OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System

OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System

Authors:

Han et al

Abstract:

We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find four degenerate triple-lens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about ${M}_{1}\sim 0.7\,{M}_{\odot }$, while the planet is a super Jupiter. In all cases, the system lies in the Galactic disk, about halfway toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low-mass brown dwarf, with relative mass ratios (1:0.03:0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source.

OGLE-2016-BLG-0263Lb: Microlensing Detection of a Very Low-mass Binary Companion through a Repeating Event Channel

OGLE-2016-BLG-0263Lb: Microlensing Detection of a Very Low-mass Binary Companion through a Repeating Event Channel 

Authors:

Han et al

Abstract:

We report the discovery of a planet-mass companion to the microlens OGLE-2016-BLG-0263L. Unlike most low-mass companions that were detected through perturbations to the smooth and symmetric light curves produced by the primary, the companion was discovered through the channel of a repeating event, in which the companion itself produced its own single-mass light curve after the event produced by the primary had ended. Thanks to the continuous coverage of the second peak by high-cadence surveys, the possibility of the repeating nature due to source binarity is excluded with a 96% confidence level. The mass of the companion estimated by a Bayesian analysis is ${M}_{{\rm{p}}}={4.1}_{-2.5}^{+6.5}\ {M}_{{\rm{J}}}$. The projected primary-companion separation is ${a}_{\perp }={6.5}_{-1.9}^{+1.3}$ au. The ratio of the separation to the snow-line distance of ${a}_{\perp }/{a}_{\mathrm{sl}}\sim 15.4$ corresponds to the region beyond Neptune, the outermost planet of the solar system. We discuss the importance of high-cadence surveys in expanding the range of microlensing detections of low-mass companions and future space-based microlensing surveys.

OGLE-2017-BLG-0173Lb: Low Mass-Ratio Planet in a "Hollywood" Microlensing Event

OGLE-2017-BLG-0173Lb: Low Mass-Ratio Planet in a "Hollywood" Microlensing Event

Authors:

Hwang et al

Abstract:
We present the discovery of microlensing planet OGLE-2017-BLG-0173Lb, with planet-host mass ratio q=6.5×10−5, among the lowest ever detected. The planetary perturbation is nevertheless quite strongly detected, with Δχ2∼10,000, because it arises from a bright (therefore, large) source passing over, and partially enveloping, the planetary caustic. We present a simple formalism that can be used to estimate the sensitivity of other giant-source ("Hollywood") events to planets and show that they can lead to detections close to, but perhaps not quite reaching, the Earth/Sun mass ratio of 3×10−6. The best estimated Bayesian parameters for this system are host-mass M=0.42+0.40−0.24M⊙, planet mass, mp=9+11−6M⊕, and projected separation $a_\perp \sim 4\,\au$. The measured lens-source relative proper motion $\mu=6\,\masyr$ will permit imaging of the lens in about 15 years or at first light on adaptive-optics imagers on next-generation ("30 meter") telescopes, whichever comes first.

OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing

OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing

Authors:

Ryu et al

Abstract:

We present an analysis of microlensing event OGLE-2016-BLG-0693, based on the survey-only microlensing observations by the OGLE and KMTNet groups. In order to analyze the light curve, we consider the effects of parallax, orbital motion, and baseline slope, and also refine the result using a Galactic model prior. From the microlensing analysis, we find that the event is a binary composed of a low-mass brown dwarf (49+-20 MJ) companion and a K- or G-dwarf host, which lies at a distance 5.0+-0.6 kpc toward the Galactic bulge. The projected separation between the brown dwarf and its host star is less than ~5 AU, and thus it is likely that the brown dwarf companion is located in the brown dwarf desert.

A Superjupiter/Small Brown Dwarf in a 10 AU Orbit Around its Host Star

A companion on the planet/brown dwarf mass boundary on a wide orbit discovered by gravitational microlensing

Authors:

Poleski et al

Abstract:
We present the discovery of a substellar companion to the primary host lens in the microlensing event MOA-2012-BLG-006. The companion-to-host mass ratio is 0.016, corresponding to a companion mass of ≈8 MJup(M∗/0.5M⊙). Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary M∗. The companion signal was separated from the peak of the primary event by a time that was as much as four times longer than the event timescale. We therefore infer a relatively large projected separation of the companion from its host of ≈10 a.u.(M∗/0.5M⊙)1/2 for a wide range (3-7 kpc) of host star distances from the Earth. We also challenge a previous claim of a planetary companion to the lens star in microlensing event OGLE-2002-BLG-045.

Terrestrial World OGLE-2016-BLG-1195Lb Orbits a Brown Dwarf at 1.16 AU

An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf

Authors:

Shvartzvald et al

Abstract:
We combine Spitzer and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass (1.43+0.45−0.32M⊕) planet OGLE-2016-BLG-1195Lb at 1.16+0.16−0.13 AU orbiting a 0.078+0.016−0.012M⊙ ultracool dwarf. This is the lowest-mass microlensing planet to date. At 3.91+0.42−0.46 kpc, it is the third consecutive case among the Spitzer "Galactic distribution" planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both ultracool dwarfs and planetary systems at the limit of low-mass protoplanetary disks.

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Light-curve Analysis and Keck AO Imaging 

Authors:

Koshimoto et al 

Abstract:
We report the discovery of a microlensing planet—MOA-2016-BLG-227Lb—with a large planet/host mass ratio of q sime 9 × 10−3. This event was located near the K2 Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light-curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light-curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar-type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lens–source relative proper motion.

OGLE-2013-BLG-1761Lb: A SuperJupiter Orbiting a M/K Dwarf Star

OGLE-2013-BLG-1761Lb: A Massive Planet around an M/K Dwarf 

Authors:
Hirao et al

Abstract:
We report the discovery and the analysis of the planetary microlensing event, OGLE-2013-BLG-1761. There are some degenerate solutions in this event because the planetary anomaly is only sparsely sampled. However, the detailed light-curve analysis ruled out all stellar binary models and shows the lens to be a planetary system. There is the so-called close/wide degeneracy in the solutions with the planet/host mass ratio of q ~ (7.0 ± 2.0) × 10−3 and q ~ (8.1 ± 2.6) × 10−3 with the projected separation in Einstein radius units of s = 0.95 (close) and s = 1.18 (wide), respectively. The microlens parallax effect is not detected, but the finite source effect is detected. Our Bayesian analysis indicates that the lens system is located ${D}_{{\rm{L}}}={6.9}_{-1.2}^{+1.0}\,\mathrm{kpc}$ away from us and the host star is an M/K dwarf with a mass of ${\text{}}{M}_{{\rm{L}}}={0.33}_{-0.19}^{+0.32}\,{\text{}}{M}_{\odot }$ orbited by a super-Jupiter mass planet with a mass of ${\text{}}{m}_{{\rm{P}}}={2.7}_{-1.5}^{+2.5}\,{M}_{\mathrm{Jup}}$ at the projected separation of ${a}_{\perp }={1.8}_{-0.5}^{+0.5}\,\mathrm{au}$. The preference of the large lens distance in the Bayesian analysis is due to the relatively large observed source star radius. The distance and other physical parameters may be constrained by the future high-resolution imaging by large ground telescopes or HST. If the estimated lens distance is correct, then this planet provides another sample for testing the claimed deficit of planets in the Galactic bulge.

MOA-2012-BLG-505Lb: A SuperEarth probably in the Galactic bulge

MOA-2012-BLG-505Lb: A super-Earth mass planet probably in the Galactic bulge

Authors:
Nagakane et al

Abstract:

We report the discovery of a super-Earth mass planet in the microlensing event MOA-2012-BLG-505. This event has the second shortest event timescale of tE=10±1 days where the observed data show evidence of planetary companion. Our 15 minute high cadence survey observation schedule revealed the short subtle planetary signature. The system shows the well known close/wide degeneracy. The planet/host-star mass ratio is q=2.1×10−4 and the projected separation normalized by the Einstein radius is s = 1.1 or 0.9 for the wide and close solutions, respectively. We estimate the physical parameters of the system by using a Bayesian analysis and find that the lens consists of a super-Earth with a mass of 6.7+10.7−3.6M⊕ orbiting around a brown-dwarf or late M-dwarf host with a mass of 0.10+0.16−0.05M⊙ with a projected star-planet separation of 0.9+0.3−0.2AU. The system is at a distance of 7.2±1.1 kpc, i.e., it is likely to be in the Galactic bulge. The small angular Einstein radius (θE=0.12±0.02 mas) and short event timescale are typical for a low-mass lens in the Galactic bulge. Such low-mass planetary systems in the Bulge are rare because the detection efficiency of planets in short microlensing events is relatively low. This discovery may suggest that such low mass planetary systems are abundant in the Bulge and currently on-going high cadence survey programs will detect more such events and may reveal an abundance of such planetary systems.

OGLE-2014-BLG-1112LB: A new Brown Dwarf Detected Through Microlensing

OGLE-2014-BLG-1112LB: A Microlensing Brown Dwarf Detected Through the Channel of a Gravitational Binary-Lens Event
Authors: 

Han et al 

Abstract: 

Due to the nature depending on only the gravitational field, microlensing, in principle, provides an important tool to detect faint and even dark brown dwarfs. However, the number of identified brown dwarfs is limited due to the difficulty of the lens mass measurement that is needed to check the substellar nature of the lensing object. In this work, we report a microlensing brown dwarf discovered from the analysis of the gravitational binary-lens event OGLE-2014-BLG-1112. We identify the brown-dwarf nature of the lens companion by measuring the lens mass from the detections of both microlens-parallax and finite-source effects. We find that the companion has a mass of (3.03±0.78)×10−2 M⊙ and it is orbiting a solar-type primary star with a mass of 1.07±0.28 M⊙. The estimated projected separation between the lens components is 9.63±1.33 au and the distance to the lens is 4.84±0.67 kpc. We discuss the usefulness of space-based microlensing observations in detecting brown dwarfs through the channel of binary-lens events.

PLANETARY CAUSTIC PERTURBATIONS OF A CLOSE-SEPARATION PLANET ON MICROLENSING

PLANETARY CAUSTIC PERTURBATIONS OF A CLOSE-SEPARATION PLANET ON MICROLENSING

Authors:

Ryu et al

Abstract:

Most planetary events discovered up to date by the planetary caustic of close-separation planets have low-mass ratios. In next-generation microlensing experiments with a wider field of view and a higher cadence, it is possible to obtain densely covered planetary signals induced by the planetary caustic of close-separation planets without missing events. Therefore, the planetary caustic perturbation of close-separation planets would be the more important channel to detect low-mass exoplanets in the next generation of microlensing surveys. In this paper, we investigate the theoretical properties and detection conditions for the planetary caustic perturbation of close-separation planets. To find the properties of the planetary caustic perturbation, we construct deviation maps by subtracting the single-lensing magnification of the lens star from the planetary lensing magnification for various lensing parameters. We find that each deviation area of the positive and negative perturbations disappears at the same normalized source radius according to a given deviation threshold regardless of mass ratio but disappears at a different normalized source radius according to the separation. We also estimate the upper limit of the normalized source radius to detect the planetary caustic perturbation. We find simple relations between the upper limit of the normalized source radius and the lensing parameters. From the relations, we obtain an analytic condition for the theoretical detection limit of the planet, which shows that we can sufficiently discover a planet with a sub-Earth-mass for typical microlensing events. Therefore, we conclude that our planet-detection condition of can be used as an important criteria for maximal planet detections, considering the source type and the photometric accuracy and expect that a number of low-mass planets will be added from the next-generation microlensing experiments.

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

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

Authors:

Bennett et al

Abstract:

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≈3.4×10−4, 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: 2-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constraints the mass of the lens system to be ML≈0.7M⊙. Hubble Space Telescope 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 2-planet, 1-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass mc=80±13M⊕, orbiting a pair of M-dwarfs with masses of MA=0.41±0.07M⊙ and MB=0.30±0.07M⊙, which makes this the lowest mass circumbinary planet system known. The ratio of the planet:center-of-mass separation to the separations 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.

How Common are Free Floating Exoplanets?

Constraining the Frequency of Free-Floating Planets from a Synthesis of Microlensing, Radial Velocity, and Direct Imaging Survey Results

Authors:

Clanton et al

Abstract:

A microlensing survey by Sumi et al. (2011) exhibits an overabundance of short-timescale events (STEs; t_E<2 a="" alone="" and="" as="" been="" between="" brown="" by="" cannot="" data="" days="" distinguish="" down="" due="" dwarf="" events="" excess="" expected="" extrapolation="" from="" has="" however="" interpreted="" is="" known="" main-sequence="" microlensing="" nearly="" objects="" of="" outnumber="" population="" populations="" power-law="" regime.="" relative="" smooth="" stars="" stellar="" that="" the="" this="" to="" twofold="" upiter-mass="" what="" wide-separation="">~10 AU) and free-floating planets. Assuming these STEs are indeed due to planetary-mass objects, we aim to constrain the fraction of these events that can be explained by bound but wide-separation planets. We fit the observed timescale distribution with a lens mass function comprised of brown dwarfs, main-sequence stars, and stellar remnants, finding and thus corroborating the initial identification of an excess of STEs. We then include a population of bound planets that are expected not to show signatures of the primary lens (host) in their microlensing light curves and that are also consistent with results from representative microlensing, radial velocity, and direct imaging surveys. We find that bound planets alone cannot explain the entire STE excess without violating the constraints from the surveys we consider and thus some fraction of these events must be due to free-floating planets, if our model for bound planets holds. We estimate a median fraction of STEs due to free-floating planets to be f=0.67 (0.23-0.85 at 95% confidence) when assuming "hot-start" planet evolutionary models and f=0.58 (0.14-0.83 at 95% confidence) for "cold-start" models. Assuming a delta-function distribution of free-floating planets of mass m_p=2 M_Jup yields a number of free-floating planets per main-sequence star of N=1.4 (0.48-1.8 at 95% confidence) in the "hot-start" case and N=1.2 (0.29-1.8 at 95% confidence) in the "cold-start" case.

Detecting Exomoons Through Micro Lensing

Properties of microlensing events by wide separation planets with a moon

Authors:

Chung et al

Abstract:

We investigate the properties of microlensing events caused by planetary systems where planets with a moon are widely separated from their host stars. From this investigation, we find that the moon feature generally appears as an very short-duration perturbation on the smooth asymmetric light curve of the lensing event induced by the wide separation planet; thus it can be easily discriminated from the planet feature responsible for the overall asymmetric light curve. For typical Galactic lensing events with the Einstein radius of ∼2 AU, the asymmetry of the light curves due to bound planets can be noticed up to ∼20AU. We also find that the perturbations of the wide planetary systems become dominated by the moon as the projected star-planet separation increases, and eventually the light curves of events produced by the systems appear as the single lensing light curve of the planet itself with a very short-duration perturbation induced by the moon, which is a representative light curve of the event induced by a star and a planet, except on the Einstein timescale of the planet. We also study the effect of a finite source star on the moon feature in the wide planetary lensing events. From this study, we find that when the lunar caustic is sufficiently separated from the planetary caustic, the lower limit on the ratio of the lunar caustic size to the source radius causing a ≥5% lunar deviation depends mostly on the projected planet-moon separation regardless of the moon/star mass ratio, and it decreases as the planet-moon separation becomes smaller or larger than the planetary Einstein radius.

OGLE-2016-BLG-0596Lb: a Gas Giant Detected by Microlensing

OGLE-2016-BLG-0596Lb: High-Mass Planet From High-Magnification Pure-Survey Microlensing Event

Authors:

Mróz et al

Abstract:

We report the discovery of a high mass-ratio planet q=0.012, i.e., 13 times higher than the Jupiter/Sun ratio. The host mass is not presently measured but can be determined or strongly constrained from adaptive optics imaging. The planet was discovered in a small archival study of high-magnification events in pure-survey microlensing data, which was unbiased by the presence of anomalies. The fact that it was previously unnoticed may indicate that more such planets lie in archival data and could be discovered by similar systematic study. In order to understand the transition from predominantly survey+followup to predominately survey-only planet detections, we conduct the first analysis of these detections in the observational (s,q) plane. Here s is projected separation in units of the Einstein radius. We find some evidence that survey+followup is relatively more sensitive to planets near the Einstein ring, but that there is no statistical difference in sensitivity by mass ratio.

OGLE-2012-BLG-0950Lb: a 2 Neptune Mass M Dwarf World

OGLE-2012-BLG-0950Lb: The Possible First Planet Mass Measurement from Only Microlens Parallax and Lens Flux

Authors:

Koshimoto et al

Abstract:

We report the discovery of a microlensing planet OGLE-2012-BLG-0950Lb with the planet/host mass ratio of q=2×10−4. A long term distortion detected in both MOA and OGLE light curve can be explained by the microlens parallax due to the Earth's orbital motion around the Sun. Although the finite source effect is not detected, we obtain the lens flux by the high resolution Keck AO observation. Combining the microlens parallax and the lens flux reveal the nature of the lens: a planet with mass of Mp=35+17−9MEarth is orbiting around a M-dwarf with mass of Mh=0.56+0.12−0.16MSun with a planet-host projected separation of rproj=2.7+0.6−0.7 AU located at DL=3.0+0.8−1.1 kpc from us. This is the first mass measurement from only microlens parallax and the lens flux without the finite source effect. The long term distortion can also be explained by the source orbital motion (xallarap) which is suspicious but not ruled out. These models can be distinguished by future high resolution imaging because of the much larger lens-source relative proper motion and brighter lens in the parallax model compared to the xallarap model. In the coming space observation-era with Spitzer, K2, Euclid, and WFIRST, we expect many such events for which we will not be able to measure any finite source effect. This work demonstrates an ability of mass measurements in such events.

The microlensing rate and distribution of free-floating planets towards the Galactic bulge

The microlensing rate and distribution of free-floating planets towards the Galactic bulge

Authors:

Ban et al

Abstract:

Ground-based optical microlensing surveys have provided tantalising, if inconclusive, evidence for a significant population of free-floating planets (FFPs). Both ground and space-based facilities are being used and developed which will be able to probe the distrubution of FFPs with much better sensitivity. It is vital also to develop a high-precision microlensing simulation framework to evaluate the completeness of such surveys. We present the first signal-to-noise limited calculations of the FFP microlensing rate using the Besancon Galactic model. The microlensing distribution towards the Galactic centre is simulated for wide-area ground-based optical surveys such as OGLE or MOA, a wide-area ground-based near-IR survey, and a targeted space-based near-IR survey which could be undertaken with Euclid or WFIRST. We present a calculation framework for the computation of the optical and near-infrared microlensing rate and optical depth for simulated stellar catalogues which are signal-to-noise limited, and take account of extinction, unresolved stellar background light and finite source size effects, which can be significant for FFPs. We find that the global ground-based I-band yield over a central 200 deg^2 region covering the Galactic centre ranges from 20 Earth-mass FFPs year^-1 up to 3,500 year^-1 for Jupiter FFPs in the limit of 100% detection efficiency, and almost an order of magnitude larger for a K-band survey. For ground-based surveys we find that the inclusion of finite source and the unresolved background reveals a mass-dependent variation in the spatial distribution of FFPs. For a space-based H-band covering 2 deg^2, the yield depends on the target field but maximizes close to the Galactic centre with around 76 Earth through to 1,700 Jupiter FFPs year^-1. For near-IR space-based surveys the spatial distribution of FFPs is found to be largely insensitive to the FFP mass scale.

Investigating the free-floating planet mass by Euclid observations

Investigating the free-floating planet mass by Euclid observations

Authors:

Hamolli et al

Abstract:

The detection of anomalies in gravitational microlensing events is nowadays one of the main goals among the microlensing community. In the case of single-lens events, these anomalies can be caused by the finite source effects, that is when the source disk size is not negligible, and by the Earth rotation around the Sun (the so-called parallax effect). The finite source and parallax effects may help to define the mass of the lens, uniquely. Free-floating planets (FFPs) are extremely dim objects, and gravitational microlensing provides at present the exclusive method to investigate these bodies. In this work, making use of a synthetic population algorithm, we study the possibility of detecting the finite source and parallax effects in simulated microlensing events caused by FFPs towards the Galactic bulge, taking into consideration the capabilities of the space-based Euclid telescope. We find a significant efficiency for detecting the parallax effect in microlensing events with detectable finite source effect, that turns out to be about 51% for mass function index .

Free-floating planets from core accretion theory: microlensing predictions

Free-floating planets from core accretion theory: microlensing predictions

Authors:

Ma et al

Abstract:

We calculate the microlensing event rate and typical time-scales for the free-floating planet (FFP) population that is predicted by the core accretion theory of planet formation. The event rate is found to be ~1.8×10−3 of that for the stellar population. While the stellar microlensing event time-scale peaks at around 20 days, the median time-scale for FFP events (~0.1 day) is much shorter. Our values for the event rate and the median time-scale are significantly smaller than those required to explain the \cite{Sum+11} result, by factors of ~13 and ~16, respectively. The inclusion of planets at wide separations does not change the results significantly. This discrepancy may be too significant for standard versions of both the core accretion theory and the gravitational instability model to explain satisfactorily. Therefore, either a modification to the planet formation theory is required, or other explanations to the excess of short-time-scale microlensing events are needed. Our predictions can be tested by ongoing microlensing experiment such as KMTNet, and by future satellite missions such as WFIRST and Euclid.

OGLE-2012-BLG-0724Lb: a Saturn Class Gas Giant Orbitng a M Dwarf Star

OGLE-2012-BLG-0724Lb: A Saturn-mass Planet around an M-dwarf

Authors:

Hirao et al

Abstract:

We report the discovery of a planet by the microlensing method, OGLE-2012-BLG-0724Lb. Although the duration of the planetary signal for this event was one of the shortest seen for a planetary event, the anomaly was well covered thanks to high cadence observations taken by the survey groups OGLE and MOA. By analyzing the light curve, this planetary system is found to have a mass ratio q=(1.58±0.15)×10−3. By conducting a Bayesian analysis, we estimate that the host star is an M-dwarf star with a mass of ML=0.29+0.33−0.16 M⊙ located at DL=6.7+1.1−1.2 kpc away from the Earth and the companion's mass is mP=0.47+0.54−0.26 MJup. The projected planet-host separation is a⊥=1.6+0.4−0.3 AU. Because the lens-source relative proper motion is relatively high, future high resolution images would detect the lens host star and determine the lens properties uniquely. This system is likely a Saturn-mass exoplanet around an M-dwarf and such systems are commonly detected by gravitational microlensing. This adds an another example of a possible pileup of sub-Jupiters (0.2 less than mP/MJup less than 1) in contrast to a lack of Jupiters (∼1−2 MJup) around M-dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M-dwarfs.