We present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0.5 and 16 $R_{\bigoplus}$ and orbital periods between 0.78 and 400 days, orbiting FGK dwarf stars. We base our results on an independent planet catalogue compiled from our search of all ~200,000 stars observed over the Kepler mission, with precise planetary radii supplemented by Gaia DR2-incorporated stellar radii. We take into account detection and vetting efficiency, planet radius uncertainty, and reliability against transit-like noise signals in the data. By analyzing our FGK occurrence rates as well as those computed after separating F-, G-, and K-type stars, we explore dependencies on stellar effective temperature, planet radius, and orbital period. We reveal new characteristics of the photoevaporation-driven "radius gap" between ~1.5 and 2 $R_{\bigoplus}$, indicating that the bimodal distribution previously revealed for $P$ < 100 days exists only over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, we provide several estimates of the "eta-Earth" value -- the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0.75 - 1.5 $R_{\bigoplus}$ orbiting in a conservatively defined habitable zone (0.99 - 1.70 AU) around G-type stars, we place an upper limit (84.1th percentile) of <0.18 planets per star.
Using our K2 Campaign 5 fully automated planet detection data set (43 planets), which has corresponding measures of completeness and reliability, we infer an underlying planet population model for the FGK dwarfs sample (9,257 stars). Implementing a broken power-law for both the period and radius distribution, we find an overall planet occurrence of $1.00^{+1.07}_{-0.51}$ planets per star within a period range of 0.5-38 days. Making similar cuts and running a comparable analysis on the Kepler sample (2,318 planets; 94,222 stars), we find an overall occurrence of $1.10\pm0.05$ planets per star. …
The Kepler mission observed thousands of transiting exoplanet candidates around hundreds of thousands of FGK dwarf stars. He, Ford, & Ragozzine (2019) (arXiv:1907.07773) applied forward modeling to infer the distribution of intrinsic architectures of planetary systems, developed a clustered Poisson point process model for exoplanetary systems (SysSim) to reproduce the marginal distributions of the observed Kepler population, and they showed that orbital periods and planet radii are clustered within a given planetary system. Here, we extend the clustered model to explore correlations between pl…
We characterize the occurrence rate of planets, ranging in size from 0.5-16 R$_\oplus$, orbiting FGK stars with orbital periods from 0.5-500 days. Our analysis is based on results from the "DR25" catalog of planet candidates produced by NASA's Kepler mission and stellar radii from Gaia "DR2". We incorporate additional Kepler data products to accurately characterize the efficiency of planets being recognized as a "threshold crossing events" (TCE) by Kepler's Transiting Planet Search pipeline and labeled as a planet candidate by the robovetter. Using a hierarchical Bayesian model, we derive plan…
We present the results of an independent search of all ~200,000 stars observed over the four year Kepler mission (Q1-Q17) for multiplanet systems, using a three-transit minimum detection criteria to search orbital periods up to hundreds of days. We incorporate both automated and manual triage, and provide estimates of the completeness and reliability of our vetting pipeline. Our search returned 17 planet candidates (PCs) in addition to thousands of known Kepler Objects of Interest (KOIs), with a 98.8% recovery rate of already confirmed planets. We highlight the discovery of one candidate, KIC-…
Observations of exoplanetary systems provide clues about the intrinsic distribution of planetary systems, their architectures, and how they formed. We develop a forward modelling framework for generating populations of planetary systems and "observed" catalogues by simulating the Kepler detection pipeline (SysSim). We compare our simulated catalogues to the Kepler DR25 catalogue of planet candidates, updated to include revised stellar radii from Gaia DR2. We constrain our model based on the observed 1D marginal distributions of orbital periods, period ratios, transit depths, transit depth rati…
Exoplanet Orbital Distribution around FGK Sun-like Host Stars I: planet occurrence rate derived from the Kepler Mission and theoretical interpretations from planet formation
University of Oslo（奥斯陆大学）；Harvard University（哈佛大学）；Natural History Museum, University of Oslo（奥斯陆大学自然历史博物馆）；Konkoly Observatory, HUN-REN CSFK（孔科利天文台，匈牙利研究网络科学院）
The true multiplicity distribution of transiting planet systems is obscured by strong observational biases, leading low-multiplicity systems to be overrepresented in the observed sample. Using the Kepler FGK planet hosts, we employ approximate Bayesian computation to infer the multiplicity distribution by comparing simulated catalogs to the observed one. After comparing a total of ten different multiplicity distributions, half of which were two-population models, to the observed data, we find that a single-population model following a Zipfian distribution is able to explain the Kepler data as …
Architectures of Exoplanetary Systems. IV: A Multi-planet Model for Reproducing the Radius Valley and Intra-system Size Similarity of Planets around Kepler's FGK Dwarfs
This paper aims to derive a map of relative planet occurrence rates that can provide constraints on the overall distribution of terrestrial planets around FGK stars. Based on the planet candidates in the Kepler DR25 data release, I first generate a continuous density map of planet distribution using a Gaussian kernel model and correct the geometric factor that the discovery space of a transit event decreases along with the increase of planetary orbital distance. Then I fit two exponential decay functions of detection efficiency along with the increase of planetary orbital distance and the decr…
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 $σ_{\mathrm{Age}}$ = 2.6 Gyr. We a…
Data from Kepler's first 136 days of operation are analyzed to determine the distribution of exoplanets with respect to radius, period, and host-star spectral type. The analysis is extrapolated to estimate the percentage of terrestrial, habitable-zone exoplanets. The Kepler census is assumed to be complete for bright stars (magnitude <14.0) having transiting planets >0.5 Earth radius and periods <42 days. It is also assumed that the size distribution of planets is independent of orbital period, and that there are no hidden biases in the data. Six significant statistical results are found: ther…
The NASA Kepler mission has revolutionised time-domain astronomy and has massively expanded the number of known extrasolar planets. However, the effect of wide multiplicity on exoplanet occurrence has not been tested with this dataset. We present a sample of 401 wide multiple systems containing at least one Kepler target star. Our method uses Pan-STARRS1 and archival data to produce an accurate proper motion catalogue of the Kepler field. Combined with Pan-STARRS1 SED fits and archival proper motions for bright stars, we use a newly developed probabilistic algorithm to identify likely wide bin…
We examine how the fraction $f$ of stars for which rotational modulation has been detected in Kepler light curves depends on the stellar mass $M_\star$ and age $t_\star$. Our sample consists of $\approx 850$ FGK stars hosting transiting planet candidates detected from the prime Kepler mission. For these stars, atmospheric parameters have been derived using high-resolution spectra from the California-Kepler survey, and rotational modulation has been searched in Kepler light curves homogeneously. We fit stellar models to the atmospheric parameters, Gaia parallax, and 2MASS magnitude of these sta…
We present a statistical study of the planet-metallicity (P-M) correlation, by comparing the 744 stars with candidate planets (SWPs) in the Kepler field which have been observed with LAMOST, and a sample of distance-independent, fake "twin" stars in the Kepler field with no planet reported (CKSNPs) yet. With the well-defined and carefully-selected large samples, we find for the first time a turn-off P-M correlation of Delta [Fe/H]_(SWPs-SNPs), which in average increases from ~0.00+-0.03 dex to 0.06+-0.03 dex, and to 0.12+-0.03 for stars with Earth, Neptune, Jupiter-sized planets successively, …
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 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 Å with spectral resolution $\fracλ{Δλ}$ = $R$ = 55,000. We identify 80 young stars that …
We present robust planet occurrence rates for Kepler planet candidates around M stars for planet radii $R_p = 0.5-4~\textrm{R}_\oplus$ and orbital periods $P = 0.5-256$ days using the approximate Bayesian computation (ABC) technique. This work incorporates the final Kepler DR25 planet candidate catalog and data products and augments them with updated stellar properties using Gaia DR2 and 2MASS PSC. We apply a set of selection criteria to select a sample of 1,746 Kepler M dwarf targets that host 89 associated planet candidates. These early M dwarfs and late K dwarfs were selected from cross-ref…
Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems. To test the accuracy of published limb-darkening models, I have compared limb-darkening profiles predicted by stellar atmosphere models to the limb-darkening profiles measured from high-quality light curves of 43 FGK-type stars in transiting exoplanet systems observed by the Kepler and TESS missions. The comparison is done using the parameters $h^{\prime}_1 = I_λ(\frac{2}{3})$ and $h^{\prime}_2 = h^{\prime}_1 - I_λ(\frac{1}{3})$, …
The planet formation environment around M dwarf stars is different than around G dwarf stars. The longer hot protostellar phase, activity levels and lower protoplanetary disk mass of M dwarfs all may leave imprints on the composition distribution of planets. We use hierarchical Bayesian modeling conditioned on the sample of transiting planets with radial velocity mass measurements to explore small planet mass-radius distributions that depend on host star mass. We find that the current mass-radius dataset is consistent with no host star mass dependence. These models are then applied to the \tex…
Dust in debris disks is produced by colliding or evaporating planetesimals, remnants of the planet formation process. Warm dust disks, known by their emission at < 24 micron, are rare (4% of FGK main sequence stars) and especially interesting because they trace material in the region likely to host terrestrial planets, where the dust has a very short dynamical lifetime. Statistical analyses of the source counts of excesses as found with the mid-IR Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates found for the Kepler transiting-planet host-star candidates can be expl…
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed $\sim$600 transiting exoplanets and exoplanet candidates from \textit{Kepler} (Kepler Objects of Interest, KOIs), most with $\geq$18 epochs. The combined multi-epoch spectra are of high signal-to-noise (typically $\geq$100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars -- the primary \textit{Kepler} host stellar type -- by comparing the ASPCAP-derived stell…
This paper introduces a new method of inferring the intrinsic exoplanet population from Kepler data, based on the assumption that the frequency of exoplanets can be represented by a smooth function of planet radius and period. The method is applied to the two most recent data releases from the Kepler project, q1-16 and q1-17, over the range of periods 0.5 to 512 days, and radii 0.5 to 16 Earth radii. Both of these releases have known biases, with the first believed to contain excess false positives, and the second excess false negatives, so any analysis of them should be viewed with caution. W…
The Kepler Mission is uniquely suited to study the frequencies of extrasolar planets. This goal requires knowledge of the incidence of false positives such as eclipsing binaries in the background of the targets, or physically bound to them, which can mimic the photometric signal of a transiting planet. We perform numerical simulations to predict the occurrence of astrophysical false positives detectable by the Mission, and quantify the fraction of them that would pass the Kepler candidate vetting procedure. By comparing their distribution with that of the Kepler Objects of Interest detected du…
We present a comprehensive catalog of cool (period $P\gtrsim 2\,\mathrm{yr}$) transiting planet candidates in the four-year light curves from the prime \kepler\ mission. Most of the candidates show only one or two transits and have largely been missed in the original Kepler Object of Interest catalog. Our catalog is based on all known such candidates in the literature as well as new candidates from the search in this paper, and provides a resource to explore the planet population near the snow line of Sun-like stars. We homogeneously performed pixel-level vetting, stellar characterization with…
The Kepler planet sample can only be used to reconstruct the underlying planet occurrence rate if the detection efficiency of the Kepler pipeline is known, here we present the results of a second experiment aimed at characterising this detection efficiency. We inject simulated transiting planet signals into the pixel data of ~10,000 targets, spanning one year of observations, and process the pixels as normal. We compare the set of detections made by the pipeline with the expectation from the set of simulated planets, and construct a sensitivity curve of signal recovery as a function of the sig…
The increasing number of super-Earths close to their host stars revealed a scarcity of close-in small planets with 1.5-2.0$\,R_\oplus$ in the radius distribution of ${\it Kepler}$ planets. The atmospheric escape of super-Earths by photoevaporation can explain the origin of the observed "radius gap." Many theoretical studies considered the in-situ mass loss of a close-in planet. Planets that undergo the atmospheric escape, however, move outward due to the change in the orbital angular momentum of their star-planet systems. In this study, we calculate the orbital evolution of an evaporating supe…
ExoMOD I. A Forward Model for the Orbital Architecture of Kepler Multi-Planet Systems
Southwest Research Institute（西南研究所）；MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡夫利天体物理学与空间研究学院）；Columbia University（哥伦比亚大学）；Instituto de Astronomía Teórica y Experimental (IATE), Observatorio Astronómico, Universidad Nacional de Córdoba（科尔多瓦国立大学理论与实验天文学研究所天文台）
Understanding the occurrence of Earth-sized planets in the habitable zone of Sun-like stars is essential to the search for Earth analogues. Yet a lack of reliable Kepler detections for such planets has forced many estimates to be derived from the close-in ($2<P_{\mathrm{orb}}<100$ days) population, whose radii may have evolved differently under the effect of atmospheric mass loss mechanisms. In this work, we compute the intrinsic occurrence rates of close-in super-Earths ($\sim1-2\,R_\oplus$) and sub-Neptunes ($\sim2-3.5\,R_\oplus$) for FGK stars ($0.56-1.63\,M_\odot$) as a function of orbital…
The Kepler mission results indicate that systems of tightly-packed inner planets (STIPs) are present around of order 5% of FGK field stars (whose median age is ~5 Gyr). We propose that STIPs initially surrounded nearly all such stars and those observed are the final survivors of a process in which long-term metastability eventually ceases and the systems proceed to collisional consolidation or destruction, losing roughly equal fractions of systems every decade in time. In this context, we also propose that our Solar System initially contained additional large planets interior to the current or…
While previous studies have shown a strong preference for a future mid-infrared nulling interferometer space mission to detect planets within the HZ around M dwarfs, we here focus on a more conservative approach toward the concept of habitability and present yield estimates for two stellar samples consisting of nearby (d<20 pc) Sun-like stars (4800-6300 K) and nearby FGK-type stars (3940-7220 K) accessible to such a mission. Our yield estimates are based on recently derived occurrence rates of rocky planets from the Kepler mission and our LIFE exoplanet observation simulation tool LIFEsim, whi…
Trends in the planet population with host star mass provide an avenue to constrain planet formation theories. We derive the planet radius distribution function for Kepler stars of different spectral types, sampling a range in host star masses. We find that M dwarf stars have 3.5 times more small planets (1.0-2.8 R_Earth) than main-sequence FGK stars, but two times fewer Neptune-sized and larger planets (>2.8 R_Earth). We find no systematic trend in the planet size distribution between spectral types F, G, and K to explain the increasing occurrence rates. Taking into account the mass-radius rel…
We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching four years of Kepler time series photometry (Data Release 25, Q1-Q17). The catalog contains 8054 KOIs of which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new and include two in multi-planet systems (KOI-82.06 and KOI-2926.05), and ten high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter which automatically vets the DR25 Threshold Crossing Events (TCEs, Twicken et al. 2016). T…
The Kepler Spacecraft has discovered a large number of planets up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperature as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius a…
The abundance and properties of planets orbiting binary stars - circumbinary planets - are largely unknown because they are difficult to detect with currently available techniques. Results from the Kepler satellite and other studies indicate a minimum occurrence rate of circumbinary giant planets of ~10 %, yet only a handful are presently known. Here, we study the potential of ESA's Gaia mission to discover and characterise extrasolar planets orbiting nearby binary stars by detecting the binary's periodic astrometric motion caused by the orbiting planet. We expect that Gaia will discover hundr…
We present an analysis of the significantly expanded HARPS 2011 radial velocity data set for GJ 581 that was presented by Forveille et al. (2011). Our analysis reaches substantially different conclusions regarding the evidence for a Super-Earth-mass planet in the star's Habitable Zone. We were able to reproduce their reported χ_ν^2 and RMS values only after removing some outliers from their models and refitting the trimmed down RV set. A suite of 4000 N-body simulations of their Keplerian model all resulted in unstable systems and revealed that their reported 3.6σdetection of e=0.32 for the ec…
Assessing PLATO's Discovery Potential across Different Observing Strategies
University of Warwick（华威大学）；Isaac Newton Group of Telescopes（艾萨克·牛顿望远镜组）；University of British Columbia（不列颠哥伦比亚大学）；Institute of Space Research, German Aerospace Center (DLR)（德国航空航天中心空间研究所）；Freie Universitaet Berlin（柏林自由大学）；Observatoire astronomique de l’Université de Genève（日内瓦大学天文台）；Aix Marseille Univ, CNRS, CNES, LAM（艾克斯马赛大学、法国国家科学研究中心、法国国家空间研究中心）
Applying the survival function analysis to the planet radius distribution of the Kepler exoplanet candidates, we have identified two natural divisions of planet radius at 4 Earth radii and 10 Earth radii. These divisions place constraints on planet formation and interior structure model. The division at 4 Earth radii separates small exoplanets from large exoplanets above. When combined with the recently-discovered radius gap at 2 Earth radii, it supports the treatment of planets 2-4 Earth radii as a separate group, likely water worlds. Thus, for planets around solar-type FGK main-sequence star…
Applying the survival function analysis to the planet radius distribution of the Kepler confirmed/candidate planets, we have identified two natural divisions of planet radius at 4 Earth radii and 10 Earth radii. These divisions place constraints on planet formation and interior structure model. The division at 4 Earth radii separates small exoplanets from large exoplanets above. When combined with the recently-discovered radius gap at 2 Earth radii, it supports the treatment of planets 2-4 Earth radii as a separate group, likely water worlds. For planets around solar-type FGK main-sequence sta…
