stellar physics & stellar populations

I'm a fifth year astronomy graduate student at Harvard University working with Charlie Conroy. I like to think about stars both as astrophysical objects and as stellar populations in clusters and galaxies.

You can contact me at: jieun.choi [at]

Harvard Smithsonian Center for Astrophysics
60 Garden Street, MS-10
Cambridge, MA 02138
p: 617-496-0239


Stars are fascinating astrophysical objects whose properties and evolution are governed by numerous complex physical processes. I use MESA, an open-source stellar evolution code, to model and study stellar evolution as part of the MIST project. Stellar evolution models (isochrones) form the backbone of stellar population synthesis models, which we use to uncover clues about the formation and evolution of galaxies through the analysis of their stellar populations.

MESA Isochrones and Stellar Tracks (MIST)

We are currently working on the MIST project using MESA to create an extensive grid of stellar evolutionary tracks and isochrones over a wide range of masses, metallicities, ages, and advanced stellar evolutionary phases. With these new models, we hope to tackle a variety of problems in both stellar evolution and extragalactic studies. The movie shows the evolution of a 2 solar mass star from the pre-main sequence to the white dwarf cooling phase. Read more about it in the first paper here.

Assembly Histories of Quiescent Galaxies

We modeled the optical spectra of a large sample of quiescent galaxies in the redshift range 0.1 < z < 0.7 from SDSS and AGES surveys. We performed full spectrum modeling to examine how the stellar ages and abundance patterns of galaxies evolve over time as a function of stellar mass. We found that there is negligible evolution in elemental abundances at fixed stellar mass over roughly 7 Gyr of cosmic time (see plot) and that the increase in stellar ages with time for massive galaxies is consistent with passive evolution since z = 0.7. Taken together, these results favor a scenario in which the inner regions of massive quiescent galaxies have been passively evolving over the last half of cosmic time. Read more about it here.

Past Undergraduate Projects


Both as a TA and as an instructor, I have taught numerous courses for students with a wide range of backgrounds, from middle school students to undergraduate astronomy majors.

  • Harvard, AY 17: Galactic and Extragalactic Astronomy (FA'14)
  • UC Santa Cruz, AY 2: Overview of the Universe (WI'13)
  • ATDP Berkeley, Intro to Modern Astrophysics (SU'12)
  • UC Berkeley, AY 10: Intro to General Astronomy (FA'11, SP'12)
  • UC Berkeley, AY 120: Optical Astronomy (FA'10)
  • UC Berkeley, The IDL Way: An Intro to Computer Programming for Astronomers (SP'10)

Curriculum Vitae

last updated: 06/07/2017