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We collected near-infrared spectra of 65 cool stars with the NASA Infrared Telescope Facility and analyzed them to calculate accurate metallicities and stellar parameters. The sample of 55 M dwarfs and 10 K dwarfs includes 25 systems with confirmed planets and 27 systems with planet candidates identified by the K2 and TESS missions. Three of the 25 confirmed planetary systems host multiple confirmed planets and two of the 27 planet candidate systems host multiple planet candidates. Using the new stellar parameters, we refit the K2 and TESS light curves to calculate updated planet properties. In general, our updated stellar properties are more precise than those previously reported and our updated planet properties agree well with those in the literature. Lastly, we briefly examine the relationship between stellar mass, stellar metallicity, and planetary system properties for targets in our sample and for previously characterized planet-hosting low-mass stars. We provide our spectra, stellar parameters, and new planetary fits to the community, expanding the sample available with which to investigate correlations between stellar and planetary properties for low-mass stars.

 

An intriguing pattern among exoplanets is the lack of detected planets between approximately 1.5R_⊕and 2.0R_⊕. One proposed explanation for this “radius gap” is the photoevaporation of planetary atmospheres, a theory that can be tested by studying individual planetary systems. Kepler-105 is an ideal system for such testing due to the ordering and sizes of its planets. Kepler-105 is a Sun-like star that hosts two planets straddling the radius gap in a rare architecture with the larger planet closer to the host star (R_b= 2.53 ± 0.07R_⊕,P_b= 5.41 days,R_c= 1.44 ± 0.04R_⊕,P_c= 7.13 days). If photoevaporation sculpted the atmospheres of these planets, then Kepler-105b would need to be much more massive than Kepler-105c to retain its atmosphere, given its closer proximity to the host star. To test this hypothesis, we simultaneously analyzed radial velocities and transit-timing variations of the Kepler-105 system, measuring disparate masses ofM_b= 10.8 ± 2.3M_⊕(ρ_b= 3.68 ± 0.84 g cm⁻³) andM_c= 5.6 ± 1.2M_⊕(ρ_c= 10.4 ± 2.39 g cm⁻³). Based on these masses, the difference in gas envelope content of the Kepler-105 planets could be entirely due to photoevaporation (in 76% of scenarios), although other mechanisms like core-powered mass loss could have played a role for some planet albedos.

 

We present and confirm TOI-1751 b, a transiting sub-Neptune orbiting a slightly evolved, solar-type, metal-poor star (T_eff= 5996 ± 110 K,$\log (g)=4.2\pm 0.1$,V= 9.3 mag, [Fe/H] = −0.40 ± 0.06 dex) every 37.47 days. We use TESS photometry to measure a planet radius of${2.77}_{-0.07}^{+0.15}{R}_{\oplus }$. We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of${14.5}_{-3.14}^{+3.15}{M}_{\oplus }$, and thus a planet density of 3.6 ± 0.9 g cm⁻³. There is also a long-period (∼400 days) signal that is observed in only the Keck/HIRES data. We conclude that this long-period signal is not planetary in nature and is likely due to the window function of the Keck/HIRES observations. This highlights the role of complementary observations from multiple observatories to identify and exclude aliases in RV data. Finally, we investigate the potential compositions of this planet, including rocky and water-rich solutions, as well as theoretical irradiated ocean models. TOI-1751 b is a warm sub-Neptune with an equilibrium temperature of ∼820 K. As TOI-1751 is a metal-poor star, TOI-1751 b may have formed in a water-enriched formation environment. We thus favor a volatile-rich interior composition for this planet.

 

The extreme environments of ultra-short-period planets (USPs) make excellent laboratories to study how exoplanets obtain, lose, retain, and/or regain gaseous atmospheres. We present the confirmation and characterization of the USP TOI-1347 b, a 1.8 ± 0.1R_⊕planet on a 0.85 day orbit that was detected with photometry from the TESS mission. We measured radial velocities of the TOI-1347 system using Keck/HIRES and HARPS-N and found the USP to be unusually massive at 11.1 ± 1.2M_⊕. The measured mass and radius of TOI-1347 b imply an Earth-like bulk composition. A thin H/He envelope (>0.01% by mass) can be ruled out at high confidence. The system is between 1 and 1.8 Gyr old; therefore, intensive photoevaporation should have concluded. We detected a tentative phase-curve variation (3σ) and a secondary eclipse (2σ) in TESS photometry, which, if confirmed, could indicate the presence of a high-mean-molecular-weight atmosphere. We recommend additional optical and infrared observations to confirm the presence of an atmosphere and investigate its composition.

 

With JWST’s successful deployment and unexpectedly high fuel reserves, measuring the masses of sub-Neptunes transiting bright, nearby stars will soon become the bottleneck for characterizing the atmospheres of small exoplanets via transmission spectroscopy. Using a carefully curated target list and observations from more than 2 yr of APF-Levy and Keck-HIRES Doppler monitoring, the TESS-Keck Survey is working toward alleviating this pressure. Here we present mass measurements for 11 transiting planets in eight systems that are particularly suited to atmospheric follow-up with JWST. We also report the discovery and confirmation of a temperate super-Jovian-mass planet on a moderately eccentric orbit. The sample of eight host stars, which includes one subgiant, spans early-K to late-F spectral types (T_eff= 5200–6200 K). We homogeneously derive planet parameters using a joint photometry and radial velocity modeling framework, discuss the planets’ possible bulk compositions, and comment on their prospects for atmospheric characterization.

 

We present the Distant Giants Survey, a three-year radial velocity campaign to measure P(DG∣CS), the conditional occurrence of distant giant planets (DG;M_p∼ 0.3–13M_J,P> 1 yr) in systems hosting a close-in small planet (CS;R_p< 10R_⊕). For the past two years, we have monitored 47 Sun-like stars hosting small transiting planets detected by TESS. We present the selection criteria used to assemble our sample and report the discovery of two distant giant planets, TOI-1669 b and TOI-1694 c. For TOI-1669 b we find that$M\sin i=0.573\pm 0.074M_{\mathrm{J}}$,P= 502 ± 16 days, ande< 0.27, while for TOI-1694 c,$M\sin i=1.05\pm 0.05M_{\mathrm{J}}$,P= 389.2 ± 3.9 days, ande= 0.18 ± 0.05. We also confirmed the 3.8 days transiting planet TOI-1694 b by measuring a true mass ofM= 26.1 ± 2.2M_⊕. At the end of the Distant Giants Survey, we will incorporate TOI-1669 b and TOI-1694 c into our calculation of P(DG∣CS), a crucial statistic for understanding the relationship between outer giants and small inner companions.

 

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, six 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. 

Abstract We report the discovery of TOI-2180 b, a 2.8 M J giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.