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  1. Abstract

    M dwarfs are favorable targets for exoplanet detection with current instrumentation, but stellar companions can induce false positives and inhibit planet characterization. Knowledge of stellar companions is also critical to our understanding of how binary stars form and evolve. We have therefore conducted a survey of stellar companions around nearby M dwarfs, and here we present our new discoveries. Using the Differential Speckle Survey Instrument at the 4.3 m Lowell Discovery Telescope, and the similar NN-EXPLORE Exoplanet Stellar Speckle Imager at the 3.5 m WIYN telescope, we carried out a volume-limited survey of M-dwarf multiplicity to 15 parsecs, with a special emphasis on including the later M dwarfs that were overlooked in previous surveys. Additional brighter targets at larger distances were included for a total sample size of 1070 M dwarfs. Observations of these 1070 targets revealed 26 new companions; 22 of these systems were previously thought to be single. If all new discoveries are confirmed, then the number of known multiples in the sample will increase by 7.6%. Using our observed properties, as well as the parallaxes and 2MASSKmagnitudes for these objects, we calculate the projected separation, and estimate the mass ratio and component spectral types, for thesemore »systems. We report the discovery of a new M-dwarf companion to the white dwarf Wolf 672 A, which hosts a known M-dwarf companion as well, making the system trinary. We also examine the possibility that the new companion to 2MASS J13092185-2330350 is a brown dwarf. Finally, we discuss initial insights from the POKEMON survey.

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  2. Abstract The observed correlation between outer giant planets and inner super-Earths is emerging as an important constraint on planet formation theories. In this study, we focus on Kepler-167, which is currently the only system known to contain both inner transiting super-Earths and a confirmed outer transiting gas giant companion beyond 1 au. Using long-term radial velocity monitoring, we measure the mass of the gas giant Kepler-167e ( P = 1071 days) to be 1.01 − 0.15 + 0.16 M J , thus confirming it as a Jupiter analog. We refit the Kepler photometry to obtain updated radii for all four planets. Using a planetary structure model, we estimate that Kepler-167e contains 66 ± 19 M ⊕ of solids and is significantly enriched in metals relative to its solar-metallicity host star. We use these new constraints to explore the broader question of how systems like Kepler-167 form in the pebble accretion framework for giant planet core formation. We utilize simple disk evolution models to demonstrate that more massive and metal-rich disks, which are the most favorable sites for giant planet formation, can also deliver enough solids to the inner disk to form systems of super-Earths. We use these same models tomore »constrain the nature of Kepler-167's protoplanetary disk and find that it likely contained ≳300 M ⊕ of dust and was ≳40 au in size. These values overlap with the upper end of the observed dust mass and size distributions of Class 0 and I disks and are also consistent with the observed occurrence rate of Jupiter analogs around Sun-like stars.« less
    Free, publicly-accessible full text available February 1, 2023
  3. Abstract

    TESS has proven to be a powerful resource for finding planets, including those that orbit the most prevalent stars in our galaxy: M dwarfs. Identification of stellar companions (both bound and unbound) has become a standard component of the transiting planet confirmation process in order to assess the level of light-curve dilution and the possibility of the target being a false positive. Studies of stellar companions have also enabled investigations into stellar multiplicity in planet-hosting systems, which has wide-ranging implications for both exoplanet detection and characterization, as well as for the formation and evolution of planetary systems. Speckle and AO imaging are some of the most efficient and effective tools for revealing close-in stellar companions; we therefore present observations of 58 M-dwarf TOIs obtained using a suite of speckle imagers at the 3.5 m WIYN telescope, the 4.3 m Lowell Discovery Telescope, and the 8.1 m Gemini North and South telescopes. These observations, as well as near-infrared adaptive optics images obtained for a subset (14) of these TOIs, revealed only two close-in stellar companions. Upon surveying the literature, and cross-matching our sample with Gaia, SUPERWIDE, and the catalog from El-Badry et al., we reveal an additional 15 widely separatedmore »common proper motion companions. We also evaluate the potential for undetected close-in companions. Taking into consideration the sensitivity of the observations, our findings suggest that the orbital period distribution of stellar companions to planet-hosting M dwarfs is shifted to longer periods compared to the expected distribution for field M dwarfs.

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  4. Abstract We combine multiple campaigns of K2 photometry with precision radial velocity measurements from Keck-HIRES to measure the masses of three sub-Neptune-sized planets. We confirm the planetary nature of the massive sub-Neptune K2-182 b ( P b = 4.7 days, R b = 2.69 R ⊕ ) and derive refined parameters for K2-199 b and c ( P b = 3.2 days, R b = 1.73 R ⊕ and P c = 7.4 days, R c = 2.85 R ⊕ ). These planets provide valuable data points in the mass–radius plane, especially as TESS continues to reveal an increasingly diverse sample of sub-Neptunes. The moderately bright ( V = 12.0 mag) early K dwarf K2-182 (EPIC 211359660) was observed during K2 campaigns 5 and 18. We find that K2-182 b is potentially one of the densest sub-Neptunes known to date (20 ± 5 M ⊕ and 5.6 ± 1.4 g cm −3 ). The K5V dwarf K2-199 (EPIC 212779596; V = 12.3 mag), observed in K2 campaigns 6 and 17, hosts two recently confirmed planets. We refine the orbital and planetary parameters for K2-199 b and c by modeling both campaigns of K2 photometry and adding 12 Keck-HIRES measurements tomore »the existing radial velocity data set ( N = 33). We find that K2-199 b is likely rocky, at 6.9 ± 1.8 M ⊕ and 7.2 − 2.0 + 2.1 g cm −3 , and that K2-199 c has an intermediate density at 12.4 ± 2.3 M ⊕ and 2.9 − 0.6 + 0.7 g cm −3 . We contextualize these planets on the mass–radius plane, discuss a small but intriguing population of “superdense” sub-Neptunes ( R p < 3 R ⊕ , M p >20 M ⊕ ), and consider our prospects for the planets’ atmospheric characterization.« less
  5. Abstract The Kepler and TESS missions have demonstrated that planets are ubiquitous. However, the success of these missions heavily depends on ground-based radial velocity (RV) surveys, which combined with transit photometry can yield bulk densities and orbital properties. While most Kepler host stars are too faint for detailed follow-up observations, TESS is detecting planets orbiting nearby bright stars that are more amenable to RV characterization. Here, we introduce the TESS-Keck Survey (TKS), an RV program using ∼100 nights on Keck/HIRES to study exoplanets identified by TESS. The primary survey aims are investigating the link between stellar properties and the compositions of small planets; studying how the diversity of system architectures depends on dynamical configurations or planet multiplicity; identifying prime candidates for atmospheric studies with JWST; and understanding the role of stellar evolution in shaping planetary systems. We present a fully automated target selection algorithm, which yielded 103 planets in 86 systems for the final TKS sample. Most TKS hosts are inactive, solar-like, main-sequence stars (4500 K ≤ T eff <6000 K) at a wide range of metallicities. The selected TKS sample contains 71 small planets ( R p ≤ 4 R ⊕ ), 11 systems with multiple transiting candidates, sixmore »sub-day-period planets and three planets that are in or near the habitable zone ( S inc ≤ 10 S ⊕ ) of their host star. The target selection described here will facilitate the comparison of measured planet masses, densities, and eccentricities to predictions from planet population models. Our target selection software is publicly available and can be adapted for any survey that requires a balance of multiple science interests within a given telescope allocation.« less
    Free, publicly-accessible full text available May 30, 2023
  6. Abstract We present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright ( V J = 12.5, K s = 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04 R ⊕ and 0.98 ± 0.06 R ⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M ⊕ and 1.4 M ⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. Amore »third planet candidate of radius 0.9 ± 0.1 R ⊕ in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung–Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.« less
    Free, publicly-accessible full text available March 7, 2023
  7. Abstract

    We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations ≳0.″2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5σupper limit ofMP< 7.1MandρP< 0.74 g cm−3, and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1–20MJ) companion with a projected separation ≲20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620more »b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date.

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  8. Abstract The James Webb Space Telescope will be able to probe the atmospheres and surface properties of hot, terrestrial planets via emission spectroscopy. We identify 18 potentially terrestrial planet candidates detected by the Transiting Exoplanet Survey Satellite (TESS) that would make ideal targets for these observations. These planet candidates cover a broad range of planet radii ( R p ∼ 0.6–2.0 R ⊕ ) and orbit stars of various magnitudes ( K s = 5.78–10.78, V = 8.4–15.69) and effective temperatures ( T eff ∼ 3000–6000 K). We use ground-based observations collected through the TESS Follow-up Observing Program (TFOP) and two vetting tools— DAVE and TRICERATOPS —to assess the reliabilities of these candidates as planets. We validate 13 planets: TOI-206 b, TOI-500 b, TOI-544 b, TOI-833 b, TOI-1075 b, TOI-1411 b, TOI-1442 b, TOI-1693 b, TOI-1860 b, TOI-2260 b, TOI-2411 b, TOI-2427 b, and TOI-2445 b. Seven of these planets (TOI-206 b, TOI-500 b, TOI-1075 b, TOI-1442 b, TOI-2260 b, TOI-2411 b, and TOI-2445 b) are ultra-short-period planets. TOI-1860 is the youngest (133 ± 26 Myr) solar twin with a known planet to date. TOI-2260 is a young (321 ± 96 Myr) G dwarf that is among the most metal-richmore »([Fe/H] = 0.22 ± 0.06 dex) stars to host an ultra-short-period planet. With an estimated equilibrium temperature of ∼2600 K, TOI-2260 b is also the fourth hottest known planet with R p < 2 R ⊕ .« less
    Free, publicly-accessible full text available January 28, 2023