Roger E Cohen

Postdoctoral Fellow

Roger Cohen joined STScI in 2016, working with Jason Kalirai. As a crowded-field photometrist with an interest in resolved stellar populations, his research extends from nearby Milky Way star clusters to distant galaxies resolvable only with HST. These projects include HST Cycle 23 and 25 PI programs imaging Milky Way globular clusters towards the Galactic bulge, as well as topics including the IMF in the Local Group and the formation of massive elliptical Galaxies.

Before joining STScI, Roger obtained his Ph.D. at the University of Florida, with a thesis on blue straggler variability and luminosity functions supervised by Ata Sarajedini. Afterwards, he spent nearly five years as a postdoc in Concepcion, Chile, winning a Gemini-CONICYT fellowship to analyze ground-based (VVV, Gemini GSAOI adaptive optics) imaging of bulge globular clusters as part of Doug Geisler's stellar populations research group. He obtained his B.A. at Wesleyan University, studying long-term T Tauri star variability with Bill Herbst, where he accidentally discovered the longest known (at the time) stellar eclipse.

Since joining STScI, Roger has served on the SOC/LOC of the annual Spring Symposium, the seasonal CoolSci weekly colloquium series, and as an invited speaker on HST imaging of the Galactic bulge. Looking forward, he is most excited about opportunities for synergy between current and forthcoming ground- and space-based facilities in the optical and infrared (DECaM, Gaia, E-ELT, LSST, JWST, Nancy Grace Roman Space Telescope, Gemini AO).

Outside of work, Roger's favorite activities include playing drums and adventuring with his wife and gigantic Newfoundland dog.


PhD in Astronomy, University of Florida
MA in Astronomy, University of Florida
BA in Physics and Astronomy (honors), Wesleyan University


Science Interests:

  • PSF Photometry
  • Near-IR Adaptive Optics Imaging
  • Resolved Stellar Populations
  • Milky Way (and Bar/Bulge) Formation and Evolution
  • Globular Cluster Chemodynamics
  • Local Group Formation and Evolution


Selected Publications:

"Deep Hubble Space Telescope Imaging of Globular Clusters Towards the Galactic Bulge: Observations, Data Reduction and Color-Magnitude Diagrams": Cohen, R. E. et al., 2018, AJ, 156, 41

"Wide Field Near-Infrared Photometry of 12 Galactic Globular Clusters: Observations versus Models on the Red Giant Branch": R. E. Cohen et al., 2015, AJ, 150, 176

"Photometric and Structural Properties of NGC 6544: A Combined VVV-Hubble Space Telescope Study": R. E. Cohen et al., 2014, AJ, 148, 18

"SX Phoenicis Period-Luminosity Relations and the Blue Straggler Connection": R. E. Cohen, A. Sarajedini, 2012, MNRAS, 419, 342

"An Unusual Eclipse of a Pre-Main Sequence Star in IC 438": R. E. Cohen, W. Herbst, E. Williams, 2003, ApJL, 596, 243


Research Topics: Star Formation, Histories, and Evolution; Local Group Galaxies; Galaxy Formation and Evolution; Stellar Populations; Star Clusters; Resolved Stellar Populations

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