Abstract

Young stars in the solar neighborhood provide a unique and insightful window into stellar evolution during the first few hundred million years after formation. Leveraging archival photometric and astrometric data from ESA’s Gaia Space Astrometry mission, as well as photometric data from NASA (2MASS and WISE) archives, I have identified over 50 new members of the nearby (D ∼ 100 pc), 3–8 Myr-old Epsilon Cha association (ECA), including six new proto-brown dwarf candidates. By modeling the kinematics and photospheric properties of both newly identified and previously known members of the ECA and Lower Centaurus Crux (LCC), I further established the connection between the two associations. During my ECA membership study, I discovered one particularly interesting candidate: TOI 1227, a very low-mass (red dwarf) pre-main sequence star with a transiting exoplanet detected by NASA’s TESS exoplanet-hunting mission. I have re-assessed the age of TOI 1227 from ∼ 11 Myr to ∼ 8 Myr, and used new Chandra X-ray observations to estimate the planet’s atmospheric mass loss and its likely long-term evolution. Drawing on newly released data from ESA’s eROSITA all-sky survey (eRASS) in combination with Gaia and TESS archival data, I conducted a large-scale statistical analysis of X-ray activity in more than 10,000 stars younger than 1 Gyr and within 200 pc of the Sun. Finally, I used Chandra X-ray imaging and NASA (GALEX/Gaia/2MASS) archival data to investigate a population of candidate nearby young stars with strong ultraviolet emission but unexpectedly weak X-ray output. I link the unusually high-energy radiation characteristics of these candidates to their binary star nature; several systems are newly resolved in X-rays by Chandra. These research efforts have yielded various new insights into the early evolution of young stars and their planetary systems. I have demonstrated that the ECA/LCC region serves as a nearby, exemplary case of sequential star formation; identified new low-mass stellar objects that are strong candidates for future investigations into planet formation around brown dwarfs; and refined the age estimate and projected the future evolution of TOI 1227, a very young and key exoplanetary system located within the ECA and LCC. I have developed techniques to differentiate genuine pre-main-sequence stars from close binary main sequence stars that mimic their characteristics. By leveraging the combined strengths of eRASS, TESS, and Gaia data, synthesizing X-ray emission, stellar rotation, and age, I produced detailed empirical rotation-activity-age relations. These relations will provide valuable benchmarks for modern models of stellar magnetic dynamos and their observable surface activity.

Publication Date

11-2025

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Joel Kastner

Advisor/Committee Member

David Messinger

Advisor/Committee Member

Jason Nordaus

Campus

RIT – Main Campus

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