Steven Giacalone (Caltech): "The Origins of Close-in Brown Dwarfs from the Stellar Obliquity Distribution"

The obliquities of hundreds of planet-hosting stars (i.e., the angles between the stellar spin axes and the planet orbital axes) have been measured over the last decade, providing unique insight into the formations and evolutions of close-in planets. The stellar obliquity distribution can shed similar light on the origins of close-in brown dwarfs (BDs), which are thought to form far from their host stars and migrate inwards via some hitherto unknown process. However, tapping into this distribution has historically been challenging. The intrinsic rarity of close-in BDs meant that most systems discovered by early transit surveys were too faint for obliquity measurements. This landscape has changed rapidly since the launch of TESS, which has nearly doubled the number of known transiting BDs to ~50, with many of the recently discovered systems being bright enough for obliquity measurements with new radial velocity spectrographs. We present a new survey to characterize the orbits of these systems with Rossiter-McLaughlin and Doppler Shadow observations, with the goal of building a sample of obliquities with which to investigate the origins of their BD companions. We discuss early results from the survey, including hints that close-in BDs and hot Jupiters arrive at their current orbits via different mechanisms.