SET-E: The Search for Extraterrestrial Environmentalism

There is currently no evidence for life on any known exoplanet. Here, we propose a form of "galactic anthropology" to detect not only the existence of life on transiting exoplanets, but also the existence of environmentalism movements. By observing the planet's atmosphere over long time baselines, the destruction and recovery of a hole in an exoplanet's ozone layer may be observable. While not readily detectable for any one system with JWST, by binning together observations of hundreds of systems we can finally determine the occurrence rate of environmental movements on Earthlike planets in the galaxy, a number we term eta-Green-Earth.Comment: 4 pages, 2 figures, Comments Welcom

Model-Independent Stellar and Planetary Masses from Multi-Transiting Exoplanetary Systems

Precise exoplanet characterization requires precise classification of exoplanet host stars. The masses of host stars are commonly estimated by comparing their spectra to those predicted by stellar evolution models. However, spectroscopically determined properties are difficult to measure accurately for stars that are substantially different from the Sun, such as M-dwarfs and evolved stars. Here, we propose a new method to dynamically measure the masses of transiting planets near mean-motion resonances and their host stars by combining observations of transit timing variations with radial velocity measurements. We derive expressions to analytically determine the mass of each member of the system and demonstrate the technique on the Kepler-18 system. We compare these analytic results to numerical simulations and find the two are consistent. We identify eight systems for which our technique could be applied if follow-up radial velocity measurements are collected. We conclude this analysis would be optimal for systems discovered by next generation missions similar to TESS or PLATO, which will target bright stars that are amenable to efficient RV follow-up.Comment: 9 pages, 1 figure, submitted to Ap

Low-Mass Stars and Their Companions

In this thesis, I present seven studies aimed towards better understanding the demographics and physical properties of M dwarfs and their companions. These studies focus in turn on planetary, brown dwarf, and stellar companions to M dwarfs. I begin with an analysis of radial velocity and transit timing analyses of multi-transiting planetary systems, finding that if both signals are measured to sufficiently high precision the stellar and planetary masses can be measured to a high precision, eliminating a need for stellar models which may have systematic errors. I then combine long-term radial velocity monitoring and a direct imaging campaign to measure the occurrence rate of giant planets around M dwarfs. I find that 6.5 +/- 3.0% of M dwarfs host a Jupiter mass or larger planet within 20 AU, with a strong dependence on stellar metallicity. I then present two papers analyzing the LHS 6343 system, which contains a widely separated M dwarf binary (AB). Star A hosts a transiting brown dwarf (LHS 6343 C) with a 12.7 day period. By combining radial velocity data with transit photometry, I am able to measure the mass and radius of the brown dwarf to 2% precision, the most precise measurement of a brown dwarf to date. I then analyze four secondary eclipses of the LHS 6343 AC system as observed by Spitzer in order to measure the luminosity of the brown dwarf in both Spitzer bandpasses. I find the brown dwarf is consistent with theoretical models of an 1100 K T dwarf at an age of 5 Gyr and empirical observations of field T5-6 dwarfs with temperatures of 1070 +/- 130 K. This is the first non-inflated brown dwarf with a measured mass, radius, and multi-band photometry, making it an ideal test of evolutionary models of field brown dwarfs. Next, I present the results of an astrometric and radial velocity campaign to measure the orbit and masses of both stars in the GJ 3305 AB system, an M+M binary comoving with 51 Eridani, a more massive star with a directly imaged planetary companion. I compare the masses of both stars to largely untested theoretical models of young M dwarfs, finding that the models are consistent with the measured mass of star A but slightly overpredict the luminosity of star B. In the final two science chapters I focus on space-based transit surveys, present and future. First, I present the first catalog of statistically validated planets from the K2 mission, as well as updated stellar and planetary parameters for all systems with candidate planets in the first K2 field. The catalog includes K2-18b, a ``mini-Neptune'' planet that receives a stellar insolation consistent with the level that the Earth receives from the Sun, making it a useful comparison against planets of a similar size that are highly irradiated, such as GJ 1214 b. Finally, I present predictions for the WFIRST mission. While designed largely as a microlensing mission, I find it will be able to detect as many as 30,000 transiting planets towards the galactic bulge, providing information about how planet occurrence changes across the galaxy. These planets will be able to be confirmed largely through direct detection of their secondary eclipses. Moreover, I find that more than 50% of the planets it detects smaller than Neptune will be found around M dwarf hosts.</p

KIC 8462852 Faded throughout the Kepler Mission

KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full-frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ~1000 days KIC 8462852 faded approximately linearly at a rate of 0.341 ± 0.041% yr^(−1), for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 years. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, none exhibit the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. Moreover, of these comparison stars, only one changes brightness as quickly as the 0.341% yr^(−1) measured for KIC 8462852 during the first three years of the Kepler mission. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding that while such a cloud could evade detection in submillimeter observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve

Measuring the galactic distribution of transiting planets with WFIRST

The WFIRST microlensing mission will measure precise light curves and relative parallaxes for millions of stars, giving it the potential to characterize short-period transiting planets all along the line of sight and into the galactic bulge. These light curves will enable the detection of more than 100,000 transiting planets whose host stars have measured distances. Although most of these planets cannot be followed up, several thousand hot Jupiters can be confirmed directly by detection of their secondary eclipses in the WFIRST data. Additionally, some systems of small planets may be confirmed by detecting transit timing variations over the duration of the WFIRST microlensing survey. Finally, many more planets may be validated by ruling out potential false positives. The combination of WFIRST transits and microlensing will provide a complete picture of planetary system architectures, from the very shortest periods to unbound planets, as a function of galactocentric distance

SET-E: The Search for Extraterrestrial Environmentalism

There is currently no evidence for life on any known exoplanet. Here, we propose a form of "galactic anthropology" to detect not only the existence of life on transiting exoplanets, but also the existence of environmental movements. By observing the planet's atmosphere over long time baselines, the destruction and recovery of a hole in an exoplanet's ozone layer may be observable. While not readily detectable for any one system with JWST, by binning together observations of hundreds of systems we can finally determine the occurrence rate of environmental movements on Earthlike planets in the galaxy, a number we term η_(Green Earth)