Dissertations, Theses, and Capstone Projects

Date of Degree

6-2026

Document Type

Master's Thesis

Degree Name

Master of Science

Program

Astrophysics

Advisor

Michael Shara

Subject Categories

Astrophysics and Astronomy | Physical Sciences and Mathematics | Stars, Interstellar Medium and the Galaxy

Keywords

white dwarf, cataclysmic variable, AM CVn, symbiotic star, photometry, space density

Abstract

Helium emission-line stars, including cataclysmic variables (CVs), AM Canum Venaticorum (AM CVn) binaries, symbiotic stars, and X-ray binaries, are tracers of compact object binary populations in the Milky Way, and may be viable progenitor systems of Type Ia supernovae. Their space densities are not well constrained - just over 100 AM CVn stars are known out of a Galactic population that may be closer to 100,000. Identifying such systems in large numbers requires wide-field, narrow-band photometric surveys capable of detecting faint emission-line sources across significant sky areas.

In this thesis, I present a narrow-band photometric search for helium emission-line stars using deep imaging data from the Condor Array Telescope in the field of M81 and M82. Condor simultaneously imaged a 3.5 square degree field in HeI (587.5 nm), HeII (468.6 nm), and [OIII] (500.7 nm) narrowband filters to a limiting magnitude of approximately 19–20. Using the [OIII] filter as a continuum reference, I created a catalog of approximately 3,000 Condor sources with photometry calibrated against Gaia Data Release 3. I identified helium-bright outliers by creating color-magnitude diagrams and sorting sources by their standard deviations from the mean helium-to-continuum magnitude ratio in each brightness bin. Then, I plotted the outlier stars on Hertzsprung-Russell diagrams using their Gaia parallaxes and photometry in order to infer their stellar types. Additionally, I visually compared the outlier stars between all three Condor filters and cross-referenced them with GALEX ultraviolet and POSS-II optical archival imaging.

Fourteen candidate helium emission-line stars were selected via this method. They include two confirmed white dwarfs and four probable red giants, which are respectively likely to be AM CVn and symbiotic stars. They also include a number of hot blue objects with UV counterparts in GALEX. The fourteen candidate stars are in the process of being sent to the OSMOS spectrograph at MDM Observatory for spectroscopic follow-up; at least one spectrum so far shows a visible emission line. The Python code pipeline developed for this thesis is designed to be applied to all 58 fields in Condor's full dataset of the Local Group, which will enable future population-level estimates of helium emission-line star space densities in the Milky Way.

Download

Share

COinS