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We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA's K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1-3 REarth is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5-sigma (51 were detected with >3-sigma significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities, and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters., Comment: 156 pages, 86 planets, 55 stars, 104 figures, 48 tables. Accepted to ApJS

Most multi-planet systems around mature ($\sim 5$-Gyr-old) host stars are non-resonant. Even the near-resonant planet pairs still display 1-2\% positive deviation from perfect period commensurabilities ($\Delta$) near first-order mean motion resonances (MMR). Resonant repulsion due to eccentricity tides was one of the first mechanisms proposed to explain the observed positive $\Delta$. However, the inferred rates of tidal dissipation are often implausibly rapid (with a reduced tidal quality factor $Q_p^\prime \lesssim 10$). In this work, we attempt to amplify eccentricity tides with three previously ignored effects. 1) Planets tend to be inflated when they were younger. 2) Kepler-like Planets likely form as resonant chains parked at the disk inner edge, overlooked inner planets could have contributed to tidal dissipation of the whole system. 3) Disk migration captures planets into first-order MMR with non-zero initial deviation $\Delta$, thereby lowering the amount of dissipation needed. We show that even after accounting for all three effects, $Q_p^\prime$ can only be amplified by about one order of magnitude, and still falls short of $Q_p^\prime$ values of Solar System planets. Therefore, eccentricity tides alone cannot fully explain the observed $\Delta$ distribution. Other effects such as obliquity tides, planetesimal scattering, expanding disk inner edge, disk turbulence, divergent encounters, and dynamical instabilities must have contributed to dislodging planets from first-order MMR., Comment: 10 pages, 5 figures, accepted to AAS Journals

We present the first asteroseismic analysis of the K3\,V planet host HD~219134, based on four consecutive nights of radial velocities collected with the Keck Planet Finder. We applied Gold deconvolution to the power spectrum to disentangle modes from sidelobes in the spectral window, and extracted 25 mode frequencies with spherical degrees $0\leq\ell\leq3$. We derive the fundamental properties using five different evolutionary-modeling pipelines and report a mass of 0.763 $\pm$ 0.020 (stat) $\pm$ 0.007 (sys) M$_\odot$, a radius of 0.748 $\pm$ 0.007 (stat) $\pm$ 0.002 (sys) R$_\odot$, and an age of 10.151 $\pm$ 1.520 (stat) $\pm$ 0.810 (sys) Gyr. Compared to the interferometric radius 0.783 $\pm$ 0.005~R$_\odot$, the asteroseismic radius is 4\% smaller at the 4-$\sigma$ level -- a discrepancy not easily explained by known interferometric systematics, modeling assumptions on atmospheric boundary conditions and mixing lengths, magnetic fields, or tidal heating. HD~219134 is the first main-sequence star cooler than 5000~K with an asteroseismic age estimate and will serve as a critical calibration point for stellar spin-down relations. We show that existing calibrated prescriptions for angular momentum loss, incorporating weakened magnetic braking with asteroseismically constrained stellar parameters, accurately reproduce the observed rotation period. Additionally, we revised the masses and radii of the super-Earths in the system, which support their having Earth-like compositions. Finally, we confirm that the oscillation amplitude in radial velocity scales as $(L/M)^{1.5}$ in K dwarfs, in contrast to the $(L/M)^{0.7}$ relation observed in G dwarfs. These findings provide significant insights into the structure and angular momentum loss of K-type stars., Comment: 23 pages, 11 figures. submitted to AAS Journals. Comments welcome

We present a correlation between the stellar metallicities and the mutual inclinations of multi-planet systems hosting short-period small planets (a/Rs<12, Rp<4Re). We analyzed 89 multi-planet systems discovered by Kepler, K2, and TESS, where the innermost planets have periods shorter than 10 days. We found that the mutual inclinations of the innermost two planets are higher and more diverse around metal-rich stars. The mutual inclinations are calculated as the absolute differences between the best-fit inclinations of the innermost two planets from transit modeling, which represent the lower limits of the true mutual inclinations. The mean and variance of the mutual inclination distribution of the metal-rich systems are 3.1+-0.5 and 3.1+-0.4 degrees, while for the metal-poor systems they are 1.3+-0.2 and 1.0+-0.2 degrees. This finding suggests that inner planetary systems around metal-rich stars are dynamically hotter. We summarized the theories that could plausibly explain this correlation, including the influence of giant planets, higher solid densities in protoplanetary disks around metal-rich stars, or secular chaos coupled with an excess of angular momentum deficits. Planet formation and population synthesis models tracking the mutual inclination evolution would be essential to fully understand this correlation., Comment: 14 pages, 5 figures, 1 table. Accepted by ApJL

We present the results of the Distant Giants Survey, a three-year radial velocity (RV) campaign to search for wide-separation giant planets orbiting Sun-like stars known to host an inner transiting planet. We defined a distant giant to have $a$ = 1--10 AU and $M_{p} \sin i = 70-4000$ \mearth~ = 0.2-12.5 \mj, and required transiting planets to have $a<1$ AU and $R_{p} = 1-4$ \rearth. We assembled our sample of 47 stars using a single selection function, and observed each star at monthly intervals to obtain $\approx$30 RV observations per target. The final catalog includes a total of twelve distant companions: four giant planets detected during our survey, two previously known giant planets, and six objects of uncertain disposition identified through RV/astrometric accelerations. Statistically, half of the uncertain objects are planets and the remainder are stars/brown dwarfs. We calculated target-by-target completeness maps to account for missed planets. We found evidence for a moderate enhancement of distant giants (DG) in the presence of close-in small planets (CS), P(DG|CS) = $30^{+14}_{-12}\%$, over the field rate of P(DG) = $16^{+2}_{-2}\%$. No enhancement is disfavored ($p \sim$ 8%). In contrast to a previous study, we found no evidence that stellar metallicity enhances P(DG|CS). We found evidence that distant giant companions are preferentially found in systems with multiple transiting planets and have lower eccentricities than randomly selected giant planets. This points toward dynamically cool formation pathways for the giants that do not disturb the inner systems., Comment: 32 pages, 20 figures, 4 tables. Comments welcome

We present spectral observations of the multiplanet host TOI-1694 during the transit of TOI-1694b, a 26.1 $M_\oplus$ hot Neptune with a 3.77-day orbit. By analyzing radial velocities obtained from the Keck Planet Finder, we modeled the Rossiter-McLaughlin effect and constrained the sky-projected obliquity to ${9\degree}^{+22\degree}_{-18\degree}$, which is strong evidence for a nearly aligned orbit. TOI-1694b is one of fewer than ten small planets accompanied by confirmed outer giant planets for which the obliquity has been measured. We consider the significance of the outer planet TOI-1694c, a Jupiter-mass planet with a 1-year orbit, and its potential role in influencing the orbit of TOI-1694b to its current state. Incorporating our measurement, we discuss the bifurcation in hot Neptune obliquities and present evidence for an independent polar population. The observed polar planets nearly ubiquitously have periods of $\le 6$ days and mass ratios of $10^{-4}$. Early perturbations by outer companions from resonance crossings in the disk-dispersal stage provide the most compelling explanation for this population. Systems which lack the necessary configuration will retain their primordial obliquity, since hot Neptunes lack the angular momentum needed to realign their hosts on relevant timescales., Comment: Submitted to AJ

Video synthesis techniques are undergoing rapid progress, with controllability being a significant aspect of practical usability for end-users. Although text condition is an effective way to guide video synthesis, capturing the correct joint distribution between text descriptions and video motion remains a substantial challenge. In this paper, we present a disentangled and unified framework, namely I2VControl, that unifies multiple motion control tasks in image-to-video synthesis. Our approach partitions the video into individual motion units and represents each unit with disentangled control signals, which allows for various control types to be flexibly combined within our single system. Furthermore, our methodology seamlessly integrates as a plug-in for pre-trained models and remains agnostic to specific model architectures. We conduct extensive experiments, achieving excellent performance on various control tasks, and our method further facilitates user-driven creative combinations, enhancing innovation and creativity. The project page is: https://wanquanf.github.io/I2VControl ., Comment: Project page: https://wanquanf.github.io/I2VControl

Hundreds of exoplanets between 1-1.8 times the size of the Earth have been discovered on close in orbits. However, these planets show such a diversity in densities that some appear to be made entirely of iron, while others appear to host gaseous envelopes. To test this diversity in composition, we update the masses of 5 rocky exoplanets (HD 93963 A b, Kepler-10 b, Kepler-100 b, Kepler-407 b, and TOI-1444 b) and present the confirmation of a new planet (TOI-1011) using 187 high precision RVs from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of the Earth than previous literature values for all planets in our sample. In particular, we report that two previously identified ``super-Mercuries'' (Kepler-100 b and HD 93963 A b) have lower masses that suggest less iron-rich compositions. We then compare the ratio of iron to rock-building species to the abundance ratios of those elements in their host stars. These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest that planets and host stars have similar abundance ratios., Comment: Submitted to AJ 09/30/2024

We report on the discovery and spectroscopic confirmation of TOI-2458 b, a transiting mini-Neptune around an F-type star leaving the main-sequence with a mass of $M_\star=1.05 \pm 0.03$ M$_{\odot}$, a radius of $R_\star=1.31 \pm 0.03$ R$_{\odot}$, an effective temperature of $T_{\rm eff}=6005\pm50$ K, and a metallicity of $-0.10\pm0.05$ dex. By combining TESS photometry with high-resolution spectra acquired with the HARPS spectrograph, we found that the transiting planet has an orbital period of $\sim$3.74 days, a mass of $M_p=13.31\pm0.99$ M$_{\oplus}$ and a radius of $R_p=2.83\pm0.20$ R$_{\oplus}$. The host star TOI-2458 shows a short activity cycle of $\sim$54 days revealed in the HARPS S-index and H$\alpha$ times series. We took the opportunity to investigate other F stars showing activity cycle periods comparable to that of TOI-2458 and found that they have shorter rotation periods than would be expected based on the gyrochronology predictions. In addition, we determined TOI-2458's stellar inclination angle to be $i_\star\,=\,10.6_{-10.6}^{+13.3}$ degrees. We discuss that both phenomena (fast stellar rotation and planet orbit inclination) could be explained by in situ formation of a hot Jupiter interior to TOI-2458 b. It is plausible that this hot Jupiter was recently engulfed by the star. Analysis of HARPS spectra has identified the presence of another planet with a period of $P\,=\,16.55\pm0.06$ days and a minimum mass of $M_p \sin i=10.22\pm1.90$ M$_{\oplus}$. Using dynamical stability analysis, we constrained the mass of this planet to the range $M_{c} \simeq (10, 25)$ M$_{\oplus}$., Comment: 25 pages, 20 figures, accepted for publication in Astronomy & Astrophysics

We present spectroscopic and photometric observations of Bernhard-2, which was previously identified as a candidate system to host a misaligned circumbinary disk. Our spectroscopic measurements confirm that Bernhard-2 indeed contains an eccentric ($e=0.69 \pm 0.08$) binary and thus that the periodic variability in the photometric light curve is best explained by the occultation by the misaligned circumbinary disk. By modeling the spectral energy distributions at different phases, we infer the masses of the two binary components to be $\sim 1.1\,M_\odot$ and $\sim 0.9\,M_\odot$, respectively. The system age is determined to be $\lesssim$ 20 Myr by combining the stellar isochrone model with lithium abundance. Our new photometric observations show clear deviations from the model prediction based on the archival data, suggesting ongoing precession of the circumbinary disk. The H$\alpha$ line of Bernhard-2 also shows an inverse P-Cygni profile at epochs close to the pericenter passage, which could be attributed to the pulsed accretion around the pericenter. Bernhard-2 therefore closely resembles the well studied KH 15D system. Further detailed observations and studies of such rare systems can provide useful information about disk physics and evolution., Comment: 12 pages, 6 figures, accepted for publication in ApJ Letters

TOI-836 is a ~2-3 Gyr K dwarf with an inner super Earth ($R=1.7 R_\oplus$, $P=3.8$ d) and an outer mini Neptune ($R=2.6 R_\oplus$, $P=8.6$ d). JWST/NIRSpec 2.8--5.2 $\mu$m transmission spectra are flat for both planets. We present Keck/NIRSPEC observations of escaping helium for super-Earth b, which shows no excess absorption in the 1083 nm triplet to deep limits (<0.2%), and mini-Neptune c, which shows strong (0.7%) excess absorption in both visits. These results demonstrate that planet c retains at least some primordial atmosphere, while planet b is consistent with having lost its entire primordial envelope. Self-consistent 1D radiative-hydrodynamic models of planet c reveal that the helium excess absorption signal is highly sensitive to metallicity: its equivalent width collapses by a factor of 13 as metallicity increases from 10x to 100x solar, and by a further factor of 12 as it increases to 200x solar. The observed equivalent width is 88\% the model prediction for 100x metallicity, suggesting an atmospheric metallicity similar to K2-18b and TOI-270d, the first two mini-Neptunes with detected absorption features in JWST transmission spectra. We highlight the helium triplet as a potentially powerful probe of atmospheric composition, with complementary strengths and weaknesses to atmospheric retrievals. The main strength is its extreme sensitivity to metallicity in the scientifically significant range of 10--200x solar, and the main weakness is the enormous model uncertainties in outflow suppression and confinement mechanisms, such as magnetic fields and stellar winds, which can suppress the signal by at least a factor of ~several., Comment: Accepted by AJ

We report the sky-projected spin-orbit angle $\lambda$ for HD 191939 b, the innermost planet in a 6 planet system, using Keck/KPF to detect the Rossiter-McLaughlin (RM) effect. Planet b is a sub-Neptune with radius 3.4 $\pm$ 0.8 R$_{\oplus}$ and mass 10.0 $\pm$ 0.7 M$_{\oplus}$ with an RM amplitude $<$1 ms$^{-1}$. We find the planet is consistent with a well-aligned orbit, measuring $\lambda= \, $ 3.7 $\pm$ 5.0 degrees. Additionally, we place new constraints on the mass and period of the distant super-Jupiter, planet f, finding it to be 2.88 $\pm$ 0.26 $M_J$ on a 2898 $\pm$ 152 day orbit. With these new orbital parameters, we perform a dynamical analysis of the system and constrain the mutual inclination of the non-transiting planet e to be smaller than 12 degrees relative to the plane shared by the inner three transiting planets. Additionally, the further planet f is inclined off this shared plane, the greater the amplitude of precession for the entire inner system, making it increasingly unlikely to measure an aligned orbit for planet b. Through this analysis, we show that this system's wide variety of planets are all well-aligned with the star and nearly co-planar, suggesting that the system formed dynamically cold and flat out of a well-aligned proto-planetary disk, similar to our own solar system., Comment: 11 pages, 4 figures, Accepted for publication in The Astronomical Journal

Observations with the Transiting Exoplanet Survey Satellite and Kepler have revealed that practically all close-in sub-Neptunes form in mean-motion resonant chains, most of which unravel on timescales of 100 Myr. Using a series of N-body integrations, we study how planetary collisions resulting from the destabilization of resonant chains produce the distribution of orbital periods observed among mature systems, focusing on the resonant fine structures that remain post-instability. In their natal chains, planets near first-order resonances have period ratios just wide of perfect commensurability, driven there by disk migration and eccentricity damping. Sufficiently large resonant libration amplitudes (of unknown origin) are needed to trigger instability. Ensuing collisions between planets ("major mergers") erode but do not completely eliminate resonant pairs; survivors which avoid mergers show up as narrow "peaks" just wide of commensurability in the histogram of neighboring-planet period ratios. Merger products exhibit a broad range of period ratios, with each resonant peak in the histogram spawning a continuum of ratios wide of the given resonance. These continua may fill in period ratios between relatively closely separated resonances such as the 5:4, 4:3, and 3:2, but may fail to bridge the relatively wide gap between the 3:2 and the 2:1. Thus a "trough" manifests just short of the 2:1 resonance (and only the 2:1 resonance), as observed. Major mergers are not perfect, and generate collisional debris which undergoes "minor mergers" with planets, in many cases further widening resonant pairs. With all this dynamical activity, free eccentricities of resonant pairs, and by extension the phases of their transit timing variations (TTVs), are readily excited. Because non-resonant planets are merger products, they are predicted to have higher masses than resonant planets., Comment: Submitted to AAS Journals, comments welcome

The stellar obliquity distribution of warm-Jupiter systems is crucial for constraining the dynamical history of Jovian exoplanets, as the warm Jupiters' tidal detachment likely preserves their primordial obliquity. However, the sample size of warm-Jupiter systems with measured stellar obliquities has historically been limited compared to that of hot Jupiters, particularly in hot-star systems. In this work, we present newly obtained sky-projected stellar obliquity measurements for warm-Jupiter systems, TOI-559, TOI-2025, TOI-2031, TOI-2485, TOI-2524, and TOI-3972, derived from the Rossiter-McLaughlin effect, and show that all six systems display alignment with a median measurement uncertainty of 13 degrees. Combining these new measurements with the set of previously reported stellar obliquity measurements, our analysis reveals that single-star warm-Jupiter systems tend to be aligned, even around hot stellar hosts. This alignment exhibits a 3.4-$\sigma$ deviation from the $T_{\rm eff}-\lambda$ dependency observed in hot-Jupiter systems, where planets around cool stars tend to be aligned, while those orbiting hot stars show considerable misalignment. The current distribution of spin-orbit measurements for Jovian exoplanets indicates that misalignments are neither universal nor primordial phenomena affecting all types of planets. The absence of misalignments in single-star warm-Jupiter systems further implies that many hot Jupiters, by contrast, have experienced a dynamically violent history., Comment: 18 pages, 2 figures, accepted for publication in ApJL

We report the observation of the transiting planet TOI-942c, a Neptunian planet orbiting a young K-type star approximately 50 Myr years old. Using Keck/HIRES, we observed a partial transit of the planet and detected an associated radial velocity anomaly. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of $\left|\lambda\right|=24^{+14}_{-14}$ degrees, indicating TOI-942c is in a prograde and likely aligned orbit. Upon incorporation of the star's inclination and the planet's orbital inclination, we determined a true obliquity for TOI-942c of $\psi< 43$ degrees at 84\% confidence, while dynamic analysis strongly suggests TOI-942c is aligned with stellar spin and coplanar with the inner planet. Furthermore, TOI-942c is also a suitable target for studying atmospheric loss of young Neptunian planets that are likely still contracting from the heat of formation. We observed a blueshifted excess absorption in the H-alpha line at 6564.7 \AA, potentially indicating atmospheric loss due to photoevaporation. However, due to the lack of pre-ingress data, additional observations are needed to confirm this measurement., Comment: 11 pages, 4 figures, 3 tables, accepted for publication in AJ

Characterizing outer companions to hot Jupiters plays a crucial role in deciphering their origins. We present the discovery of a long-period giant planet, HD 118203 c ($m_{c}=11.79^{+0.69}_{-0.63}\ \mathrm{M_{J}}$, $a_{c}=6.28^{+0.10}_{-0.11}$ AU) exterior to a close-in eccentric hot Jupiter HD 118203 b ($P_{b}=6.135\ \mathrm{days}$, $m_{b}=2.14\pm{0.12}\ \mathrm{M_{J}}$, $r_{b}=1.14\pm{0.029}\ \mathrm{R_{J}}$, $e_{b}=0.31\pm{0.007}$) based on twenty-year radial velocities. Using Rossiter-McLaughlin (RM) observations from the Keck Planet Finder (KPF), we measured a low sky-projected spin-orbit angle $\lambda_{b}=-11^{\circ}.7^{+7.6}_{-10.0}$ for HD 118203 b and detected stellar oscillations in the host star, confirming its evolved status. Combining the RM observation with the stellar inclination measurement, we constrained the true spin-orbit angle of HD 118203 b as $\Psi_{b}<33^{\circ}.5\ (2\sigma)$, indicating the orbit normal of the hot Jupiter nearly aligned with the stellar spin axis. Furthermore, by combining radial velocities and Hipparcos-Gaia astrometric acceleration, we constrained the line-of-sight mutual inclination between the hot Jupiter and the outer planet to be $9^{\circ}.8^{+16.2}_{-9.3}$ at $2\sigma$ level. HD 118203 is one of first hot Jupiter systems where both the true spin-orbit angle of the hot Jupiter and the mutual inclination between inner and outer planets have been determined. Our results are consistent with a system-wide alignment, with low mutual inclinations between the outer giant planet, the inner hot Jupiter, and the host star. This alignment, along with the moderate eccentricity of HD 118203 c, implies that the system may have undergone coplanar high-eccentricity tidal migration. Under this framework, our dynamical analysis suggests an initial semi-major axis of 0.3 to 3.2 AU for the proto-hot Jupiter., Comment: 30 pages, 12 figures, accepted by AJ

The degree of alignment between a star's spin axis and the orbital plane of its planets (the stellar obliquity) is related to interesting and poorly understood processes that occur during planet formation and evolution. Hot Jupiters orbiting hot stars ($\gtrsim$6250 K) display a wide range of obliquities, while similar planets orbiting cool stars are preferentially aligned. Tidal dissipation is expected to be more rapid in stars with thick convective envelopes, potentially explaining this trend. Evolved stars provide an opportunity to test the damping hypothesis, particularly stars that were hot on the main sequence and have since cooled and developed deep convective envelopes. We present the first systematic study of the obliquities of hot Jupiters orbiting subgiants that recently developed convective envelopes using Rossiter-McLaughlin observations. Our sample includes two newly discovered systems in the Giants Transiting Giants Survey (TOI-6029 b, TOI-4379 b). We find that the orbits of hot Jupiters orbiting subgiants that have cooled below $\sim$6250 K are aligned or nearly aligned with the spin-axis of their host stars, indicating rapid tidal realignment after the emergence of a stellar convective envelope. We place an upper limit for the timescale of realignment for hot Jupiters orbiting subgiants at $\sim$500 Myr. Comparison with a simplified tidal evolution model shows that obliquity damping needs to be $\sim$4 orders of magnitude more efficient than orbital period decay to damp the obliquity without destroying the planet, which is consistent with recent predictions for tidal dissipation from inertial waves excited by hot Jupiters on misaligned orbits., Comment: 22 pages, 14 figures, 3 tables

We introduce the OATMEAL survey, an effort to measure the obliquities of stars with transiting brown dwarf companions. We observed a transit of the close-in ($P_{\rm orb} = 1.74 \,$ days) brown dwarf GPX-1 b using the Keck Planet Finder (KPF) spectrograph to measure the sky-projected angle between its orbital axis and the spin axis of its early F-type host star ($\lambda$). We measured $\lambda = 6.88 \pm 1.72 ^\circ$ (with additional unquantified systematic uncertainty), suggesting an orbit that is prograde and well aligned with the stellar equator. Hot Jupiters around early F stars are frequently found to have highly misaligned orbits, with polar and retrograde orbits being commonplace. It has been theorized that these misalignments stem from dynamical interactions, such as von Zeipel-Kozai-Lidov cycles, and are retained over long timescales due to weak tidal dissipation in stars with radiative envelopes. By comparing GPX-1 to similar systems under the frameworks of different tidal evolution theories, we argued that the rate of tidal dissipation is too slow to have re-aligned the system. This suggests that GPX-1 may have arrived at its close-in orbit via coplanar high-eccentricity migration or migration through an aligned protoplanetary disk. Our result for GPX-1 is one of few measurements of the obliquity of a star with a transiting brown dwarf. By enlarging the number of such measurements and comparing them with hot Jupiter systems, we will more clearly discern the differences between the mechanisms that dictate the formation and evolution of both classes of objects., Comment: 8 pages, 4 figures

Asteroseismology of dwarf stars cooler than the Sun is very challenging due to the low amplitudes and rapid timescales of oscillations. Here, we present the asteroseismic detection of solar-like oscillations at 4-minute timescales ($\nu_{\mathrm{max}}\sim4300\mu$Hz) in the nearby K-dwarf $\sigma$ Draconis using extreme precision Doppler velocity observations from the Keck Planet Finder and 20-second cadence photometry from NASA's Transiting Exoplanet Survey Satellite. The star is the coolest dwarf star to date with both velocity and luminosity observations of solar-like oscillations, having amplitudes of $5.9\pm0.8\,$cm$\,\text{s}^{-1}$ and $0.8\pm0.2$ ppm, respectively. These measured values are in excellent agreement with established luminosity-velocity amplitude relations for oscillations and provide further evidence that mode amplitudes for stars with $T_{\mathrm{eff}}<\,5500\,$K diminish in scale following a $(L/M)^{1.5}$ relation. By modeling the star's oscillation frequencies from photometric data, we measure an asteroseismic age of $4.5\pm0.9\,\rm{(ran)} \pm 1.2\,\rm{(sys)}$ Gyr. The observations demonstrate the capability of next-generation spectrographs and precise space-based photometry to extend observational asteroseismology to nearby cool dwarfs, which are benchmarks for stellar astrophysics and prime targets for directly imaging planets using future space-based telescopes., Comment: Accepted for publication in The Astrophysical Journal

We present the first spectroscopic transit results from the newly commissioned Keck Planet Finder on the Keck-I telescope at W. M. Keck Observatory. We observed a transit of KELT-18 b, an inflated ultra-hot Jupiter orbiting a hot star ($T_\text{eff} = 6670$ K) with a binary stellar companion. By modeling the perturbation to the measured cross correlation functions using the Reloaded Rossiter-McLaughlin technique, we derived a sky projected obliquity of $\lambda = -94.8 \pm 0.7$ deg ($\psi = 93.8_{-1.8}^{+1.6}$ deg for isotropic $i_\star$). The data are consistent with an extreme stellar differential rotation ($\alpha = 0.9$), though a more likely explanation is moderate center-to-limb variations of the emergent stellar spectrum. We see additional evidence for the latter from line widths increasing towards the limb. Using loose constraints on the stellar rotation period from observed variability in the available TESS photometry, we were able to constrain the stellar inclination and thus the true 3D stellar obliquity to $\psi = 91.7_{-1.8}^{+2.2}$ deg. KELT-18 b could have obtained its polar orbit through high-eccentricity migration initiated by Kozai-Lidov oscillations induced by the binary stellar companion KELT-18 B, as the two likely have a large mutual inclination as evidenced by Gaia astrometry. KELT-18 b adds another data point to the growing population of close-in polar planets, particularly around hot stars., Comment: 17 pages, 8 figures, submitted to AJ (in revision)

The orbits of close-in exoplanets provide clues to their formation and evolutionary history. Many close-in exoplanets likely formed far out in their protoplanetary disks and migrated to their current orbits, perhaps via high-eccentricity migration (HEM), a process that can also excite obliquities. A handful of known exoplanets are perhaps caught in the act of HEM, as they are observed on highly eccentric orbits with tidal circularization timescales shorter than their ages. One such exoplanet is Kepler-1656 b, which is also the only known non-giant exoplanet (<100 $M_\oplus$) with an extreme eccentricity (e=0.84). We measured the sky-projected obliquity of Kepler-1656 b by observing the Rossiter-McLaughlin effect during a transit with the Keck Planet Finder. Our data are consistent with an aligned orbit, but are also consistent with moderate misalignment with $\lambda < 50$ deg at 95% confidence, with the most likely solution of $35^{+14.9}_{-21.6}$ deg. A low obliquity would be an unlikely outcome of most eccentricity-exciting scenarios, but we show that the properties of the outer companion in the system are consistent with the coplanar HEM mechanism. Alternatively, if the system is not relatively coplanar (<20 deg mutual inclination), Kepler-1656 b may be presently at a rare snapshot of long-lived eccentricity oscillations that do not induce migration. Kepler-1656 b is only the fourth exoplanet with e>0.8 to have its obliquity constrained; expanding this population will help establish the degree to which orbital misalignment accompanies migration. Future work that constrains the mutual inclinations of outer perturbers will be key for distinguishing plausible mechanisms., Comment: 11 pages, 5 figures, accepted to ApJL

TOI-6255~b (GJ 4256) is an Earth-sized planet (1.079$\pm0.065$ $R_\oplus$) with an orbital period of only 5.7 hours. With the newly commissioned Keck Planet Finder (KPF) and CARMENES spectrographs, we determined the planet's mass to be 1.44$\pm$0.14 $M_{\oplus}$. The planet is just outside the Roche limit, with $P_{\rm orb}/P_{\rm Roche}$ = 1.13 $\pm0.10$. The strong tidal force likely deforms the planet into a triaxial ellipsoid with a long axis that is $\sim$10\% longer than the short axis. Assuming a reduced stellar tidal quality factor $Q_\star^\prime \approx10^7$, we predict that tidal orbital decay will cause TOI-6255 to reach the Roche limit in roughly 400 Myr. Such tidal disruptions may produce the possible signatures of planet engulfment that have been on stars with anomalously high refractory elemental abundances compared to its conatal binary companion. TOI-6255 b is also a favorable target for searching for star-planet magnetic interactions, which might cause interior melting and hasten orbital decay. TOI-6255 b is a top target (Emission Spectroscopy Metric of about 24) for phase curve observations with the James Webb Space Telescope., Comment: 18 pages, 7 figures, 5 tables, accepted to AAS Journals. The first RV mass measurement from the Keck Planet Finder

In 2010, Bakos and collaborators discovered a Neptune-sized planet transiting the K-dwarf HAT-P-11 every five days. Later in 2018, Yee and collaborators reported an additional Jovian-mass companion on a nine year orbit based on a decade of Doppler monitoring. The eccentric outer giant HAT-P-11c may be responsible for the peculiar polar orbit of the inner planet HAT-P-11b. However, Basilicata et al. (2024) recently suggested that the HAT-P-11c Doppler signal could be caused by stellar activity. In this research note, we extend the Yee et al. (2018) Doppler time series by six years. The combined dataset spanning 17 years covers nearly two orbits of the outer planet. Importantly, we observe two periastron passages of planet c and do not observe a coherent activity signature. Together with the previously reported astrometric acceleration of HAT-P-11 from Hipparcos and Gaia, we believe there is strong evidence for HAT-P-11c as a bona fide planet., Comment: 4 pages, 1 figure

We present optical spectroscopy of 710 solar neighborhood stars collected over twenty years to catalog chromospheric activity and search for stellar activity cycles. The California Legacy Survey stars are amenable to exoplanet detection using precise radial velocities, and we present their Ca II H and K time series as a proxy for stellar and chromospheric activity. Using the HIRES spectrometer at Keck Observatory, we measured stellar flux in the cores of the Ca II H and K lines to determine S-values on the Mt. Wilson scale and the log(R'HK) metric, which is comparable across a wide range of spectral types. From the 710 stars, with 52,372 observations, 285 stars are sufficiently sampled to search for stellar activity cycles with periods of 2-25 years, and 138 stars show stellar cycles of varying length and amplitude. S-values can be used to mitigate stellar activity in the detection and characterization of exoplanets. We use them to probe stellar dynamos and to place the Sun's magnetic activity into context among solar neighborhood stars. Using precise stellar parameters and time-averaged activity measurements, we find tightly constrained cycle periods as a function of stellar temperature between log(R'HK) of -4.7 and -4.9, a range of activity in which nearly every star has a periodic cycle. These observations present the largest sample of spectroscopically determined stellar activity cycles to date., Comment: 40 pages, 26 figures, submitted to ApJS

Measuring the obliquities of stars hosting giant planets may shed light on the dynamical history of planetary systems. Significant efforts have been made to measure the obliquities of FGK stars with hot Jupiters, mainly based on observations of the Rossiter-McLaughlin effect. In contrast, M dwarfs with hot Jupiters have hardly been explored, because such systems are rare and often not favorable for such precise observations. Here, we report the first detection of the Rossiter-McLaughlin effect for an M dwarf with a hot Jupiter, TOI-4201, using the Gemini-North/MAROON-X spectrograph. We find TOI-4201 to be well-aligned with its giant planet, with a sky-projected obliquity of $\lambda=-3.0_{-3.2}^{+3.7}\ ^{\circ}$ and a true obliquity of $\psi=21.3_{-12.8}^{+12.5}\ ^{\circ}$ with an upper limit of $40^{\circ}$ at a 95% confidence level. The result agrees with dynamically quiet formation or tidal obliquity damping that realigned the system. As the first hot Jupiter around an M dwarf with its obliquity measured, TOI-4201b joins the group of aligned giant planets around cool stars ($T_{\rm eff}<6250\ K$), as well as the small but growing sample of planets with relatively high planet-to-star mass ratio ($M_p/M_\ast\gtrsim 3\times 10^{-3}$) that also appear to be mostly aligned., Comment: 12 pages, 5 figures, 3 tables, accepted to ApJL

Planets may be rotationally flattened, and their oblateness thus provide useful information on their formation and evolution. Here we develop a new algorithm that can compute the transit light curve due to an oblate planet very efficiently and use it to study the detectability of planet oblateness (and spin obliquity) with the James Webb Space Telescope (JWST). Using the Jupiter analog, Kepler-167e, as an example, we show that observations of a single transit with JWST are able to detect a Saturn-like oblateness ($f=0.1$) with high confidence, or set a stringent upper limit on the oblateness parameter, as long as the planetary spin is slightly misaligned ($\gtrsim 20^\circ$) with respect to its orbital direction. Based on known obliquity measurements and theoretical arguments, it is reasonable to believe that this level of misalignment may be common. We estimate the sensitivity limit of JWST in oblateness detections and highlight the importance of better characterizations of cold planets in planning future JWST transit observations. The potential to detect rings, moons, and atmospheric species of the cold giants with JWST is also discussed., Comment: 17 pages, 8 figures. Published in Astronomical Journal

Multiple planets undergoing disk migration may be captured into a chain of mean-motion resonances with the innermost planet parked near the disk's inner edge. Subsequent dynamical evolution may disrupt these resonances, leading to the non-resonant configurations typically observed among {\it Kepler} planets that are Gyrs old. In this scenario, resonant configurations are expected to be more common in younger systems. This prediction can now be tested, thanks to recent discoveries of young planets, particularly those in stellar clusters, by NASA's {\it TESS} mission. We divided the known planetary systems into three age groups: young ($<$100-Myr-old), adolescent (0.1-1-Gyr-old), and mature ($>1$-Gyr-old). The fraction of neighboring planet pairs having period ratios within a few percent of a first-order commensurability (e.g.~4:3, 3:2, or 2:1) is 70$\pm$15\% for young pairs, 24$\pm$8\% for adolescent pairs, and 15$\pm$2\% for mature pairs. The fraction of systems with at least one nearly commensurable pair (either first or second-order) is 86$\pm13$\% among young systems, 38$\pm12$\% for adolescent systems, and 23$\pm3$\% for mature systems. First-order commensurabilities prevail across all age groups, with an admixture of second-order commensurabilities. Commensurabilities are more common in systems with high planet multiplicity and low mutual inclinations. Observed period ratios often deviate from perfect commensurability by $\sim$1\% even among young planets, too large to be explained by resonant repulsion with equilibrium eccentricity tides. We also find that super-Earths in the radius gap ($1.5-1.9R_\oplus$) are less likely to be near-resonant (11.9$\pm2.0\%$) compared to Earth-sized planets ($R_p<1R_\oplus$; 25.3$\pm4.4\%$) or mini-Neptunes ($1.9R_\oplus \leq R_p<2.5R_\oplus$; 14.4$\pm1.8\%$)., Comment: 17 pages, 9 figures, accepted to AAS

WASP-107 b seems to be a poster child of the long-suspected high-eccentricity migration scenario. It is on a 5.7-day, polar orbit. The planet is Jupiter-like in radius but Neptune-like in mass with exceptionally low density. WASP-107 c is on a 1100-day, $e=0.28$ orbit with at least Saturn mass. Planet b may still have a residual eccentricity of $0.06\pm 0.04$: the ongoing tidal dissipation leads to the observed internally heated atmosphere and hydrodynamic atmospheric erosion. We present a population synthesis study coupling octopole Lidov-Kozai oscillations with various short-range forces, while simultaneously accounting for the radius inflation and tidal disruption of the planet. We find that a high-eccentricity migration scenario can successfully explain nearly all observed system properties. Our simulations further suggest that the initial location of WASP-107 b at the onset of migration is likely within the snowline ($<0.5\,{\rm AU}$). More distant initial orbits usually lead to tidal disruption or orbit crossing. WASP-107 b most likely lost no more than 20% of its mass during the high-eccentricity migration, i.e. it did not form as a Jupiter-mass object. More vigorous tidally-induced mass loss leads to disruption of the planet during migration. We predict that the current-day mutual inclination between the planets b and c is substantial: at least 25-55$^\circ$ which may be tested with future Gaia astrometric observations. Knowing the current-day mutual inclination may further constrain the initial orbit of planet b. We suggest that the proposed high-eccentricity migration scenario of WASP-107 may be applicable to HAT-P-11, GJ-3470, HAT-P-18, and GJ-436 which have similar orbital architectures., Comment: 19 pages, 10 figures. Accepted by ApJ

The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from $\textit{Kepler}$. Owing to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey's (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data which has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached $\geq5\sigma$ precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three year survey. We took the opportunity to assess the performance of our survey, and found that we achieved many of our goals including measuring the mass of 38 small ($<4R_{\oplus}$) planets, nearly achieving the TESS mission's basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder (APF) as survey support and observed meaningful constraints on system parameters due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass-radius relations and investigated evidence of systematic bias., Comment: 51 pages (22 of text), 24 figures

Exoplanet discoveries have revealed a dramatic diversity of planet sizes across a vast array of orbital architectures. Sub-Neptunes are of particular interest; due to their absence in our own solar system, we rely on demographics of exoplanets to better understand their bulk composition and formation scenarios. Here, we present the discovery and characterization of TOI-1437 b, a sub-Neptune with a 18.84 day orbit around a near-Solar analog (Mstar = 1.10 +/- 0.10 Msun, Rstar = 1.17 +/- 0.12 Rsun). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) mission and radial velocity follow-up observations were carried out as a part of the TESS-Keck Survey (TKS) using both the HIRES instrument at Keck Observatory and the Levy Spectrograph on the Automated Planet Finder (APF) telescope. A combined analysis of these data reveal a planet radius of Rp = 2.24 +/- 0.23 Rearth and a mass measurement of Mp = 9.6 +/- 3.9 Mearth). TOI-1437 b is one of few (~50) known transiting sub-Neptunes orbiting a solar-mass star that has a radial velocity mass measurement. As the formation pathway of these worlds remains an unanswered question, the precise mass characterization of TOI-1437 b may provide further insight into this class of planet., Comment: This arxiv update reflects the version of the manuscript that was accepted for publication in The Astronomical Journal

We conduct a comprehensive search for transiting exomoons and exosatellites within 44 archival Spitzer light curves of 32 substellar worlds with estimated masses ranging between 3-30M$_{\rm Jup}$. This sample's median host mass is 16M$_{\rm Jup}$, inclusive of 14 planetary-mass objects, among which one is a wide-orbit exoplanet. We search the light curves for exosatellite signatures and implement a transit injection-recovery test, illustrating our survey's capability to detect $>$0.7R$_{\oplus}$ exosatellites. Our findings reveal no substantial ($>$5$\sigma$) evidence for individual transit events. However, an unusual fraction of light curves favor the transit model at the 2-3$\sigma$ significance level, with fitted transit depths consistent with terrestrial-sized (0.7-1.6R$_{\oplus}$) bodies. Comparatively, fewer than 2.2% of randomly generated normal distributions from an equivalent sample size exhibit a similar prevalence of outliers. Should one or two of these outliers represent a real exosatellite transit, it would imply an occurrence rate of $\eta = 0.61^{+0.49}_{-0.34}$ short-period terrestrial exosatellites per system, consistent with the known occurrences rates for both solar system moons and mid M-dwarf exoplanets. We explore alternative astrophysical interpretations for these outliers, underscoring that transits are not the only plausible explanation. For orbital periods $<$0.8 days, the typical duration of the light curves, we constrain the occurrence rate of sub-Neptunes to $\eta<$0.35 (95% confidence) and, if none of the detected outlier signals are real, the occurrence rate of terrestrial ($\sim$Earth-sized) exosatellites to $\eta<$0.51 (95% confidence). Forthcoming JWST observations of substellar light curves will enable detection of sub-Io-sized exosatellites, allowing for much stronger constraints on this exosatellite population., Comment: 15 pages, 11 figures, in review at AJ, includes revisions from first round of review

Stellar chemical compositions can be altered by ingestion of planetary material and/or planet formation which removes refractory material from the proto-stellar disc. These "planet signatures" appear as correlations between elemental abundance differences and the dust condensation temperature. Detecting these planet signatures, however, is challenging due to unknown occurrence rates, small amplitudes, and heterogeneous star samples with large differences in stellar ages, and therefore stars born together (i.e., co-natal) with identical compositions can facilitate such detections. While previous spectroscopic studies were limited to small number of binary stars, the Gaia satellite provides new opportunities for detecting stellar chemical signatures of planets among co-moving pairs of stars confirmed to be co-natal. Here we report high-precision chemical abundances for a homogeneous sample of 91 co-natal pairs of stars with a well-defined selection function and identify at least seven new instances of planetary ingestion, corresponding to an occurrence rate of 8%. An independent Bayesian indicator is deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion. Our study provides new evidence of planet signatures and facilitates a deeper understanding of the star-planet-chemistry connection by providing new observational constraints on the mechanisms of planet engulfment, formation and evolution., Comment: 29 pages, 11 figures. Author's submitted version before final edits. Published in Nature on March 21, 2024: https://www.nature.com/articles/s41586-024-07091-y

In order to understand the relationship between planet multiplicity, mass, and composition, we present newly measured masses of five planets in two planetary systems: Kepler-323 and Kepler-104. We used the HIRES instrument at the W.M. Keck Observatory to collect 79 new radial velocity measurements (RVs) for Kepler-323, which we combined with 48 literature RVs from TNG/HARPS-N. We also conducted a reanalysis of the Kepler-104 system, using 44 previously published RV measurements. Kepler-323 b and c have masses of $2.0^{+1.2}_{-1.1}$ M$_\oplus$ and 6.5$\pm1.6$ M$_\oplus$, respectively, whereas the three Kepler-104 planets are more massive (10.0$\pm2.8$ M$_\oplus$, $7.1^{+3.8}_{-3.5}$ M$_\oplus$, and $5.5^{+4.6}_{-3.5}$ M$_\oplus$ for planets b, c, and d, respectively). The Kepler-104 planets have densities consistent with rocky cores overlaid with gaseous envelopes ($4.1^{+1.2}_{-1.1}$ g/cc, $2.9^{+1.7}_{-1.5}$ g/cc, and $1.6^{+1.5}_{-1.1}$ g/cc respectively), whereas the Kepler-323 planets are consistent with having rocky compositions ($4.5^{+2.8}_{-2.4}$ g/cc and $9.9^{+2.7}_{-2.5}$ g/cc). The Kepler-104 system has among the lowest values for gap complexity ($\mathcal{C}$ = 0.004) and mass partitioning ($\mathcal{Q}$ = 0.03); whereas, the Kepler-323 planets have a mass partitioning similar to that of the Inner Solar System ($\mathcal{Q}$ = 0.28 and $\mathcal{Q}$ = 0.24, respectively). For both exoplanet systems, the uncertainty in the mass partitioning is affected equally by (1) individual mass errors of the planets and (2) the possible existence of undetected low-mass planets, meaning that both improved mass characterization and improved sensitivity to low-mass planets in these systems would better elucidate the mass distribution among the planets., Comment: Accepted for publication in Astronomical Journal

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., Comment: 22 pages, 9 figures, accepted for publication in The Astronomical Journal

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., Comment: 22 pages, 9 figures, 9 tables

We present and confirm TOI-1751 b, a transiting sub-Neptune orbiting a slightly evolved, solar-type, metal-poor star ($T_{eff} = 5996 \pm 110$ K, $log(g) = 4.2 \pm 0.1$, V = 9.3 mag, [Fe/H] = $-0.40 \pm 0.06$ dex) every 37.47 d. We use TESS photometry to measure a planet radius of $2.77_{-0.07}^{+0.15}~\rm{R_\oplus}$. We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of $14.5_{-3.14}^{+3.15} ~\rm{M_\oplus}$, and thus a planet density of $3.6 \pm 0.9 \, {\rm g}\,{\rm cm}^{-3}$. There is also a long-period ($\sim400~\rm{d}$) 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 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 $\sim 820$ 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., Comment: 30 pages, 9 figures. Accepted for publication in AJ

The Transiting Exoplanet Survey Satellite (TESS) continues to dramatically increase the number of known transiting exoplanets, and is optimal for monitoring bright stars amenable to radial velocity (RV) and atmospheric follow-up observations. TOI-1386 is a solar-type (G5V) star that was detected via TESS photometry to exhibit transit signatures in three sectors with a period of 25.84 days. We conducted follow-up RV observations using Keck/HIRES as part of the TESS-Keck Survey (TKS), collecting 64 RV measurements of TOI-1386 with the HIRES spectrograph over 2.5 years. Our combined fit of the TOI-1386 photometry and RV data confirm the planetary nature of the detected TESS signal, and provide a mass and radius for planet b of $0.148\pm0.019$ $M_J$ and $0.540\pm0.017$ $R_J$, respectively, marking TOI-1386 b as a warm sub-Saturn planet. Our RV data further reveal an additional outer companion, TOI-1386 c, with an estimated orbital period of 227.6 days and a minimum mass of $0.309\pm0.038$ $M_J$. The dynamical modeling of the system shows that the measured system architecture is long-term stable, although there may be substantial eccentricity oscillations of the inner planet due to the dynamical influence of the outer planet., Comment: Accepted for publication in The Astronomical Journal. 15 pages, 7 figures

Discovering and characterizing exoplanets at the outer edge of the transit method's sensitivity has proven challenging owing to geometric biases and the practical difficulties associated with acquiring long observational baselines. Nonetheless, a sample of giant exoplanets on orbits longer than 100 days has been identified by transit hunting missions. We present long-term Doppler spectroscopy for 11 such systems with observation baselines spanning a few years to a decade. We model these radial velocity observations jointly with transit photometry to provide initial characterizations of these objects and the systems in which they exist. Specifically, we make new precise mass measurements for four long-period giant exoplanets (Kepler-111 c, Kepler-553 c, Kepler-849 b, and PH-2 b), we place new upper limits on mass for four others (Kepler-421 b, KOI-1431.01, Kepler-1513 b, and Kepler-952 b), and we show that several "confirmed" planets are in fact not planetary at all. We present these findings to complement similar efforts focused on closer-in short-period giant planets, and with the hope of inspiring future dedicated studies of cool giant exoplanets., Comment: 35 pages, 24 figures, 11 tables. Accepted for publication in ApJ Supplement

We present the mid-infrared (5-12 $\mu$m) phase curve of GJ 367b observed by the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). GJ 367b is a hot (T_eq=1370 K), extremely dense (10.2 +- 1.3 g/cm^3) sub-Earth orbiting a M dwarf on a 0.32 d orbit. We measure an eclipse depth of 79 +- 4 ppm, a nightside planet-to-star flux ratio of 4 +- 8 ppm, and a relative phase amplitude of 0.97 +- 0.10 -- all fully consistent with a zero-albedo planet with no heat recirculation. Su ch a scenario is also consistent with the phase offset of 11 +- 5 degrees East to within 2.2$\sigma$. The emission spectrum is likewise consistent with a blackbody with no heat redistribution and a low albedo of A_B ~ 0.1, with the exception of one anomalous wavelength bin that we attribute to unexplained systematics. The emission spectrum puts few constraints on the surface composition, but rules out a CO2 atmosphere >~ 1 bar, an outgassed atmosphere >~10 mbar (under heavily reducing conditions), or an outgassed atmosphere >~0.01 mbar (under heavily oxidizing conditions). The lack of day-night heat recirculation implies that 1 bar atmospheres are ruled out for a wide range of compositions, while 0.1 bar atmospheres are consistent with the data. Taken together with the fact that most of the dayside should be molten, our JWST observations suggest the planet must have lost the vast majority of its initial inventory of volatiles., Comment: Published by ApJL

We present a radial velocity (RV) analysis of TOI-1136, a bright TESS system with six confirmed transiting planets, and a seventh single-transiting planet candidate. All planets in the system are amenable to transmission spectroscopy, making TOI-1136 one of the best targets for intra-system comparison of exoplanet atmospheres. TOI-1136 is young ($\sim$ 700 Myr), and the system exhibits transit timing variations (TTVs). The youth of the system contributes to high stellar variability on the order of 50 m s$^{-1}$, much larger than the likely RV amplitude of any of the transiting exoplanets. Utilizing 359 HIRES and APF RVs collected as a part of the TESS-Keck Survey (TKS), and 51 HARPS-N RVs, we experiment with a joint TTV-RV fit. With seven possible transiting planets, TTVs, more than 400 RVs, and a stellar activity model, we posit that we may be presenting the most complex mass recovery of an exoplanet system in the literature to date. By combining TTVs and RVs, we minimized GP overfitting and retrieved new masses for this system: (m$_{b-g}$ = 3.50$^{+0.8}_{-0.7}$, 6.32$^{+1.1}_{-1.3}$, 8.35$^{+1.8}_{-1.6}$, 6.07$^{+1.09}_{-1.01}$, 9.7$^{+3.9}_{-3.7}$, 5.6$^{+4.1}_{-3.2}$ M$_{\oplus}$). We are unable to significantly detect the mass of the seventh planet candidate in the RVs, but we are able to loosely constrain a possible orbital period near 80 days. Future TESS observations might confirm the existence of a seventh planet in the system, better constrain the masses and orbital properties of the known exoplanets, and generally shine light on this scientifically interesting system., Comment: Accepted for publication in the Astronomical Journal

M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similar $T_{\rm eff}\sim2300-2800~K$. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution ($R\sim35,000$) $K$ band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find $M_B=88.0_{-3.2}^{+3.4}$ $M_{\rm Jup}$, putting HIP 55507 B above the stellar-substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with $a=38^{+4}_{-3}$ AU and $e=0.40\pm0.04$. From atmospheric retrievals of HIP 55507 B, we measure $\rm [C/H]=0.24\pm0.13$, $\rm [O/H]=0.15\pm0.13$, and $\rm C/O=0.67\pm0.04$. Moreover, we strongly detect $\rm ^{13}CO$ ($7.8\sigma$ significance) and tentatively detect $\rm H_2^{18}O$ ($3.7\sigma$ significance) in companion's atmosphere, and measure $\rm ^{12}CO/^{13}CO=98_{-22}^{+28}$ and $\rm H_2^{16}O/H_2^{18}O=240_{-80}^{+145}$ after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure $\rm ^{12}CO/^{13}CO=79_{-16}^{+21}$ and $\rm C^{16}O/C^{18}O=288_{-70}^{+125}$ for the primary star. These results demonstrate that HIP 55507 A and B have consistent $\rm ^{12} C/^{13}C$ and $\rm ^{16}O/^{18}O$ to the $<1\sigma$ level, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young, substellar companions, our results open the door to systematically measuring $\rm ^{13}CO$ and $\rm H_2^{18}O$ abundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types., Comment: Accepted to ApJ, 28 pages, 14 figures