Emily K. Pass

We report the direct imaging detection of a stellar companion to HD 101452 (HIP 56925; Gaia DR3 5384905720847544192), an A star historically used as an infrared flux calibrator. The companion was identified from an asymmetry in the stellar point-spread function (PSF) using short-integration (μ m that was obtained as part of the absolute flux calibration program CAL 4496. We detect the stellar companion in four MIRI imaging filters at a projected separation of 1 . ″ 3 with a mid-infrared flux ratio of approximately 27×, warranting its removal from the ensemble of JWST flux calibrator systems. This detection also demonstrates that noncoronagraphic MIRI imaging can recover companions at separations below 3 λ / D when a reference star with a closely matched flux level to the science target is available. Using the measured contrast curves from the calibration data, we evaluate the predicted sensitivity achievable with similar short MIRI observations for nearby stars (<30 pc) that are of interest to the direct imaging community with comparable brightness to HD 101452 (W4 ∼ 6.8 mag). We find that integrations of only 17–42 s are capable of detecting sub-Jupiter-mass planets at solar system–like separations around a subset of neighboring systems if the PSF subtraction is conducted with closely flux-matched references. These results demonstrate that minutes-length, noncoronagraphic MIRI observations can provide a powerful and efficient new avenue for exploring the cold giant planet population around nearby stars.

While no conclusive detections of exomoons have been reported to date, planet formation theories predict that Luna-analog satellites should be a common outcome of the collisional dynamics in early extrasolar systems. Such satellites have the potential to unlock new avenues to learn about exoplanet systems, speaking to topics of habitability, tidal heating, planet formation, late-stage growth, planetary compositions, and more. Here we describe the results of our JWST program to search for Luna-analog exomoons around the rocky, habitable-zone M-dwarf planets TOI 700 d and e. We refine the ephemerides of both worlds, providing an order-of-magnitude improvement in period precision and a factor of 2–3 improvement in planetary radii. We identify a strong correlated noise signal with a timescale of 16 ± 4 minutes and an amplitude of 46 ± 4 parts per million (ppm); similar signals have been observed in previous JWST analyses of other stars and have been ascribed to stellar granulation. This noise source inflates our error by a factor of 4 relative to photon-noise expectations in 10 minute bins and limits our sensitivity to moons: we determine that our observations are sensitive mainly to moons larger than Ganymede on periods longer than 2 days (i.e., moons larger than our solar system’s natural satellites). If this noise could be corrected, we would be sensitive to Luna-analog moons. Future work to address this noise source will thus be critical for detecting exomoons in stellar transits, as well as for all other science cases that hope to take advantage of JWST white-light curves in the photon-noise limit.

We present the discovery of the planetary system orbiting the bright ( V = 7.2), nearby (35 pc), Sun-like ( M _⋆ = 1.050 ± 0.044 M _⊙ , R _⋆ = 1.129 ± 0.013 R _⊙ ) star, HD 60779. We report two Transiting Exoplanet Survey Satellite transits and a subsequent Characterising Exoplanet Satellite transit of HD 60779 b, a sub-Neptune ( 3.24 6 − 0.097 + 0.100 R ⊕ ) planet on a 29.98617 5 − 0.000033 + 0.000030 day orbit. Additionally, 313 High Accuracy Radial velocity Planet Searcher for the Northern hemisphere radial velocity (RV) measurements reveal the mass of planet b ( 14.1 9 − 0.96 + 0.97 M ⊕ ) and the presence of an outer planet, HD 60779 c ( P _orb = 104.79 ± 0.23 days, M p sin i = 28.3 ± 1.5 M ⊕ ). Both of these planets’ orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779’s uniquely high systemic RV (129.75 ± 0.12 km s ⁻¹ ) allows its Ly α emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third brightest host of a P _orb > 25 day sub-Neptune with a measured mass and radius, distinguishing it in terms of accessibility to spectroscopic characterization.

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 a uniform spectroscopic characterization of 625 F, G, and K stars hosting 859 confirmed exoplanets using high-resolution archival optical spectra from the Tillinghast Reflector Echelle Spectrograph (TRES). We use the neural network spectral code uberMS , which combines spectra with broadband photometry to estimate precise and accurate stellar parameters. We determine stellar effective temperatures, surface gravities, radii, luminosities, projected rotational velocities, [Fe/H] abundances, and [ α /Fe] enrichments for most confirmed planet hosts observed by TRES. This uniform catalog can be used for a broad range of astrophysical studies, particularly to explore links between stellar [ α /Fe] and a suite of observed exoplanet properties. Combining our metallicity measurements with Galactic kinematics, we identify 58 planet hosts that are likely members of the thick disk. We investigate the chemical environments of giant-planet formation by comparing the [ α /Fe] distributions of giant-planet host stars across different metallicity regimes. We find that subsolar metallicity giant-planet hosts are significantly enhanced in [ α /Fe] relative to Fe-rich giant-planet hosts and to the average Fe-poor field star, at high statistical significance. This suggests that enhanced α -element abundances may partially compensate for low-Fe content and thus enable the formation of giant planets in metal-poor environments. We additionally compare the [ α /Fe] distributions of single- and multiplanet hosts and find modest evidence that α -enhanced stars may preferentially host multiplanet systems. Finally, we recover previously observed trends between stellar metallicity and planetary eccentricity.

We present the deepest systematic search for planets around mid-to-late M dwarfs to date. We have surveyed 8134 mid-to-late M dwarfs observed by the Transiting Exoplanet Survey Satellite with a custom-built pipeline and recover 77 vetted transiting planet candidates. We characterize the sensitivity of our survey via injection–recovery and measure the occurrence rate of planets as a function of orbital period, instellation, and planet radius. We measure a cumulative occurrence rate of 1.10 ± 0.16 planets per star with radii >1 R _⊕ orbiting within 30 days. This value is consistent with the cumulative occurrence rate around early M dwarfs, making M dwarfs collectively the most prolific hosts of small close-in planets. Unlike the bimodal radius valley exhibited by close-in planet populations around FGK and early M dwarfs, we recover a unimodal planet radius distribution peaking at 1.25 ± 0.05 R _⊕ . We additionally find 0.954 ± 0.147 super-Earths and 0.148 ± 0.045 sub-Neptunes per star, with super-Earths outnumbering sub-Neptunes 5.5:1, firmly demonstrating that the radius valley disappears around the lowest-mass stars. The dearth of sub-Neptunes around mid-to-late M dwarfs is consistent with predictions from water-rich pebble accretion models that predict a fading radius valley with decreasing stellar mass. Our results support the emerging idea that the sub-Neptune population around M dwarfs is composed of water-rich worlds. We find no hot Jupiters in our survey and set an upper limit of 0.012 hot Jupiters per mid-to-late M dwarf within 10 days.

As the field of exoplanetary astronomy has matured, demand has grown for precise stellar abundances to probe subtle correlations between stellar compositions and planetary demographics. However, drawing population-level conclusions from the disparate measurements in the literature is challenging, with various groups measuring metallicities using bespoke codes with differing line lists, radiative transfer models, and other assumptions. Homogeneous analyses are thus critical. Here we use the neural-net framework uberMS to measure iron abundances and alpha enrichments from high-resolution optical spectra observed by the Tillinghast Reflector Echelle Spectrograph (TRES), a key resource used for the follow-up of candidate exoplanet hosts. To contextualize these measurements and benchmark our method’s performance, we compare to external constraints on metallicity using the Hyades cluster, wide binaries, and asteroids, to external constraints on T _eff and log g using stars with interferometric radii, and to the results of other abundance measurement methods using overlap samples with the APOGEE and SPOCS catalogs, as well as by applying the Stellar Parameter Classification method directly to TRES spectra. We find that TRES- uberMS provides reliable parameter estimates with errors of roughly 100 K in T _eff , 0.09 dex in log g , and 0.04 dex in [Fe/H] for many nearby dwarf stars, although [Fe/H] performance is poorer for mid-to-late K dwarfs, with the bias worsening with decreasing T _eff . Performance is also worse for evolved stars. For [ α /Fe], our error may be as good as 0.03 dex for dwarfs based on external benchmarks, despite sizable and variable systematic differences when comparing with specific alpha-element abundances from other catalogs.

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.