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Interior compositions are key for our understanding of Earth-like exoplanets. The composition of the core can influence the presence of a magnetic dynamo and the strength of gravity on the planetary surface, both of which heavily impact thermal and possible biological processes and thus the habitability for life and its evolution on the planet. However, detailed measurements of the planetary interiors are extremely challenging for small exoplanets, and existing data suggest a wide diversity in planet compositions. Hitherto, only certain photospheric chemical abundances of the host stars have been considered as tracers to explain the diversity of exoplanet compositions. Here we present a homogeneous analysis of stars hosting rocky exoplanets, with ages between 2 and 14 Gyr, revealing a correlation between rocky exoplanet compositions and the ages of the planetary systems. Denser rocky planets are found around younger stars. This suggests that the compositional diversity of rocky exoplanets can be linked to the ages of their host stars. We interpret this to be a result of chemical evolution of stars in the Milky Way, which modifies the material out of which stars and planets form. The results imply that rocky planets which form today, at similar galactocentric radii, may have different formation conditions, and thus different properties than planets which formed several billion years ago, such as the Earth.

Identifying and removing binary stars from stellar samples is a crucial but complicated task. Regardless of how carefully a sample is selected, some binaries will remain and complicate interpretation of results, especially via flux contamination of survey photometry. One such sample is the data from the Gaia spacecraft, which is collecting photometry and astrometry of more than $10^{9}$ stars. To quantify the impact of binaries on Gaia photometry, we assembled a sample of known binary stars observed with adaptive optics and with accurately measured parameters, which we used to predict Gaia photometry for each stellar component. We compared the predicted photometry to the actual Gaia photometry for each system, and found that the contamination of Gaia photometry because of multiplicity decreases non-linearly from near-complete contamination ($\rho \leq 0''.15$) to no contamination (binary projected separation, or $\rho > 0''.3$). We provide an analytic relation to analytically correct photometric bias in a sample of Gaia stars using the binary separation. This correction is necessary because the Gaia PSF photometry extraction does not fully remove the secondary star flux for binaries with separations with $\rho \lesssim 0''.3$. We also evaluated the utility of various Gaia quality-of-fit metrics for identifying binary stars and found that RUWE remains the best indicator for unresolved binaries, but multi-peak image fraction probes a separation regime not currently accessible to RUWE., Comment: 12 pages, 6 figures, 2 tables. Accepted to AJ

Very metal-poor stars ([Fe/H]<-2) are important laboratories for testing stellar models and reconstructing the formation history of our galaxy. Asteroseismology is a powerful tool to probe stellar interiors and measure ages, but few asteroseismic detections are known in very metal-poor stars and none have allowed detailed modeling of oscillation frequencies. We report the discovery of a low-luminosity Kepler red giant (KIC 8144907) with high S/N oscillations, [Fe/H]=-2.66+/-0.08 and [alpha/Fe]=0.38+/-0.06, making it by far the most metal-poor star to date for which detailed asteroseismic modeling is possible. By combining the oscillation spectrum from Kepler with high-resolution spectroscopy we measure an asteroseismic mass and age of 0.79+/-0.02(ran)+/-0.01(sys) Msun and 12.0+/-0.6(ran)+/-0.4(sys) Gyr, with remarkable agreement across different codes and input physics, demonstrating that stellar models and asteroseismology are reliable for very metal-poor stars when individual frequencies are used. The results also provide a direct age anchor for the early formation of the Milky Way, implying that substantial star formation did not commence until redshift z~3 (if the star formed in-situ) or that the Milky Way has undergone merger events for at least ~12 Gyr (if the star was accreted by a dwarf satellite merger such as Gaia Enceladus)., Comment: 10 pages, 4 figures, accepted for publication in ApJ

Small planets ($R_{p} \leq 4 R_{\oplus}$) are divided into rocky super-Earths and gaseous sub-Neptunes separated by a radius gap, but the mechanisms that produce these distinct planet populations remain unclear. Binary stars are the only main-sequence systems with an observable record of the protoplanetary disk lifetime and mass reservoir, and the demographics of planets in binaries may provide insights into planet formation and evolution. To investigate the radius distribution of planets in binary star systems, we observed 207 binary systems hosting 283 confirmed and candidate transiting planets detected by the Kepler mission, then recharacterized the planets while accounting for the observational biases introduced by the secondary star. We found that the population of planets in close binaries ($\rho \leq 100$ au) is significantly different from the planet population in wider binaries ($\rho > 300$ au) or single stars. In contrast to planets around single stars, planets in close binaries appear to have a unimodal radius distribution with a peak near the expected super-Earth peak of $R_{p} \sim 1.3 R_{\oplus}$ and a suppressed population of sub-Neptunes. We conclude that we are observing the direct impact of a reduced disk lifetime, smaller mass reservoir, and possible altered distribution of solids reducing the sub-Neptune formation efficiency. Our results demonstrate the power of binary stars as a laboratory for exploring planet formation and as a controlled experiment of the impact of varied initial conditions on mature planet populations., Comment: 19 pages, 9 figures, 6 tables. Accepted to AJ. Full tables available upon request to the first author prior to publication

The exquisite angular resolution and sensitivity of JWST is opening a new window for our understanding of the Universe. In nearby galaxies, JWST observations are revolutionizing our understanding of the first phases of star formation and the dusty interstellar medium. Nineteen local galaxies spanning a range of properties and morphologies across the star-forming main sequence have been observed as part of the PHANGS-JWST Cycle 1 Treasury program at spatial scales of $\sim$5-50pc. Here, we describe pjpipe, an image processing pipeline developed for the PHANGS-JWST program that wraps around and extends the official JWST pipeline. We release this pipeline to the community as it contains a number of tools generally useful for JWST NIRCam and MIRI observations. Particularly for extended sources, pjpipe products provide significant improvements over mosaics from the MAST archive in terms of removing instrumental noise in NIRCam data, background flux matching, and calibration of relative and absolute astrometry. We show that slightly smoothing F2100W MIRI data to 0.9" (degrading the resolution by about 30 percent) reduces the noise by a factor of $\approx$3. We also present the first public release (DR1.1.0) of the pjpipe processed eight-band 2-21 $\mu$m imaging for all nineteen galaxies in the PHANGS-JWST Cycle 1 Treasury program. An additional 55 galaxies will soon follow from a new PHANGS-JWST Cycle 2 Treasury program., Comment: 49 pages (27 in Appendices), 54 Figures (39 in Appendices), 3 Tables. Accepted for publication in ApJS. Updated to match accepted version. Data available at https://archive.stsci.edu/hlsp/phangs/phangs-jwst

We report the detection and validation of two planets orbiting TOI-2095 (TIC 235678745). The host star is a 3700K M1V dwarf with a high proper motion. The star lies at a distance of 42 pc in a sparsely populated portion of the sky and is bright in the infrared (K=9). With data from 24 Sectors of observation during TESS's Cycles 2 and 4, TOI-2095 exhibits two sets of transits associated with super-Earth-sized planets. The planets have orbital periods of 17.7 days and 28.2 days and radii of 1.30 and 1.39 Earth radii, respectively. Archival data, preliminary follow-up observations, and vetting analyses support the planetary interpretation of the detected transit signals. The pair of planets have estimated equilibrium temperatures of approximately 400 K, with stellar insolations of 3.23 and 1.73 times that of Earth, placing them in the Venus zone. The planets also lie in a radius regime signaling the transition between rock-dominated and volatile-rich compositions. They are thus prime targets for follow-up mass measurements to better understand the properties of warm, transition radius planets. The relatively long orbital periods of these two planets provide crucial data that can help shed light on the processes that shape the composition of small planets orbiting M dwarfs., Comment: Submitted to AAS Journals

Binary stars are ubiquitous; the majority of solar-type stars exist in binaries. Exoplanet occurrence rate is suppressed in binaries, but some multiples do still host planets. Binaries cause observational biases in planet parameters, with undetected multiplicity causing transiting planets to appear smaller than they truly are. We have analyzed the properties of a sample of 119 planet-host binary stars from the Kepler mission to study the underlying population of planets in binaries that fall in and around the radius valley, which is a demographic feature in period-radius space that marks the transition from predominantly rocky to predominantly gaseous planets. We found no statistically significant evidence for a radius gap for our sample of 122 planets in binaries when assuming the primary stars are the planet hosts, with a low probability ($p < 0.05$) of the binary planet sample radius distribution being consistent with the single-star small planet population via an Anderson-Darling test. These results reveal demographic differences in the planet size distribution between planets in binary and single stars for the first time, showing that stellar multiplicity may fundamentally alter the planet formation process. A larger sample and further assessment of circumprimary versus circumsecondary transits is needed to either validate this non-detection or explore other scenarios, such as a radius gap with a location that is dependent on binary separation., Comment: 18 pages, 6 figures, 4 tables, with full-length tables available in the supplemental files. Accepted to AJ

The dearth of planets with sizes around 1.8 $\mathrm{R_\oplus}$ is a key demographic feature discovered by the $Kepler$ mission. Two theories have emerged as potential explanations for this valley: photoevaporation and core-powered mass-loss. However, Rogers et al. (2021) shows that differentiating between the two theories is possible using the three-dimensional parameter space of planet radius, incident flux, and stellar mass. We use homogeneously-derived stellar and planetary parameters to measure the $Kepler$ exoplanet radius gap in this three-dimensional space. We compute the slope of the gap as a function of incident flux at constant stellar mass ($\alpha$ $\equiv$ $\left(\partial \log R_{\mathrm{gap}} / \partial \log S \right)_{M_\star}$) and the slope of the gap as a function of stellar mass at constant incident flux ($\beta$ $\equiv$ $\left(\partial \log R_{\mathrm{gap}} / \partial \log M_\star \right)_{S}$) and find $\alpha$ = 0.069$^{+0.019}_{-0.023}$ and $\beta$ = $-$0.046$^{+0.125}_{-0.117}$. Given that Rogers et al. (2021) shows that core-powered mass-loss predicts $\alpha$ $\approx$ 0.08 and $\beta$ $\approx$ 0.00 while photoevaporation predicts $\alpha$ $\approx$ 0.12 and $\beta$ $\approx$ --0.17, our measurements are more consistent with core-powered mass-loss than photoevaporation. However, we caution that different gap-determination methods can produce systematic offsets in both $\alpha$ and $\beta$; therefore, we motivate a comprehensive re-analysis of $Kepler$ light curves with modern, updated priors on eccentricity and mean stellar density to improve both the accuracy and precision of planet radii and subsequent measurements of the gap., Comment: 10 pages, 4 figures. Submitted to ApJL

We present the first homogeneous catalog of $Kepler$, $K2$, and $TESS$ host stars and the corresponding catalog of exoplanet properties, which contain 7993 stars and 9324 planets, respectively. We used isochrone fitting and $Gaia$ DR3 photometry, parallaxes, and spectrophotometric metallicities to compute precise, homogeneous $T_{\mathrm{eff}}$, $\log g$, masses, radii, mean stellar densities, luminosities, ages, distances, and V-band extinctions for 3248, 565, and 4180 $Kepler$, $K2$, and $TESS$ stars, respectively. We compared our stellar properties to studies using fundamental and precise constraints, such as interferometry and asteroseismology, and find residual scatters of 2.8%, 5.6%, 5.0%, and 31%, with offsets of 0.2%, 1.0%, 1.2%, and 0.7% between our $T_{\mathrm{eff}}$, radii, masses, and ages and those in the literature, respectively. In addition, we compute planet radii, semimajor axes, and incident fluxes for 4281, 676, and 4367 $Kepler$, $K2$, and $TESS$ planets, respectively, and find that the exoplanet radius gap is less prominent in the $K2$, $TESS$, and combined samples than it is in the $Kepler$ sample alone. We suspect this difference is largely due to heterogeneous planet-to-star radius ratios, shorter time baselines of $K2$ and $TESS$, and smaller sample sizes. Finally, we identify a clear radius inflation trend in our large sample of hot Jupiters and find 150 hot sub-Neptunian desert planets, in addition to a population of over 400 young host stars as potential opportunities for testing theories of planet formation and evolution., Comment: 18 pages, 13 figures, and 5 tables. Tables 2, 4, and 5 are included as ancillary files in the sidebar. Submitted to AJ

Dynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planets. Multi-star systems are excellent environments to search for such abundance trends because stellar companions form from the same natal gas cloud and are thus expected to share primordial chemical compositions to within 0.03$-$0.05 dex. Abundance measurements have occasionally yielded rocky enhancements, but few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multi-star systems where at least one star is a known planet host. We found that only HAT-P-4 exhibits an abundance pattern suggestive of engulfment, but is more likely primordial based on its large projected separation (30,000 $\pm$ 140 AU) that exceeds typical turbulence scales in molecular clouds. To understand the lack of engulfment detections among our systems, we quantified the strength and duration of refractory enrichments in stellar photospheres using MESA stellar models. We found that observable signatures from 10 $M_{\oplus}$ engulfment events last for $\sim$90 Myr in 1 $M_{\odot}$ stars. Signatures are largest and longest lived for 1.1$-$1.2 $M_{\odot}$ stars, but are no longer observable $\sim$2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old., Comment: 15 pages, 12 figures; submitted to MNRAS

Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium to magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet host stars observed by $Kepler$. We find that the [Y/Mg] "Clock" is most precise for solar twins, with a [Y/Mg]/Age slope of $m$ = $-$0.0370 $\pm$ 0.0071 dex/Gyr and $\sigma_{\mathrm{Age}}$ = 2.6 Gyr. We attribute the lower precision compared to literature results to non-solar twins contaminating our solar twin sample and recommend a 1.5 Gyr systematic uncertainty for stellar ages derived with any [Y/Mg]-Age relation. We also analyzed the [Y/Mg] Clock as a function of $T_{\mathrm{eff}}$, $\log g$, and metallicity individually and find no strong trends, but compute statistically significant [Y/Mg]-Age relations for subsamples defined by ranges in $T_{\mathrm{eff}}$, $\log g$, and metallicity. Finally, we compare [Y/Mg] and rotation ages and find statistically similar trends as for isochrone ages, although we find that rotation ages perform better for GK dwarfs while isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock is most precise for solar twins and analogs but is also a useful age diagnostic for FGK stars., Comment: 18 pages, 13 figures, 2 tables. Accepted by ApJ

Hot Jupiters are generally observed to lack close planetary companions, a trend that has been interpreted as evidence for high-eccentricity migration. We present the discovery and validation of WASP-132 c (TOI-822.02), a 1.85 $\pm$ 0.10 $R_{\oplus}$ planet on a 1.01 day orbit interior to the hot Jupiter WASP-132 b. Transiting Exoplanet Survey Satellite (TESS) and ground-based follow-up observations, in conjunction with vetting and validation analysis, enable us to rule out common astrophysical false positives and validate the observed transit signal produced by WASP-132 c as a planet. Running the validation tools \texttt{vespa} and \texttt{triceratops} on this signal yield false positive probabilities of $9.02 \times 10^{-5}$ and 0.0107, respectively. Analysis of archival CORALIE radial velocity data leads to a 3$\sigma$ upper limit of 28.23 ms$^{-1}$ on the amplitude of any 1.01-day signal, corresponding to a 3$\sigma$ upper mass limit of 37.35 $M_{\oplus}$. Dynamical simulations reveal that the system is stable within the 3$\sigma$ uncertainties on planetary and orbital parameters for timescales of $\sim$100 Myr. The existence of a planetary companion near the hot Jupiter WASP-132 b makes the giant planet's formation and evolution via high-eccentricity migration highly unlikely. Being one of just a handful of nearby planetary companions to hot Jupiters, WASP-132 c carries with it significant implications for the formation of the system and hot Jupiters as a population., Comment: 19 pages, 8 figures, Accepted for publication in AJ

Stellar rotation is a complex function of mass, metallicity, and age and can be altered by binarity. To understand the importance of these parameters in main sequence stars, we have assembled a sample of observations that spans a range of these parameters using a combination of observations from The Transiting Exoplanet Survey Satellite (TESS) and the Kepler Space Telescope. We find that while we can measure rotation periods and identify other classes of stellar variability (e.g., pulsations) from TESS lightcurves, instrument systematics prevent the detection of rotation signals longer than the TESS orbital period of 13.7 days. Due to this detection limit, we also utilize rotation periods constrained using rotational velocities measured by the APOGEE spectroscopic survey and radii estimated using the Gaia mission for both TESS and Kepler stars. From these rotation periods, we 1) find we can track rotational evolution along discrete mass tracks as a function of stellar age, 2) find we are unable to recover trends between rotation and metallicity that were observed by previous studies, and 3) note that our sample reveals that wide binary companions do not affect rotation, while close binary companions cause stars to exhibit more rapid rotation than single stars., Comment: 19 pages, 13 figures, Accepted for publication in the Astrophysical Journal

The unexpectedly large radii of hot Jupiters are a longstanding mystery whose solution will provide important insights into their interior physics. Many potential solutions have been suggested, which make diverse predictions about the details of inflation. In particular, although any valid model must allow for maintaining large planetary radii, only some allow for radii to increase with time. This reinflation process would potentially occur when the incident flux on the planet is increased. In this work, we examine the observed population of hot Jupiters to see if they grow as their parent stars brighten along the main sequence. We consider the relation between radius and other observables, including mass, incident flux, age, and fractional age (age over main sequence lifetime), and show that main sequence brightening is often sufficient to produce detectable reinflation. We further argue that these provide strong evidence for the relatively rapid reinflation of giant planets, and discuss the implications for proposed heating mechanisms. In our population analysis we also find evidence for a "delayed-cooling effect", wherein planets cool and contract far more slowly than expected. While not capable of explaining the observed radii alone, it may represent an important component of the effect. Finally, we identify a weak negative relationship between stellar metallicity and planet radius which is presumably the result of enhanced planetary bulk metallicity around metal-rich stars and has important implications for planet formation theory., Comment: 10 pages, 3 figures, 1 table. Revision improves clarity, but scientific results are unchanged. Accepted to The Astrophysical Journal Letters

The Kepler Mission revolutionized exoplanet science and stellar astrophysics by obtaining highly precise photometry of over 200,000 stars over 4 years. A critical piece of information to exploit Kepler data is its selection function, since all targets had to be selected from a sample of half a million stars on the Kepler CCDs using limited information. Here we use Gaia DR2 to reconstruct the Kepler selection function and explore possible biases with respect to evolutionary state, stellar multiplicity, and kinematics. We find that the Kepler target selection is nearly complete for stars brighter than $Kp < 14$ mag and was effective at selecting main-sequence stars, with the fraction of observed stars decreasing from 95% to 60% between $14 < Kp < 16$ mag. We find that the observed fraction for subgiant stars is only 10% lower, confirming that a significant number of subgiants selected for observation were believed to be main-sequence stars. Conversely we find a strong selection bias against low-luminosity red giant stars ($R \approx 3-5 R_\odot$, $T_{eff} \approx 5500$K), dropping from 90% at $Kp = 14$ mag to below 30% at $Kp = 16$ mag, confirming that the target selection was efficient at distinguishing dwarfs from giants. We compare the Gaia Re-normalized Unit Weight Error (RUWE) values of the observed and non-observed main sequence stars and find a difference in elevated ($>$ 1.2) RUWE values at $\sim\,5\,\sigma$ significance, suggesting that the Kepler target selection shows some bias against either close or wide binaries. We furthermore use the Gaia proper motions to show that the Kepler selection function was unbiased with respect to kinematics., Comment: 15 pages, 11 figures. Submitted to the AAS Astrophysical Journal. Presented at AAS 237

Asteroseismology of bright stars has become increasingly important as a method to determine fundamental properties (in particular ages) of stars. The Kepler Space Telescope initiated a revolution by detecting oscillations in more than 500 main-sequence and subgiant stars. However, most Kepler stars are faint, and therefore have limited constraints from independent methods such as long-baseline interferometry. Here, we present the discovery of solar-like oscillations in $\alpha$ Men A, a naked-eye (V=5.1) G7 dwarf in TESS's Southern Continuous Viewing Zone. Using a combination of astrometry, spectroscopy, and asteroseismology, we precisely characterize the solar analog alpha Men A (Teff = 5569 +/- 62 K, R = 0.960 +/- 0.016 Rsun, M = 0.964 +/- 0.045 Msun). To characterize the fully convective M dwarf companion, we derive empirical relations to estimate mass, radius, and temperature given the absolute Gaia magnitude and metallicity, yielding M = 0.169 +/- 0.006, R = 0.19 +/- 0.01 and Teff = 3054 +/- 44 K. Our asteroseismic age of 6.2 +/- 1.4 (stat) +/- 0.6 (sys) Gyr for the primary places $\alpha$ Men B within a small population of M dwarfs with precisely measured ages. We combined multiple ground-based spectroscopy surveys to reveal an activity cycle of 13.1 +/- 1.1 years, a period similar to that observed in the Sun. We used different gyrochronology models with the asteroseismic age to estimate a rotation period of ~30 days for the primary. Alpha Men A is now the closest (d=10pc) solar analog with a precise asteroseismic age from space-based photometry, making it a prime target for next-generation direct imaging missions searching for true Earth analogs., Comment: Accepted to The Astrophysical Journal; 15 pages, 10 figures

We present occurrence rates for rocky planets in the habitable zones (HZ) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define $\eta_\oplus$ as the HZ occurrence of planets with radius between 0.5 and 1.5 $R_\oplus$ orbiting stars with effective temperatures between 4800 K and 6300 K. We find that $\eta_\oplus$ for the conservative HZ is between $0.37^{+0.48}_{-0.21}$ (errors reflect 68\% credible intervals) and $0.60^{+0.90}_{-0.36}$ planets per star, while the optimistic HZ occurrence is between $0.58^{+0.73}_{-0.33}$ and $0.88^{+1.28}_{-0.51}$ planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates using both a Poisson likelihood Bayesian analysis and Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with $95\%$ confidence that, on average, the nearest HZ planet around G and K dwarfs is about 6 pc away, and there are about 4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun., Comment: To appear in The Astronomical Journal

Studies of exoplanet demographics require large samples and precise constraints on exoplanet host stars. Using the homogeneous Kepler stellar properties derived using Gaia Data Release 2 by Berger et al. (2020), we re-compute Kepler planet radii and incident fluxes and investigate their distributions with stellar mass and age. We measure the stellar mass dependence of the planet radius valley to be $d \log R_{\mathrm{p}}$/$d \log M_\star = 0.26^{+0.21}_{-0.16}$, consistent with the slope predicted by a planet mass dependence on stellar mass ($0.24-0.35$) and core-powered mass-loss (0.33). We also find first evidence of a stellar age dependence of the planet populations straddling the radius valley. Specifically, we determine that the fraction of super-Earths ($1-1.8 \mathrm{R_\oplus}$) to sub-Neptunes ($1.8-3.5 \mathrm{R_\oplus}$) increases from $0.61 \pm 0.09$ at young ages (< 1 Gyr) to $1.00 \pm 0.10$ at old ages (> 1 Gyr), consistent with the prediction by core-powered mass-loss that the mechanism shaping the radius valley operates over Gyr timescales. Additionally, we find a tentative decrease in the radii of relatively cool ($F_{\mathrm{p}} < 150 \mathrm{F_\oplus}$) sub-Neptunes over Gyr timescales, which suggests that these planets may possess H/He envelopes instead of higher mean molecular weight atmospheres. We confirm the existence of planets within the hot sub-Neptunian "desert" ($2.2 < R_{\mathrm{p}} < 3.8 \mathrm{R_\oplus}$, $F_{\mathrm{p}} > 650 \mathrm{F_\oplus}$) and show that these planets are preferentially orbiting more evolved stars compared to other planets at similar incident fluxes. In addition, we identify candidates for cool ($F_{\mathrm{p}} < 20 \mathrm{F_\oplus}$) inflated Jupiters, present a revised list of habitable zone candidates, and find that the ages of single- and multiple-transiting planet systems are statistically indistinguishable., Comment: 22 pages, 13 figures, 1 table. Accepted by AJ. The electronic version of Table 1 is available as an ancillary file (sidebar on the right). For a brief video explaining this paper, see https://youtu.be/d42ffDq1D94

The rotational evolution of cool dwarfs is poorly constrained after around 1-2 Gyr due to a lack of precise ages and rotation periods for old main-sequence stars. In this work we use velocity dispersion as an age proxy to reveal the temperature-dependent rotational evolution of low-mass Kepler dwarfs, and demonstrate that kinematic ages could be a useful tool for calibrating gyrochronology in the future. We find that a linear gyrochronology model, calibrated to fit the period-Teff relationship of the Praesepe cluster, does not apply to stars older than around 1 Gyr. Although late-K dwarfs spin more slowly than early-K dwarfs when they are young, at old ages we find that late-K dwarfs rotate at the same rate or faster than early-K dwarfs of the same age. This result agrees qualitatively with semi-empirical models that vary the rate of surface-to-core angular momentum transport as a function of time and mass. It also aligns with recent observations of stars in the NGC 6811 cluster, which indicate that the surface rotation rates of K dwarfs go through an epoch of inhibited evolution. We find that the oldest Kepler stars with measured rotation periods are late-K and early-M dwarfs, indicating that these stars maintain spotted surfaces and stay magnetically active longer than more massive stars. Finally, based on their kinematics, we confirm that many rapidly rotating GKM dwarfs are likely to be synchronized binaries., Comment: Accepted for publication in the Astronomical Journal

An accurate and precise Kepler Stellar Properties Catalog is essential for the interpretation of the Kepler exoplanet survey results. Previous Kepler Stellar Properties Catalogs have focused on reporting the best-available parameters for each star, but this has required combining data from a variety of heterogeneous sources. We present the Gaia-Kepler Stellar Properties Catalog, a set of stellar properties of 186,301 Kepler stars, homogeneously derived from isochrones and broadband photometry, Gaia Data Release 2 parallaxes, and spectroscopic metallicities, where available. Our photometric effective temperatures, derived from $g-K_s$ colors, are calibrated on stars with interferometric angular diameters. Median catalog uncertainties are 112 K for $T_{\mathrm{eff}}$, 0.05 dex for $\log g$, 4% for $R_\star$, 7% for $M_\star$, 13% for $\rho_\star$, 10% for $L_\star$, and 56% for stellar age. These precise constraints on stellar properties for this sample of stars will allow unprecedented investigations into trends in stellar and exoplanet properties as a function of stellar mass and age. In addition, our homogeneous parameter determinations will permit more accurate calculations of planet occurrence and trends with stellar properties., Comment: 22 pages, 13 figures, 2 tables. Published in AJ. Electronic versions of Tables 1 & 2 are now, in this submission, included as ancillary files (sidebar on the right)

We analyze the full $\mathit{Kepler}$ phase curve of KOI-964, a binary system consisting of a hot white dwarf on an eclipsing orbit around an A-type host star. Using all 18 quarters of long-cadence photometry, we carry out a joint light curve fit and obtain improved phase curve amplitudes, occultation depths, orbital parameters, and transit ephemeris over the previous results of Carter et al. 2011. A periodogram of the residuals from the phase curve fit reveals an additional stellar variability signal from the host star with a characteristic period of $0.620276\pm0.000011$ days and a full amplitude of $24\pm2$ ppm. We also present new Keck/HIRES radial velocity observations which we use to measure the orbit and obtain a mass ratio of $q=0.106\pm0.012$. Combining this measurement with the results of a stellar isochrone analysis, we find that the masses of the host star and white dwarf companion are $2.23\pm0.12\,M_{\odot}$ and $0.236^{+0.028}_{-0.027}\,M_{\odot}$, respectively. The effective temperatures of the two components are $9940^{+260}_{-230}$ K and $15080\pm400$ K, respectively, and we determine the age of the system to be $0.21^{+0.11}_{-0.08}$ Gyr. We use the measured system properties to compute predicted phase curve amplitudes and find that while the measured Doppler boosting and mutual illumination components agree well with theory, the ellipsoidal distortion amplitude is significantly underestimated. We detail possible explanations for this discrepancy, including interactions between the dynamical tide of the host star and the tidal bulge and possible non-synchronous rotation of the host star., Comment: Accepted for publication in AJ, 18 pages, 5 figures

We infer the number of planets-per-star as a function of orbital period and planet size using $Kepler$ archival data products with updated stellar properties from the $Gaia$ Data Release 2. Using hierarchical Bayesian modeling and Hamiltonian Monte Carlo, we incorporate planet radius uncertainties into an inhomogeneous Poisson point process model. We demonstrate that this model captures the general features of the outcome of the planet formation and evolution around GK stars, and provides an infrastructure to use the $Kepler$ results to constrain analytic planet distribution models. We report an increased mean and variance in the marginal posterior distributions for the number of planets per $GK$ star when including planet radius measurement uncertainties. We estimate the number of planets-per-$GK$ star between 0.75 and 2.5 $R_{\oplus}$ and 50 to 300 day orbital periods to have a $68\%$ credible interval of $0.49$ to $0.77$ and a posterior mean of $0.63$. This posterior has a smaller mean and a larger variance than the occurrence rate calculated in this work and in Burke et al. (2015) for the same parameter space using the $Q1-Q16$ (previous $Kepler$ planet candidate and stellar catalog). We attribute the smaller mean to many of the instrumental false positives at longer orbital periods being removed from the $DR25$ catalog. We find that the accuracy and precision of our hierarchical Bayesian model posterior distributions are less sensitive to the total number of planets in the sample, and more so on the characteristics of the catalog completeness and reliability and the span of the planet parameter space., Comment: 16 pages, 3 figures, published in the Astrophysical Journal

The radii and orbital periods of 4000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. The radii show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) and larger intermediate-size planets, respectively. While only the masses of the planets orbiting the brightest stars can be determined by ground-based spectroscopic observations, these observations allow calculation of their average densities placing constraints on the bulk compositions and internal structures. Yet an important question about the composition of planets ranging from 2 to 4 Earth radii still remains. They may either have a rocky core enveloped in a H2-He gaseous envelope (gas dwarfs) or contain a significant amount of multi-component, H2O-dominated ices/fluids (water worlds). Planets in the mass range of 10-15 Earth masses, if half-ice and half-rock by mass, have radii of 2.5 Earth radii, which exactly match the second peak of the exoplanet radius bimodal distribution. Any planet in the 2-4 Earth radii range requires a gas envelope of at most a few mass percentage points, regardless of the core composition. To resolve the ambiguity of internal compositions, we use a growth model and conduct Monte Carlo simulations to demonstrate that many intermediate-size planets are water worlds., Comment: PNAS link: https://www.pnas.org/content/116/20/9723 Complete data and mass-radius tables are available at: https://www.cfa.harvard.edu/~lzeng/planetmodels.html

Exoplanet catalogs produced by surveys suffer from a lack of completeness (not every planet is detected) and less than perfect reliability (not every planet in the catalog is a true planet), particularly near the survey's detection limit. Exoplanet occurrence rate studies based on such a catalog must be corrected for completeness and reliability. The final Kepler data release, DR25, features a uniformly vetted planet candidate catalog and data products that facilitate corrections. We present a new probabilistic approach to the characterization of Kepler completeness and reliability, making full use of the Kepler DR25 products. We illustrate the impact of completeness and reliability corrections with a Poisson-likelihood occurrence rate method, using a recent stellar properties catalog that incorporates Gaia stellar radii and essentially uniform treatment of the stellar population. Correcting for reliability has a significant impact: the exoplanet occurrence rate for orbital period and radius within 20% of Earth's around GK dwarf stars, corrected for reliability, is 0.015+0.011-0.007, whereas not correcting results in 0.034+0.018-0.012 - correcting for reliability reduces this occurrence rate by more than a factor of two. We further show that using Gaia-based vs. DR25 stellar properties impacts the same occurrence rate by a factor of two. We critically examine the the DR25 catalog and the assumptions behind our occurrence rate method. We propose several ways in which confidence in both the Kepler catalog and occurrence rate calculations can be improved. This work provides an example of how the community can use the DR25 completeness and reliability products., Comment: Accepted for publication in The Astronomical Journal

The discovery of thousands of planetary systems by Kepler has demonstrated that planets are ubiquitous. However, a major challenge has been the confirmation of Kepler planet candidates, many of which still await confirmation. One of the most enigmatic examples is KOI 4.01, Kepler's first discovered planet candidate detection (as KOI 1.01, 2.01, and 3.01 were known prior to launch). Here we present the confirmation and characterization of KOI 4.01 (now Kepler-1658), using a combination of asteroseismology and radial velocities. Kepler-1658 is a massive, evolved subgiant (Mstar = 1.45 +/- 0.06 Msun, Rstar = 2.89 +/- 0.12 Rsun) hosting a massive (Mp = 5.88 +/- 0.47 MJ, Rp = 1.07 +/- 0.05 RJ) hot Jupiter that orbits every 3.85 days. Kepler-1658 joins a small population of evolved hosts with short-period (<=100 days) planets and is now the closest known planet in terms of orbital period to an evolved star. Because of its uniqueness and short orbital period, Kepler-1658 is a new benchmark system for testing tidal dissipation and hot Jupiter formation theories. Using all 4 years of Kepler data, we constrain the orbital decay rate to be Pdot <= -0.42 s/yr, corresponding to a strong observational limit of Qstar >= 4.826 x 10^3 for the tidal quality factor in evolved stars. With an effective temperature Teff ~6200 K, Kepler-1658 sits close to the spin-orbit misalignment boundary at ~6250 K, making it a prime target for follow-up observations to better constrain its obliquity and to provide insight into theories for hot Jupiter formation and migration., Comment: 18 pages, 11 figures, 5 tables; accepted for publication in AJ

We present the spectral analysis of 21 blue supergiant stars of spectral type late B to early A within the Local Group dwarf galaxy IC 1613 based on VLT-FORS2 low resolution spectra. Combining our results with studies of early B type blue supergiants we report a wide bi-modal distribution of metallicities with two peaks around [Z] $\sim -0.50$ dex and [Z] $\sim -0.85$ dex. The bi-modal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [Z] objects appear in regions of relatively high ISM HI column densities or close to them, the high [Z] supergiants are found in the central HI hole almost devoid of hydrogen. This suggests varied chemical evolution histories of the young stellar populations in IC 1613. Utilizing the Flux-Weighted Gravity-Luminosity Relation (FGLR), we determine IC 1613's distance modulus as $m - M$ = 24.39 $\pm$ 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period-luminosity relationship of Cepheids and the tip of the red giant branch., Comment: 12 pages, 9 figures, 1 table. Accepted for publication in ApJ. For a brief video explaining this paper, see https://youtu.be/hsnU62pYsIQ

One bottleneck for the exploitation of data from the $Kepler$ mission for stellar astrophysics and exoplanet research has been the lack of precise radii and evolutionary states for most of the observed stars. We report revised radii of 177,911 $Kepler$ stars derived by combining parallaxes from $Gaia$ Data Release 2 with the DR25 $Kepler$ Stellar Properties Catalog. The median radius precision is $\approx$ 8%, a typical improvement by a factor of 4-5 over previous estimates for typical $Kepler$ stars. We find that $\approx$ 67% ($\approx$ 120,000) of all $Kepler$ targets are main-sequence stars, $\approx$ 21% ($\approx$ 37,000) are subgiants, and $\approx$ 12% ($\approx$ 21,000) are red giants, demonstrating that subgiant contamination is less severe than some previous estimates and that Kepler targets are mostly main-sequence stars. Using the revised stellar radii, we recalculate the radii for 2123 confirmed and 1922 candidate exoplanets. We confirm the presence of a gap in the radius distribution of small, close-in planets, but find that the gap is mostly limited to incident fluxes $>$ 200$F_\oplus$ and its location may be at a slightly larger radius (closer to $\approx$ 2$R_\oplus$) when compared to previous results. Further, we find several confirmed exoplanets occupying a previously-described "hot super-Earth desert" at high irradiance, show the relation between gas-giant planet radius and incident flux, and establish a bona-fide sample of eight confirmed planets and 30 planet candidates with $R_{\mathrm{p}}$ $<$ 2$R_\oplus$ in circumstellar "habitable zones" (incident fluxes between 0.25--1.50 $F_\oplus$). The results presented here demonstrate the potential for transformative characterization of stellar and exoplanet populations using $Gaia$ data., Comment: 17 pages, 10 figures, 2 tables. Accepted for publication in ApJ. Electronic versions of Tables 1 & 2 are available as ancillary files (sidebar on the right). For a brief video explaining this paper, see https://youtu.be/RmzkKjtaVf4

The lithium doublet at 6708 \AA\ provides an age diagnostic for main sequence FGK dwarfs. We measured the abundance of lithium in 1305 stars with detected transiting planets from the Kepler Mission using high-resolution spectroscopy. Our catalog of lithium measurements from this sample have a range of abundance from A(Li) = 3.11 $\pm$ 0.07 to an upper limit of $-$0.84 dex. For a magnitude-limited sample that comprises 960 of the 1305 stars, our Keck-HIRES spectra have a median S/N = 45 per pixel at $\sim$6700 \AA\ with spectral resolution $\frac{\lambda}{\Delta \lambda}$ = $R$ = 55,000. We identify 80 young stars that have A(Li) values greater than the Hyades at their respective effective temperatures; these stars are younger than $\sim$650 Myr old, the approximate age of the Hyades. We then compare the distribution of A(Li) with planet size, multiplicity, orbital period, and insolation flux. We find larger planets preferentially in younger systems, with an A-D two-sided test p-value = 0.002, a $>3\sigma$ confidence that the older and younger planet samples do not come from the same parent distribution. This is consistent with planet inflation/photoevaporation at early ages. The other planet parameters ($Kepler$ planet multiplicity, orbital period, and insolation flux) are uncorrelated with age., Comment: 22 pages, 15 figures, 3 tables. Accepted for publication in ApJ. For a brief video explaining this paper, see https://youtu.be/TkO-ef28Vao