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 paper, a short-duration (~7 days) low-amplitude deviation in the light curve due to a single-lens profile was observed in both the MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment) survey observations.
Abstract: We present observations of the unusual microlensing event OGLE 2003-BLG-235/MOA 2003-BLG-53. In this event, a short-duration (~7 days) low-amplitude deviation in the light curve due to a single-lens profile was observed in both the MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment) survey observations. We find that the observed features of the light curve can only be reproduced using a binary microlensing model with an extreme (planetary) mass ratio of 0.0039 for the lensing system. If the lens system comprises a main-sequence primary, we infer that the secondary is a planet of about 1.5 Jupiter masses with an orbital radius of ~3 AU.
TL;DR: In this paper, the authors presented the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval during 2005-2008 microlensing events during the survey-plus-follow-up high-magnification channel.
Abstract: We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.
TL;DR: In this paper, it was shown that the probability of detecting a planet of Jupiter mass or greater in the lensing zone is nearly 100%, with the probability remaining high down to Saturn masses and substantial even at 10 Earth masses.
Abstract: Hundreds of gravitational microlensing events have now been detected towards the Galactic bulge, with many more to come. The detection of fine structure in these events has been theorized to be an excellent way to discover extra-solar planetary systems along the line-of-sight to the Galactic center. We show that by focusing on high magnification events the probability of detecting planets of Jupiter mass or greater in the lensing zone (.6 -1.6 $R_E$) is nearly 100%, with the probability remaining high down to Saturn masses and substantial even at 10 Earth masses. This high probability allows a nearly definitive statement to made about the existence of lensing zone planets in each such system that undergoes high magnification. One might expect lightcurve deviations caused by the source passing near the small primary lens caustic to be small due to the large distance of the perturbing planet, but this effect is overcome by the high magnification. High magnification events are relatively rare (e.g. $\sim 1/20$th of events have peak magnifications greater than 20), but they occur regularly and the peak can be predicted in advance, allowing extra-solar planet detection with a relatively small use of resources over a relatively small amount of time.
TL;DR: The OGLE-2003-BLG-262 microlensing event as mentioned in this paper was generated by a point-mass lens transiting the face of a K giant source in the Galactic bulge, and the resulting finite-source effects were used to measure the angular Einstein radius, theta_E=195+-17muas, and so constrain the lens mass to the fullwidth half-maximum interval 0.08 < M/M_sun < 0.54.
Abstract: We analyze OGLE-2003-BLG-262, a relatively short, t_E=12.5+-0.1day, microlensing event generated by a point-mass lens transiting the face of a K giant source in the Galactic bulge. We use the resulting finite-source effects to measure the angular Einstein radius, theta_E=195+-17muas, and so constrain the lens mass to the full-width half-maximum interval 0.08 < M/M_sun < 0.54. The lens-source relative proper motion is mu_rel = 27+-2 km/s/kpc. Both values are typical of what is expected for lenses detected toward the bulge. Despite the short duration of the event, we detect marginal evidence for a "parallax asymmetry", but argue that this is more likely to be induced by acceleration of the source, a binary lens, or possibly by statistical fluctuations. Although OGLE-2003-BLG-262 is only the second published event to date in which the lens transits the source, such events will become more common with the new OGLE-III survey in place. We therefore give a detailed account of the analysis of this event to facilitate the study of future events of this type.
TL;DR: Two planets with masses that could not have been detected with other techniques are identified; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
Abstract: Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ∼0.71 and ∼0.27 times the mass of Jupiter and orbital separations of ∼2.3 and ∼4.6 astronomical units orbiting a primary star of mass ∼0.50 solar mass at a distance of ∼1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
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 ).