Big Planets around Small Stars: Masses and Upper Limits for Six Giant Planets

Transiting giant exoplanets around M-dwarf stars (GEMS) are rare, owing to the low-mass host stars. However the all-sky coverage of TESS has enabled the detection of an increasingly large number of them to enable statistical surveys like the Searching for GEMS survey. As part of this endeavour, we describe the confirmation of six transiting giant planets, which includes precise mass measurements for two GEMS (TOI-5176 A b, TOI-6034 b) and upper limits for four TOIs. Two of these four orbit M-dwarfs (TOI-5616 b, TOI-5634 A b), while two orbit late Ks (TOI-5218 b, TOI-5414 b). Our observations include radial velocities from the Habitable-zone Planet Finder on the Hobby-Eberly Telescope, and MAROON-X on Gemini-North, along with photometry and high-contrast imaging from a multitude of ground-based facilities. In addition to TESS photometry for all our targets, TOI-5176 A b was also observed by K2 in Campaigns 5 and 18, which provides exquisite orbital and planetary constraints despite the faint host star and long orbital period ∼ 20.4 days. With an equilibrium temperature of only 380 K, it is one of the coolest known well-characterized transiting planets. TOI-6034 has a late F-type companion about 40′′ away, making it the first GEMS host star to have an earlier main-sequence binary companion. These confirmations, in addition to the existing sample, are hinting at differences in bulk-densities between transiting GEMS and FGK hot Jupiters.