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Faculty of Graduate Studies

Anya Dovgal

  • B.Sc. (University of British Columbia, 2024)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Ultrafaint Dwarf Galaxies as the Most Pristine Laboratories of Early Chemical Evolution

Department of Physics and Astronomy

Date & location

  • Tuesday, August 4, 2026
  • 10:00 A.M.
  • Hickman Building, Room 110

Examining Committee

Supervisory Committee

  • Dr. Kim Venn, Department of Physics and Astronomy, University of Victoria (Supervisor)
  • Dr. Alan McConnachie, Department of Physics and Astronomy, UVic (Member)

External Examiner

  • Dr. Stephanie Monty, Department of Astronomy, New Mexico State University

Chair of Oral Examination

  • Dr. Kieka Mynhardt, Department of Mathematics and Statistics, UVic

Abstract

Metal-poor stars are relics from the early Universe, mostly untouched by the billions of years of galactic evolution that has occurred since their formation. The light emitting from their atmospheres have imprints from the very first stars in the universe, and the environment in which they, and subsequent generations, formed. While the field of stellar archaeology has extensively mapped the Milky Way and its evolutionary history, only recently have we been able to observe stars beyond the Galaxy. Surrounding the Milky Way are dozens of satellite dwarf galaxies, where star formation occurred independently, on a smaller scale, for a short period of time – leading to a higher fraction of pristine stars compared to the Milky Way. By studying the chemical abundances of these fossil stars, we can learn about the environments of the first galaxies. The smallest galaxies that we know of, the ultrafaint dwarf galaxies (UFDs), are only observable in the Local Universe. Although they have few bright stars, new instruments like GHOST at large optical telescopes are powerful enough to obtain high-resolution spectroscopy for detailed analysis. The commissioning team for GHOST was awarded 200 hours for an observing program, ultimately implemented to target stars in UFDs. GHOULS (The GHOST Ultrafaint Legacy Survey) is observing stars that have not yet been published in the literature (as of 2024) to determine precise radial velocities and chemical abundances, for the goal of understanding the formation and nature of the first stars and galaxies. As part of the GHOULS survey, I’ve measured the abundances of several UFD stars for the very first time, finding that similar to previously studied UFDs, they continue to exhibit trends that diverge from the Milky Way at similar metallicities. In particular, their neutron-capture abundances occupy a region that is rare for Milky Way halo stars. Other than detailed chemistry, I measure radial velocities for a few UFDs for the first time in the literature. I find that one of the target galaxies is a satellite of the Large Magellanic Cloud, making it a rare satellite of a satellite. Within the rest of the GHOULS data, I find that one of the UFDs (Carina II) is home to a star with an extraordinarily low metallicity. This star, found in its birth environment, has no detectable iron lines, and has extreme enhancements in carbon, nitrogen, sodium, and magnesium. As the most metal-poor systems, it is not surprising that such a star was found in a UFD, but this discovery is still exciting proof that similar stars that have been found in the Milky Way likely originated from UFDs, and excellent motivation to continue measuring the chemistry of as many stars as possible in these systems.

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