Author
T. Yamada
Other affiliations: Osaka University
Bio: T. Yamada is an academic researcher from Kyoto Sangyo University. The author has contributed to research in topics: Gravitational microlensing & Light curve. The author has an hindex of 10, co-authored 13 publications receiving 244 citations. Previous affiliations of T. Yamada include Osaka University.
Papers
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Osaka University1, California Institute of Technology2, Goddard Space Flight Center3, University of Notre Dame4, Ohio State University5, Niels Bohr Institute6, Heidelberg University7, Massey University8, Zhejiang University9, Tsinghua University10, University of Auckland11, Nagoya University12, Vaughn College of Aeronautics and Technology13, Victoria University of Wellington14, Kyoto Sangyo University15, Centre national de la recherche scientifique16, University of Tasmania17, Tel Aviv University18, European Southern Observatory19, University of Salerno20, Ames Research Center21, University of Toulouse22, Las Cumbres Observatory Global Telescope Network23, University of St Andrews24, Vision Institute25, Open University26, INAF27, Qatar Airways28
TL;DR: In this article, the authors reported the discovery of a microlensing planet, MOA-2016-BLG-227Lb, with a large planet/host mass ratio of q ≃ 9 × 10^(−3).
Abstract: We report the discovery of a microlensing planet—MOA-2016-BLG-227Lb—with a large planet/host mass ratio of q ≃ 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.
49 citations
Korea Astronomy and Space Science Institute1, Harvard University2, University of Warsaw3, Massey University4, California Institute of Technology5, Zhejiang University6, Tsinghua University7, University of St Andrews8, European Southern Observatory9, University of Copenhagen10, Ohio State University11, University of Toronto12, Massachusetts Institute of Technology13, University of Canterbury14, Korea University of Science and Technology15, Max Planck Society16, Chungbuk National University17, Kyung Hee University18, University of Salerno19, Nagoya University20, Goddard Space Flight Center21, University of Auckland22, Osaka University23, Vaughn College of Aeronautics and Technology24, Victoria University of Wellington25, Japan Aerospace Exploration Agency26, Kyoto Sangyo University27, Ames Research Center28, Vanderbilt University29, Chinese Academy of Sciences30, University of Manchester31, University of Toulouse32, Las Cumbres Observatory Global Telescope Network33, Heidelberg University34, Institut d'Astrophysique de Paris35, Tel Aviv University36, Open University37, Liverpool John Moores University38, Istituto Nazionale di Fisica Nucleare39, University of Hamburg40, Stockholm University41, INAF42, Keele University43, University of Antofagasta44, Pontifical Catholic University of Chile45, Sharif University of Technology46, Isfahan University of Technology47, Aarhus University48
TL;DR: The OGLE-2016-BLG-1190Lb is the first Spitzer microlensing planet in the Galactic bulge/bar, an assignation that can be confirmed by two epochs of high-resolution imaging of the combined source-lens baseline object as discussed by the authors.
Abstract: We report the discovery of OGLE-2016-BLG-1190Lb, which is likely to be the first Spitzer microlensing planet in the Galactic bulge/bar, an assignation that can be confirmed by two epochs of high-resolution imaging of the combined source–lens baseline object. The planet's mass, M p = 13.4 ± 0.9 M J , places it right at the deuterium-burning limit, i.e., the conventional boundary between "planets" and "brown dwarfs." Its existence raises the question of whether such objects are really "planets" (formed within the disks of their hosts) or "failed stars" (low-mass objects formed by gas fragmentation). This question may ultimately be addressed by comparing disk and bulge/bar planets, which is a goal of the Spitzer microlens program. The host is a G dwarf, M host = 0.89 ± 0.07 M ⊙, and the planet has a semimajor axis a ~ 2.0 au. We use Kepler K2 Campaign 9 microlensing data to break the lens-mass degeneracy that generically impacts parallax solutions from Earth–Spitzer observations alone, which is the first successful application of this approach. The microlensing data, derived primarily from near-continuous, ultradense survey observations from OGLE, MOA, and three KMTNet telescopes, contain more orbital information than for any previous microlensing planet, but not quite enough to accurately specify the full orbit. However, these data do permit the first rigorous test of microlensing orbital-motion measurements, which are typically derived from data taken over <1% of an orbital period.
39 citations
University of Toronto1, Ohio State University2, University of Warsaw3, Massachusetts Institute of Technology4, California Institute of Technology5, University of Salerno6, Osaka University7, University of Warwick8, Korea Astronomy and Space Science Institute9, Max Planck Society10, Smithsonian Astrophysical Observatory11, University of Maryland, College Park12, Massey University13, Goddard Space Flight Center14, Japan Aerospace Exploration Agency15, University of Auckland16, Nagoya University17, University of Notre Dame18, College of Industrial Technology19, Victoria University of Wellington20, University of Canterbury21, Kyoto Sangyo University22
TL;DR: In this paper, the authors present the result of microlensing event MOA-2016-BLG-290, which received observations from the two-wheel Kepler (K2), Spitzer, as well as ground-based observatories.
Abstract: We present the result of microlensing event MOA-2016-BLG-290, which received observations from the two-wheel Kepler (K2), Spitzer, as well as ground-based observatories. A joint analysis of data from K2 and the ground leads to two degenerate solutions of the lens mass and distance. This degeneracy is effectively broken once the (partial) Spitzer light curve is included. Altogether, the lens is found to be an extremely low-mass star or brown dwarf (77^(+34)_(-23) M_J) located in the Galactic bulge (6.8 ± 0.4 kpc). MOA-2016-BLG-290 is the first microlensing event for which we have signals from three well-separated (~1 au) locations. It demonstrates the power of two-satellite microlensing experiment in reducing the ambiguity of lens properties, as pointed out independently by S. Refsdal and A. Gould several decades ago.
31 citations
Max Planck Society1, Massey University2, University of Canterbury3, Korea Astronomy and Space Science Institute4, Korea University of Science and Technology5, Ohio State University6, Chungbuk National University7, Harvard University8, Kyung Hee University9, University of Warsaw10, Nagoya University11, University of Auckland12, Osaka University13, Victoria University of Wellington14, Goddard Space Flight Center15, Japan Aerospace Exploration Agency16, Kyoto Sangyo University17
TL;DR: The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU as discussed by the authors, and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia.
Abstract: Work by K.H.H. was support by KASI grant 2017-1-830-03. Work by W.Z., Y.K.J., and A.G. were supported by AST-1516842 from the US NSF. W.Z., I.G.S., and A.G. were supported by JPL grant 1500811. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. Work by C.H. was supported by the grant (2017R1A4A101517) of National Research Foundation of Korea. The OGLE Team thanks Prof. G. Pietrzynski for his contribution to the collection of the OGLE photometric data. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU. The MOA project is supported by JSPS KAKENHI Grant Number JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, and JP16H06287.
30 citations
University of Tokyo1, Spanish National Research Council2, Japan Aerospace Exploration Agency3, Goddard Space Flight Center4, Las Cumbres Observatory Global Telescope Network5, American Association of Variable Star Observers6, Subaru7, Kyoto Sangyo University8, Tokyo Institute of Technology9, University of Maryland, College Park10, Istituto Nazionale di Fisica Nucleare11, University of Salerno12, California Institute of Technology13, Ohio State University14, National Astronomical Research Institute of Thailand15, Boston University16, Westminster College (Pennsylvania)17, University of La Laguna18, Chinese Academy of Sciences19, European Space Research and Technology Centre20, Graduate University for Advanced Studies21, National Institutes of Natural Sciences, Japan22, Sternberg Astronomical Institute23, Slovak Academy of Sciences24, Massachusetts Institute of Technology25, Heidelberg University26, NASA Exoplanet Science Institute27, University of Paris28, University of Tasmania29, University of North Carolina at Chapel Hill30
TL;DR: In this article, Nucita et al. reported the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017.
Abstract: We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 ± 0.033 M⊙) located at 505 ± 47 pc, and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 ± 2.0 M⊕) with a semimajor axis of 1.08^(+0.62)_(-0.18) au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only ~35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (K_s = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities.
19 citations
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TL;DR: In this paper, it was shown that Earth mass planets orbiting stars in the Galactic disk and bulge can be detected by monitoring microlensed stars in a Galactic bulge, and that the planetary signal remains detectable for planetary masses as small as an Earth mass when realistic source star sizes are included in the lightcurve calculation.
Abstract: We show that Earth mass planets orbiting stars in the Galactic disk and bulge can be detected by monitoring microlensed stars in the Galactic bulge. The star and its planet act as a binary lens which generates a lightcurve which can differ substantially from the lightcurve due only to the star itself. We show that the planetary signal remains detectable for planetary masses as small as an Earth mass when realistic source star sizes are included in the lightcurve calculation. These planets are detectable if they reside in the ``lensing zone" which is centered between 1 and 4 AU from the lensing star and spans about a factor of 2 in distance. If we require a minimum deviation of 4\% from the standard point-lens microlensing lightcurve, then we find that more than 2\% of all $\mearth$ planets and 10\% of all $10\mearth$ in the lensing zone can be detected. If a third of all lenses have no planets, a third have $1\mearth$ planets and the remaining third have $10\mearth$ planets then we estimate that an aggressive ground based microlensing planet search program could find one earth mass planet and half a dozen $10\mearth$ planets per year.
210 citations
Hiroshima University1, Institute for the Physics and Mathematics of the Universe2, Konan University3, Subaru4, Kagoshima University5, Kyoto University6, University of Tokyo7, Nagoya University8, Massey University9, Osaka University10, University of Canterbury11, University of Hyogo12, Tokyo Institute of Technology13, Osaka City University14, Chinese Academy of Sciences15, Toho University16
TL;DR: In this paper, the Japanese collaboration for gravitational wave electro-magnetic (J-GEM) follow-up observations of SSS17a, an electromagnetic counterpart of GW170817, showed a 2.5mag decline in the z band during the period between 1.7 and 7.7 d after the merger.
Abstract: GW170817 is the first detected gravitational wave source from a neutron star merger. We present the Japanese collaboration for gravitational-wave electro-magnetic (J-GEM) follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5mag decline in the z band during the period between 1.7 and 7.7 d after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder during later epochs: the z - H color has changed by approximately 2.5mag during the period between 0.7 and 7.7 d. The rapid evolutions of both the color and the optical brightness are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with an ejectamass of 0.01M(circle dot), which suggests a more intensemass ejection (similar to 0.03M(circle dot)) or possibly an additional energy source.
174 citations
TL;DR: The first detected gravitational wave from a neutron star merger was GW170817 as discussed by the authors, which showed a 2.5-mag decline in the $z-H$ band from 1.7 days to 7 days after the merger, which is not comparable with supernovae light curves at any epoch.
Abstract: The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the $z-H$ color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized $r$-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that $r$-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 $\Msun$, which suggests a more intense mass ejection ($\sim 0.03 \Msun$) or possibly an additional energy source.
172 citations
TL;DR: In this article, the authors used Gaia DR2 data on the distances and proper motions of non-blended sources and recompute the masses of lenses in parallax events.
Abstract: Context. Gravitational microlensing is sensitive to compact-object lenses in the Milky Way, including white dwarfs, neutron stars, or black holes, and could potentially probe a wide range of stellar-remnant masses. However, the mass of the lens can be determined only in very limited cases, due to missing information on both source and lens distances and their proper motions.Aims. Our aim is to improve the mass estimates in the annual parallax microlensing events found in the eight years of OGLE-III observations towards the Galactic Bulge with the use of Gaia Data Release 2 (DR2).Methods. We use Gaia DR2 data on distances and proper motions of non-blended sources and recompute the masses of lenses in parallax events. We also identify new events in that sample which are likely to have dark lenses; the total number of such events is now 18.Results. The derived distribution of masses of dark lenses is consistent with a continuous distribution of stellar-remnant masses. A mass gap between neutron star and black hole masses in the range between 2 and 5 solar masses is not favoured by our data, unless black holes receive natal kicks above 20−80 km s−1 . We present eight candidates for objects with masses within the putative mass gap, including a spectacular multi-peak parallax event with mass of located just at 600 pc. The absence of an observational mass gap between neutron stars and black holes, or conversely the evidence of black hole natal kicks if a mass gap is assumed, can inform future supernova modelling efforts.
82 citations
University of Maryland, College Park1, Goddard Space Flight Center2, University of Tasmania3, Institut d'Astrophysique de Paris4, Space Telescope Science Institute5, University of Tokyo6, University of California, Berkeley7, Massey University8, NASA Exoplanet Science Institute9, Osaka University10, University of Warsaw11
TL;DR: In this article, an analysis of the simultaneous high-resolution images from the Hubble Space Telescope and Keck adaptive optics system of the planetary event OGLE-2012-BLG-0950 was presented.
Abstract: We present the analysis of the simultaneous high-resolution images from the Hubble Space Telescope and Keck adaptive optics system of the planetary event OGLE-2012-BLG-0950 that determine that the system consists of a 0.58 ± 0.04 M_⊕ host star orbited by a 39 ± 8 M_⊕ planet at a projected separation of 2.54 ± 0.23 au. The planetary system is located at a distance of 2.19 ± 0.23 kpc from Earth. This is the second microlens planet beyond the snow line with a mass measured to be in the mass range 20–80 M_⊕. The runaway gas accretion process of the core accretion model predicts fewer planets in this mass range. This is because giant planets are thought to be growing rapidly at these masses, and they rarely complete growth at this mass. So this result suggests that the core accretion theory may need revision. This analysis also demonstrates the techniques that will be used to measure the masses of planets and their host stars by the WFIRST exoplanet microlensing survey: one-dimensional microlensing parallax combined with the separation and brightness measurement of the unresolved source and host stars to yield multiple redundant constraints on the masses and distance of the planetary system.
74 citations