CHARACTERIZATION OF EXOPLANETS AND STELLAR SYSTEMS WITH NEW ROBOTS

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  • March 21, 2019
Creator
  • Ziegler, Carl
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
Abstract
  • Large astronomical surveys find thousands of interesting transient events, such as exoplanets. Beyond detection, these surveys are limited in their ability to study the properties of these discoveries. In particular, a common problem with wide-field surveys is because they observe huge swaths of the sky, their resolution is often quite coarse, leading to source confusion and photometric contamination. In this dissertation, I discuss the use of robotic, high-resolution instruments to confirm and characterize exoplanets and also better understand the demographics of stellar populations. These surveys are only feasible with autonomous instruments due to the order-of-magnitude increase in observational time efficiency gained with automation. I present first the design and construction of Robo-SOAR, a moderate-order NGS-AO system in development for the SOAR telescope. With robotic software adapted from Robo-AO, Robo-SOAR will be capable of observing hundreds of targets a night. With an innovative, low-cost dual knife-edge WFS, similar in concept to a pyramid WFS but with reduced chromatic aberrations, Robo-SOAR can reach the diffraction limit on brighter targets. I then discuss the observations of 348 cool subdwarf stars with Robo-AO, a pilot study for future kilo-target surveys. Cool subdwarfs are remnants of the first population of stars formed in the Milky Way. I find that approximately 12% of cool subdwarfs have binary companions, a multiplicity fraction three times lower than similar dwarf stars. The disparity between the two populations may be evidence of the different environments in which they formed. The lack of companions to cool subdwarfs suggests they may have formed in less dense regions, or over their long lifetimes may have had more disruptive encounters with other stars and the Galactic tide. It is also possible that they are galactic interlopers, and formed in small, less-dense galaxies that merged with the Milky Way. We show that the disparity between cool subdwarf and red dwarf multiplicity is consistent with this scenario. I report the results of the Robo-AO survey of every planetary candidate discovered with Kepler to search for previously unknown nearby stars. These stars contaminate the exquisite photometry of Kepler and can either dilute the transit signal from a real planet, resulting in underestimated radii estimates, or be the source of an astrophysical false positive transit signal. More than half of the over 4000 Kepler planetary candidates have only been observed with Robo-AO. We find 610 stars within 4'' of a planetary candidate host star, and correct the derived radii estimates of the more than 800 planets within these systems. On average, we find that the planetary radii increase by a factor of approximately 1.59 in systems with a detected nearby star. We quantify the probability of association for over 150 multiple systems hosting planets using multi-band photometry. In particular, we examine five planetary candidate host stars with four nearby stars detected by Robo-AO and quantify the probability they are high-order planet-hosting systems. Lastly, I use the results of the Robo-AO Kepler survey to search for evidence of the impact multiple star systems have on planets. The presence of a companion star is believed to have a significant impact on the properties of planetary systems. I find that hot Jupiters are more likely than any other planet to be found in a binary star system. This suggests that stellar companions drive orbital migration of giant planets. I also find that single and multiple-transiting planet systems are equally likely to be found in a binary. I find that KOIs from later data releases are less likely to have a nearby star than systems from earlier data releases, possibly a result of the automation of the Kepler vetting pipeline. I find that KOIs follow trends observed in field stars with respect to the relationship between stellar multiplicity and stellar effective temperature and metallicity.
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Advisor
  • Clemens, Christopher
  • Reichart, Daniel
  • Oldenburg, Amy
  • Heitsch, Fabian
  • Law, Nicholas
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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