We determine the orbital eccentricities of individual small Kepler planets, through a combination of asteroseismology and transit light-curve analysis. We are able to constrain the eccentricities of ...51 systems with a single transiting planet, which supplement our previous measurements of 66 planets in multi-planet systems. Through a Bayesian hierarchical analysis, we find evidence that systems with only one detected transiting planet have a different eccentricity distribution than systems with multiple detected transiting planets. The eccentricity distribution of the single-transiting systems is well described by the positive half of a zero-mean Gaussian distribution with a dispersion e = 0.32 0.06, while the multiple-transit systems are consistent with . A mixture model suggests a fraction of of single-transiting systems have a moderate eccentricity, represented by a Rayleigh distribution that peaks at . This finding may reflect differences in the formation pathways of systems with different numbers of transiting planets. We investigate the possibility that eccentricities are self-excited in closely packed planetary systems, as well as the influence of long-period giant companion planets. We find that both mechanisms can qualitatively explain the observations. We do not find any evidence for a correlation between eccentricity and stellar metallicity, as has been seen for giant planets. Neither do we find any evidence that orbital eccentricity is linked to the detection of a companion star. Along with this paper, we make available all of the parameters and uncertainties in the eccentricity distributions, as well as the properties of individual systems, for use in future studies.
ABSTRACT
We present a systematic search for transiting giant planets ($0.6 \mbox{$R_{\rm J}$}\le \mbox{$R_{\rm P}$}\le 2.0 \mbox{$R_{\rm J}$}$) orbiting nearby low-mass stars ($\mbox{$M_{*}$}\le 0.71 ...\mbox{${\rm M}_{\odot }$}$). The formation of giant planets around low-mass stars is predicted to be rare by the core-accretion planet formation theory. We search 91 306 low-mass stars in the TESS 30 min cadence photometry detecting fifteen giant planet candidates, including seven new planet candidates which were not known planets or identified as TOIs prior to our search. Our candidates present an exciting opportunity to improve our knowledge of the giant planet population around the lowest mass stars. We perform planet injection-recovery simulations and find that our pipeline has a high detection efficiency across the majority of our targeted parameter space. We measure the occurrence rates of giant planets with host stars in different stellar mass ranges spanning our full sample. We find occurrence rates of 0.137 ± 0.097 per cent (0.088–0.26 M⊙), 0.108 ± 0.083 per cent (0.26–0.42 M⊙), and 0.29 ± 0.15 per cent (0.42–0.71 M⊙). For our full sample (0.088–0.71 M⊙), we find a giant planet occurrence rate of 0.194 ± 0.072 per cent. We have measured for the first time the occurrence rate for giant planets orbiting stars with $\mbox{$M_{*}$}\le 0.4\, \mbox{${\rm M}_{\odot }$}$ and we demonstrate this occurrence rate to be non-zero. This result contradicts currently accepted planet formation models and we discuss some possibilities for how these planets could have formed.
ABSTRACT The rate of tidal circularization is predicted to be faster for relatively cool stars with convective outer layers, compared to hotter stars with radiative outer layers. Observing this ...effect is challenging because it requires large and well-characterized samples that include both hot and cool stars. Here we seek evidence of the predicted dependence of circularization upon stellar type, using a sample of 945 eclipsing binaries observed by Kepler. This sample complements earlier studies of this effect, which employed smaller samples of better-characterized stars. For each Kepler binary we measure e cos based on the relative timing of the primary and secondary eclipses. We examine the distribution of e cos as a function of period for binaries composed of hot stars, cool stars, and mixtures of the two types. At the shortest periods, hot-hot binaries are most likely to be eccentric; for periods shorter than four days, significant eccentricities occur frequently for hot-hot binaries, but not for hot-cool or cool-cool binaries. This is in qualitative agreement with theoretical expectations based on the slower dissipation rates of hot stars. However, the interpretation of our results is complicated by the largely unknown ages and evolutionary states of the stars in our sample.
ABSTRACT
The characteristics of the radius valley, i.e. an observed lack of planets between 1.5 and 2 Earth radii at periods shorter than about 100 d, provide insights into the formation and ...evolution of close-in planets. We present a novel view of the radius valley by refitting the transits of 431 planets using Kepler 1-min short cadence observations, the vast majority of which have not been previously analysed in this way. In some cases, the updated planetary parameters differ significantly from previous studies, resulting in a deeper radius valley than previously observed. This suggests that planets are likely to have a more homogeneous core composition at formation. Furthermore, using support vector machines, we find that the radius valley location strongly depends on orbital period and stellar mass and weakly depends on stellar age, with $\partial \log {\left(R_{\rm p, \text{valley}} \right)}/ \partial \log {P} = -0.096_{-0.027}^{+0.023}$, $\partial \log {\left(R_{\rm p, \text{valley}} \right)}/ \partial \log {M_{\star }} = 0.231_{-0.064}^{+0.053}$, and $\partial \log {\left(R_{\rm p, \text{valley}} \right)}/ \partial \log {\left(\text{age} \right)} = 0.033_{-0.025}^{+0.017}$. These findings favour thermally driven mass-loss models such as photoevaporation and core-powered mass-loss, with a slight preference for the latter scenario. Finally, this work highlights the value of transit observations with a short photometric cadence to precisely determine planet radii, and we provide an updated list of precisely and homogeneously determined parameters for the planets in our sample.
The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity ...(RV) measurements of three of these systems, revealing significantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moderately eccentric phase where they shrink faster than they circularize due to tides raised on evolved host stars. Additional RV measurements of currently known systems, along with new systems discovered by the recently launched NASA Transiting Exoplanet Survey Satellite (TESS) mission, may constrain the timescale and mass dependence of this process.
We report on the discovery of three transiting planets around GJ 9827. The planets have radii of 1.75 0.18, 1.36 0.14, and R⊕, and periods of 1.20896, 3.6480, and 6.2014 days, respectively. The ...detection was made in Campaign 12 observations as part of our K2 survey of nearby stars. GJ 9827 is a V = 10.39 mag K6V star at a distance of 30.3 1.6 parsecs and the nearest star to be found hosting planets by Kepler and K2. The radial velocity follow-up, high-resolution imaging, and detection of multiple transiting objects near commensurability drastically reduce the false positive probability. The orbital periods of GJ 9827 b, c, and d planets are very close to the 1:3:5 mean motion resonance. Our preliminary analysis shows that GJ 9827 planets are excellent candidates for atmospheric observations. Besides, the planetary radii span both sides of the rocky and gaseous divide, hence the system will be an asset in expanding our understanding of the threshold.
44 Validated Planets from K2 Campaign 10 Livingston, John H.; Endl, Michael; Dai, Fei ...
The Astronomical journal,
08/2018, Letnik:
156, Številka:
2
Journal Article
Recenzirano
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We present 44 validated planets from the 10th observing campaign of the NASA K2 mission, as well as high-resolution spectroscopy and speckle imaging follow-up observations. These 44 planets come from ...an initial set of 72 vetted candidates, which we subjected to a validation process incorporating pixel-level analyses, light curve analyses, observational constraints, and statistical false positive probabilities. Our validated planet sample has median values of = , Porb = days, = K, and J = mag. Of particular interest are four ultra-short period planets ( day), 16 planets smaller than 2 , and two planets with large predicted amplitude atmospheric transmission features orbiting infrared-bright stars. We also present 27 planet candidates, most of which are likely to be real and worthy of further observations. Our validated planet sample includes 24 new discoveries and has enhanced the number of currently known super-Earths ( 1-2 ), sub-Neptunes ( 2-4 ), and sub-Saturns ( 4-8 ) orbiting bright stars (J = 8-10 mag) by ∼4%, ∼17%, and ∼11%, respectively.
We report on the discovery of three transiting super-Earths around K2-155 (EPIC 210897587), a relatively bright early M dwarf (V = 12.81 mag) observed during Campaign 13 of the NASA K2 mission. To ...characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are and 6.34365 0.00028 days for the inner planet; and 13.85402 0.00088 days for the middle planet; and and 40.6835 0.0031 days for the outer planet. The outer planet (K2-155d) is near the habitable zone, with an insolation 1.67 0.38 times that of the Earth. The planet's radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of three-dimensional global climate simulations, assuming that K2-155d is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than ∼1.5 times that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, as K2-155 is one of the optically brightest M dwarfs known to harbor transiting planets.
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 (M = 1.45 0.06 M , R = 2.89 0.12 R ) hosting a massive ( = 5.88 0.47 , = 1.07 0.05 ) 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 four years of the Kepler data, we constrain the orbital decay rate to be ≤ −0.42 s yr−1, corresponding to a strong observational limit of ≥ 4.826 × for the tidal quality factor in evolved stars. With an effective temperature of ∼ 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.
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