Microlensing exoplanet discoveries

An Earth-mass Planet in a Time of Covid-19: KMT-2020-BLG-0414Lb
https://arxiv.org/abs/2103.01896

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We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q2=0.9--1.2×10−5=3--4 q⊕ at 1σ, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries (4≲q/q⊕≲6), it fills out the previous empty sector at the bottom of the triangular (logs,logq) diagram, where s is the planet-host separation in units of the angular Einstein radius θE. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets. Due to the extreme magnification of the event, Amax∼1450 for the underlying single-lens event, its light curve revealed a second companion with q3∼0.05 and |logs3|∼1, i.e., a factor ∼10 closer to or farther from the host in projection. The measurements of the microlens parallax πE and the angular Einstein radius θE allow estimates of the host, planet, and second companion masses, (M1,M2,M3)∼(0.3M⊙,1.0M⊕,17MJ), the planet and second companion projected separations, (a⊥,2,a⊥,3)∼(1.5,0.15 or 15)~au, and system distance DL∼1 kpc. The lens could account for most or all of the blended light (I∼19.3) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by Covid-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program.

Sirius_Alpha wrote:

An Earth-mass Planet in a Time of Covid-19: KMT-2020-BLG-0414Lb
https://arxiv.org/abs/2103.01896

Quote :

We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q2=0.9--1.2×10−5=3--4 q⊕ at 1σ, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries (4≲q/q⊕≲6), it fills out the previous empty sector at the bottom of the triangular (logs,logq) diagram, where s is the planet-host separation in units of the angular Einstein radius θE. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets. Due to the extreme magnification of the event, Amax∼1450 for the underlying single-lens event, its light curve revealed a second companion with q3∼0.05 and |logs3|∼1, i.e., a factor ∼10 closer to or farther from the host in projection. The measurements of the microlens parallax πE and the angular Einstein radius θE allow estimates of the host, planet, and second companion masses, (M1,M2,M3)∼(0.3M⊙,1.0M⊕,17MJ), the planet and second companion projected separations, (a⊥,2,a⊥,3)∼(1.5,0.15 or 15)~au, and system distance DL∼1 kpc. The lens could account for most or all of the blended light (I∼19.3) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by Covid-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program.

Maybe COVID-2019-BLG-1Lb? Since that was (or was supposed to be) the virus strain. Yet too much honour for such a worldwide horror or hoax...

By the way what reassures us is to have serious scientific research going on working and providing good results and this is a nice example.

Seemingly a multi-planet system with highly unequal mass ratio components or a circumbinary Earth-sized planet orbiting an M dwarf + brown dwarf pair. Just astonishing!

Systematic KMTNet Planetary Anomaly Search, Paper I: OGLE-2019-BLG-1053Lb, A Buried Terrestrial Planet
https://arxiv.org/abs/2103.11880

It looks like there's a microlensing circumbinary planet, though the orbital configuration seems weird.

KMT-2019-BLG-1715: planetary microlensing event with three lens masses and two source stars

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We investigate the gravitational microlensing event KMT-2019-BLG-1715, of which light curve shows two short-term anomalies from a caustic-crossing binary-lensing light curve: one with a large deviation and the other with a small deviation. We identify five pairs of solutions, in which the anomalies are explained by adding an extra lens or source component in addition to the base binary-lens model. We resolve the degeneracies by applying a method, in which the measured flux ratio between the first and second source stars is compared with the flux ratio deduced from the ratio of the source radii. Applying this method leaves a single pair of viable solutions, in both of which the major anomaly is generated by a planetary-mass third body of the lens, and the minor anomaly is generated by a faint second source. A Bayesian analysis indicates that the lens comprises three masses: a planet-mass object with ∼2.6 MJ and binary stars of K and M dwarfs lying in the galactic disk. We point out the possibility that the lens is the blend, and this can be verified by conducting high-resolution followup imaging for the resolution of the lens from the source.

Wide-orbit exoplanets are common. Analysis of nearly 20 years of OGLE microlensing survey data
https://arxiv.org/abs/2104.02079

They find a new microlensing planet, and find that

Quote :

On average, every microlensing star hosts 1.4+0.9−0.6 ice giant planets.

Another microlensing planet:
OGLE-2018-BLG-1185b : A Low-Mass Microlensing Planet Orbiting a Low-Mass Dwarf
https://arxiv.org/abs/2104.02157

Shortest Microlensing Event with a Bound Planet: KMT-2016-BLG-2605
https://arxiv.org/abs/2104.07906

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KMT-2016-BLG-2605, with planet-host mass ratio q=0.012±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.

Five new microlensers, all of which are sub-Jovian.

Systematic KMTNet Planetary Anomaly Search, Paper II: Five New q<2×10−4 Mass-ratio Planets
https://arxiv.org/abs/2106.06686

A planet around M dwarf in binary system

KMT-2018-BLG-1743: Planetary Microlensing Event Occurring on Two Source Stars

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We present the analysis of the microlensing event KMT-2018-BLG-1743. The light curve of the event, with a peak magnification Apeak∼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 Δχ2∼188 and ∼91 over the 2L1S and 3L1S solutions, respectively. Assuming that these Δχ2 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_host/M_⊙,M_planet/M_J,D_L/kpc)∼(0.19^+0.27_-0.111,0.25^+0.34-0.14,6.48^+0.94_-1.03) and ∼(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, μwide∼2.3mas yr^-1 and μclose∼4.1mas yr^-1, are substantially different, and thus the degeneracy can be broken by resolving the lens and source from future high-resolution imaging observations.

New Giant Planet beyond the Snow Line for an Extended MOA Exoplanet Microlens Sample
https://arxiv.org/abs/2107.03400

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Characterizing a planet detected by microlensing is hard if the planetary signal is weak or the lens-source relative trajectory is far from caustics. However, statistical analyses of planet demography must include those planets to accurately determine occurrence rates. As part of a systematic modeling effort in the context of a >10-year retrospective analysis of MOA's survey observations to build an extended MOA statistical sample, we analyze the light curve of the planetary microlensing event MOA-2014-BLG-472. This event provides weak constraints on the physical parameters of the lens, as a result of a planetary anomaly occurring at low magnification in the light curve. We use a Bayesian analysis to estimate the properties of the planet, based on a refined Galactic model and the assumption that all Milky Way's stars have an equal planet-hosting probability. We find that a lens consisting of a 1.9+2.2−1.2MJ giant planet orbiting a 0.31+0.36−0.19M⊙ host at a projected separation of 0.75±0.24au is consistent with the observations and is most likely, based on the Galactic priors. The lens most probably lies in the Galactic bulge, at 7.2+0.6−1.7kpc from Earth. The accurate measurement of the measured planet-to-host star mass ratio will be included in the next statistical analysis of cold planet demography detected by microlensing.

Three new microlensing planets

Three faint-source microlensing planets detected via resonant-caustic channel

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We conducted a project of reinvestigating the 2017--2019 microlensing data collected by the 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. The project led us to find three planets including KMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The lensing light curves of the events have a common characteristic that 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. 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/MJ≲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 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.

Confirming that long-period Jupiter-like planets are rather common around M dwarfs.

The host star of MOA-2010-BLG-477L b turns out to be a white dwarf.

A Jovian analogue orbiting a white dwarf star

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Studies have shown that the remnants of destroyed planets and debris-disk planetesimals can survive the volatile evolution of their host stars into white dwarfs, but few intact planetary bodies around white dwarfs have been detected. Simulations predict that planets in Jupiter-like orbits around stars of ≲8 M☉ (solar mass) avoid being destroyed by the strong tidal forces of their stellar host, but as yet, there has been no observational confirmation of such a survivor. Here we report the non-detection of a main-sequence lens star in the microlensing event MOA-2010-BLG-477Lb12 using near-infrared observations from the Keck Observatory. We determine that this system contains a 0.53 ± 0.11 M☉ white-dwarf host orbited by a 1.4 ± 0.3 Jupiter-mass planet with a separation on the plane of the sky of 2.8 ± 0.5 astronomical units, which implies a semi-major axis larger than this. This system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host’s evolution, and supports the prediction that more than half of white dwarfs have Jovian planetary companions13. Located at approximately 2.0 kiloparsecs towards the centre of our Galaxy, it is likely to represent an analogue to the end stages of the Sun and Jupiter in our own Solar System.

OGLE-2019-BLG-0468Lb,c: two microlensing giant planets around a G-type star
https://arxiv.org/abs/2111.03755

KMT-2021-BLG-0912Lb: A microlensing super Earth around a K-type star

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The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly. We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found under the assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of a binary-star system (1L2S model). The 1L2S model is ruled out based on the contradiction that the faint source companion is bigger than its primary, and one of the 2L1S solutions is excluded from the combination of the relatively worse fit, blending constraint, and lower overall probability, leaving two surviving solutions with the planet/host mass ratios of q∼2.8×10−5 and ∼1.1×10−5. A subtle central deviation supports the possibility of a tertiary lens component, either a binary companion to the host with a very large or small separation or a second planet lying near the Einstein ring, but it is difficult to claim a secure detection due to the marginal fit improvement, lack of consistency among different data sets, and difficulty in uniquely specifying the nature of the tertiary component. With the observables of the event, it is estimated that the masses of the planet and host are ∼(6.9 M⊕,0.75 M⊙) according to one solution and ∼(2.8 M⊕,0.80 M⊙) according to the other solution, indicating that the planet is a super Earth around a K-type star, regardless of the solution.

KMT-2018-BLG-1988Lb: microlensing super-Earth orbiting a low-mass disk dwarf
https://arxiv.org/abs/2111.08955

New far away low-mass planet (OGLE-2018-BLG-0383) and brown dwarf in close orbit (OGLE-2018-BLG-0271)

Systematic KMTNet Planetary Anomaly Search, Paper III: One Wide-Orbit Planet And Two Stellar Binaries

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Only a few wide-orbit planets around old stars have been detected, which limits our statistical understanding of this planet population. Following the systematic search for planetary anomalies in microlensing events found by the Korea Microlensing Telescope Network (KMTNet), we present the discovery and analysis of three events that were initially thought to contain wide-orbit planets. The anomalous feature in the light curve of OGLE-2018-BLG-0383 is caused by a planet with mass ratio q=2.1×10−4 and a projected separation s=2.45. This makes it the lowest mass-ratio microlensing planet at such wide orbits. The other two events, KMT-2018-BLG-0998 and OGLE-2018-BLG-0271, are shown to be stellar binaries (q>0.1) with rather close (s<1) separations. We briefly discuss the properties of known wide-orbit microlensing planets and show that the survey observations are crucial in discovering and further statistically constraining such a planet population.

…and a new microlensing planet too

OGLE-2014-BLG-0319: A Sub-Jupiter-Mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-Source Relative Proper Motions

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We report the discovery of a sub-Jovian-mass planet, OGLE-2014-BLG-0319Lb. The characteristics of this planet will be added into a future extended statistical analysis of the Microlensing Observations in Astrophysics (MOA) collaboration. The planetary anomaly of the light curve is characterized by MOA and OGLE survey observations and results in three degenerate models with different planetary mass-ratios of q=(10.3,6.6,4.5)×10⁻⁴, respectively. We find that the last two models require unreasonably small lens-source relative proper motions of μ_rel∼1mas/yr. Considering Galactic prior probabilities, we rule out these two models from the final result. We conduct a Bayesian analysis to estimate physical properties of the lens system using a Galactic model and find that the lens system is composed of a 0.49^+0.35_−0.27M_Jup sub-Jovian planet orbiting a 0.47^+0.33 _−0.25,M⊙ M-dwarf near the Galactic bulge. This analysis demonstrates that Galactic priors are useful to resolve this type of model degeneracy. This is important for estimating the mass ratio function statistically. However, this method would be unlikely successful in shorter timescale events, which are mostly due to low-mass objects, like brown dwarfs or free-floating planets. Therefore, careful treatment is needed for estimating the mass ratio function of the companions around such low-mass hosts which only the microlensing can probe.

OGLE-2016-BLG-1093Lb: A Sub-Jupiter-mass Spitzer Planet Located in Galactic Bulge
https://arxiv.org/abs/2201.04312

Four new planets

Mass Production of 2021 KMTNet Microlensing Planets I

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We inaugurate a program of "mass production" of microlensing planets discovered in 2021 KMTNet data, with the aim of laying the basis for future statistical studies. While we ultimately plan to quickly publish all 2021 planets meeting some minimal criteria, the current sample of four was chosen simply on the basis of having low initial estimates of the planet-host mass ratio, q. It is therefore notable that 2 members of this sample suffer from a degeneracy in the normalized source radius ρ that arises from different morphologies of closely spaced caustics. All four planets [KMT-2021-BLG-(1391,1253,1372,0748)] have well-characterized mass ratios, q, and therefore are suitable for mass-ratio frequency studies. Both of the ρ degeneracies can be resolved by future adaptive optics (AO) observations on 30m class telescopes. We provide general guidance for such AO observations for all events in anticipation of the prospect that they will revolutionize the field of microlensing planets.

Precision measurement of a brown dwarf mass in a binary system in the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035

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Brown dwarfs are poorly understood transition objects between stars and planets, with several competing mechanisms having been proposed for their formation. Mass measurements are generally difficult for isolated objects but also for brown dwarfs orbiting low-mass stars, which are often too faint for spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here we present the analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is due to a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including parallax, source radius and orbital motion of the binary lens. Results. After accurate modeling, we find that the lens is composed of a red dwarf with mass M1=0.149±0.010M⊙ and a brown dwarf with mass M2=0.0463±0.0031M⊙, at a projected separation of a⊥=0.585 au. The system has a peculiar velocity that is typical of old metal-poor populations in the thick disk. Percent precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become common with the Roman space telescope.

A couple from the field of rakes that is April 1st arXiv...

Han et al. "KMT-2021-BLG-1077L: The fifth confirmed multiplanetary system detected by microlensing"
https://arxiv.org/abs/2203.16734

Planets of 0.22 and 0.25 Mjup at projected separations of 1.26 and 0.96 au from a 0.15 Msun star.

Specht et al. "Kepler K2 Campaign 9: II. First space-based discovery of an exoplanet using microlensing"
https://arxiv.org/abs/2203.16959

1.1 Mjup planet at projected separation of 4.2 au from a 0.58 Msun star.

Has this been missed?

MOA-2020-BLG-135Lb: A New Neptune-class Planet for the Extended MOA-II Exoplanet Microlens Statistical Analysis

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We report the light-curve analysis for the event MOA-2020-BLG-135, which leads to the discovery of a new Neptune-class planet, MOA-2020-BLG-135Lb. With a derived mass ratio of q=1.52+0.39−0.31×10−4 and separation s≈1, the planet lies exactly at the break and likely peak of the exoplanet mass-ratio function derived by the MOA collaboration (Suzuki et al. 2016). We estimate the properties of the lens system based on a Galactic model and considering two different Bayesian priors: one assuming that all stars have an equal planet-hosting probability and the other that planets are more likely to orbit more massive stars. With a uniform host mass prior, we predict that the lens system is likely to be a planet of mass mplanet=11.3+19.2−6.9M⊕ and a host star of mass Mhost=0.23+0.39−0.14M⊙, located at a distance DL=7.9+1.0−1.0kpc. With a prior that holds that planet occurrence scales in proportion to the host star mass, the estimated lens system properties are mplanet=25+22−15M⊕, Mhost=0.53+0.42−0.32M⊙, and DL=8.3+0.9−1.0kpc. This planet qualifies for inclusion in the extended MOA-II exoplanet microlens sample.

At least eight more microlensing planetary systems.

Systematic KMTNet Planetary Anomaly Search. V. Complete Sample of 2018 Prime-Field
https://arxiv.org/abs/2204.04354

A lot of microlensing planets lately and the latest one is likely circumbinary (or at least circumprimary)

OGLE-2019-BLG-1470LABc: Another Microlensing Giant Planet in a Binary System

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We report the discovery and analysis of a triple-lens single-source (3L1S) microlensing event, OGLE-2019-BLG-1470. This event was first classified as a normal binary-lens single-source (2L1S) event, but a careful 2L1S modelling showed that it needs an additional lens or source to fit the observed data. It is found that the 3L1S model provides the best fit. The binary-lens binary-source (2L2S) model is excluded by Δχ2=47 and is also strong disfavored by its unreasonably small lens-source relative proper motion μrel∼0.8 mas,yr−1. We find that four 3L1S solutions can fit the observed data, and all of them contain a planet in a binary system. A Bayesian analysis based on a Galactic model indicates that the planet is super-Jovian and the binary stars are likely two M or K dwarfs. The projected primary-planet separation is about 3 AU. By investigating the properties of all microlensing planets in binary systems, we find another "missing planetary caustics" problem in the KMTNet planetary simple. A systematic KMTNet planetary anomaly search for planets in binary systems is needed.

KMT-2021-BLG-1898: Planetary microlensing event involved with binary source stars
https://arxiv.org/abs/2204.11378

KMT-2021-BLG-0240: Microlensing event with a deformed planetary signal
https://arxiv.org/abs/2204.11383

MOA-2019-BLG-008Lb: a new microlensing detection of an object at the planet/brown dwarf boundary

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We report on the observations, analysis and interpretation of the microlensing event MOA-2019- BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite source effects were observed. Therefore the angular Einstein ring radius cannot be measured from the light curve alone. However, the large event duration, t E about 80 days, allows a precise measurement of the microlensing parallax. In addition to the constraints on the angular radius and the apparent brightness I s of the source, we employ the Besancon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two Galactic models: the companion is likely a resident of the brown dwarf desert with a mass Mp about 30 MJup and the host is a main sequence dwarf star. The lens lies along the line of sight to the Galactic Bulge, at a distance of less then4 kpc. We estimate that in about 10 years, the lens and source will be separated by 55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground or space-based observatories.