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We present the discovery of TOI-5205b, a transiting Jovian planet orbiting a solar metallicity M4V star, which was discovered using Transiting Exoplanet Survey Satellite photometry and then confirmed using a combination of precise radial velocities, ground-based photometry, spectra, and speckle imaging. TOI-5205b has one of the highest mass ratios for M-dwarf planets, with a mass ratio of almost 0.3%, as it orbits a host star that is just 0.392 ± 0.015M_⊙. Its planetary radius is 1.03 ± 0.03R_J, while the mass is 1.08 ± 0.06M_J. Additionally, the large size of the planet orbiting a small star results in a transit depth of ∼7%, making it one of the deepest transits of a confirmed exoplanet orbiting a main-sequence star. The large transit depth makes TOI-5205b a compelling target to probe its atmospheric properties, as a means of tracing the potential formation pathways. While there have been radial-velocity-only discoveries of giant planets around mid-M dwarfs, this is the first transiting Jupiter with a mass measurement discovered around such a low-mass host star. The high mass of TOI-5205b stretches conventional theories of planet formation and disk scaling relations that cannot easily recreate the conditions required to form such planets.

Abstract We present the discovery of a new Jovian-sized planet, TOI-3757 b, the lowest-density transiting planet known to orbit an M dwarf (M0V). This planet was discovered around a solar-metallicity M dwarf, using Transiting Exoplanet Survey Satellite photometry and confirmed with precise radial velocities from the Habitable-zone Planet Finder (HPF) and NEID. With a planetary radius of 12.0 − 0.5 + 0.4 R ⊕ and mass of 85.3 − 8.7 + 8.8 M ⊕ , not only does this object add to the small sample of gas giants (∼10) around M dwarfs, but also its low density ( ρ = 0.27 − 0.04 + 0.05 g cm −3 ) provides an opportunity to test theories of planet formation. We present two hypotheses to explain its low density; first, we posit that the low metallicity of its stellar host (∼0.3 dex lower than the median metallicity of M dwarfs hosting gas giants) could have played a role in the delayed formation of a solid core massive enough to initiate runaway accretion. Second, using the eccentricity estimate of 0.14 ± 0.06, we determine it is also plausible for tidal heating to at least partially be responsible for inflating the radius of TOI-3757bmore »b. The low density and large scale height of TOI-3757 b makes it an excellent target for transmission spectroscopy studies of atmospheric escape and composition (transmission spectroscopy measurement of ∼ 190). We use HPF to perform transmission spectroscopy of TOI-3757 b using the helium 10830 Å line. Doing this, we place an upper limit of 6.9% (with 90% confidence) on the maximum depth of the absorption from the metastable transition of He at ∼10830 Å, which can help constraint the atmospheric mass-loss rate in this energy-limited regime.« less

Abstract We report the discovery of an M = 67 ± 2 M J brown dwarf transiting the early M dwarf TOI-2119 on an eccentric orbit ( e = 0.3362 ± 0.0005) at an orbital period of 7.200861 ± 0.000005 days. We confirm the brown dwarf nature of the transiting companion using a combination of ground-based and space-based photometry and high-precision velocimetry from the Habitable-zone Planet Finder. Detection of the secondary eclipse with TESS photometry enables a precise determination of the eccentricity and reveals the brown dwarf has a brightness temperature of 2100 ± 80 K, a value which is consistent with an early L dwarf. TOI-2119 is one of the most eccentric known brown dwarfs with P < 10 days, possibly due to the long circularization timescales for an object orbiting an M dwarf. We assess the prospects for determining the obliquity of the host star to probe formation scenarios and the possibility of additional companions in the system using Gaia EDR3 and our radial velocities.

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 warmmore »gas giants amenable to additional characterization with transmission spectroscopy to probe atmospheric chemistry and, for TOI-3714, obliquity measurements to probe formation scenarios.« less

Abstract We validate the planetary nature of an ultra-short-period planet orbiting the M dwarf KOI-4777. We use a combination of space-based photometry from Kepler, high-precision, near-infrared Doppler spectroscopy from the Habitable-zone Planet Finder, and adaptive optics imaging to characterize this system. KOI-4777.01 is a Mars-sized exoplanet ( R p = 0.51 ± 0.03 R ⊕ ) orbiting the host star every 0.412 days (∼9.9 hr). This is the smallest validated ultra-short period planet known and we see no evidence for additional massive companions using our HPF RVs. We constrain the upper 3 σ mass to M p < 0.34 M ⊕ by assuming the planet is less dense than iron. Obtaining a mass measurement for KOI-4777.01 is beyond current instrumental capabilities.

We present the validation of two planets orbiting M dwarfs, TOI-1696b and TOI-2136b. Both planets are mini-Neptunes orbiting nearby stars, making them promising prospects for atmospheric characterization with the James Webb Space Telescope (JWST). We validated the planetary nature of both candidates using high-contrast imaging, ground-based photometry, and near-infrared radial velocities. Adaptive optics images were taken using the ShARCS camera on the 3 m Shane Telescope. Speckle images were taken using the NN-Explore Exoplanet Stellar Speckle Imager on the WIYN 3.5 m telescope. Radii and orbital ephemerides were refined using a combination of the Transiting Exoplanet Survey Satellite, the diffuser-assisted Astrophysical Research Consortium (ARC) Telescope Imaging Camera (ARCTIC) imager on the 3.5 m ARC telescope at Apache Point Observatory, and the 0.6 m telescope at Red Buttes Observatory. We obtained radial velocities using the Habitable-Zone Planet Finder on the 10 m Hobby–Eberly Telescope, which enabled us to place upper limits on the masses of both transiting planets. TOI-1696b (P= 2.5 days;R_p= 3.24R_⊕;M_p< 56.6M_⊕) falls into a sparsely populated region of parameter space considering its host star’s temperature (T_eff= 3168 K, M4.5), as planets of its size are quite rare around mid- to late-M dwarfs. On the other hand, TOI-2136bmore »(P= 7.85 days;R_p= 2.09R_⊕;M_p< 15.0M_⊕) is an excellent candidate for atmospheric follow-up with the JWST.

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We present high-resolution observations of a flaring event in the M8 dwarf vB 10 using the near-infrared Habitable-zone Planet Finder (HPF) spectrograph on the Hobby-Eberly Telescope. The high stability of HPF enables us to accurately subtract a vB 10 quiescent spectrum from the flare spectrum to isolate the flare contributions and study the changes in the relative energy of the Caiiinfrared triplet, several Paschen lines, the Heλ10830 triplet lines, and to select iron and magnesium lines in HPF's bandpass. Our analysis reveals the presence of a red asymmetry in the Heλ10830 triplet, which is similar to signatures of coronal rain in the Sun. Photometry of the flare derived from an acquisition camera before spectroscopic observations and the ability to extract spectra from up-the-ramp observations with the HPF infrared detector enable us to perform time-series analysis of part of the flare and provide coarse constraints on the energy and frequency of such flares. We compare this flare with historical observations of flares around vB 10 and other ultracool M dwarfs and attempt to place limits on flare-induced atmospheric mass loss for hypothetical planets around vB 10.