Microlens Parallax Research Articles

Influence of Black Hole Kick Velocity on Microlensing Distributions

The natal kick velocity distribution for black holes (BHs) is unknown regardless of its importance for understanding the BH formation process. Gravitational microlensing is a unique tool for studying the distribution of BHs in our Galaxy, and the first isolated stellar-mass BH event, OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462), was recently identified by astrometric microlensing. This study investigates how the natal kick velocity for Galactic BHs affects the microlensing event rate distribution. We consider a Maxwell distribution with various average kick velocities, as well as the consequent variation of the spatial distribution of BHs. We find that the event rate for the BH lenses toward the Galactic bulge decreases as v avg increases, mainly due to the scale height inflation. We focus on the unique microlensing parameters measured for OB110462, with microlens parallax π E larger than 0.06 for its long timescale of t E > 200 days. We calculate the expected number of BH events occurring with parameters similar to OB110462 during the OGLE-IV survey by Mróz et al. and compare it with the actual number that occurred, at least one. Our fiducial model predicts 0.52, 0.38, 0.18, 0.042, and 4.0 × 10−3 events occurring for v avg = 25, 50, 100, 200, and 400 km s−1, respectively, which suggests that the average kick velocity is likely to be v avg ≲ 100 km s−1. The expected number smaller than unity even at maximum might indicate our luck in finding OB110462, which can be tested with future surveys by, e.g., the Roman Space Telescope.

Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-velocity Characterization

We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with Mp=0.59−0.05+0.15MJ at a projected orbital separation r⊥=1.4−0.3+0.8 au, and the host is a ∼1.1 M ⊙ turnoff star at ∼1.3 kpc. At r′≈14 , the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet’s orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the “inner–outer correlation” inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius θ E but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system.

Systematic KMTNet Planetary Anomaly Search. X. Complete Sample of 2017 Prime-field Planets

We complete the analysis of planetary candidates found by the KMT AnomalyFinder for the 2017 prime fields that cover ∼13 deg2. We report three unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and OGLE-2017-BLG-1237. The first two of these were not previously identified, while the last was not previously published due to technical complications induced by a nearby variable. We further report that a fourth anomalous event, the previously recognized OGLE-2017-BLG-1777, is very likely to be planetary, although its light curve requires unusually complex modeling because the lens and source both have orbiting companions. One of the three unambiguous planets, OGLE-2017-BLG-1275, is the first AnomalyFinder discovery that has a Spitzer microlens parallax measurement, π E ≃ 0.045 ± 0.015, implying that this planetary system almost certainly lies in the Galactic bulge. In the order listed, the four planetary events have planet-host mass ratios q and normalized projected separations s of (logq,s)=(−2.31,0.61) , (−2.06, 0.63/1.09), (−2.10, 1.04), and (−2.86, 0.72). Combined with previously published events, the 2017 prime fields contain 11 unambiguous planets with well-measured q and one very likely candidate, of which three are AnomalyFinder discoveries. In addition to these 12, there are three other unambiguous planets with large uncertainties in q.

OGLE-2019-BLG-1180Lb: Discovery of a Wide-orbit Jupiter-mass Planet around a Late-type Star

We report on the discovery and analysis of the planetary microlensing event OGLE-2019-BLG-1180 with a planet-to-star mass ratio q ∼ 0.003. The event OGLE-2019-BLG-1180 has unambiguous cusp-passing and caustic-crossing anomalies, which were caused by a wide planetary caustic with s ≃ 2, where s is the star–planet separation in units of the angular Einstein radius θ E. Thanks to well-covered anomalies by the Korea Micorolensing Telescope Network (KMTNet), we measure both the angular Einstein radius and the microlens parallax in spite of a relatively short event timescale of t E = 28 days. However, because of a weak constraint on the parallax, we conduct a Bayesian analysis to estimate the physical lens parameters. We find that the lens system is a super-Jupiter-mass planet of orbiting a late-type star of at a distance . The projected star–planet separation is , which means that the planet orbits at about four times the snow line of the host star. Considering the relative lens–source proper motion of μ rel = 6 mas yr−1, the lens will be separated from the source by 60 mas in 2029. At that time one can measure the lens flux from adaptive optics imaging of Keck or a next-generation 30 m class telescope. OGLE-2019-BLG-1180Lb represents a growing population of wide-orbit planets detected by KMTNet, so we also present a general investigation into prospects for further expanding the sample of such planets.

MOA-2022-BLG-249Lb: Nearby microlensing super-Earth planet detected from high-cadence surveys

Aims. We investigate the data collected by the high-cadence microlensing surveys during the 2022 season in search of planetary signals appearing in the light curves of microlensing events. From this search, we find that the lensing event MOA-2022-BLG-249 exhibits a brief positive anomaly that lasted for about one day, with a maximum deviation of ~0.2 mag from a single-source, single-lens model. Methods. We analyzed the light curve under the two interpretations of the anomaly: one originated by a low-mass companion to the lens (planetary model) and the other originated by a faint companion to the source (binary-source model). Results. We find that the anomaly is better explained by the planetary model than the binary-source model. We identified two solutions rooted in the inner-outer degeneracy and for both of them, the estimated planet-to-host mass ratio, q ~ 8 × 10−5, is very small. With the constraints provided by the microlens parallax and the lower limit on the Einstein radius, as well as the blend-flux constraint, we find that the lens is a planetary system, in which a super-Earth planet, with a mass of (4.83 ± 1.44) Μ⊕, orbits a low-mass host star, with a mass of (0.18 ± 0.05) M⊙, lying in the Galactic disk at a distance of (2.00 ± 0.42) kpc. The planet detection demonstrates the elevated microlensing sensitivity of the current high-cadence lensing surveys to low-mass planets.

OGLE-2018-BLG-0799Lb: a q ∼ 2.7 × 10−3 planet with Spitzer parallax

ABSTRACT We report the discovery and analysis of a planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is q = (2.65 ± 0.16) × 10−3. The ground-based observations yield a constraint on the angular Einstein radius θE, and the microlensing parallax vector $\boldsymbol{{\pi} }_{\rm E}$, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $M_{\rm planet} = 0.26_{-0.11}^{+0.22}M_{\rm J}$ planet orbiting an $M_{\rm host} = 0.093_{-0.038}^{+0.082}~\mathrm{M}_{\odot }$, at a distance of $D_{\rm L} = 3.71_{-1.70}^{+3.24}$ kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of $0.13 {\, \mathrm{M}_{\odot }}$ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.

OGLE-2016-BLG-1093Lb: A Sub-Jupiter-mass Spitzer Planet Located in the Galactic Bulge

OGLE-2016-BLG-1093 is a planetary microlensing event that is part of the statistical Spitzer microlens parallax sample. The precise measurement of the microlens parallax effect for this event, combined with the measurement of finite-source effects, leads to a direct measurement of the lens masses and system distance, M host =0.38–0.57 M ⊙ and m p = 0.59–0.87 M Jup, and the system is located at the Galactic bulge (D L ∼ 8.1 kpc). Because this was a high-magnification event, we are also able to empirically show that the “cheap-space parallax” concept produces well-constrained (and consistent) results for ∣π E∣. This demonstrates that this concept can be extended to many two-body lenses. Finally, we briefly explore systematics in the Spitzer light curve in this event and show that their potential impact is strongly mitigated by the color constraint.

Using Source Proper Motion to Validate Terrestrial Parallax: OGLE-2019-BLG-1058

Abstract We show that because the conditions for producing terrestrial microlens parallax (TPRX; i.e., a nearby disk lens) will also tend to produce a large lens-source relative proper motion (μ rel), source proper motion ( μ S) measurements in general provide a strong test of TPRX signals, which Gould & Yee (2013) showed were an important probe of free-floating planet (FFP) candidates. As a case study, we report a single-lens/single-source microlensing event designated as OGLE-2019-BLG-1058. For this event, the short timescale (∼2.5 days) and very fast μ rel (∼17.6 mas yr−1) suggest that this isolated lens is an FFP candidate located in the disk of our Galaxy. For this event, we find a TPRX signal consistent with a disk FFP, but at low significance. A direct measurement of the μ S shows that the large μ rel is due to an extreme μ S, and thus, the lens is consistent with being a very-low-mass star in the bulge and the TPRX measurement is likely spurious. By contrast, we show how a precise measurement of μ S with the mean properties of the bulge proper motion distribution would have given the opposite result; i.e., provided supporting evidence for an FFP in the disk and the TPRX measurement.

KMT-2021-BLG-0322: Severe degeneracy between triple-lens and higher-order binary-lens interpretations

Aims. We investigate the microlensing event KMT-2021-BLG-0322, for which the light curve exhibits three distinctive sets of caustic-crossing features. It is found that the overall features of the light curve are approximately described by a binary-lens (2L1S) model, but the model leaves substantial residuals. We test various interpretations with the aim of explaining the residuals. Methods. We find that the residuals can be explained either by considering a nonrectilinear lens-source motion caused by the microlens-parallax and lens-orbital effects or by adding a low-mass companion to the binary lens (3L1S model). The degeneracy between the higher-order 2L1S model and the 3L1S model is very severe, making it difficult to single out a correct solution based on the photometric data. This degeneracy was known before for two previous events (MACHO-97-BLG-41 and OGLE-2013-BLG-0723), which led to the false detections of planets in binary systems, and thus the identification of the degeneracy for KMT-2021-BLG-0322 illustrates that the degeneracy can be not only common but also very severe, emphasizing the need to check both interpretations of deviations from 2L1S models. Results. From the Bayesian analysis conducted with the measured lensing observables of the event timescale, angular Einstein radius, and microlens parallax, it was estimated that the binary lens components have masses (M1,M2) = (0.62−0.26+0.25 M⊙, 0.07−0.03+0.03 M⊙), for both 2L1S and 3L1S solutions, and the mass of the tertiary lens component according to the 3L1S solution is M3 = 6.40−2.78+2.64 MJ.

An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb

We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q 2 = 0.9–1.2 × 10−5 = 3–4 ⊕ 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 (log s, log q) 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, A max ∼ 1450 for the underlying single-lens event, its light curve revealed a second companion with q 3 ∼ 0.05 and |log s 3| ∼ 1, i.e., a factor ∼ 10 closer to or farther from the host in projection. The measurements of the microlens parallax π E and the angular Einstein radius θE allow estimates of the host, planet and second companion masses, (M 1, M 2, M 3) ∼ (0.3 M ⊙, 1.0 M ⊕, 17 MJ ), the planet and second companion projected separations, (a ⊥,2, a ⊥,3) ∼ (1.5, 0.15 or 15) au, and system distance D L ∼ 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.

OGLE-2018-BLG-1185b: A Low-mass Microlensing Planet Orbiting a Low-mass Dwarf

Abstract We report an analysis of the planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number of ground-based telescopes and by the Spitzer Space Telescope. The ground-based light curve indicates a low planet–host star mass ratio of q = (6.9 ± 0.2) × 10−5, which is near the peak of the wide-orbit exoplanet mass-ratio distribution. We estimate the host star and planet masses with a Bayesian analysis using the measured angular Einstein radius under the assumption that stars of all masses have an equal probability of hosting the planet. The flux variation observed by Spitzer is marginal, but still places a constraint on the microlens parallax. Imposing a conservative constraint that this flux variation should be Δf Spz < 4 instrumental flux units yields a host mass of M host = 0.37 − 0.21 + 0.35 M ⊙ and a planet mass of m p = 8.4 − 4.7 + 7.9 M ⊕ . A Bayesian analysis including the full parallax constraint from Spitzer suggests smaller host star and planet masses of M host = 0.091 − 0.018 + 0.064 M ⊙ and m p = 2.1 − 0.4 + 1.5 M ⊕ , respectively. Future high-resolution imaging observations with the Hubble Space Telescope or Extremely Large Telescope could distinguish between these two scenarios and help reveal the planetary system properties in more detail.

OGLE-2018-BLG-1428Lb: a Jupiter-mass planet beyond the snow line of a dwarf star

ABSTRACT We present the analysis of the microlensing event OGLE-2018-BLG-1428, which has a short-duration (∼1 d) caustic-crossing anomaly. The event was caused by a planetary lens system with planet/host mass ratio q = 1.7 × 10−3. Because of the detection of the caustic-crossing anomaly, the finite source effect was well measured, but the microlens parallax was not constrained due to the relatively short time-scale (tE = 24 d). From a Bayesian analysis, we find that the host star is a dwarf star $M_{\rm host}=0.43^{+0.33}_{-0.22} \ \mathrm{M}_{\odot }$ at a distance $D_{\rm L}=6.22^{+1.03}_{-1.51}\ {\rm kpc}$ and the planet is a Jovian-mass planet $M_{\rm p}=0.77^{+0.77}_{-0.53} \ M_{\rm J}$ with a projected separation $a_{\perp }=3.30^{+0.59}_{-0.83}\ {\rm au}$. The planet orbits beyond the snow line of the host star. Considering the relative lens-source proper motion of $\mu _{\rm rel} = 5.58 \pm 0.38\ \rm mas\ yr^{-1}$, the lens can be resolved by adaptive optics with a 30 m telescope in the future.

MagAO Observations of the Binary Microlens OGLE-2014-BLG-1050 Prefer the Higher-mass Solution*

Abstract We report adaptive optics (AO) follow-up imaging of OGLE-2014-BLG-1050, which is the second binary microlensing event with space-based parallax measurements. The degeneracy in microlens parallax π E led to two sets of solutions, either a ∼ (0.9, 0.35)M ⊙ binary at ∼3.5 kpc or a ∼(0.2, 0.07)M ⊙ binary at ∼1.1 kpc. We measure the flux blended with the microlensed source by conducting Magellan AO observations, and find that the blending is consistent with the predicted lens flux from the higher-mass solution. From the combination of the AO flux measurement together with previous lensing constraints, it is estimated that the lens system consists of a primary and a secondary at kpc.

OGLE-2007-BLG-224L: A Direct Test of Terrestrial Parallax

Abstract We present limits on the lens flux of OGLE-2007-BLG-224 based on MagAO imaging taken seven years after the microlensing event. At the time of the observations, the lens should have been separated from the microlensing source by 292 mas. However, no new sources are detected with MagAO. We place an upper limit on the lens flux of H > 20.57. This measurement supports the conclusion of Gould et al. that the lens in this event should be a brown dwarf. This is the first test of a prediction based on the terrestrial microlens parallax effect and the first AO confirmation of a substellar/dark microlens.

Evidence of Systematic Errors in Spitzer Microlens Parallax Measurements

Abstract The microlensing parallax campaign with the Spitzer space telescope aims to measure masses and distances of microlensing events seen toward the Galactic bulge, with a focus on planetary microlensing events. The hope is to measure how the distribution of planets depends on position within the Galaxy. In this paper, we compare 50 microlens parallax measurements from the 2015 Spitzer campaign to three different Galactic models commonly used in microlensing analyses, and we find that ≥74% of these events have microlensing parallax values higher than the medians predicted by Galactic models. The Anderson–Darling tests indicate probabilities of p AD < 6.6 × 10−5 for these three Galactic models, while the binomial probability of such a large fraction of large microlensing parallax values is <4.6 × 10−4. Given that many Spitzer light curves show evidence of large correlated errors, we conclude that this discrepancy is probably due to systematic errors in the Spitzer photometry. We find formally acceptable probabilities of p AD > 0.05 for subsamples of events with bright source stars (I S ≤ 17.75) or Spitzer coverage of the light-curve peak. This indicates that the systematic errors have a more serious influence on faint events, especially when the light-curve peak is not covered by Spitzer. We find that multiplying an error bar renormalization factor of 2.2 by the reported error bars on the Spitzer microlensing parallax measurements provides reasonable agreement with all three Galactic models. However, corrections to the uncertainties in the Spitzer photometry itself are a more effective way to address the systematic errors.

OGLE-2018-BLG-1269Lb: A Jovian Planet with a Bright I = 16 Host

Abstract We report the discovery of a planet in the microlensing event OGLE-2018-BLG-1269 with a planet–host mass ratio q ∼ 6 × 10−4, i.e., 0.6 times smaller than the Jupiter/Sun mass ratio. Combined with the Gaia parallax and proper motion, a strong one-dimensional constraint on the microlens parallax vector allows us to significantly reduce the uncertainties of lens physical parameters. A Bayesian analysis that ignores any information about light from the host yields that the planet is a cold giant orbiting a Sun-like star at a distance of . The projected planet–host separation is . Using Gaia astrometry, we show that the blended light lies from the host and therefore must be either the host star or a stellar companion to the host. An isochrone analysis favors the former possibility at >99.6%. The host is therefore a subgiant. For host metallicities in the range of , the host and planet masses are then in the range of and , respectively. Low host metallicities are excluded. The brightness and proximity of the lens make the event a strong candidate for spectroscopic follow-up both to test the microlensing solution and to further characterize the system.

Pixel level decorrelation in service of the Spitzer microlens parallax survey

ABSTRACT Microlens parallax measurements combining space-based and ground-based observatories can be used to study planetary demographics. In recent years, the Spitzer Space Telescope was used as a microlens parallax satellite. Meanwhile, Spitzer IRAC has been employed to study short-period exoplanets and their atmospheres. As these investigations require exquisite photometry, they motivated the development of numerous self-calibration techniques now widely used in the exoplanet atmosphere community. Specifically, pixel level decorrelation (PLD) was developed for starring-mode observations in uncrowded fields. We adapt and extend PLD to make it suitable for observations obtained as part of the Spitzer Microlens Parallax Campaign. We apply our method to two previously published microlensing events, OGLE-2017-BLG-1140 and OGLE-2015-BLG-0448, and compare its performance to the state-of-the-art pipeline used to analyses Spitzer microlensing observation. We find that our method yields photometry 1.5–6 times as precise as previously published. In addition to being useful for Spitzer, a similar approach could improve microlensing photometry with the forthcoming Nancy Grace Roman Space Telescope.

OGLE-2017-BLG-0406: Spitzer Microlens Parallax Reveals Saturn-mass Planet Orbiting M-dwarf Host in the Inner Galactic Disk

Abstract We report the discovery and analysis of the planetary microlensing event OGLE-2017-BLG-0406, which was observed both from the ground and by the Spitzer satellite in a solar orbit. At high magnification, the anomaly in the light curve was densely observed by ground-based-survey and follow-up groups, and it was found to be explained by a planetary lens with a planet/host mass ratio of from the light-curve modeling. The ground-only and Spitzer-“only” data each provide very strong one-dimensional (1D) constraints on the 2D microlens parallax vector . When combined, these yield a precise measurement of and of the masses of the host and planet M planet = 0.41 ± 0.05 M Jup. The system lies at a distance D L = 5.2 ± 0.5 kpc from the Sun toward the Galactic bulge, and the host is more likely to be a disk population star according to the kinematics of the lens. The projected separation of the planet from the host is (i.e., just over twice the snow line). The Galactic-disk kinematics are established in part from a precise measurement of the source proper motion based on OGLE-IV data. By contrast, the Gaia proper-motion measurement of the source suffers from a catastrophic 10σ error.

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

Abstract We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this determination with the angular Einstein radius measured by VLTI-GRAVITY observations, we find that the lens is a star with mass at a distance D L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is , so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge

Abstract We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60 ± 0.03 M ⊙ star with D LS = 0.53 ± 0.11 kpc, where D LS is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a star with D LS = 0.40 ± 0.12 kpc or a star with D LS = 0.53 ± 0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurring in single-lens events.