Precision Radial Velocities and Photometry in Pursuit of Exoplanets around Low-Mass Stars

Open Access
- Author:
- Lin, Andrea
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 08, 2024
- Committee Members:
- Robin Ciardullo, Major Field Member
Suvrath Mahadevan, Chair & Dissertation Advisor
Jason Wright, Major Field Member
Eric Ford, Major Field Member
James Kasting, Outside Unit & Field Member
Rebekah Dawson, Program Head/Chair - Keywords:
- astronomy instrumentation
exoplanets
radial velocity
transit photometry
EPRV
optical fibers
spectroscopy
solar
K-dwarfs
M-dwarfs
Warm Jupiter
sub-Neptune
super-Earth - Abstract:
- The radial velocity (RV) technique is one of the core methods of exoplanet detection and characterization. Over the past thirty years, RVs have been extremely fruitful for determining masses of exoplanets, and have become even more prolific since the advent of large-scale transit surveys, since the transit geometry eliminates the M sin i degeneracy, allowing both planetary mass and radius to be determined unambiguously. A true “Earth-twin”—an Earth-radius, Earth-mass planet orbiting a Sun-like (G2V) star at a distance of ∼1 au—is still beyond the grasp of the current generation of RV instruments and near the limits of precision space-based photometry, but low-mass stars (K- and M-dwarfs) offer larger RV and transit signals, making them prime targets for exoplanet discovery while the next generation of instrumentation is under development. In this dissertation I will discuss my contributions to the design and construction of the recent generation of extreme-precision radial velocity (EPRV) spectrographs, followed by my various efforts to use these EPRV instruments, often in conjunction with precision transit photometry, to search for and characterize a diverse variety of planets around low-mass stars. First, I discuss the construction, testing, and integration of the fiber-optic feed of NEID, the new ultra-stabilized red-optical EPRV spectrograph on the WIYN 3.5m Telescope at Kitt Peak National Observatory. I also present the design and implementation of the NEID solar feed, which provides densely-sampled RVs of the Sun “as a star” intended for investigation of instrumental systematics and stellar activity mitigation techniques in order to push toward the level of 10 cm/s RV precision necessary to detect an Earth-twin exoplanet. I was one of the key personnel on the NEID instrument team responsible for the fiber feed, as well as the project lead for the NEID solar feed subsystem. I then present my ongoing blind RV survey, SNEAK—the Search for Nearby Exoplanets Around K-dwarfs—which uses NEID to look for super-Earths (M ≲ 10 M_Earth) around mid/late K-dwarfs. I discuss the motivation behind this narrowly-targeted survey and the survey target selection, and include a preliminary analysis of the first two years of SNEAK data. SNEAK and similar efforts leverage our current instrumentation to help maximize scientific return from next-generation facilities like the Extremely Large Telescopes and the Habitable Worlds Observatory. I also discuss several results illustrating the ample diversity of exoplanets around M-dwarfs, which are based upon RV data from NEID and the near-infrared (NIR) Habitable-zone Planet Finder (HPF) as well as both space- and ground-based transit photometry. These efforts include further characterization of TOI-1899b, the only known transiting Warm Jupiter orbiting an M-dwarf; the discovery of TOI-2120b, a radius-gap planet around a mid-M dwarf sitting at the intersection of water-rich and gaseous planets; and confirmation of the radius of LTT 1445Ac, the closest transiting Earth-sized planet (orbiting the mid-M dwarf LTT 1445A), a feat demonstrating the capabilities of precision ground-based photometry. Finally, I conclude by summarizing my work and placing it into the greater context of the immense diversity of planets around low-mass stars, and I outline my plans for future efforts in both instrumentation and exoplanet science to work toward the detection and characterization of Earth-like and eventually, Earth-twin, exoplanets.