The California Legacy Survey: a Three-Decade Census of Extrasolar Planets

Author: Rosenthal, Lee Jesse

Year: 2022

Degree: Dissertation (Ph.D.)

Advisor: Howard, Andrew W.

Committee Members: Hillenbrand, Lynne A.; Knutson, Heather A.; Howard, Andrew W.; Batygin, Konstantin; Hallinan, Gregg W.

Option: Astrophysics

DOI: 10.7907/1yh3-5g50

Abstract

Taking an accurate census of planets orbiting other stars, otherwise known as exoplanets, is a crucial step toward understanding the nature of planet formation and placing Earth and the Solar System in a broader context. For my thesis, I present the culmination of a three-decade a high-precision radial velocity (RV) survey of 719 FGKM stars, known as the California Legacy Survey (CLS), and use this survey to perform a statistical study of exoplanets. I developed computational methods for planet search and RV sensitivity characterization, and detected 164 known exoplanets and 14 newly discovered or revised exoplanets and substellar companions in the CLS. I used this star and planet catalog to measure the occurrence rates of several exoplanet subtypes and probe formation pathways. I found that giant planet occurrence is greatly enhanced beyond 1 Earth-Sun distance (au), then decreases beyond 8 au. This implies that giant planet formation is much easier beyond the water-ice line of most stars, possibly due to greater ease of solid coagulation and pebble accretion, and eventually decreases with the density profile of of protoplanetary disks. It also means that Jupiter and Saturn are located in the orbital space of greatest giant planet occurrence, making the Solar System typical in giant placement. I then investigated the relationship between small close-in planets and cold outer giants, and found that not all giants host inner rocky companions. Rather, giants under about one-third of a Jupiter mass or beyond 3 au are more likely to have small companions than their warmer and more massive counterparts. Finally, I compared single giant and multi giant planetary systems. I performed novel characterizations of the orbital eccentricity distributions of these two populations, and discovered that multi-giant stellar hosts are on average significantly more metal-rich than single-giant hosts. This means that the Sun with its two giant planets is atypical among much more metal-rich giant hosts. I also found that lonely giants present a pile-up of `super-hot Jupiters' within 0.06 au not shared by neighborly giants, and that giants orbiting the same star tend to have similar masses. Taken together, these findings are a substantial leap forward in understanding the architectures and origins of planetary systems.

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