# # Program information file # PROGRAM_ID 2022B046 PROGRAM_TITLE Characterizing the Ultracool TESS Targets: Investigating the Role of Gravity in Planet Hosts PROGRAM_INV1 Christopher Theissen PROGRAM_INV2 Daniella Bardalez Gagliuffi PROGRAM_INV3 Elisabeth Newton PROGRAM_INV4 Adam Burgasser PROGRAM_INV5 Jacqueline Faherty PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Exoplanets have been found in abundance over the past two decades, with the lowest-mass stars found to have the highest likelihood of harboring terrestrial planets. However, planet statistics around the lowest-mass stars [>M5] are not well constrained, with a handful of discoveries hinting that planets may be plentiful at the bottom of the main sequence [i.e., TRAPPIST-1, Teegarden's Star]. The two lowest-mass, 'ultracool dwarf,' planet hosts also show spectral signatures of low surface gravity, although their kinematics and magnetic activity tracers are consistent with older stellar populations. The discovery of multiple planets around both of these stars has suggested that the peak incidence of Earth/super-Earth sized planets may be as low as 10% the mass of the Sun. On the other hand, recent pebble accretion models suggest a peak at stars with 50% the mass of the Sun, with essentially no such planets around the smallest stars. This proposal aims to improve the ultracool dwarf sample by characterizing a volume complete sample being targeted by current planet-hunting surveys [e.g., TESS, TRAPPIST, SPECULOOS, MEarth], and investigating the role of surface gravity in planet occurrence. The proposed project will obtain low-resolution [R ~ 120] near-infrared [0.7-2.52 microns] spectra for a volume complete sample of ultracool dwarfs within 30 pc with spectral types later than M5, sourced from Gaia, 2MASS, and WISE. By quantifying in detail the spectral peculiarities observed in the lowest-mass planet hosts, we will elucidate if these peculiarities manifest from low-gravity, low-metallicity, or some other mechanism possibly induced by the orbiting planets; and deduce whether Teegarden's Star and TRAPPIST-1 are rare systems or representatives of a vast population of very-low-mass planet host stars. The proposed observations will also produce a legacy dataset that will enable a multitude of ultracool dwarf science. PROGRAM_ABSTRACT_END