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1. TOI-2084 b and TOI-4184 b: Two new sub-Neptunes around M dwarf stars

   https://doi.org/10.1051/0004-6361/202346838  

   Barkaoui, K; Timmermans, M; Soubkiou, A; Rackham, B V; Burgasser, A J; Chouqar, J; Pozuelos, F J; Collins, K A; Howell, S B; Simcoe, R; et al (September 2023, Astronomy & Astrophysics)

   We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, and TOI-4184b. We characterized the host stars by combining spectra fromShane/Kast andMagellan/FIRE, spectral energy distribution analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour photometric data from TESS and ground-based facilities in order to derive the stellar and planetary physical parameters for each system. We find that TOI-2084 band TOI-4184 bare sub-Neptune-sized planets with radii ofR_p= 2.47 ± 0.13R_⊕andR_p= 2.43 ± 0.21R_⊕, respectively. TOI-2084 b completes an orbit around its host star every 6.08 days, has an equilibrium temperature ofT_eq= 527 ± 8 K and an irradiation ofS_p= 12.8 ± 0.8S_⊕. Its host star is a dwarf of spectral M2.0 ± 0.5 at a distance of 114 pc with an effective temperature ofT_eff= 3550 ± 50 K, and has a wide, co-moving M8 companion at a projected separation of 1400 au. TOI-4184 b orbits around an M5.0 ± 0.5 type dwarf star (K_mag= 11.87) each 4.9 days, and has an equilibrium temperature ofT_eq= 412 ± 8 K and an irradiation ofS_p= 4.8 ± 0.4S_⊕. TOI-4184 is a metal poor star ([Fe/H] = −0.27 ± 0.09 dex) at a distance of 69 pc with an effective temperature ofT_eff= 3225 ± 75 K. Both planets are located at the edge of the sub-Jovian desert in the radius-period plane. The combination of the small size and the large infrared brightness of their host stars make these new planets promising targets for future atmospheric exploration with JWST. 

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2. TOI-3984 A b and TOI-5293 A b: Two Temperate Gas Giants Transiting Mid-M Dwarfs in Wide Binary Systems

   https://doi.org/10.3847/1538-3881/acdac7  

   Cañas, Caleb I.; Kanodia, Shubham; Libby-Roberts, Jessica; Lin, Andrea S.; Schutte, Maria; Powers, Luke; Jones, Sinclaire; Monson, Andrew; Wang, Songhu; Stefánsson, Guđmundur; et al (June 2023, The Astronomical Journal)

   Abstract We confirm the planetary nature of two gas giants discovered by TESS to transit M dwarfs with stellar companions at wide separations. TOI-3984 A ( J = 11.93) is an M4 dwarf hosting a short-period (4.353326 ± 0.000005 days) gas giant ( M p = 0.14 ± 0.03 M J and R p = 0.71 ± 0.02 R J ) with a wide-separation white dwarf companion. TOI-5293 A ( J = 12.47) is an M3 dwarf hosting a short-period (2.930289 ± 0.000004 days) gas giant ( M p = 0.54 ± 0.07 M J and R p = 1.06 ± 0.04 R J ) with a wide-separation M dwarf companion. We characterize both systems using a combination of ground- and space-based photometry, speckle imaging, and high-precision radial velocities from the Habitable-zone Planet Finder and NEID spectrographs. TOI-3984 A b ( T eq = 563 ± 15 K and TSM = 138 − 27 + 29 ) and TOI-5293 A b ( T eq = 675 − 30 + 42 K and TSM = 92 ± 14) are two of the coolest gas giants among the population of hot Jupiter–sized gas planets orbiting M dwarfs and are favorable targets for atmospheric characterization of temperate gas giants and 3D obliquity measurements to probe system architecture and migration scenarios. 

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3. TOI-3714 b and TOI-3629 b: Two Gas Giants Transiting M Dwarfs Confirmed with the Habitable-zone Planet Finder and NEID

   https://doi.org/10.3847/1538-3881/ac7804  

   Cañas, Caleb I.; Kanodia, Shubham; Bender, Chad F.; Mahadevan, Suvrath; Stefánsson, Guđhmundur; Cochran, William D.; Lin, Andrea S.; Hwang, Hsiang-Chih; Powers, Luke; Monson, Andrew; et al (July 2022, The Astronomical Journal)

   Abstract We confirm the planetary nature of two gas giants discovered by the Transiting Exoplanet Survey Satellite to transit M dwarfs. TOI-3714 ( V = 15.24, J = 11.74) is an M2 dwarf hosting a hot Jupiter ( M p = 0.70 ± 0.03 M J and R p = 1.01 ± 0.03 R J ) on an orbital period of 2.154849 ± 0.000001 days with a resolved white dwarf companion. TOI-3629 ( V = 14.63, J = 11.42) is an M1 dwarf hosting a hot Jupiter ( M p = 0.26 ± 0.02 M J and R p =0.74 ± 0.02 R J ) on an orbital period of 3.936551 − 0.000006 + 0.000005 days. We characterize each transiting companion using a combination of ground-based and space-based photometry, speckle imaging, and high-precision velocimetry from the Habitable-zone Planet Finder and the NEID spectrographs. With the discovery of these two systems, there are now nine M dwarfs known to host transiting hot Jupiters. Among this population, TOI-3714 b ( T eq = 750 ± 20 K and TSM = 98 ± 7) and TOI-3629 b ( T eq = 690 ± 20 K and TSM = 80 ± 9) are warm gas giants amenable to additional characterization with transmission spectroscopy to probe atmospheric chemistry and, for TOI-3714, obliquity measurements to probe formation scenarios. 

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4. TOI 762 A b and TIC 46432937 b: Two Giant Planets Transiting M-dwarf Stars

   https://doi.org/10.3847/1538-3881/ad6f07  

   Hartman, Joel D; Bayliss, Daniel; Brahm, Rafael; Bryant, Edward M; Jordán, Andrés; Bakos, Gáspár Á; Hobson, Melissa J; Sedaghati, Elyar; Bonfils, Xavier; Cointepas, Marion; et al (October 2024, The Astronomical Journal)

   Abstract We present the discovery of TOI 762 A b and TIC 46432937 b, two giant planets transiting M-dwarf stars. Transits of both systems were first detected from observations by the NASA TESS mission, and the transiting objects are confirmed as planets through high-precision radial velocity observations carried out with Very Large Telescope/ESPRESSO. TOI 762 A b is a warm sub-Saturn with a mass of 0.251 ± 0.042M_J, a radius of 0.744 ± 0.017R_J, and an orbital period of 3.4717 days. It transits a mid-M-dwarf star with a mass of 0.442 ± 0.025M_☉and a radius of 0.4250 ± 0.0091R_☉. The star TOI 762 A has a resolved binary star companion, TOI 762 B, that is separated from TOI 762 A by 3.″2 (∼319 au) and has an estimated mass of 0.227 ± 0.010M_☉. The planet TIC 46432937 b is a warm super-Jupiter with a mass of 3.20 ± 0.11M_Jand radius of 1.188 ± 0.030R_J. The planet’s orbital period isP= 1.4404 days, and it undergoes grazing transits of its early M-dwarf host star, which has a mass of 0.563 ± 0.029M_☉and a radius of 0.5299 ± 0.0091R_☉. TIC 46432937 b is one of the highest-mass planets found to date transiting an M-dwarf star. TIC 46432937 b is also a promising target for atmospheric observations, having the highest transmission spectroscopy metric or emission spectroscopy metric value of any known warm super-Jupiter (mass greater than 3.0M_J, equilibrium temperature below 1000 K). 

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5. TOI-3785 b: A Low-density Neptune Orbiting an M2-dwarf Star

   https://doi.org/10.3847/1538-3881/acd8bf  

   Powers, Luke C.; Libby-Roberts, Jessica; Lin, Andrea S. J.; Cañas, Caleb I.; Kanodia, Shubham; Mahadevan, Suvrath; Ninan, Joe P.; Stefánsson, Guđmundur; Gupta, Arvind F.; Jones, Sinclaire; et al (July 2023, The Astronomical Journal)

   Abstract Using both ground-based transit photometry and high-precision radial velocity spectroscopy, we confirm the planetary nature of TOI-3785 b. This transiting Neptune orbits an M2-Dwarf star with a period of ∼4.67 days, a planetary radius of 5.14 ± 0.16R_⊕, a mass of ${14.95}_{-3.92}^{+4.10}$M_⊕, and a density of $\rho ={0.61}_{-0.17}^{+0.18}$g cm⁻³. TOI-3785 b belongs to a rare population of Neptunes (4R_⊕<R_p< 7R_⊕) orbiting cooler, smaller M-dwarf host stars, of which only ∼10 have been confirmed. By increasing the number of confirmed planets, TOI-3785 b offers an opportunity to compare similar planets across varying planetary and stellar parameter spaces. Moreover, with a high-transmission spectroscopy metric of ∼150 combined with a relatively cool equilibrium temperature ofT_eq= 582 ± 16 K and an inactive host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune targets for atmospheric follow up. Future investigation into atmospheric mass-loss rates of TOI-3785 b may yield new insights into the atmospheric evolution of these low-mass gas planets around M dwarfs. 

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