Dwarfing expectations: The rapid expansion of the transiting brown dwarf population in the era of the TESS mission

Abstract

This thesis presents an analysis of transiting brown dwarf (BD) systems and examines their effectiveness as tests to substellar evolutionary models. The radius, mass, and age of transiting BD systems are the parameters most useful in testing these models and in this work, I show how my collaborators and I have used three facilities to derive these parameters for transiting BD systems. These facilities are: 1) NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, 2) the Tillinghast Reflector Echelle Spectrograph (TRES), and 3) ESA’s Gaia mission. In this work, I use TESS, TRES, and Gaia in tandem to detect and characterize 10 new transiting BD systems with precise radius, mass, and age determinations (in most cases). Most of the age determinations in this work come solely from stellar isochrone models of the host star, but several systems have age constraints from stellar clusters and gyrochronology, which we use to constrain the youth of one transiting BD, TOI-811b, to less than 200 Myr. This is important because it is at these young ages when the radii of BDs changes most rapidly.

In addition, I apply parallax measurements from the Gaia mission’s second data release (Gaia DR2) to improve the radius determinations of 10 transiting BD systems published prior to Gaia DR2 and the launch of the TESS mission. For these 10 previously published systems, new light curves from TESS are used, when possible, and the stellar distances, luminosities, and radii are updated with the parallaxes from Gaia DR2, which improves our constraint on the companion BD’s radius. This work has significantly improved the radius determinations of 7 previously known transiting BDs, including CoRoT-15b and AD 3116b, whose radius uncertainties have been improved from 15% to 5-7%, making them much more effective for testing substellar evolutionary models.

Using these 20 new and previously known transiting BD systems, I have shown that the substellar evolutionary models ranging from young to old substellar isochrones are generally able to reproduce the observed radius, mass, and age determinations of the known transiting BD population.