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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

THE FALSE POSITIVE RATE OF KEPLER AND THE OCCURRENCE OF PLANETS

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 of the Kepler targets and of physical companions or stars in the background to predict the occurrence of astrophysical false positives detectable by the mission. Using real noise level estimates, we compute the number and characteristics of detectable eclipsing pairs involving main-sequence stars and non-main-sequence stars or planets, and we quantify the fraction of those that would pass the Kepler candidate vetting procedure. By comparing their distribution with that of the Kepler Objects of Interest (KOIs) detected during the first six quarters of operation of the spacecraft, we infer the false positive rate of Kepler and study its dependence on spectral type, candidate planet size, and orbital period. We find that the global false positive rate of Kepler is 9.4%, peaking for giant planets (6-22 R{sub Circled-Plus }) at 17.7%, reaching a low of 6.7% for small Neptunes (2-4 R{sub Circled-Plus }), and increasing again for Earth-size planets (0.8-1.25 R{sub Circled-Plus }) to 12.3%. Most importantly, we also quantify and characterize the distribution and rate of occurrence of planets down to Earth size with no prior assumptions on their frequency, by subtracting from the population of actual Kepler candidates our simulated population of astrophysical false positives. We find that 16.5% {+-} 3.6% of main-sequence FGK stars have at least one planet between 0.8 and 1.25 R{sub Circled-Plus} with orbital periods up to 85 days. This result is a significant step toward the determination of eta-earth, the occurrence of Earth-like planets in the habitable zone of their parent stars. There is no significant dependence of the rates of planet occurrence between 0.8 and 4 Earth radii with spectral type. In the process, we also derive a prescription for the signal recovery rate of Kepler that enables a good match to both the KOI size and orbital period distribution, as well as their signal-to-noise distribution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Diversity of extrasolar planets and diversity of molecular cloud cores. I. Semimajor axes

We show that the diversity of extrasolar planetary systems may be related to the diversity of molecular cloud cores. In previous studies of planet formation, artificial initial conditions of protoplanetary disks or steady state disks, such as the minimum mass nebula model, have often been used so that the influence of cloud core properties on planet formation is not realized. To specifically and quantitatively demonstrate our point, we calculate the dependence of disk properties on cloud core properties and show that the boundary of the giant planet formation region in a disk is a function of cloud core properties with the conventional core accretion model of giant planet formation. The gravitational stability of a disk depends on the properties of its progenitor cloud core. We also compare our calculations with observations of extrasolar planets. From the observational data of cloud cores, our model could infer the range and most frequent values of observed semimajor axes of extrasolar planets. Our calculations suggest that planet formation at the snowline alone could not completely explain the semimajor axis distribution. If the current observations are not biased, our calculations indicate that the planet formation at the snowline is inefficient. We suggest that there will be more observed planets with semimajor axis <9 AU than >9 AU, even with a longer duration of observations, if the planet formation at the snowline is inefficient.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Detection of planets in extremely weak central perturbation microlensing events via next-generation ground-based surveys

Even though the recently discovered high-magnification event MOA-2010-BLG-311 had complete coverage over its peak, confident planet detection did not happen due to extremely weak central perturbations (EWCPs, fractional deviations of ≲ 2%). For confident detection of planets in EWCP events, it is necessary to have both high cadence monitoring and high photometric accuracy better than those of current follow-up observation systems. The next-generation ground-based observation project, Korea Microlensing Telescope Network (KMTNet), satisfies these conditions. We estimate the probability of occurrence of EWCP events with fractional deviations of ≤2% in high-magnification events and the efficiency of detecting planets in the EWCP events using the KMTNet. From this study, we find that the EWCP events occur with a frequency of >50% in the case of ≲ 100 M {sub E} planets with separations of 0.2 AU ≲ d ≲ 20 AU. We find that for main-sequence and sub-giant source stars, ≳ 1 M {sub E} planets in EWCP events with deviations ≤2% can be detected with frequency >50% in a certain range that changes with the planet mass. However, it is difficult to detect planets in EWCP events of bright stars like giant stars because it is easy for KMTNet to be saturated around the peak of the events because of its constant exposure time. EWCP events are caused by close, intermediate, and wide planetary systems with low-mass planets and close and wide planetary systems with massive planets. Therefore, we expect that a much greater variety of planetary systems than those already detected, which are mostly intermediate planetary systems, regardless of the planet mass, will be significantly detected in the near future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Asymmetric orbital distribution near mean motion resonance: Application to planets observed by Kepler and radial velocities

Many multiple-planet systems have been found by the Kepler transit survey and various radial velocity (RV) surveys. Kepler planets show an asymmetric feature, namely, there are small but significant deficits/excesses of planet pairs with orbital period spacing slightly narrow/wide of the exact resonance, particularly near the first order mean motion resonance (MMR), such as 2:1 and 3:2 MMR. Similarly, if not exactly the same, an asymmetric feature (pileup wide of 2:1 MMR) is also seen in RV planets, but only for massive ones. We analytically and numerically study planets' orbital evolutions near and in the MMR. We find that their orbital period ratios could be asymmetrically distributed around the MMR center regardless of dissipation. In the case of no dissipation, Kepler planets' asymmetric orbital distribution could be partly reproduced for 3:2 MMR but not for 2:1 MMR, implying that dissipation might be more important to the latter. The pileup of massive RV planets just wide of 2:1 MMR is found to be consistent with the scenario that planets formed separately then migrated toward the MMR. The location of the pileup infers a K value of 1-100 on the order of magnitude for massive planets, where K is the damping rate ratio between orbital eccentricity and semimajor axis during planet migration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HOW LOW CAN YOU GO? THE PHOTOECCENTRIC EFFECT FOR PLANETS OF VARIOUS SIZES

It is well-known that the light curve of a transiting planet contains information about the planet's orbital period and size relative to the host star. More recently, it has been demonstrated that a tight constraint on an individual planet's eccentricity can sometimes be derived from the light curve via the ''photoeccentric effect'', the effect of a planet's eccentricity on the shape and duration of its light curve. This has only been studied for large planets and high signal-to-noise scenarios, raising the question of how well it can be measured for smaller planets or low signal-to-noise cases. We explore the limits of the photoeccentric effect over a wide range of planet parameters. The method hinges upon measuring g directly from the light curve, where g is the ratio of the planet's speed (projected on the plane of the sky) during transit to the speed expected for a circular orbit. We find that when the signal-to-noise in the measurement of g is <10, the ability to measure eccentricity with the photoeccentric effect decreases. We develop a ''rule of thumb'' that for per-point relative photometric uncertainties σ = (10{sup –3}, 10{sup –4}, 10{sup –5}), the critical values of the planet-star radius ratio are R{sub p} /R {sub *} ≈ (0.1, 0.05, 0.03) for Kepler-like 30 minute integration times. We demonstrate how to predict the best-case uncertainty in eccentricity that can be found with the photoeccentric effect for any light curve. This clears the path to study eccentricities of individual planets of various sizes in the Kepler sample and future transit surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

On the gap-opening criterion of migrating planets in protoplanetary disks

We perform two-dimensional hydrodynamical simulations to quantitatively explore the torque balance criterion for gap-opening (as formulated by Crida et al.) in a variety of disks when considering a migrating planet. We find that even when the criterion is satisfied, there are instances when planets still do not open gaps. We stress that gap-opening is not only dependent on whether a planet has the ability to open a gap, but whether it can do so quickly enough. This can be expressed as an additional condition on the gap-opening timescale, t{sub gap}, versus the crossing time, t{sub cross}, i.e., the time it takes the planet to cross the region which it is carving out. While this point has been briefly made in the previous literature, our results quantify it for a range of protoplanetary disk properties and planetary masses, demonstrating how crucial it is for gap-opening. This additional condition has important implications for the survival of planets formed by core accretion in low mass disks as well as giant planets or brown dwarfs formed by gravitational instability in massive disks. It is particularly important for planets with intermediate masses susceptible to Type III-like migration. For some observed transition disks or disks with gaps, we expect that estimates on the potential planet masses based on the torque balance gap-opening criterion alone may not be sufficient. With consideration of this additional timescale criterion theoretical studies may find a reduced planet survivability or that planets may migrate further inwards before opening a gap.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CHANGING PHASES OF ALIEN WORLDS: PROBING ATMOSPHERES OF KEPLER PLANETS WITH HIGH-PRECISION PHOTOMETRY

We present a comprehensive analysis of planetary phase variations, including possible planetary light offsets, using eighteen quarters of data from the Kepler space telescope. Our analysis found fourteen systems with significant detections in each of the phase curve components: planet’s phase function, secondary eclipse, Doppler boosting, and ellipsoidal variations. We model the full phase curve simultaneously, including primary and secondary transits, and derive albedos, day- and night-side temperatures and planet masses. Most planets manifest low optical geometric albedos (< 0.25), with the exception of Kepler-10b, Kepler-91b, and KOI-13b. We find that KOI-13b, with a small eccentricity of 0.0006 ± 0.0001, is the only planet for which an eccentric orbit is favored. We detect a third harmonic for HAT-P-7b for the first time, and confirm the third harmonic for KOI-13b reported in Esteves et al.: both could be due to their spin–orbit misalignments. For six planets, we report a planetary brightness peak offset from the substellar point: of those, the hottest two (Kepler-76b and HAT-P-7b) exhibit pre-eclipse shifts or on the evening-side, while the cooler four (Kepler-7b, Kepler-8b, Kepler-12b, and Kepler-41b) peak post-eclipse or on the morning-side. Our findings dramatically increase the number of Kepler planets with detected planetary light offsets, and provide the first evidence in the Kepler data for a correlation between the peak offset direction and the planet’s temperature. Such a correlation could arise if thermal emission dominates light from hotter planets that harbor hot spots shifted toward the evening-side, as theoretically predicted, while reflected light dominates cooler planets with clouds on the planet’s morning-side.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The five planets in the Kepler-296 binary system all orbit the primary: A Statistical and analytical analysis

Kepler-296 is a binary star system with two M-dwarf components separated by 0.″2. Five transiting planets have been confirmed to be associated with the Kepler-296 system; given the evidence to date, however, the planets could in principle orbit either star. This ambiguity has made it difficult to constrain both the orbital and physical properties of the planets. Using both statistical and analytical arguments, this paper shows that all five planets are highly likely to orbit the primary star in this system. We performed a Markov-Chain Monte Carlo simulation using a five transiting planet model, leaving the stellar density and dilution with uniform priors. Using importance sampling, we compared the model probabilities under the priors of the planets orbiting either the brighter or the fainter component of the binary. A model where the planets orbit the brighter component, Kepler-296A, is strongly preferred by the data. Combined with our assertion that all five planets orbit the same star, the two outer planets in the system, Kepler-296 Ae and Kepler-296 Af, have radii of 1.53 ± 0.26 and 1.80 ± 0.31 R{sub ⊕}, respectively, and receive incident stellar fluxes of 1.40 ± 0.23 and 0.62 ± 0.10 times the incident flux the Earth receives from the Sun. This level of irradiation places both planets within or close to the circumstellar habitable zone of their parent star.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The 3D flow field around an embedded planet

3D modifications to the well-studied 2D flow topology around an embedded planet have the potential to resolve long-standing problems in planet formation theory. We present a detailed analysis of the 3D isothermal flow field around a 5 Earth-mass planet on a fixed circular orbit, simulated using our graphics processing unit hydrodynamics code PEnGUIn. We find that, overall, the horseshoe region has a columnar structure extending vertically much beyond the Hill sphere of the planet. This columnar structure is only broken for some of the widest horseshoe streamlines, along which high altitude fluid descends rapidly into the planet’s Bondi sphere, performs one horseshoe turn, and exits the Bondi sphere radially in the midplane. A portion of this flow exits the horseshoe region altogether, which we refer to as the “transient” horseshoe flow. The flow continues as it rolls up into a pair of up–down symmetric horizontal vortex lines shed into the wake of the planet. This flow, unique to 3D, affects both planet accretion and migration. It prevents the planet from sustaining a hydrostatic atmosphere due to its intrusion into the Bondi sphere, and leads to a significant corotation torque on the planet, unanticipated by 2D analysis. In the reported simulation, starting with a Σ∼r{sup −3/2} radial surface density profile, this torque is positive and partially cancels with the negative differential Lindblad torque, resulting in a factor of three slower planet migration rate. Finally, we report 3D effects can be suppressed by a sufficiently large disk viscosity, leading to results similar to 2D.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

ZODIACAL EXOPLANETS IN TIME (ZEIT). IV. SEVEN TRANSITING PLANETS IN THE PRAESEPE CLUSTER

Open clusters and young stellar associations are attractive sites to search for planets and to test theories of planet formation, migration, and evolution. We present our search for, and characterization of, transiting planets in the 800 Myr old Praesepe (Beehive, M44) Cluster from K2 light curves. We identify seven planet candidates, six of which we statistically validate to be real planets, the last of which requires more data. For each host star, we obtain high-resolution NIR spectra to measure its projected rotational broadening and radial velocity, the latter of which we use to confirm cluster membership. We combine low-resolution spectra with the known cluster distance and metallicity to provide precise temperatures, masses, radii, and luminosities for the host stars. Combining our measurements of rotational broadening, rotation periods, and our derived stellar radii, we show that all planetary orbits are consistent with alignment to their host star’s rotation. We fit the K2 light curves, including priors on stellar density to put constraints on the planetary eccentricities, all of which are consistent with zero. The difference between the number of planets found in Praesepe and Hyades (8 planets, ≃800 Myr) and a similar data set for Pleiades (0 planets, ≃125 Myr) suggests a trend with age, but may be due to incompleteness of current search pipelines for younger, faster-rotating stars. We see increasing evidence that some planets continue to lose atmosphere past 800 Myr, as now two planets at this age have radii significantly larger than their older counterparts from Kepler.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

VULCAN PLANETS: INSIDE-OUT FORMATION OF THE INNERMOST SUPER-EARTHS

The compact multi-transiting systems discovered by Kepler challenge traditional planet formation theories. These fall into two broad classes: (1) formation further out followed by migration and (2) formation in situ from a disk of gas and planetesimals. In the former, an abundance of resonant chains is expected, which the Kepler data do not support. In the latter, required disk mass surface densities may be too high. A recently proposed mechanism hypothesizes that planets form in situ at the pressure trap associated with the dead-zone inner boundary (DZIB) where radially drifting ''pebbles'' accumulate. This scenario predicts planet masses (M{sub p} ) are set by the gap-opening process that then leads to DZIB retreat, followed by sequential, inside-out planet formation (IOPF). For typical disk accretion rates, IOPF predictions for M{sub p} , M{sub p} versus orbital radius r, and planet-planet separations are consistent with observed systems. Here we investigate the IOPF prediction for how the masses, M{sub p,} {sub 1}, of the innermost (''Vulcan'') planets vary with r. We show that for fiducial parameters, M {sub p,} {sub 1} ≅ 5.0(r/0.1 AU) M {sub ⊕}, independent of the disk's accretion rate at time of planet formation. Then, using Monte Carlo sampling of a population of these innermost planets, we test this predicted scaling against observed planet properties, allowing for intrinsic dispersions in planetary densities and Kepler's observational biases. These effects lead to a slightly shallower relation M{sub p,} {sub 1}∝r {sup 0.9} {sup ±} {sup 0.2}, which is consistent with M{sub p,} 1∝r {sup 0.7} {sup ±} {sup 0.2} of the observed Vulcans. The normalization of the relation constrains the gap-opening process, favoring relatively low viscosities in the inner dead zone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE FIRST CIRCUMBINARY PLANET FOUND BY MICROLENSING: OGLE-2007-BLG-349L(AB)c

We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of q ≈ 3.4 × 10{sup −4}, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light-curve fits with two classes of models: two-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be M {sub L} ≈ 0.7 M{sub ⊙}. Hubble Space Telescope (HST) images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the two-planet, one-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass m {sub c} = 80 ± 13 M{sub ⊕}, orbiting a pair of M dwarfs with masses of M {sub A} = 0.41 ± 0.07 and M {sub B} = 0.30 ± 0.07, which makes this the lowest-mass circumbinary planet system known. The ratio of the separation between the planet and the center of mass to the separation of the two stars is ∼40, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Revised masses and densities of the planets around KEPLER-10

Determining which small exoplanets have stony-iron compositions is necessary for quantifying the occurrence of such planets and for understanding the physics of planet formation. Kepler-10 hosts the stony-iron world Kepler-10b, and also contains what has been reported to be the largest solid silicate-ice planet, Kepler-10c. Using 220 radial velocities (RVs), including 72 precise RVs from Keck-HIRES of which 20 are new from 2014 to 2015, and 17 quarters of Kepler photometry, we obtain the most complete picture of the Kepler-10 system to date. We find that Kepler-10b (R{sub p}=1.47 R{sub ⊕}) has mass 3.72 ± 0.42 M{sub ⊕} and density 6.46 ± 0.73 g cm{sup −3}. Modeling the interior of Kepler-10b as an iron core overlaid with a silicate mantle, we find that the iron core constitutes 0.17 ± 0.11 of the planet mass. For Kepler-10c (R{sub p}=2.35 R{sub ⊕}) we measure mass 13.98 ± 1.79 M{sub ⊕} and density 5.94 ± 0.76 g cm{sup −3}, significantly lower than the mass computed in Dumusque et al. (17.2±1.9 M{sub ⊕}). Our mass measurement of Kepler-10c rules out a pure stony-iron composition. Internal compositional modeling reveals that at least 10% of the radius of Kepler-10c is a volatile envelope composed of hydrogen–helium (0.2% of the mass, 16% of the radius) or super-ionic water (28% of the mass, 29% of the radius). However, we note that analysis of only HIRES data yields a higher mass for planet b and a lower mass for planet c than does analysis of the HARPS-N data alone, with the mass estimates for Kepler-10 c being formally inconsistent at the 3σ level. Moreover, dividing the data for each instrument into two parts also leads to somewhat inconsistent measurements for the mass of planet c derived from each observatory. Together, this suggests that time-correlated noise is present and that the uncertainties in the masses of the planets (especially planet c) likely exceed our formal estimates. Transit timing variations (TTVs) of Kepler-10c indicate the likely presence of a third planet in the system, KOI-72.X. The TTVs and RVs are consistent with KOI-72.X having an orbital period of 24, 71, or 101 days, and a mass from 1 to 7 M{sub ⊕}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

197 candidates and 104 validated planets in K2's first five fields

We present 197 planet candidates discovered using data from the first year of the NASA K2 mission (Campaigns 0–4), along with the results of an intensive program of photometric analyses, stellar spectroscopy, high-resolution imaging, and statistical validation. We distill these candidates into sets of 104 validated planets (57 in multi-planet systems), 30 false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of R {sub P} = 2.3 R{sub ⊕}, P = 8.6 days, T{sub eff} = 5300 K, and Kp = 12.7 mag. Stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. We show that K2 has increased by 30% the number of small planets known to orbit moderately bright stars (1–4 R {sub ⊕}, Kp = 9–13 mag). Of particular interest are 76 planets smaller than 2 R {sub ⊕}, 15 orbiting stars brighter than Kp = 11.5 mag, 5 receiving Earth-like irradiation levels, and several multi-planet systems—including 4 planets orbiting the M dwarf K2–72 near mean-motion resonances. By quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15%–30%, with rates substantially lower for small candidates (<2R{sub ⊕}) and larger for candidates with radii >8R{sub ⊕} and/or with P<3 days. Extrapolation of the current planetary yield suggests that K2 will discover between 500 and 1000 planets in its planned four-year mission, assuming sufficient follow-up resources are available. Efficient observing and analysis, together with an organized and coherent follow-up strategy, are essential for maximizing the efficacy of planet-validation efforts for K2, TESS, and future large-scale surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Ultra-short-period Planets Are Stable against Tidal Inspiral

It has been unambiguously shown both in individual systems and at the population level that hot Jupiters experience tidal inspiral before the end of their host stars’ main-sequence lifetimes. Ultra-short-period (USP) planets have orbital periods P < 1 day, rocky compositions, and are expected to experience tidal decay on similar timescales to hot Jupiters if the efficiency of tidal dissipation inside their host stars parameterized as Q{sub ∗}{sup ′} is independent of P and/or secondary mass M {sub p}. Any difference between the two classes of systems would reveal that a model with constant Q{sub ∗}{sup ′} is insufficient. If USP planets experience tidal inspiral, then USP planet systems will be relatively young compared to similar stars without USP planets. Because it is a proxy for relative age, we calculate the Galactic velocity dispersions of USP planet candidate host and non-host stars using data from Gaia Data Release 2 supplemented with ground-based radial velocities. We find that main-sequence USP planet candidate host stars have kinematics consistent with similar stars in the Kepler field without observed USP planets. This indicates that USP planet hosts have similar ages to field stars and that USP planets do not experience tidal inspiral during the main-sequence lifetimes of their host stars. The survival of USP planets requires that Q{sub ∗}{sup ′} ≳ 10{sup 7} at P ≈ 0.7 day and M{sub p}≈2.6 M{sub ⊕}. This result demands that Q{sub ∗}{sup ′} depend on the orbital period and/or mass of the secondary in the range 0.5 day≲P≲5 days and 1 M{sub ⊕}≲M{sub p}≲1000 M{sub ⊕}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Interaction cross sections and survival rates for proposed solar system member planet nine

Motivated by the report of a possible new planetary member of the solar system, this work calculates cross sections for interactions between passing stars and this proposed Planet Nine. Evidence for the new planet is provided by the orbital alignment of Kuiper belt objects, and other solar system properties, which suggest a Neptune-mass object on an eccentric orbit with a semimajor axis a{sub 9} ≈ 400–1500 au. With such a wide orbit, Planet Nine has a large interaction cross section and is susceptible to disruption by passing stars. Using a large ensemble of numerical simulations (several million) and Monte Carlo sampling, we calculate the cross sections for different classes of orbit-altering events: (A) scattering the planet into its proposed orbit from a smaller orbit, (B) ejecting it from the solar system from its current orbit, (C) capturing the planet from another system, and (D) capturing a free-floating planet. Results are presented for a range of orbital elements with planetary mass m{sub 9} = 10 M {sub ⊕}. Removing Planet Nine from the solar system is the most likely outcome. Specifically, we obtain ejection cross sections σ{sub int} ∼ 5 × 10{sup 6} au{sup 2} (5 × 10{sup 4} au{sup 2}) for environments corresponding to the birth cluster (field). With these cross sections, Planet Nine is likely to be ejected if the Sun resides within its birth cluster longer than Δt ≳ 100 Myr. The probability of ejecting Planet Nine due to passing field stars is ≲3% over the age of the Sun. Probabilities for producing the inferred Planet Nine orbit are low (≲5%).

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2016

The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c

We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of q approx. = 3.4×10(exp −4), but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light-curve fits with two classes of models: two-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be M(sub L) approx. = 0.7 Stellar Mass. Hubble Space Telescope (HST) images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the two-planet, one-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass m(sub c) = 80 +/- 13 Stellar Mass, orbiting a pair of M dwarfs with masses of M(sub A) = 0.41+/- 0.07 and M(sub B) = 0.30 +/- 0.07, which makes this the lowest-mass circumbinary planet system known. The ratio of the separation between the planet and the center of mass to the separation of the two stars is approx.40, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.

OGLE-2007-BLG-349↗
DOE OSTI2014

Synthesizing exoplanet demographics from radial velocity and microlensing surveys. II. The frequency of planets orbiting M dwarfs

In contrast to radial velocity (RV) surveys, results from microlensing surveys indicate that giant planets with masses greater than the critical mass for core accretion (∼0.1 M {sub Jup}) are relatively common around low-mass stars. Using the methodology developed in the first paper, we predict the sensitivity of M-dwarf RV surveys to analogs of the population of planets inferred by microlensing. We find that RV surveys should detect a handful of super-Jovian (>M {sub Jup}) planets at the longest periods being probed. These planets are indeed found by RV surveys, implying that the demographic constraints inferred from these two methods are consistent. Finally, we combine the results from both methods to estimate planet frequencies spanning wide regions of parameter space. We find that the frequency of Jupiters and super-Jupiters (1 ≲ m{sub p} sin i/M {sub Jup} ≲ 13) with periods 1 ≤ P/days ≤ 10{sup 4} is f{sub J}=0.029{sub −0.015}{sup +0.013}, a median factor of 4.3 (1.5-14 at 95% confidence) smaller than the inferred frequency of such planets around FGK stars of 0.11 ± 0.02. However, we find the frequency of all giant planets with 30 ≲ m{sub p} sin i/M {sub ⊕} ≲ 10{sup 4} and 1 ≤ P/days ≤ 10{sup 4} to be f{sub G}=0.15{sub −0.07}{sup +0.06}, only a median factor of 2.2 (0.73-5.9 at 95% confidence) smaller than the inferred frequency of such planets orbiting FGK stars of 0.31 ± 0.07. For a more conservative definition of giant planets (50 ≲ m{sub p} sin i/M {sub ⊕} ≲ 10{sup 4}), we find f{sub G{sup ′}}=0.11±0.05, a median factor of 2.2 (0.73-6.7 at 95% confidence) smaller than that inferred for FGK stars of 0.25 ± 0.05. Finally, we find the frequency of all planets with 1 ≤ m{sub p} sin i/M {sub ⊕} ≤ 10{sup 4} and 1 ≤ P/days ≤ 10{sup 4} to be f{sub p} = 1.9 ± 0.5.

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