Roberto Sanchis Ojeda
Investigations of close-in exoplanets: starspot transits, and ultra-short period planets
Friday, April 18, 2014
3:30pm (Marlar Lounge; 37-252)
Committee: Professors Joshua N. Winn, Saul A. Rappaport, and Sara Seager
Over the past 20 years, over 1700 planets outside of the solar system have been found. These planets, known as exoplanets, represent a great opportunity to answer some of the most complex questions about the origin and evolution of our solar system. In this thesis, I focus on transiting exoplanets, which are planets that eclipse their host star from our point of view, reducing momentarily the stellar flux detected by our telescopes.
In the first part of this thesis, I discuss a new method I developed to study a key geometrical property of a planetary system, the spin-orbit angle. Also known as the obliquity, it is defined as the angle between the spin axis of the star and orbital planet of each of the planets. This new technique uses the passage of a transiting planet over starspots to obtain information about the obliquity of its host star. When a planet occults a dark spot, it blocks less light than expected for a short period of time, and a small brightening appears on the transit light curve. This can be used to track the trajectory of the starspots, and learn about the direction of rotation of the star with respect to the orbit of the planet. I will discuss the lessons learned from applying this technique to several systems, and the relevance of the extension of this technique to multi-transiting planet systems for the first time.
In the second part of this thesis, I describe a survey to detect the shortest-period planets discovered with the Kepler space telescope, using a non-standard approach. Planets are detected by interpreting the amplitudes and frequencies of the different peaks of the Fourier spectrum of the Kepler flux time series. I will then discuss the most significant discovery of the survey, Kepler-78b, currently the smallest planet with a mass and radius measurement, with an extremely short orbital period of 8.5 hours. Finally, I will characterize the general population of ultra-short period planets based on the properties of 106 planet candidates with orbital periods shorter than 1 day studied in our survey.