Theses and Dissertations

ORCID

https://orcid.org/0000-0001-9596-8820

Advisor

Tanner, Angelle

Committee Member

Pierce, Donna

Committee Member

Winger, Jeffrey A.

Committee Member

Crider, Benjamin

Committee Member

Plavchan, Peter

Date of Degree

5-16-2025

Original embargo terms

Visible MSU Only 6 months

Document Type

Dissertation - Campus Access Only

Major

Physics

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Physics and Astronomy

Abstract

A precise radial velocity (RV) monitoring campaign was conducted for two Targets of Interest (TOI), TOI-2443 b and TOI-139 b, identified by the Transiting Exoplanet Survey Satellite (TESS) as exoplanet candidates orbiting K dwarf stars. Preliminary estimates of the transmission spectroscopy metric (TSM) indicate that the transiting planets are promising targets for atmospheric follow-up. I perform a multi-planet RV analysis of the TOI-2443 system, combining infrared and optical RV data. The model robustly recovers the signal of TOI-2443 b, an eccentric warm sub-Neptune, with a semi-amplitude of 2.54 ± 0.24 m/s, corresponding to a mass of 7.11 ± 0.67 ��⊕ . With a radius of 2.69 ± 0.55 ��⊕ and an equilibrium temperature of 515 K, TOI-2443 b has a TSM value of 157, highlighting it as a strong atmospheric characterization candidate. TOI-2443 c, a potential habitable zone companion orbiting with a period of 92.39 ± 0.95 days, is recovered with a semi-amplitude of 1.67 ± 0.26 m/s and a weakly constrained eccentricity of 0.33 ± 0.18, warranting additional RVs to refine its ephemeris and assess transit probability, ultimately determining whether it is suitable for atmospheric follow-up. The TOI-139 system hosts at least one transiting sub-Neptune candidate and exhibits youth indicators, including chromospheric emission and quasi-periodic photometric variability in the TESS light curves. Despite collecting 31 infrared RVs, stellar variability produces RV scatter of ∼10–20 m/s, obscuring the planetary signal. These results emphasize the necessity of Gaussian Process (GP) modeling to mitigate stellar-induced noise in young, active stars. A future GP fit with additional infrared and optical RVs is necessary to isolate the planetary signal. This work demonstrates the importance of combining high-cadence photometry, precise RVs, and modern GP modeling techniques to constrain the orbital and physical properties of planets around K dwarfs. These systems contribute to our understanding of planet formation and migration in dynamically rich environments and represent valuable targets for future atmospheric studies.

Sponsorship (Optional)

NASA Jet Propulsion Laboratory (JPL)

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