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 the Gaia Data Release 2 with the DR25 Kepler Stellar Properties Catalog. The median radius precision is 8%, a typical improvement by a factor of 4-5 over previous estimates for typical Kepler stars. We find that 67% ( 120,000) of all Kepler targets are main-sequence stars, 21% ( 37,000) are subgiants, and 12% ( 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 , and its location may be at a slightly larger radius (closer to 2 R⊕) when compared to previous results. Furthermore, we find several confirmed exoplanets occupying a previously described "hot super-Earth desert" at high irradiance, show the relation between a gas-giant planet's radius and its incident flux, and establish a bona fide sample of eight confirmed planets and 30 planet candidates with < 2 R⊕ in circumstellar "habitable zones" (incident fluxes between 0.25 and 1.50 ). The results presented here demonstrate the potential for transformative characterization of stellar and exoplanet populations using Gaia data.
Studies of exoplanet demographics require large samples and precise constraints on exoplanet host stars. Using the homogeneous Kepler stellar properties derived using the Gaia Data Release 2 by ...Berger et al., we recompute 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 / = , 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 the 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 ) to sub-Neptunes (1.8-3.5 ) increases from 0.61 0.09 at young ages (<1 Gyr) to 1.00 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 (Fp < 150 ) 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⊕ < Rp < 3.8 , Fp > 650 ) 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 (Fp < 20 ) 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.
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 colors, are calibrated on stars with interferometric angular diameters. Median catalog uncertainties are 112 K for , 0.05 dex for , 4% for , 7% for , 13% for , 10% for , 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.
The radii and orbital periods of 4,000+ 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. However, an important question about the composition of planets ranging from 2 to 4 Earth radii (R⊕) still remains. They may either have a rocky core enveloped in a H₂–He gaseous envelope (gas dwarfs) or contain a significant amount of multicomponent, H₂O-dominated ices/fluids (water worlds). Planets in the mass range of 10–15 M⊕, if half-ice and half-rock by mass, have radii of 2.5 R⊕, which exactly match the second peak of the exoplanet radius bimodal distribution. Any planet in the 2- to 4-R⊕ 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.”
Abstract
The lithium doublet at 6708 Å 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 has a range of abundance from A(Li) = 3.11 ± 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 signal-to-noise ratio of 45 per pixel at ∼6700 Å with spectral resolution
=
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 ∼650 Myr, 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
σ
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.
Abstract
The Kepler Mission revolutionized exoplanet science and stellar astrophysics by obtaining highly precise photometry of over 200,000 stars over 4 yr. 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
≈ 3–5
R
⊙
,
T
eff
≈ 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 nonobserved main-sequence stars and find a difference in elevated (>1.2) RUWE values at ∼
σ
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.
ABSTRACT
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. Multistar 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 a few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multistar 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 ± 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⊕ engulfment events last for ∼90 Myr in 1 M⊙ stars. Signatures are largest and longest lived for 1.1–1.2 M⊙ stars, but are no longer observable ∼2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old.
Abstract
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 that is presumably the result of enhanced planetary bulk metallicity around metal-rich stars and has important implications for planet formation theory.
Abstract
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 that 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 population of small planets 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 nondetection or explore other scenarios, such as a radius gap with a location that is dependent on binary separation.
Abstract
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 light curves, 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 use 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.
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