained in Cycle 1 of the Milky Way ultra-faint dwarf galaxy Draco II, the Local Group "isolated" dwarf WLM, and the globular cluster M92. For this program, I wrote a research note highlighting photometric criteria for star-galaxy separation in JWST NIRCam catalogs produced with DOLPHOT. I am currently working on characterizing the systematics in measuring proper motions from a combination of HST and JWST imaging using this ERS data along with data from my HST Cycle 31 and JWST Cycle 2 programs. Making and understanding these cross-observatory measurements will be crucial moving forward if we wish to fully leverage the long time baselines afforded by the extensive HST archive with new data from JWST and Roman.