[HTML][HTML] A close-in puffy Neptune with hidden friends: The enigma of TOI 620
The Astronomical Journal, 2022•iopscience.iop.org
We present the validation of a transiting low-density exoplanet orbiting the M2. 5 dwarf TOI
620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We
utilize photometric data from both TESS and ground-based follow-up observations to
validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios.
High-contrast imaging data are used to resolve the stellar host and exclude stellar
companions at separations≳ 0 farcs 2. We obtain follow-up spectroscopy and corresponding�…
620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We
utilize photometric data from both TESS and ground-based follow-up observations to
validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios.
High-contrast imaging data are used to resolve the stellar host and exclude stellar
companions at separations≳ 0 farcs 2. We obtain follow-up spectroscopy and corresponding�…
Abstract
We present the validation of a transiting low-density exoplanet orbiting the M2. 5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations≳ 0 farcs 2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5σ upper limit of M P< 7.1 M⊕ and ρ P< 0.74 g cm− 3, and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1–20 M J) companion with a projected separation≲ 20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date.
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