We present the stellar and planetary properties for 85 TESS Objects of Interest (TOIs) hosting 108 planet candidates which comprise the TESS-Keck Survey (TKS) sample. We combine photometry, ...high-resolution spectroscopy, and Gaia parallaxes to measure precise and accurate stellar properties. We then use these parameters as inputs to a lightcurve processing pipeline to recover planetary signals and homogeneously fit their transit properties. Among these transit fits, we detect significant transit-timing variations among at least three multi-planet systems (TOI-1136, TOI-1246, TOI-1339) and at least one single-planet system (TOI-1279). We also reduce the uncertainties on planet-to-star radius ratios \(R_p/R_\star\) across our sample, from a median fractional uncertainty of 8.8\(\%\) among the original TOI Catalog values to 3.0\(\%\) among our updated results. With this improvement, we are able to recover the Radius Gap among small TKS planets and find that the topology of the Radius Gap among our sample is broadly consistent with that measured among Kepler planets. The stellar and planetary properties presented here will facilitate follow-up investigations of both individual TOIs and broader trends in planet properties, system dynamics, and the evolution of planetary systems.
K2-136 is a late-K dwarf (\(0.742\pm0.039\) M\(_\odot\)) in the Hyades open cluster with three known, transiting planets and an age of \(650\pm70\) Myr. Analyzing K2 photometry, we found that planets ...K2-136b, c, and d have periods of \(8.0\), \(17.3\), and \(25.6\) days and radii of \(1.014\pm0.050\) R\(_\oplus\), \(3.00\pm0.13\) R\(_\oplus\), and \(1.565\pm0.077\) R\(_\oplus\), respectively. We collected 93 radial velocity measurements (RVs) with the HARPS-N spectrograph (TNG) and 22 RVs with the ESPRESSO spectrograph (VLT). Analyzing HARPS-N and ESPRESSO data jointly, we found K2-136c induced a semi-amplitude of \(5.49\pm0.53\) m s\(^{-1}\), corresponding to a mass of \(18.1\pm1.9\) M\(_\oplus\). We also placed \(95\)% upper mass limits on K2-136b and d of \(4.3\) and \(3.0\) M\(_\oplus\), respectively. Further, we analyzed HST and XMM-Newton observations to establish the planetary high-energy environment and investigate possible atmospheric loss. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. K2-136c has \(\sim\)75% the radius of Neptune but is similar in mass, yielding a density of \(3.69^{+0.67}_{-0.56}\) g cm\(^{-3}\) (\(\sim\)2-3 times denser than Neptune). Mass estimates for K2-136b (and possibly d) may be feasible with more RV observations, and insights into all three planets' atmospheres through transmission spectroscopy would be challenging but potentially fruitful. This research and future mass measurements of young planets are critical for investigating the compositions and characteristics of small exoplanets at very early stages of their lives and providing insights into how exoplanets evolve with time.
We present a dedicated transit and radial velocity survey of planets orbiting subgiant stars observed by the TESS Mission. Using $\sim$$16\( nights on Keck/HIRES, we confirm and characterize \)12\( ...new transiting planets -- \)\rm TOI-329\,b\(, \)\rm HD\,39688\,b\( (\)\rm TOI-480\(), \)\rm TOI-603\,b\(, \)\rm TOI-1199\,b\(, \)\rm TOI-1294\,b\(, \)\rm TOI-1439\,b\(, \)\rm TOI-1605\,b\(, \)\rm TOI-1828\,b\(, \)\rm HD\,148193\,b\( (\)\rm TOI-1836\(), \)\rm TOI-1885\,b\(, \)\rm HD\,83342\,b\( (\)\rm TOI-1898\(), \)\rm TOI-2019\,b\( -- and provide updated properties for 9 previously confirmed TESS subgiant systems (\)\rm TOI-197\(, \)\rm TOI-954\(, \)\rm TOI-1181\(, \)\rm TOI-1296\(, \)\rm TOI-1298\(, \)\rm TOI-1601\(, \)\rm TOI-1736\(, \)\rm TOI-1842\(, \)\rm TOI-2145\(). We also report the discovery of an outer, non-transiting planet, \)\rm TOI-1294\,c\( (\)P=160.1\pm2.5\( days, \)M_{\mathrm{p}}=148.3^{+18.2}_{-16.4} \,M_{\oplus}\(), and three additional stars with long-term RV trends. We find that at least \)19\pm8\%\( of subgiants in our sample of \)21\( stars have outer companions, comparable to main-sequence stars. We perform a homogeneous analysis of the stars and planets in the sample, with median uncertainties of \)3\%\(, \)8\%\( and \)15\%\( for planet radii, masses and ages, doubling the number of known planets orbiting subgiant stars with bulk densities measured to better than \)10\%$. We observe a dearth of giant planets around evolved stars with short orbital periods, consistent with tidal dissipation theories that predict the rapid inspiral of planets as their host stars leave the main sequence. We note the possible evidence for two distinct classes of hot Jupiter populations, indicating multiple formation channels to explain the observed distributions around evolved stars. Finally, continued RV monitoring of planets in this sample will provide a more comprehensive understanding of demographics for evolved planetary systems.
We present a near-infrared transmission spectrum of the long period (P=542 days), temperate (\(T_{eq}\)=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard ...the Hubble Space Telescope (HST). With a measured mass of 12 \(\pm\) 3 \(M_{\oplus}\) and a radius of 9.2 \(\pm\) 0.1 \(R_{\oplus}\), HIP 41378 f has an extremely low bulk density (0.09 \(\pm\) 0.02 g/cm\(^{3}\)). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.
We report the discovery of an eccentric hot Neptune and a non-transiting outer planet around TOI-1272. We identified the eccentricity of the inner planet, with an orbital period of 3.3 d and \(R_{\rm ...p,b} = 4.1 \pm 0.2\) \(R_\oplus\), based on a mismatch between the observed transit duration and the expected duration for a circular orbit. Using ground-based radial velocity measurements from the HIRES instrument at the Keck Observatory, we measured the mass of TOI-1272b to be \(M_{\rm p,b} = 25 \pm 2\) \(M_\oplus\). We also confirmed a high eccentricity of \(e_b = 0.34 \pm 0.06\), placing TOI-1272b among the most eccentric well-characterized sub-Jovians. We used these RV measurements to also identify a non-transiting outer companion on an 8.7-d orbit with a similar mass of \(M_{\rm p,c}\) sin\(i= 27 \pm 3\) \(M_\oplus\) and \(e_c \lesssim 0.35\). Dynamically stable planet-planet interactions have likely allowed TOI-1272b to avoid tidal eccentricity decay despite the short circularization timescale expected for a close-in eccentric Neptune. TOI-1272b also maintains an envelope mass fraction of \(f_{\rm env} \approx 11\%\) despite its high equilibrium temperature, implying that it may currently be undergoing photoevaporation. This planet joins a small population of short-period Neptune-like planets within the "Hot Neptune Desert" with a poorly understood formation pathway.
Multi-planet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf ...(\(\rm{V=11.6,~K=9.9}\)) and four transiting sub-Neptunes identified by TESS with orbital periods of \(4.31~\rm{d},~5.90~\rm{d},~18.66~\rm{d}\), and \(~37.92~\rm{d}\). We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (\(\rm{2.97 \pm 0.06~R_\oplus},\rm{2.47 \pm 0.08~R_\oplus}, \rm{3.46 \pm 0.09~R_\oplus}\), \(\rm{3.72 \pm 0.16~R_\oplus}\)), and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (\(\rm{8.1 \pm 1.1 M_\oplus}\), \(\rm{8.8 \pm 1.2 M_\oplus}\), \(\rm{5.3 \pm 1.7 M_\oplus}\), \(\rm{14.8 \pm 2.3 M_\oplus}\)). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (\(\rm{P_{e}/P_{d}=2.03}\)) and exhibit transit timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only six systems with measured masses and radii for all four transiting planets. The planet densities range from \(\rm{0.70 \pm 0.24}\) to \(3.21 \pm 0.44 \rm{g/cm^3}\), implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 \(\pm\) 3.6 \(\rm{M_\oplus}\). This planet candidate is exterior to TOI-1246 e with a candidate period of 93.8 d, and we discuss the implications if it is confirmed to be planetary in nature.
We report the discovery of TOI-2180 b, a 2.8 \(M_{\rm J}\) 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\(\pm\)0.6 days, revealed an orbital eccentricity of 0.368\(\pm\)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.
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 \(1.8 \pm 0.1\) R\(_\oplus\) 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 \(11.1 \pm 1.2\) M\(_\oplus\). 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 (3\(\sigma\)) and a secondary eclipse (2\(\sigma\)) 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.
