About: This article is published in The Astronomical Journal.The article was published on 2021-06-01 and is currently open access. It has received 5 citations till now. The article focuses on the topics: Gravitational microlensing.
The signature of a microlensing planet is almost always a short-lasting anomaly in the smooth and symmetric lensing light curve produced by the host of the planet.
The bias toward central anomalies is mostly attributed to the limitation of early lensing surveys.
The observational cadence of the lensing surveys in this phase has greatly increased with the employment of largeformat cameras yielding very wide fields of view.
Planets are detected through the planetary-caustic channel as anomalies produced by the source’s approach close to the planetary caustic, which denotes one of the two sets of planet-induced caustics lying away from the host.
2. Observation
The two planetary events were observed by the two lensing surveys conducted by the OGLE and KMTNet groups.
In both surveys, observations were mainly conducted in the I band, and a fraction of the images were taken in the V band to determine the color of the microlensed source stars.
The OGLE cadence for this direction is 3–10 times per night.
The KMTNet collaboration also observed the event, with designation KMT-2018-BLG-2071, located in their two overlapping fields (BLG41 and BLG22).
3. Light Curve Analysis
The next three (s, q, α) describe the binary-lens geometry: the projected binary separation (scaled to θE), the binary mass ratio (q=M2/M1), and the angle between the source trajectory and the binary axis as measured in a clockwise sense, respectively.
From the configurations, it is found that the anomalies of both events are produced by the source crossing over the planetary caustic of the lens system.
4. Physical Parameters
The results in Table 1 show that for both events, the normalized source radii are precisely measured.
For the disk VD, the authors adopt Gaussian forms of f (vy, vz)= f (vy)f (vz) from Han & Gould (1995), which they then modify to consider the change in the matter distribution.
The estimated lens properties for the individual events are listed in Table 4.
This implies that the effective cross-section of these caustics for a planet-induced perturbation and their lensing behavior are similar to those of resonant caustics.
TL;DR: The analysis of the microlensing event KMT-2018-BLG-1743 is presented in this article, where it is shown that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with the values of the relative lens-source proper motion expected from the two degenerate solutions.
Abstract: We present the analysis of the microlensing event KMT-2018-BLG-1743. The light curve of the event, with a peak magnification $A_{\rm peak}\sim 800$, exhibits two anomaly features, one around the peak and the other on the falling side of the light curve. An interpretation with a binary lens and a single source (2L1S) cannot describe the anomalies. By conducting additional modeling that includes an extra lens (3L1S) or an extra source (2L2S) relative to a 2L1S interpretation, we find that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with $\Delta\chi^2\sim 188$ and $\sim 91$ over the 2L1S and 3L1S solutions, respectively. Assuming that these $\Delta\chi^2$ values are adequate for distinguishing the models, the event is the fourth 2L2S event and the second 2L2S planetary event. The 2L2S interpretations are subject to a degeneracy, resulting in two solutions with $s>1.0$ (wide solution) and $s<1.0$ (close solution). The masses of the lens components and the distance to the lens are $(M_{\rm host}/M_\odot, M_{\rm planet}/M_{\rm J}, D_{\rm L}/{\rm kpc}) \sim (0.19^{+0.27}_{-0.111}, 0.25^{+0.34}_{-0.14}, 6.48^{+0.94}_{-1.03})$ and $\sim (0.42^{+0.34}_{-0.25}, 1.61^{+1.30}_{-0.97}, 6.04^{+0.93}_{-1.27})$ according to the wide and close solutions, respectively. The source is a binary composed of an early G dwarf and a mid M dwarf. The values of the relative lens-source proper motion expected from the two degenerate solutions, $\mu_{\rm wide}\sim 2.3 $mas yr$^{-1}$ and $\mu_{\rm close} \sim 4.1 $mas yr$^{-1}$, are substantially different, and thus the degeneracy can be broken by resolving the lens and source from future high-resolution imaging observations.
TL;DR: The analysis of the microlensing event KMT-2018-BLG-1743 is presented in this article, where it is shown that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with the values of the relative lens-source proper motion expected from the two degenerate solutions.
Abstract: We present the analysis of the microlensing event KMT-2018-BLG-1743. The light curve of the event, with a peak magnification $A_{\rm peak}\sim 800$, exhibits two anomaly features, one around the peak and the other on the falling side of the light curve. An interpretation with a binary lens and a single source (2L1S) cannot describe the anomalies. By conducting additional modeling that includes an extra lens (3L1S) or an extra source (2L2S) relative to a 2L1S interpretation, we find that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with $\Delta\chi^2\sim 188$ and $\sim 91$ over the 2L1S and 3L1S solutions, respectively. Assuming that these $\Delta\chi^2$ values are adequate for distinguishing the models, the event is the fourth 2L2S event and the second 2L2S planetary event. The 2L2S interpretations are subject to a degeneracy, resulting in two solutions with $s>1.0$ (wide solution) and $s<1.0$ (close solution). The masses of the lens components and the distance to the lens are $(M_{\rm host}/M_\odot, M_{\rm planet}/M_{\rm J}, D_{\rm L}/{\rm kpc}) \sim (0.19^{+0.27}_{-0.111}, 0.25^{+0.34}_{-0.14}, 6.48^{+0.94}_{-1.03})$ and $\sim (0.42^{+0.34}_{-0.25}, 1.61^{+1.30}_{-0.97}, 6.04^{+0.93}_{-1.27})$ according to the wide and close solutions, respectively. The source is a binary composed of an early G dwarf and a mid M dwarf. The values of the relative lens-source proper motion expected from the two degenerate solutions, $\mu_{\rm wide}\sim 2.3 $mas yr$^{-1}$ and $\mu_{\rm close} \sim 4.1 $mas yr$^{-1}$, are substantially different, and thus the degeneracy can be broken by resolving the lens and source from future high-resolution imaging observations.
TL;DR: In this paper, the authors examined the full sample of 7 short (t_\e <7\,$day) planetary microlensing events with good $q$ measurements and found that six have clustered Einstein radii and relative proper motions.
Abstract: KMT-2016-BLG-2605, with planet-host mass ratio $q=0.012\pm 0.001$, has the shortest Einstein timescale, $t_\e = 3.41\pm 0.13\,$days, of any planetary microlensing event to date. This prompts us to examine the full sample of 7 short ($t_\e<7\,$day) planetary events with good $q$ measurements. We find that six have clustered Einstein radii $\theta_\e = 115\pm 20\,\muas$ and lens-source relative proper motions $\mu_\rel\simeq 9.5\pm 2.5\,\masyr$. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic-bulge population of very low-mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive-optics light on next-generation (30m) telescopes. Based on a preliminary assessment of the sample, "planetary" companions (i.e., below the deuterium-burning limit) are divided into "genuine planets", formed in their disks by core accretion, and very low-mass brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar "anomaly dominated" morphology of the KMT-2016-BLG-2605 light curve.
TL;DR: In this article, the authors conducted a project of reinvestigating the 2017-2019 microlensing data collected by high-cadence surveys with the aim of finding planets that were missed due to the deviations of planetary signals from the typical form of short-term anomalies.
Abstract: Aims. We conducted a project of reinvestigating the 2017–2019 microlensing data collected by high-cadence surveys with the aim of finding planets that were missed due to the deviations of planetary signals from the typical form of short-term anomalies.Methods. The project led us to find three planets, KMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The lensing light curves of the events have a common characteristic: the planetary signals were produced by the crossings of faint source stars over the resonant caustics formed by giant planets located near the Einstein rings of host stars.Results. For all planetary events, the lensing solutions are uniquely determined without any degeneracy. It is estimated that the host masses are in the range of 0.45 ≲ M ∕M ⊙ ≲ 0.59, which corresponds to early M to late K dwarfs, and thus the host stars are less massive than the Sun. On the other hand, the planets, with masses in the range of 2.1 ≲ M ∕M J ≲ 6.2, are heavier than the heaviest planet of the Solar System, that is, Jupiter. The planets in all systems lie beyond the snow lines of the hosts, and thus the discovered planetary systems, together with many other microlensing planetary systems, support the idea that massive gas-giant planets are commonplace around low-mass stars. We discuss the role of late-time high-resolution imaging in clarifying resonant-image lenses with very faint sources.
TL;DR: In this paper, the authors examined the full sample of 7 short (t_\e <7\,$day) planetary microlensing events with good $q$ measurements and found that six have clustered Einstein radii and relative proper motions.
Abstract: KMT-2016-BLG-2605, with planet-host mass ratio $q=0.012\pm 0.001$, has the shortest Einstein timescale, $t_\e = 3.41\pm 0.13\,$days, of any planetary microlensing event to date. This prompts us to examine the full sample of 7 short ($t_\e<7\,$day) planetary events with good $q$ measurements. We find that six have clustered Einstein radii $\theta_\e = 115\pm 20\,\muas$ and lens-source relative proper motions $\mu_\rel\simeq 9.5\pm 2.5\,\masyr$. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic-bulge population of very low-mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive-optics light on next-generation (30m) telescopes. Based on a preliminary assessment of the sample, "planetary" companions (i.e., below the deuterium-burning limit) are divided into "genuine planets", formed in their disks by core accretion, and very low-mass brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar "anomaly dominated" morphology of the KMT-2016-BLG-2605 light curve.
TL;DR: In this article, the authors combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a highmagnification event.
Abstract: We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include photometric and astrometric measurements from Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve, such as microlens parallax, planetary orbital motion and finite-source effects. Our primary analysis leads to the conclusion that the host of Jovian planet OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M= 0.46 +/- 0.04 Msun, distance D_l = 3.3 +/- 0.4 kpc, and thick-disk kinematics v_LSR ~ 103 km/s. From the best-fit model, the planet has mass M_p = 3.8 +/- 0.4 M_Jup, lies at a projected separation r_perp = 3.6 +/- 0.2 AU from its host and so has an equilibrium temperature of T ~ 55 K, i.e., similar to Neptune. A degenerate model less favored by \Delta\chi^2 = 2.1 (or 2.2, depending on the sign of the impact parameter) gives similar planetary mass M_p = 3.4 +/- 0.4 M_Jup with a smaller projected separation, r_\perp = 2.1 +/- 0.1 AU, and higher equilibrium temperature T ~ 71 K. These results from the primary analysis suggest that OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that is hosted by an M dwarf. However, the formation of such high-mass planetary companions in the outer regions of M-dwarf planetary systems is predicted to be unlikely within the core-accretion scenario. There are a number of caveats to this primary analysis, which assumes (based on real but limited evidence) that the unlensed light coincident with the source is actually due to the lens, that is, the planetary host. However, these caveats could mostly be resolved by a single astrometric measurement a few years after the event.
TL;DR: The OGLE-2006-BLG-109Lb,c was the first double planet system discovered with the gravitational microlensing method as discussed by the authors, which was the only multi-planet system discovered by any method with measured masses for the star and both planets.
Abstract: We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of M_* = 0.51(+0.05-0.04) M_sun, M_b = 231+-19 M_earth, M_c = 86+-7 M_earth. The Saturn-analog planet in this system had a planetary light curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of eccentricity = 0.15 (+0.17-0.10) and an orbital inclination of i = 64 (+4-7) deg. The 95% confidence level lower limit on the inclination of i > 49 deg. implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of >30m aperture.
TL;DR: In this article, the authors derive analytic expressions for binary-source events in the extreme flux-ratio limit and use these to demonstrate the basic degeneracy between binary source and planet perturbations.
Abstract: A planetary microlensing event is characterized by a short-lived perturbation to the standard microlensing curve. Planetary perturbations typically last from a few hours to a day, have maximum amplitudes, ?max, of ?5%-20% of the standard curve, and come in two classes: major and minor image perturbations. There exist a subset of binary-source events that can reproduce the main features of major image perturbations, which are likely to represent more than half of all planetary events, and thus masquerade as planetary events. These events require a binary source with a small flux ratio, ~ 10-2 to 10-4, and a small impact parameter for the fainter source, ?2 /?max. The detection probability of events of this type is ~?2, and can be as high as ~30%; this is comparable to planetary detection rates. Thus a sample of planetary-like perturbations could be seriously contaminated by binary-source events, and there exists the possibility that completely meaningless physical parameters would be derived for any given major image perturbation. Here I derive analytic expressions for a binary-source event in the extreme flux-ratio limit and use these to demonstrate the basic degeneracy between binary-source and planet perturbations. I describe how the degeneracy can be broken by dense and accurate sampling of the perturbation, optical/infrared photometry, or spectroscopic measurements.
TL;DR: In this paper, high precision calibrations of the surface brightness-color relations using exclusively Cepheid observations were derived using a Baade-Wesselink type technique, and the results showed that the astrophysical dispersion of these relations appears to be very small and below the present detection sensitivity.
Abstract: The recent VINCI/VLTI observations presented in Paper I have nearly doubled the total number of available angular diameter measurements of Cepheids. Taking advantage of the significantly larger color range covered by these observations, we derive in the present paper high precision calibrations of the surface brightness-color relations using exclusively Cepheid observations. These empirical laws make it possible to determine the distance to Cepheids through a Baade-Wesselink type technique. The least dispersed relations are based on visible-infrared colors, for instance FV(V-K) = -0.1336 ± 0.0008 (V-K) + 3.9530 ± 0.0006}. The convergence of the Cepheid (this work) and dwarf star (Kervella et al. \cite{kervella04c}) visible-infrared surface brightness-color relations is strikingly good. The astrophysical dispersion of these relations appears to be very small, and below the present detection sensitivity. Table \ref{table_measurements1} is only available in electronic form at http://www.edpsciences.org
TL;DR: In this paper, a comprehensive and analytic analysis of the properties of the planetary caustics, which are one of the two sets of Caustics in planetary microlensing, those located away from the central star, is presented.
Abstract: Although some of the properties of the caustics in planetary microlensing have been known, our understanding of them is mostly from scattered information based on numerical approaches. In this paper, we conduct a comprehensive and analytic analysis of the properties of the planetary caustics, which are one of the two sets of caustics in planetary microlensing, those located away from the central star. Under the perturbative approximation, we derive analytic expressions for the location, size, and shape of the planetary caustic as a function of the star-planet separation and the planet/star mass ratio. Based on these expressions combined with those for the central caustic, which is the other set of caustics and is located close to the central star, we compare the similarities and differences between the planetary and central caustics. We also present the expressions for the size ratio between the two types of caustics and for the condition of the merging of the two types of caustics. These analytic expressions will be useful in understanding the dependence of the planetary lensing behavior on the planet parameters and thus in interpreting the planetary lensing signals.
Q1. What are the contributions in "Ogle-2018-blg-0567lb and ogle-2018-blg-0962lb: two microlensing planets through the planetary-caustic channel" ?
The authors present the analyses of two microlensing events, OGLE-2018-BLG-0567 and OGLE-2018-BLG-0962. 7. 06 kpc 1. 15 0. 93 for OGLE-2018-BLG-0567 and + 6. 50 kpc 1. 75 1. 06 for OGLE-2018-BLG-0962, suggesting that they are likely to be near the Galactic bulge.
Q2. What future works have the authors mentioned in the paper "Ogle-2018-blg-0567lb and ogle-2018-blg-0962lb: two microlensing planets through the planetary-caustic channel" ?
The authors present the discovery of two cold, giant planets orbiting M-dwarfs in two events, OGLE-2018-BLG-0567 and OGLE2018-BLG-0962. From this, the authors estimate planet masses of - + M0. 32 0. 17 0. 34 J for OGLE-2018-BLG-0567Lb and - + M1. 34 0. 70 0. 82 J for OGLE2018-BLG-0962Lb, and their physical projected separations of - +2. 72 au0. 59 0. 53 and - +3. 59 au1. 12 0. 81, respectively. The planet hosts can be precisely constrained by future high-resolution imaging with adaptive optics ( AO ) mounted on 30 m class telescopes. The Bayesian estimates suggest that the dereddened H-band magnitude of the host is = - +H 21. 790 1. 85 1. 79 for OGLE-2018-BLG-0567 and = - +H 19. 630 1. 67 1. 89 for OGLE-2018-BLG-0962 ( Pecaut & Mamajek 2013 ).