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 apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model.
Abstract: The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass Mp through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semimajor axis a through tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate an Mp-a distribution. Our results reproduce the observed lack of planets with intermediate mass Mp = 10-100 M⊕ and a 3 AU and with large mass Mp 103 M⊕ and a 0.2 AU. Based on the simulated Mp-a distributions, we also evaluate the metallicity dependence of the fraction of stars harboring planets that are detectable with current radial velocity surveys. If protostellar disks attain the same fraction of heavy elements as contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observations. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependences of the planet distributions that can be tested by ongoing observations.
TL;DR: In this paper, the authors used a semianalytic circumstellar disk model that considers the movement of the snow line through evolution of accretion and the central star to investigate how gas giant frequency changes with stellar mass.
Abstract: We use a semianalytic circumstellar disk model that considers movement of the snow line through evolution of accretion and the central star to investigate how gas giant frequency changes with stellar mass. The snow line distance changes weakly with stellar mass; thus, giant planets form over a wide range of spectral types. The probability that a given star has at least one gas giant increases linearly with stellar mass from 0.4 to 3 M☉. Stars more massive than 3 M☉ evolve quickly to the main sequence, which pushes the snow line to 10-15 AU before protoplanets form and limits the range of disk masses that form giant planet cores. If the frequency of gas giants around solar mass stars is 6%, we predict occurrence rates of 1% for 0.4 M☉ stars and 10% for 1.5 M☉ stars. This result is largely insensitive to our assumed model parameters. Finally, the movement of the snow line as stars 2.5 M☉ move to the main sequence may allow the ocean planets suggested by Leger et al. to form without migration.
TL;DR: In this paper, the authors describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration.
Abstract: We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.
TL;DR: In this article, the smallest intrinsic dispersions of σ ≤ 1% in θ LD are obtained for the surface brightness relations of these stars using exclusively direct angular diameter measurements.
Abstract: The availability of a number of new interferometric measurements of Main Sequence and subgiant stars makes it possible to calibrate the surface brightness relations of these stars using exclusively direct angular diameter measurements. These empirical laws make it possible to predict the limb darkened angular diameters θ LD of dwarfs and subgiants using their dereddened Johnson magnitudes, or their effective temperature. The smallest intrinsic dispersions of σ ≤ 1% in θ LD are obtained for the relations based on the K and L magnitudes, for instance log θ LD = 0.0502 (B - L) + 0.5133 - 0.2 L or log θ LD = 0.0755 (V - K) + 0.5170 - 0.2 K. Our calibrations are valid between the spectral types A0 and M2 for dwarf stars (with a possible extension to later types when using the effective temperature), and between A0 and K0 for subgiants. Such relations are particularly useful for estimating the angular sizes of calibrators for long-baseline interferometry from readily available broadband photometry.
TL;DR: In this article, the apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model.
Abstract: The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass $M_{\rm p}$ through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semi-major axis $a$ through their tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate $M_{\rm p}$-$a$ distribution. Our results reproduce the observed lack of planets with intermediate mass $M_{\rm p} = 10$--100$M_{\oplus}$ and $a \la 3$AU and with large mass $M_{\rm p} \ga 10^3 M_{\oplus}$ and $a \la 0.2$AU. Based on the simulated $M_{\rm p}$-$a$ distributions, we also evaluate the metallicity dependence of fraction of stars harboring planets that are detectable with current radial velocity survey. If protostellar disks attain the same fraction of heavy elements which are contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observation. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependence of the planet distributions that can be tested by on-going observations.
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 ).