Michael L. Calkins

We present results from a five year campaign to gather multiepoch, high-resolution spectra of a volume-complete sample of 413 M dwarfs with masses 10%–30% that of the Sun within 15 pc. We report weighted mean systemic radial velocities (RV) and rotational broadening measurements ( v sin i ) for our targets. Our typical relative RV uncertainties are less than 50 m s ⁻¹ for the isolated, slowly rotating targets in our sample and increase, though remain less than 1 km s ⁻¹ , for more rapidly rotating stars. The majority of the single stars in our sample (71 ± 3%) have rotational broadening below our detection limit of 3.4 km s ⁻¹ . When combined with astrometric data, our RVs allow us to calculate Galactic space motions, which we use to assign thin or thick disk membership. We determine that 81% and 8% of our sample are highly probable thin and highly probable thick disk members, respectively. We report seven new multilined multiple systems and identify six additional targets with velocity variations indicative of long-period binaries, of which three are new detections. Finally, we find no significant difference in the stellar multiplicity rates of the thin disk (22 ± 2%) and thick disk (21 ± 8%) populations in our sample, implying that mid-M dwarfs do not significantly lose companions at these relative ages. Our survey more than triples the number of these fully convective stars with complete astrometric data and uniformly derived, multiepoch, high-resolution RVs and rotational broadening measurements.

We present TOI-2155 b, a massive transiting companion, discovered using data from NASA’s Transiting Exoplanet Survey Satellite mission and confirmed with ground-based radial velocity measurements from the Tillinghast Reflector Echelle Spectrograph. We also analyze ground-based follow-up photometric data from the Wendelstein Observatory, Las Cumbres Observatory Global Telescope, and Wild Boar Remote Observatory. TOI-2155 b is a short-period companion with P = 3.7246950 ± 0.0000014 days. The radius and mass of TOI-2155 b are found to be R b = 0.97 2 − 0.008 + 0.009 R J and M b = 80 . 6 − 1.1 + 1.0 M J , respectively, corresponding to a density of ρ b = 10 9 − 3.3 + 3.1 g cm ⁻³ . The F-type subgiant host star has an effective temperature of T _eff = 6085 ± 78 K, a radius R ⋆ = 1.70 5 − 0.064 + 0.066 R _⊙ , and a mass M _⋆ = 1.33 ± 0.008 M _⊙ . With a mass close to the hydrogen-burning minimum mass, TOI-2155 b lies at the boundary between brown dwarfs and low-mass stars. Its measured mass, radius, and density place it in a transitional region, where distinguishing between a massive brown dwarf and a very low-mass star is not straightforward. TOI-2155 b therefore provides a valuable benchmark for testing evolutionary models of stellar and substellar structure near the hydrogen-burning limit.

We present the TESS-based discoveries of planetary systems orbiting the late G dwarfs TOI-2494 and TOI-5143, each of which harbors a hot giant planet and a smaller interior planet. TOI-2494 hosts a transiting mini-Neptune ( P = 2.41 days, R P = 2.3 5 − 0.15 + 0.16 R _⊕ ) and a hot Saturn ( P = 8.38 days) with grazing transits, while TOI-5143 hosts a transiting mini-Neptune ( P = 2.38 days, R P = 2.7 3 − 0.17 + 0.19 R _⊕ ) and a hot Jupiter ( P = 5.21 days) with grazing transits. We measure the masses of TOI-2494 c (80 ± 19 M _⊕ ) and TOI-5143 c (208 ± 14 M _⊕ ), place upper limits on the masses of the smaller planets, and explore the architectures of the planetary systems. TOI-2494 c and TOI-5143 c join a small but growing number of short-period giant planets known to be flanked by smaller companions. While the absence of close neighbors to most hot Jupiters would be consistent with disruptive dynamical evolution, the presence of nearby small planets in some hot Jupiter systems points to a separate, dynamically quiet formation pathway. In support of this conclusion, we present preliminary evidence that hot giant planets with small nearby companions tend to have low mutual orbital inclinations, consistent with the mutual inclination distribution of the dynamically quiet population of compact systems of multiple super-Earths and mini-Neptunes.

As the intermediate-mass siblings of stars and planets, brown dwarfs (BDs) are vital to study for a better understanding of how objects change across the planet-to-star mass range. Here, we report two low-mass transiting BD systems discovered by TESS, TOI-4776 (TIC 196286578) and TOI-5422 (TI 80611440), located in an underpopulated region of the BD mass–period space. These two systems have comparable masses but different ages. The younger and larger BD is TOI-4776 b with 32 . 3 − 1.7 + 1.8 M Jup and 1.01 ± 0.05 R _Jup , orbiting a late-F star about 4 . 7 − 2.5 + 3.1 Gyr old in an ∼10.41 day period. The older TOI-5422 b has 28 . 0 − 1.2 + 1.6 M Jup and 0.81 ± 0.03 R _Jup in an ∼5.38 day orbit around a subgiant star about 7 . 6 − 2.6 + 2.5 Gyr old. Compared with substellar mass–radius evolution models, TOI-4776 b has an inflated radius. In contrast, TOI-5422 b is slightly “underluminous” with respect to model predictions, which is not commonly seen in the BD population. In addition, TOI-5422 shows apparent photometric modulations with a rotation period of 10.8 ± 0.5 days found by rotation analysis, and the stellar inclination angle is obtained to be I ⋆ = 7 6 − 12 + 10 deg. Therefore, it is likely that TOI-5422 b is spinning up the host star and its orbit is aligned with the stellar spin axis.

Observations over the past few decades have found that planets are common around nearby stars in our Galaxy, but little is known about planets that formed outside the Milky Way. We describe the design and early implementation of a survey to test whether planets also exist orbiting the remnant stars of ancient dwarf galaxies that merged with the Milky Way, and if so, how they differ from their Milky Way counterparts. VOYAGERS ( Views Of Yore —Ancient Gaia-enceladus Exoplanet Revealing Survey ) is a radial velocity (RV) search using precision spectrographs to discover exoplanets orbiting very low metallicity (−2.8 < [Fe/H] ≤ −0.8) stars born in the dwarf galaxy Enceladus, which merged with the Milky Way galaxy about 10 Gyr ago. A sample of 22 candidates have been screened from a catalog of Gaia–Enceladus–Sausage (GES) members using a combination of stellar properties and reconnaissance observations from the TRES spectrograph. Precision RV measurements have been initiated using the NEID, HARPS-N, and CARMENES spectrographs. We plan to focus most upcoming observations on 10 main sequence targets. Data collection is well underway, with 778 observations on 22 candidates (385 of which are on 10 focus targets), but far from complete. This survey is designed to be sensitive to sub-Neptune mass planets with periods up to hundreds of days. We note that the RV analysis gives mass multiplied by sin ( inclination ) or the minimum mass for exoplanets. The expected survey yield is three planets, assuming that occurrence rates are similar to those in the Milky Way and taking into account the degeneracy with inclination in our yield models. Our survey is designed to detect at least one exoplanet if occurrence rates are similar to known Milky Way exoplanets or, if no exoplanets are discovered, to rule out a Milky Way-like planet population in GES with 95% confidence level.

We present ExoMiner++ , an enhanced deep learning model that builds on the success of ExoMiner to improve transit signal classification in 2-minute TESS data. ExoMiner++ incorporates additional diagnostic inputs, including periodogram, flux trend, difference image, unfolded flux, and spacecraft attitude control data, all of which are crucial for effectively distinguishing transit signals from more challenging sources of false positives (FPs). To further enhance performance, we leverage multisource training by combining high-quality labeled data from the Kepler space telescope with TESS data. This approach mitigates the impact of TESS’s noisier and more ambiguous labels. ExoMiner++ achieves high accuracy across various classification and ranking metrics, significantly narrowing the search space for follow-up investigations to confirm new planets. To serve the exoplanet community, we introduce a new TESS catalog containing ExoMiner++ classifications and confidence scores for each transit signal. Among the 147,568 unlabeled TCEs, ExoMiner++ identifies 7330 as planet candidates (PCs), with the remainder classified as FPs. These 7330 PCs correspond to 1868 existing TESS Objects of Interest (TOIs), 69 Community TESS Objects of Interest (CTOIs), and 50 newly introduced CTOIs. 1797 out of the 2506 TOIs previously labeled as PCs in ExoFOP are classified as PCs by ExoMiner++ . This reduction in plausible candidates, combined with the excellent ranking quality of ExoMiner++ , allows the follow-up efforts to be focused on the most likely candidates, increasing the overall planet yield.

Though missions such as Kepler, K2, and TESS have discovered >2000 sub-Neptune and Neptunian planets, there is a dearth of such planets at close-in (P ≲ 3 days) orbits. This feature, called the Neptune desert or the evaporation desert, is believed to be primarily shaped by planetary migration and photoevaporation. However, this region is not completely devoid of planets—a small number of very hot Neptunes reside within the desert. These planets provide an opportunity to directly probe the effects of migration and photoevaporation. We present confirmation of TOI-5800 b, an eccentric sub-Neptune on an ≈2.6 day period that is likely actively undergoing tidal migration. We use radial velocity measurements from the Carnegie Planet Finder Spectrograph to constrain TOI-5800 b’s mass and eccentricity. We find that it has an unusually high eccentricity (0.39 ± 0.07) for its short orbit. TOI-5800 b is therefore currently experiencing high levels of tidal heating as it moves into the desert. Ranked as a top candidate for transmission and emission spectroscopy within its temperature and radius regime, TOI-5800 b is a prime target for atmospheric characterization with the James Webb Space Telescope. TOI-5800 b presents a unique opportunity to study the atmosphere of a planet undergoing tidal heating and to probe the composition of sub-Neptune planets.

We present the discovery of 11 new transiting brown dwarfs (BDs) and low-mass M dwarfs from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission: TOI-2844, TOI-3122, TOI-3577, TOI-3755, TOI-4462, TOI-4635, TOI-4737, TOI-4759, TOI-5240, TOI-5467, and TOI-5882. They consist of five BD companions and six very-low-mass stellar companions ranging in mass from 25 M _J to 128 M _J. We used a combination of photometric time-series, spectroscopic, and high-resolution imaging follow-up as a part of the TESS Follow-up Observing Program (or TFOP) to characterize each system. With over 50 transiting BDs confirmed, we now have a large enough sample to directly test different formation and evolutionary scenarios. We provide a renewed perspective on the transiting “brown dwarf desert” and its role in differentiating between planetary and stellar formation mechanisms. Our analysis of the eccentricity distribution for the transiting BD sample does not support previous claims of a transition between planetary and stellar formation at ∼42 M _J. We also contribute a first look into the metallicity distribution of transiting companions in the range 7–150 M _J, showing that this does not support a ∼42 M _J transition too. Finally, we also detect a significant lithium absorption feature in one of the BD hosts (TOI-5882). However, we determine that the host star is likely old based on rotation, kinematic, and photometric mdeasurements. We therefore claim that TOI-5882 may be a candidate for planetary engulfment.

The present study confirms BD-14 3065b as a transiting planet-brown dwarf in a triple-star system, with a mass near the deuterium-burning boundary. BD-14 3065b has the largest radius observed within the sample of giant planets and brown dwarfs around post-main sequence stars. Its orbital period is 4.3 days and it transits a subgiant F-type star with a mass of M_* = 1.41 ± 0.05 M_⊙, a radius of R_* = 2.35 ± 0.08 R_⊙, an effective temperature of T_eff = 6935 ± 90 K, and a metallicity of −0.34 ± 0.05 dex. By combining TESS photometry with high-resolution spectra acquired with the TRES and Pucheros+ spectrographs, we measured a mass of M_⊙ = 12.37 ± 0.92 M_Jup and a radius of R_p = 1.926 ± 0.094 R_Jup. Our discussion of potential processes that could be responsible for the inflated radius led us to conclude that deuterium burning is a plausible explanation for the heating taking place in BD-14 3065b’s interior. Detections of the secondary eclipse with TESS photometry enabled a precise determination of the eccentricity, e_p = 0.066 ± 0.011, and reveal that BD-14 3065b has a brightness temperature of 3520 ± 130 K. With its unique characteristics, BD-14 3065b presents an excellent opportunity to study its atmosphere via thermal emission spectroscopy.

Fully convective M dwarfs typically remain rapidly rotating and magnetically active for billions of years, followed by an abrupt and mass-dependent transition to slow rotation and quiescence. A robust understanding of this process is complicated by difficulties in estimating M dwarf ages and potential dependencies on other variables such as birth environment or metallicity. To isolate the effect of mass, we consider M dwarfs in wide binaries. We identify 67 widely separated, fully convective (0.08–0.35 M _⊙) M dwarf binary systems using Gaia and measure the Hα feature for each component. We classify the pairs into three categories: systems where both components are active, systems where both are inactive, and candidate transition systems, where one component is active and the other inactive. We gather higher-resolution spectra of the candidate transition systems to verify that their behavior does not result from an unresolved third component, yielding one new triple with surprising activity levels. Neglecting this triple, we find 22 active, 36 inactive, and eight transition pairs. Our results are consistent with the epoch of spindown for these binaries being primarily determined by mass, with mild second-order effects; we place a 1σ upper limit of 0.5 Gyr or 25% on the dispersion in the mass-dependent spindown relation. Our findings suggest that the large dispersion in the spindown epoch previously observed for field stars of a given mass may stem from differences in birth environment, in addition to modest intrinsic stochasticity. We also see evidence that the wide binary population is dispersed over time due to dynamical processing.