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Register a new userFull characterization of binary-lens event OGLE-2002-BLG-069 from PLANET observations
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We analyze the photometric data obtained by PLANET and OGLE on the caustic-crossing binary-lens microlensing event OGLE-2002-BLG-069. Thanks to the excellent photometric and spectroscopic coverage of the event, we are able to constrain the lens model up to the known ambiguity between close and wide binary lenses. The detection of annual parallax in combination with measurements of extended-source effects allows us to determine the mass, distance and velocity of the lens components for the competing models. While the model involving a close binary lens leads to a Bulge-Disc lens scenario with a lens mass of M=(0.51 +- 0.15) M_sol and distance of D_L=(2.9 +- 0.4) kpc, the wide binary lens solution requires a rather implausible binary black-hole lens (M >=126 M_sol). Furthermore we compare current state-of-the-art numerical and empirical models for the surface brightness profile of the source, a G5III Bulge giant. We find that a linear limb-darkening model for the atmosphere of the source star is consistent with the data whereas a PHOENIX atmosphere model assuming LTE and with no free parameter does not match our observations.
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We present the analysis result of a gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by 2 adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling of the light curve considering the parallax effect and Keplerian orbital motion, we are able to measure not only the physical parameters but also a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance $6.7pm 0.3$ kpc from the Earth. The individual lens components with masses $0.9pm 0.3 M_odot$ and $0.5pm 0.1 M_odot$ are separated with a semi-major axis of $a=2.5 pm 1.0$ AU and orbiting each other with a period $P=3.1 pm 1.3$ yr. The event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.
We report a giant exoplanet discovery in the microlensing event OGLE-2017-BLG-1049, which is a planet-host star mass ratio of $q=9.53pm0.39times10^{-3}$ and has a caustic crossing feature in the Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of $theta_{rm E}=0.52 pm 0.11 {rm mas}$. However, the microlens parallax is not measured because of the time scale of the event $t_{rm E}simeq 29 {rm days}$, which is not long enough in this case to determine the microlens parallax. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. From this, we find that the lens system has a star with mass $M_{rm h}=0.55^{+0.36}_{-0.29} M_{odot}$ hosting a giant planet with $M_{rm p}=5.53^{+3.62}_{-2.87} M_{rm Jup}$, at a distance of $D_{rm L}=5.67^{+1.11}_{-1.52} {rm kpc}$. The projected star-planet separation in units of the Einstein radius $(theta_{rm E})$ corresponding to the total mass of the lens system is $a_{perp}=3.92^{+1.10}_{-1.32} rm{au}$. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is $mu_{rm rel}sim 7 rm{mas yr^{-1}}$, thus the lens and source will be separated from each other within 10 years. Then the flux of the host star can be measured by a 30m class telescope with high-resolution imaging in the future, and thus its mass can be determined.
We analyze the microlensing event OGLE-2019-BLG-0304, whose light curve exhibits two distinctive features: a deviation in the peak region and a second bump appearing $sim 61$~days after the main peak. Although a binary-lens model can explain the overall features, it leaves subtle but noticeable residuals in the peak region. We find that the residuals can be explained by the presence of either a planetary companion located close to the primary of the binary lens (3L1S model) or an additional close companion to the source (2L2S model). Although the 3L1S model is favored over the 2L2S model, with $Deltachi^2sim 8$, securely resolving the degeneracy between the two models is difficult with the currently available photometric data. According to the 3L1S interpretation, the lens is a planetary system, in which a planet with a mass $0.51^{+0.51}_{-0.23}~M_{rm J}$ is in an S-type orbit around a binary composed of stars with masses $0.27^{+0.27}_{-0.12}~M_odot$ and $0.10^{+0.10}_{-0.04}~M_odot$. According to the 2L2S interpretation, on the other hand, the source is composed of G- and K-type giant stars, and the lens is composed of a low-mass M dwarf and a brown dwarf with masses $0.12^{+0.12}_{-0.05}~M_odot$ and $0.045^{+0.045}_{-.019}~M_odot$, respectively. The event illustrates the need for through model testing in the interpretation of lensing events with complex features in light curves.
We present the analysis of the caustic-crossing binary microlensing event OGLE-2017-BLG-0039. Thanks to the very long duration of the event, with an event time scale $t_{rm E}sim 130$ days, the microlens parallax is precisely measured despite its small value of $piesim 0.06$. The analysis of the well-resolved caustic crossings during both the source stars entrance and exit of the caustic yields the angular Einstein radius $thetaesim 0.6$~mas. The measured $pie$ and $thetae$ indicate that the lens is a binary composed of two stars with masses $sim 1.0~M_odot$ and $sim 0.15~M_odot$, and it is located at a distance of $sim 6$ kpc. From the color and brightness of the lens estimated from the determined lens mass and distance, it is expected that $sim 2/3$ of the $I$-band blended flux comes from the lens. Therefore, the event is a rare case of a bright lens event for which high-resolution follow-up observations can confirm the nature of the lens.
We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based on observations obtained from 13 different telescopes. Intensive coverage of the anomalous parts of the light curve was achieved by automated follow-up observations from the robotic telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of an anomalous microlensing event are well covered by follow-up data, allowing us to estimate the physical parameters of the lens. The strong detection of second-order effects in the event light curve necessitates the inclusion of longer-baseline survey data in order to constrain the parallax vector. We find that the event was most likely caused by a stellar binary-lens with masses $M_{star1} = 0.87 pm 0.12 M_{odot}$ and $M_{star2} = 0.77 pm 0.11 M_{odot}$. The distance to the lensing system is 6.41 $pm 0.14$ kpc and the projected separation between the two components is 13.85 $pm 0.16$ AU. Alternative interpretations are also considered.
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