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Planet Host Star Properties as Probes of Planet Formation and Evolution


Behmard, Aida (2023) Planet Host Star Properties as Probes of Planet Formation and Evolution. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4mta-xt79.


Over the past three decades, we have discovered over 5000 exoplanets that exhibit sizes, orbital architectures, and other properties that are often dramatically different from those of planets in our own Solar System. To understand the various processes that sculpted this diversity of planets, we can examine the stars they orbit. In the first project of my thesis, I modified a machine learning framework that models stellar spectra (The Cannon, Ness et al. 2015) to measure iron abundances for M dwarfs - small, cool stars that dominate the stellar population of our galaxy. Next, I combined Bayesian statistical methods and astrometric data that tracks the movements of stars to examine orbital alignment between planet host stars and their stellar companions. I discovered that close-in gas giant planet systems tend to be misaligned, which suggests that their dynamical histories include obliquity excitation through interactions with e.g., the protoplanetary disk and/or nearby stars. I then used Keck-HIRES spectroscopic observations and MESA stellar evolution models to uncover planet formation signatures encoded in host star elemental abundance patterns. I found that abundance differences between stars in binary systems may increase as a function of their separation, which has important implications for studies that rely on binary star chemistry. Most recently, I extended my abundance methodology to large spectroscopic samples to examine abundance patterns in planet host versus non-planet host stars, and thus explore planet formation signatures on a galactic scale.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:extrasolar planets, stars, planet-star interactions, stellar chemical abundances, high-resolution spectroscopy, statistical techniques
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Planetary Sciences
Awards:Caltech Three Minute Thesis (3MT) competition, 2022, 1st Place
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Knutson, Heather A.
Group:3MT Competition (Caltech)
Thesis Committee:
  • Blake, Geoffrey A. (chair)
  • Batygin, Konstantin
  • Fuller, James
  • Knutson, Heather A.
Defense Date:8 May 2023
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE1745301
Record Number:CaltechTHESIS:05162023-173813482
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Ch.2 adapted for Ch.3 adapted for Ch.4 adapted for Ch.5 adapted for Ch.6
Behmard, Aida0000-0003-0012-9093
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15178
Deposited By: Aida Behmard
Deposited On:31 May 2023 15:17
Last Modified:07 Jun 2023 16:31

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