OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge

Chung, S.-J.,Zhu, W.,Udalski, A.,Lee, C.-U.,Ryu, Y.-H.,Jung, Y. K.,Shin, I.-G.,Yee, J. C.,Hwang, K.-H.,Gould, A.,Albrow, M.,Cha, S.-M.,Han, C.,Kim, D.-J.,Kim, H.-W.,Kim, S.-L.,Kim, Y.-H.,Lee, Y.,Park, American Astronomical Society 2017 The Astrophysical Journal Vol.838 No.2

<P>We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are. due to the passage of the lens close to or directly over. the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves. yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a. mass 0.10 +/- 0.02 M-circle dot or a brown dwarf with a. mass 55 +/- 9MJ, which are. located at D-LS = 0.80 +/- 0.19 kpc and D-LS = 0.54 +/- 0.08 kpc, respectively,. where DLS is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe ( Delta chi(2) = 0.3). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for rho, the angular size of the source in units of the angular Einstein ring radius. Because the rho degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically similar to 1 day(-1), we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this rho degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is mu(rel) = 9.0 +/- 1.9 mas yr(-1), while for the brown dwarf it is 5.5 +/- 0.5 mas yr(-1). Hence, the degeneracy can be resolved within similar to 10 years from direct-lens imaging by using next-generation instruments with high spatial resolution.</P>

OGLE-2017-BLG-1049: ANOTHER GIANT PLANET MICROLENSING EVENT

Kim, Yun Hak,Chung, Sun-Ju,Udalski, A.,Bond, Ian A.,Jung, Youn Kil,Gould, Andrew,Albrow, Michael D.,Han, Cheongho,Hwang, Kyu-Ha,Ryu, Yoon-Hyun,Shin, In-Gu,Shvartzvald, Yossi,Yee, Jennifer C.,Zang, Wei The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.6

We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.

A NEW TYPE OF AMBIGUITY IN THE PLANET AND BINARY INTERPRETATIONS OF CENTRAL PERTURBATIONS OF HIGH-MAGNIFICATION GRAVITATIONAL MICROLENSING EVENTS

Choi, J.-Y.,Shin, I.-G.,Han, C.,Udalski, A.,Sumi, T.,Gould, A.,Bozza, V.,Dominik, M.,Fouqué,, P.,Horne, K.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R. IOP Publishing 2012 The Astrophysical journal Vol.756 No.1

<P>High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion. It is known that central perturbations induced by both types of companions can be generally distinguished due to the essentially different magnification pattern around caustics. In this paper, we present a case of central perturbations for which it is difficult to distinguish the planetary and binary interpretations. The peak of a lensing light curve affected by this perturbation appears to be blunt and flat. For a planetary case, this perturbation occurs when the source trajectory passes the negative perturbation region behind the back end of an arrowhead-shaped central caustic. For a binary case, a similar perturbation occurs for a source trajectory passing through the negative perturbation region between two cusps of an astroid-shaped caustic. We demonstrate the degeneracy for two high-magnification events of OGLE-2011-BLG-0526 and OGLE-2011-BLG-0950/MOA-2011-BLG-336. For OGLE-2011-BLG-0526, the chi(2) difference between the planetary and binary model is similar to 3, implying that the degeneracy is very severe. For OGLE-2011-BLG-0950/MOA-2011-BLG-336, the stellar binary model is formally excluded with Delta chi(2) similar to 105 and the planetary model is preferred. However, it is difficult to claim a planet discovery because systematic residuals of data from the planetary model are larger than the difference between the planetary and binary models. Considering that two events observed during a single season suffer from such a degeneracy, it is expected that central perturbations experiencing this type of degeneracy is common.</P>

A POSSIBLE BINARY SYSTEM OF A STELLAR REMNANT IN THE HIGH-MAGNIFICATION GRAVITATIONAL MICROLENSING EVENT OGLE-2007-BLG-514

Miyake, N.,Udalski, A.,Sumi, T.,Bennett, D. P.,Dong, S.,Street, R. A.,Greenhill, J.,Bond, I. A.,Gould, A.,Kubiak, M.,Szymań,ski, M. K.,Pietrzyń,ski, G.,Soszyń,ski, I.,Ulaczyk, K.,Wyrzyk IOP Publishing 2012 The Astrophysical journal Vol.752 No.2

<P>We report the extremely high-magnification (A > 1000) binary microlensing event OGLE-2007-BLG-514. We obtained good coverage around the double peak structure in the light curve via follow-up observations from different observatories. The binary lens model that includes the effects of parallax (known orbital motion of the Earth) and orbital motion of the lens yields a binary lens mass ratio of q = 0.321 +/- 0.007 and a projected separation of s = 0.072 +/- 0.001 in units of the Einstein radius. The parallax parameters allow us to determine the lens distance D-L = 3.11 +/- 0.39 kpc and total mass M-L = 1.40 +/- 0.18 M-circle dot; this leads to the primary and secondary components having masses of M-1 = 1.06 +/- 0.13 M-circle dot and M-2 = 0.34 +/- 0.04 M-circle dot, respectively. The parallax model indicates that the binary lens system is likely constructed by the main-sequence stars. On the other hand, we used a Bayesian analysis to estimate probability distributions by the model that includes the effects of xallarap (possible orbital motion of the source around a companion) and parallax (q = 0.270 +/- 0.005, s = 0.083 +/- 0.001). The primary component of the binary lens is relatively massive, with M-1 = 0.9(-0.3)(+4.6) M-circle dot and it is at a distance of D-L = 2.6(-0.9)(+3.8) kpc. Given the secure mass ratio measurement, the companion mass is therefore M-2 = 0.2(-0.1)(+1.2) M-circle dot. The xallarap model implies that the primary lens is likely a stellar remnant, such as a white dwarf, a neutron star, or a black hole.</P>

A VENUS-MASS PLANET ORBITING A BROWN DWARF: A MISSING LINK BETWEEN PLANETS AND MOONS

Udalski, A.,Jung, Y. K.,Han, C.,Gould, A.,Kozłowski, S.,Skowron, J.,Poleski, R.,Soszyń,ski, I.,Pietrukowicz, P.,Mró,z, P.,Szymań,ski, M. K.,Wyrzykowski, Ł.,Ulaczyk, K.,Pietrzyń,sk IOP Publishing 2015 The Astrophysical journal Vol.812 No.1

<P>The co-planarity of solar system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. Here we report the discovery of an intermediate system, OGLE-2013-BLG-0723LB/Bb, composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled-down version of a planet plus a star or as a scaled-up version of a moon plus a planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that the formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.</P>

OGLE-2012-BLG-0563Lb: A SATURN-MASS PLANET AROUND AN M DWARF WITH THE MASS CONSTRAINED BY<i>SUBARU</i>AO IMAGING

Fukui, A.,Gould, A.,Sumi, T.,Bennett, D. P.,Bond, I. A.,Han, C.,Suzuki, D.,Beaulieu, J.-P.,Batista, V.,Udalski, A.,Street, R. A.,Tsapras, Y.,Hundertmark, M.,Abe, F.,Bhattacharya, A.,Freeman, M.,Itow, IOP Publishing 2015 The Astrophysical journal Vol.809 No.1

<P>We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio of similar to 1 x 10(-3). Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and Infrared Camera and Spectrograph instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of spectroscopic information about the source star obtained during the high-magnification state by Bensby et al., we find that the lens system is located at 1.3(-0.8)(+0.6) kpc from us, and consists of an M dwarf (0.34(-0.20)(+0.12)M(circle dot)) orbited by a Saturn-mass planet (0.39(-0.23)(+0.14)M(Jup)) at the projected separation of 0.74(-0.42)(+0.26)AU (close model) or 4.3(-2.5)(+1.5)AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to three, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J - K-s) and (H - K-s) colors of the host star, which are marginally consistent with a low metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2 < m(p)/M-Jup < 1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of similar to 1-2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core-accretion scheme.</P>

THE FIRST NEPTUNE ANALOG OR SUPER-EARTH WITH A NEPTUNE-LIKE ORBIT: MOA-2013-BLG-605LB

Sumi, T.,Udalski, A.,Bennett, D. P.,Gould, A.,Poleski, R.,Bond, I. A.,Skowron, J.,Rattenbury, N.,Pogge, R. W.,Bensby, T.,Beaulieu, J. P.,Marquette, J. B.,Batista, V.,Brillant, S.,Abe, F.,Asakura, Y.,B American Astronomical Society 2016 The Astrophysical journal Vol.825 No.2

<P>We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at 9 similar to 14 times the expected position of the snow line, a(snow), which is similar to Neptune's separation of 11 a(snow) from the Sun. The planet/host-star mass ratio is q = (3.6 +/- 0.7) x 10(-4) and the projected separation normalized by the Einstein radius is s = 2.39 +/- 0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate 'the wide degeneracy.' The three models have (i) a Neptune-mass planet with a mass of M-p = 21(-7)(+6)M(circle plus) orbiting a low-mass M-dwarf with a mass of M-h = 0.19(-0.06)(+0.05)M(circle dot), (ii) a mini-Neptune with M-p = 7.9(-1.2)(+1.8)M(circle plus) orbiting a brown dwarf host with M-h = 0.068(-0.011)(+0.019)M(circle dot), and (iii) a super-Earth with M-p = 3.2(-0.3)(+0.5)M(circle plus) orbiting a low-mass brown dwarf host with M-h = 0.025(-0.004)(+0.005)M(circle dot), which is slightly favored. The 3D planet-host separations are 4.6(-1.2)(+4.7) au, 2.1(-0.2) (+1.0) au, and 0.94(-0.02)(+0.67) au, which are 8.9(-1.4)(+10.5), 12(-1)(+7), or 14(-1)(+11) times larger than a(snow) for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems.</P>

A COLD NEPTUNE-MASS PLANET OGLE-2007-BLG-368Lb: Cold neptunes are common

Sumi, T.,Bennett, D. P.,Bond, I. A.,Udalski, A.,Batista, V.,Dominik, M.,Fouqué,, P.,Kubas, D.,Gould, A.,Macintosh, B.,Cook, K.,Dong, S.,Skuljan, L.,Cassan, A.,Abe, F.,Botzler, C. S.,Fukui, A.,Fu IOP Publishing 2010 The Astrophysical journal Vol.710 No.2

<P>We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = [9.5 +/- 2.1] x 10(-5) via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the Microlensing Observations in Astrophysics survey, real-time light-curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at M(l) = 0.64(-0.26)(+0.21) M(circle dot) and D(l) = 5.9(-1.4)(+ 0.9) kpc, respectively, so the mass and separation of the planet are M(p) = 20(-8)(+7) M(circle plus) and a = 3.3(-0.8)(+1.4) AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprises four cold Neptune/super-Earths, five gas giant planets, and another sub-Saturn mass planet whose nature is unclear. The discovery of these 10 cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN(pl)/d log q alpha q(-0.7+/-0.2) with a 95% confidence level upper limit of n < -0.35 ( where dN(pl)/d log q alpha q(n)). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level.</P>

OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-peak Gravitational Microlensing Event

Udalski, A.,Han, C.,Bozza, V.,Gould, A.,Bond, I. A.,Mró,z, P.,Skowron, J.,Wyrzykowski, Ł.,Szymań,ski, M. K.,Soszyń,ski, I.,Ulaczyk, K.,Poleski, R.,Pietrukowicz, P.,Kozłowski, S.,Abe, F American Astronomical Society 2018 The Astrophysical journal Vol.853 No.1

<P>We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits five very unusual peaks, four of which were produced by caustic crossings and the other by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax pi(E). Furthermore, the three resolved caustics allow us to measure the angular Einstein radius theta(E). From the combination of pE and qE, the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses M-1 = 0.52 +/- 0.04 M-circle dot and M-2 = 0.42 +/- 0.03 M-circle dot separated in projection by a(perpendicular to) = 6.4 +/- 0.5 au. The lens is located in the disk with a distance of D-L = 3.3 +/- 0.3 kpc. The reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.</P>

MOA-2011-BLG-293Lb: A TEST OF PURE SURVEY MICROLENSING PLANET DETECTIONS

Yee, J. C.,Shvartzvald, Y.,Gal-Yam, A.,Bond, I. A.,Udalski, A.,Kozłowski, S.,Han, C.,Gould, A.,Skowron, J.,Suzuki, D.,Abe, F.,Bennett, D. P.,Botzler, C. S.,Chote, P.,Freeman, M.,Fukui, A.,Furusawa, K. IOP Publishing 2012 The Astrophysical journal Vol.755 No.2

<P>Because of the development of large-format, wide-field cameras, microlensing surveys are now able to monitor millions of stars with sufficient cadence to detect planets. These new discoveries will span the full range of significance levels including planetary signals too small to be distinguished from the noise. At present, we do not understand where the threshold is for detecting planets. MOA-2011-BLG-293Lb is the first planet to be published from the new surveys, and it also has substantial follow-up observations. This planet is robustly detected in survey+follow-up data (Delta chi(2) similar to 5400). The planet/host mass ratio is q = (5.3 similar to 0.2) x 10(-3). The best-fit projected separation is s = 0.548 +/- 0.005 Einstein radii. However, due to the s <-> s(-1) degeneracy, projected separations of s-1 are only marginally disfavored at Delta chi(2) = 3. A Bayesian estimate of the host mass gives M-L = 0.43(-0.17)(+0.27) M-circle dot, with a sharp upper limit of M-L < 1.2 M-circle dot from upper limits on the lens flux. Hence, the planet mass is m(p) = 2.4(-0.9)(+1.5) M-Jup, and the physical projected separation is either r(perpendicular to) similar or equal to 1.0 AU or r(perpendicular to) similar or equal to 3.4 AU. We show that survey data alone predict this solution and are able to characterize the planet, but the Delta chi(2) is much smaller (Delta chi(2) similar to 500) than with the follow-up data. The Delta chi(2) for the survey data alone is smaller than for any other securely detected planet. This event suggests a means to probe the detection threshold, by analyzing a large sample of events like MOA-2011-BLG-293, which have both follow-up data and high-cadence survey data, to provide a guide for the interpretation of pure survey microlensing data.</P>