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Abstract We present statistical results from the Epoch of Giant Planet Migration RV planet search program. This survey was designed to measure the occurrence rate of giant planets interior to the water ice line of young Sun-like stars, compare this to the prevalence of giant planets at older ages, and provide constraints on the timescale and dominant inward migration mechanism of giant planets. Our final sample amounts to 85 single young (20–200 Myr) G and K dwarfs that we target across a 4 yr time baseline with the near-infrared Habitable-zone Planet Finder spectrograph at McDonald Observatory’s Hobby-Eberly Telescope. As part of this survey, we discovered the young hot Jupiter HS Psc b. We characterize survey detection completeness with realistic injection-recovery tests and measure an occurrence rate of $1.9_{-1.4}^{+2.6}$% for intermediate-age giant planets ( $0.3M_{\mathrm{J}}<m\sin i<13M_{\mathrm{J}}$) within 2.5 au. This is lower than the field age occurrence rate for the same planet masses and separations and favors an increase in the prevalence of giant planets over time from ∼100 Myr to several Gyr, although our results cannot rule out a constant rate. A decaying planet occurrence rate is, however, strongly excluded. This suggests that giant planets located inside the water ice line originate from a combination of in situ formation or early migration coupled with longer-term inward scattering. The completeness-corrected prevalence of young hot Jupiters in our sample is $1.5_{-1.1}^{+2.2}$% —similar to the rate for field stars—and the 95% upper limit for young brown dwarfs within 5000 days is <3.6% . 

Abstract We describe the discovery and characterization of TOI-7149 b, a 0.705 ± 0.075M_J, 1.18 ± 0.045R_Jgas giant on a ∼2.65 days period orbit transiting an M4V star with a mass of 0.344 ± 0.030M_⊙and an effective temperature of 3363 ± 59 K. The planet was first discovered using NASA’s TESS mission, which we confirmed using a combination of ground-based photometry, radial velocities, and speckle imaging. The planet has one of the deepest transits of all known main-sequence planet hosts at ∼12% (R_p/R_⋆∼ 0.33). Pushing the bounds of previous discoveries of giant exoplanets around M-dwarf stars (GEMS), TOI-7149 is one of the lowest mass M-dwarfs to host a transiting giant planet. We compare the sample of transiting GEMS to stars within 200 pc with a Gaia color–magnitude diagram and find that the GEMS hosts are likely to be high metallicity stars. We also analyze the sample of transiting giant planets using the nonparametricMRExoframework to compare the bulk density of warm Jupiters across stellar masses. We confirm our previous result that transiting Jupiters around early M-dwarfs have similar masses and densities to warm Jupiters around FGK stars, and extend this to mid M-dwarfs, thereby suggesting a potential commonality in their formation mechanisms. 

Abstract We present the discovery of GJ 251 c, a candidate super-Earth orbiting in the habitable zone (HZ) of its M dwarf host star. Using high-precision Habitable-zone Planet Finder and NEID RVs, in conjunction with archival RVs from the Keck I High Resolution Echelle Spectrometer, the Calar Alto High-resolution Search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrograph, and the Spectropolarimétre Infrarouge, we improve the measured parameters of the known planet, GJ 251 b (P_b= 14.2370 days; $m\sin \left(i\right)$= 3.85 ${}_{-0.33}^{+0.35}$M_⊕), and we significantly constrain the minimum mass of GJ 251 c, placing it in a plausibly terrestrial regime (P_c= 53.647 ± 0.044 days; $m\sin i_c$= 3.84 ± 0.75M_⊕). Using activity mitigation techniques that leverage chromatic information content, we perform a color-dependent analysis of the system and a detailed comparison of more than 50 models that describe the nature of the planets and stellar activity in the system. Due to GJ 251’s proximity to Earth (5.5 pc), next generation, 30 meter class telescopes will likely be able to image terrestrial planets in GJ 251’s HZ. In fact, GJ 251 c is currently the best candidate for terrestrial, HZ planet imaging in the northern sky. 

Abstract We revisit the long-studied radial velocity (RV) target HD 26965 using recent observations from the NASA-NSF “NEID” precision Doppler facility. Leveraging a suite of classical activity indicators, combined with line-by-line RV analyses, we demonstrate that the claimed 45-day signal previously identified as a planet candidate is most likely an activity-induced signal. Correlating the bulk (spectrally averaged) RV with canonical line activity indicators confirms a multiday “lag” between the observed activity indicator time series and the measured RV. When accounting for this lag, we show that much of the observed RV signal can be removed by a linear detrending of the data. Investigating activity at the line-by-line level, we find a depth-dependent correlation between individual line RVs and the bulk RVs, further indicative of periodic suppression of convective blueshift causing the observed RV variability, rather than an orbiting planet. We conclude that the combined evidence of the activity correlations and depth dependence is consistent with an RV signature dominated by a rotationally modulated activity signal at a period of ∼42 days. We hypothesize that this activity signature is due to a combination of spots and convective blueshift suppression. The tools applied in our analysis are broadly applicable to other stars and could help paint a more comprehensive picture of the manifestations of stellar activity in future Doppler RV surveys. 

Abstract We present the confirmation of TOI-5573 b, a Saturn-sized exoplanet on an 8.79 days orbit around an early M dwarf (3790 K, 0.59R_⊙, 0.61M_⊙, 12.30 Jmag). TOI-5573 b has a mass of $112_{-19}^{+18}$M_⊕(0.35 ± 0.06M_Jup) and a radius of 9.75 ± 0.47R_⊕(0.87 ± 0.04R_Jup), resulting in a density of $0.66_{-0.13}^{+0.16}$g cm⁻³, akin to that of Saturn. The planet was initially discovered by the Transiting Exoplanet Survey Satellite (TESS) and confirmed using a combination of 11 transits from four TESS Sectors (20, 21, 47, and 74), ground-based photometry from the Red Buttes Observatory, and high-precision radial velocity data from the Habitable-zone Planet Finder and NN-EXPLORE Exoplanet Investigations with Doppler spectrographs, achieving a 5σprecision on the planet’s mass. TOI-5573 b is one of the coolest Saturn-like exoplanets discovered around an M-dwarf, with an equilibrium temperature of only 528 ± 10 K, making it a valuable target for atmospheric characterization. Saturn-like exoplanets around M dwarfs likely form through core accretion, with increased disk opacity slowing gas accretion and limiting their mass. The host star’s supersolar metallicity supports core accretion, but uncertainties in M-dwarf metallicity estimates complicate definitive conclusions. Compared to other GEMS (Giant Exoplanets around M-dwarf Stars) orbiting metal-rich stars, TOI-5573 b aligns with the observed pattern that giant planets preferentially form around M-dwarfs with supersolar metallicity. Further high-resolution spectroscopic observations are needed to explore the role of stellar metallicity in shaping the formation and properties of giant exoplanets like TOI-5573 b. 

Abstract We present the discovery of a low-density planet orbiting the high-metallicity early M-dwarf TOI-5688 A b. This planet was characterized as part of the search for transiting giant planets (R ≳ 8R_⊕) through the Searching for Giant Exoplanets around M-dwarf Stars (GEMS) survey. The planet was discovered with the Transiting Exoplanet Survey Satellite, and characterized with ground-based transits from Red Buttes Observatory, the Table Mountain Observatory of Pomona College, and radial velocity (RV) measurements with the Habitable-Zone Planet Finder on the 10 m Hobby Eberly Telescope and NEID on the WIYN 3.5 m telescope. From the joint fit of transit and RV data, we measure a planetary mass and radius of 124 ± 24M_⊕(0.39 ± 0.07M_J) and 10.4 ± 0.7R_⊕(0.92 ± 0.06R_J), respectively. The spectroscopic and photometric analysis of the host star TOI-5688 A shows that it is a metal-rich ([Fe/H] = 0.47 ± 0.16 dex) M2V star, favoring the core-accretion formation pathway as the likely formation scenario for this planet. Additionally, Gaia astrometry suggests the presence of a wide-separation binary companion, TOI-5688 B, which has a projected separation of ~5″ (1110 au) and is an M4V, making TOI-5688 A b part of the growing number of GEMS in wide-separation binary systems. 

Abstract We report the characterization of 28 low-mass (0.02 M ⊙ ≤ M 2 ≤ 0.25 M ⊙ ) companions to Kepler objects of interest (KOIs), eight of which were previously designated confirmed planets. These objects were detected as transiting companions to Sunlike stars (G and F dwarfs) by the Kepler mission and are confirmed as single-lined spectroscopic binaries in the current work using the northern multiplexed Apache Point Observatory Galactic Evolution Experiment near-infrared spectrograph (APOGEE-N) as part of the third and fourth Sloan Digital Sky Surveys. We have observed hundreds of KOIs using APOGEE-N and collected a total of 43,175 spectra with a median of 19 visits and a median baseline of ∼1.9 yr per target. We jointly model the Kepler photometry and APOGEE-N radial velocities to derive fundamental parameters for this subset of 28 transiting companions. The radii for most of these low-mass companions are overinflated (by ∼10%) when compared to theoretical models. Tidally locked M dwarfs on short-period orbits show the largest amount of inflation, but inflation is also evident for companions that are well separated from the host star. We demonstrate that APOGEE-N data provide reliable radial velocities when compared to precise high-resolution spectrographs that enable detailed characterization of individual systems and the inference of orbital elements for faint ( H > 12) KOIs. The data from the entire APOGEE-KOI program are public and present an opportunity to characterize an extensive subset of the binary population observed by Kepler. 

Abstract We confirm TOI-4201 b as a transiting Jovian-mass planet orbiting an early M dwarf discovered by the Transiting Exoplanet Survey Satellite. Using ground-based photometry and precise radial velocities from NEID and the Planet Finder Spectrograph, we measure a planet mass of ${2.59}_{-0.06}^{+0.07}$M_J, making this one of the most massive planets transiting an M dwarf. The planet is ∼0.4% of the mass of its 0.63M_⊙host and may have a heavy-element mass comparable to the total dust mass contained in a typical class II disk. TOI-4201 b stretches our understanding of core accretion during the protoplanetary phase and the disk mass budget, necessitating giant planet formation to take place either much earlier in the disk lifetime or perhaps through alternative mechanisms like gravitational instability. 

Abstract Gaia astrometry of nearby stars is precise enough to detect the tiny displacements induced by substellar companions, but radial velocity (RV) data are needed for definitive confirmation. Here we present RV follow-up observations of 28 M and K stars with candidate astrometric substellar companions, which led to the confirmation of two systems, Gaia-4b and Gaia-5b, identification of five systems that are single lined but require additional data to confirm as substellar companions, and the refutation of 21 systems as stellar binaries. Gaia-4b is a massive planet (M = 11.8 ± 0.7M_J) in aP = 571.3 ± 1.4 day orbit with a projected semimajor axisa₀ = 0.312 ± 0.040 mas orbiting a 0.644 ± 0.02M_⊙star. Gaia-5b is a brown dwarf (M = 20.9 ± 0.5M_J) in aP = 358.62 ± 0.20 days eccentrice = 0.6423 ± 0.0026 orbit with a projected angular semimajor axis ofa₀ = 0.947 ± 0.038 mas around a 0.34 ± 0.03M_⊙star. Gaia-4b is one of the first exoplanets discovered via the astrometric technique, and is one of the most massive planets known to orbit a low-mass star.