Microlensing exoplanet discoveries

A cold super-Neptune/sub-Saturn:

Poleski et al. "An ice giant exoplanet interpretation of the anomaly in microlensing event OGLE-2011-BLG-0173"
https://arxiv.org/abs/1805.00049

KMT-2016-BLG-1820 and KMT-2016-BLG-2142: Two Microlensing Binaries Composed of Planetary-mass Companions and Very-Low-Mass Primaries
https://arxiv.org/abs/1805.09983

A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291
https://arxiv.org/abs/1806.06106

An almanac of predicted microlensing events for the 21st century
https://arxiv.org/abs/1806.10003

Lensing targets of interest:
LAWD 37 will produce 41 events between 2026 and 2100. HD 180617, GJ 674 (1 planet), HD 39194 (3 planets), HD 145417 and GJ 588 will all produce more than 10 microlensing events. GJ 674's microlensing events will not be close enough to probe it's planetary system, but one of HD 39194's will on 16 Oct 2094 (±3 days).

OGLE-2014-BLG-1186: gravitational microlensing providing evidence for a planet orbiting the foreground star or for a close binary source?
https://arxiv.org/abs/1808.03149

Quote :

(abridged) Using the particularly long gravitational microlensing event OGLE-2014-BLG-1186 with a time-scale tE ~ 300 d, we present a methodology for identifying the nature of localised deviations from single-lens point-source light curves, which ensures that 1) the claimed signal is substantially above the noise floor, 2) the inferred properties are robustly determined and their estimation not subject to confusion with systematic noise in the photometry, 3) there are no alternative viable solutions within the model framework that might have been missed. Annual parallax and binarity could be separated and robustly measured from the wing and the peak data, respectively. We find matching model light curves that involve either a binary lens or a binary source. Our binary-lens models indicate a planet of mass M2 = (45 ± 9) M⊕, orbiting a star of mass M1 = (0.35 ± 0.06) M⊙, located at a distance DL = (1.7 ± 0.3) kpc from Earth, whereas our binary-source models suggest a brown-dwarf lens of M = (0.046 ± 0.007) M⊙, located at a distance DL = (5.7 ± 0.9) kpc, with the source potentially being a (partially) eclipsing binary involving stars predicted to be of similar colour given the ratios between the luminosities and radii. The ambiguity in the interpretation would be resolved in favour of a lens binary by observing the luminous lens star separating from the source at the predicted proper motion of μ = (1.6 ± 0.3) mas yr−1, whereas it would be resolved in favour of a source binary if the source could be shown to be a (partially) eclipsing binary matching the obtained model parameters. We experienced that close binary source stars pose a challenge for claiming the detection of planets by microlensing in events where the source passes very close to the lens star hosting the planet.

KMT-2017-BLG-0165Lb: A Super-Neptune mass planet Orbiting a Sun-like Host Star
https://arxiv.org/abs/1809.01288

Quote :

We report the discovery of a low mass-ratio planet (q=1.3×10−4), i.e., 2.5 times higher than the Neptune/Sun ratio. The planetary system was discovered from the analysis of the KMT-2017-BLG-0165 microlensing event, which has an obvious short-term deviation from the underlying light curve produced by the host of the planet. Although the fit improvement with the microlens parallax effect is relatively low, one component of the parallax vector is strongly constrained from the light curve, making it possible to narrow down the uncertainties of the lens physical properties. A Bayesian analysis yields that the planet has a super-Neptune mass (M2=34+15−12 M⊕) orbiting a Sun-like star (M1=0.76+0.34−0.27 M⊙) located at 4.5 kpc. The blended light is consistent with these host properties. The projected planet-host separation is a⊥=3.45+0.98−0.95 AU, implying that the planet is located outside the snowline of the host, i.e., asl∼2.1 AU. KMT-2017-BLG-0165Lb is the sixteenth microlensing planet with mass ratio q<3×10−4. Using the fifteen of these planets with unambiguous mass-ratio measurements, we apply a likelihood analysis to investigate the form of the mass-ratio function in this regime. If we adopt a broken power law for the form of this function, then the break is at qbr≃0.56×10−4, which is much lower than previously estimated. Moreover, the strength of the break, ζ>3.5 is quite severe. Alternatively, the distribution is also suggestive of a "pile-up" of planets at Neptune-like mass ratios, below which there is a dramatic drop in frequency.

"WFIRST Exoplanet Mass Measurement Method Finds a Planetary Mass of 39±8M_⊕ for OGLE-2012-BLG-0950Lb"
https://arxiv.org/abs/1809.02654

How is this linked to WFIRST I hear you ask? Especially given that mission is currently planned for launch in the mid-2020s (barring JWST-style shenanigans and other delays)...

Quote :

This analysis also demonstrates the techniques that will be used to measure the masses of planets and their host stars by the WFIRST exoplanet microlensing survey: one-dimensional microlensing parallax combined with the separation and brightness measurement of the unresolved source and host stars to yield multiple redundant constraints on the masses and distance of the planetary system.

Because degeneracies make model fitting fun, here's microlensing degeneraacy #304,717.

MOA-2016-BLG-319Lb: Microlensing Planet Subject to Rare Minor-Image Perturbation Degeneracy in Determining Planet Parameter
https://arxiv.org/abs/1809.07898

Quote :

We present the analysis of the planetary microlensing event MOA-2016-BLG-319. The event light curve is characterized by a brief (∼3 days) anomaly near the peak produced by minor-image perturbations. From modeling, we find two distinct solutions that describe the observed light curve almost equally well. From the investigation of the lens-system configurations, we find that the confusion in the lensing solution is caused by the degeneracy between the two solutions resulting from the source passages on different sides of the planetary caustic. These degeneracies can be severe for major-image perturbations but it is known that they are considerably less severe for minor-image perturbations. From the comparison of the lens-system configuration with those of two previously discovered planetary events, for which similar degeneracies were reported, we find that the degeneracies are caused by the special source trajectories that passed the star-planet axes at approximately right angles. By conducting a Bayesian analysis, it is estimated that the lens is a planetary system in which a giant planet with a mass Mp=0.62+1.16−0.33 MJ (0.65+1.21−0.35 MJ) is orbiting a low-mass M-dwarf host with a mass Mh=0.15+0.28−0.08 M⊙. Here the planet masses in and out of the parentheses represent the masses for the individual degenerate solutions. The projected host-planet separations are a⊥∼0.95 au and ∼1.05 au for the two solutions. The identified degeneracy indicates the need to check similar degeneracies in future analyses of planetary lensing events with minor-image perturbations.

A Cold Neptune Beyond the Snow Line in the Provisional WFIRST Field
https://arxiv.org/abs/1810.00014

Quote :

We present the analysis of the microlensing event OGLE-2015-BLG-1670, detected in a high extinction field, very close to the Galactic plane. Due to the dust extinction along the line of sight, this event was too faint to be detected before it reached the peak of magnification. The microlensing light-curve models indicate a high-magnification event with a maximum of Amax≳200, very sensitive to planetary deviations. An anomaly in the light curve has been densely observed by the microlensing surveys MOA, KMTNet, and OGLE. From the light-curve modeling, we find a planetary anomaly characterized by a planet-to-host mass ratio, q=(1.00+0.18−0.16)×10−4, at the peak recently identified in the mass-ratio function of microlensing planets. Thus, this event is interesting to include in future statistical studies about planet demography. We have explored the possible degeneracies and find two competing planetary models resulting from the s↔1/s degeneracy. However, because the projected separation is very close to s=1, the physical implications for the planet for the two solutions are quite similar, except for the value of s. By combining the light-curve parameters with a Galactic model, we have estimated the planet mass M2=17.9+9.6−8.8M⊕, and the lens distance DL=6.7+1.0−1.3kpc, corresponding to a Neptune-mass planet close to the Galactic bulge. Such events with a low absolute latitude (|b|≈1.1deg) are subject to both high extinction and more uncertain source distances, two factors that may affect the mass measurements in the provisional WFIRST fields. More events are needed to investigate the potential trade-off between the higher lensing rate and the difficulty in measuring masses in these low-latitude fields.

Kmt-2016-blg-1397b: Kmtnet-only discovery of a microlens giant planet
https://arxiv.org/abs/1810.10792

Quote :

We report the discovery of a giant planet in the KMT-2016-BLG-1397 microlensing event, which was found by The Korea Microlensing Telescope Network (KMTNet) alone. The time scale of this event is t_E = 40.0 +- 0.5 days and the mass ratio between the lens star and its companion is q = 0.016 +- 0.002. The planetary perturbation in the light curve is a smooth bump, resulting in the classical binary-lens/binary-source (2L1S/1L2S) degeneracy. We measure the V - I color of the (putative) two sources in the 1L2S model, and then effectively rule out the binary source solution. The finite-source effect is marginally detected. Combined with the limits on the blend flux and the probability distribution of the source size normalized by the Einstein radius rho, a Bayesian analysis yields the lens mass M_L = 0.45+0.33-0.28 M_sun, at distance of D_L = 6.60+1.10-1.30 kpc. Thus the companion is a super-Jupiter of a mass m_p = 7.0+5.2-4.3 M_J , at a projected separation r = 5.1+1.5-1.7 AU, indicating that the planet is well beyond the snow line of the host star.

Two new free-floating planet candidates from microlensing
https://arxiv.org/abs/1811.00441

Two Jupiter-Mass Planets Discovered by the KMTNet Survey in 2017
https://arxiv.org/abs/1811.12505

Quote :

We report two microlensing events, KMT-2017-BLG-1038 and KMT-2017-BLG-1146 that are caused by planetary systems. These events were discovered by KMTNet survey observations from the 2017 bulge season. The discovered systems consist of a planet and host star with mass ratios, 5.3+0.2−0.4×10−3 and 2.0+0.6−0.1×10−3, respectively. Based on a Bayesian analysis assuming a Galactic model without stellar remnant hosts, we find that the planet, KMT-2017-BLG-1038Lb, is a super Jupiter-mass planet (Mp=2.04+2.02−1.15MJ) orbiting a mid-M dwarf host (Mh=0.37+0.36−0.20M⊙) that is located at 6.01+1.27−1.72 kpc toward the Galactic bulge. The other planet, KMT-2017-BLG-1146Lb, is a sub Jupiter-mass planet (Mp=0.71+0.80−0.42MJ) orbiting a mid-M dwarf host (Mh=0.33+0.36−0.20M⊙) at a distance toward the Galactic bulge of 6.50+1.38−2.00 kpc. Both are potentially gaseous planets that are beyond their hosts' snow lines. These typical microlensing planets will be routinely discovered by second-generation microlensing surveys, rapidly increasing the number of detections.

It seems that the planets in the OGLE-2012-BLG-0026L system may be in a mean-motion resonance

Madsen & Zhu "A Pair of Planets Likely in Mean-Motion Resonance From Gravitational Microlensing"
https://arxiv.org/abs/1901.04495

A Wide Orbit Exoplanet OGLE-2012-BLG-0838Lb
https://arxiv.org/abs/1901.05466

Quote :

We present the discovery of a planet on a very wide orbit in the microlensing event OGLE-2012-BLG-0838. The signal of the planet is well separated from the main peak of the event and the planet-star projected separation is found to be twice larger than the Einstein ring radius, which roughly corresponds to a projected separation of ~4 AU. Similar planets around low-mass stars are very hard to find using any technique other than microlensing. We discuss microlensing model fitting in detail and discuss the prospects for measuring the mass and distance of lens system directly.

Spectroscopic Mass and Host-star Metallicity Measurements for Newly Discovered Microlensing Planet OGLE-2018-BLG-0740Lb
https://arxiv.org/abs/1905.00155

MOA-bin-29b : A Microlensing Gas Giant Planet Orbiting a Low-mass Host Star
https://arxiv.org/abs/1905.01239

Has this one passed unnoticed? It also seems to orbit a rather massive star...

KMT-2018-BLG-1292: A Super-Jovian Microlens Planet in the Galactic Plane

Quote :

We report the discovery of KMT-2018-BLG-1292Lb, a super-Jovian Mplanet=4.5±1.3MJ planet orbiting an F or G dwarf Mhost=1.5±0.4M⊙, which lies physically within ${\cal O}(10\,\pc)$ of the Galactic plane. The source star is a heavily extincted AI∼5.2 luminous giant that has the lowest Galactic latitude, b=−0.28∘, of any planetary microlensing event. The relatively blue blended light is almost certainly either the host or its binary companion, with the first explanation being substantially more likely. This blend dominates the light at I band and completely dominates at R and V bands. Hence, the lens system can be probed by follow-up observations immediately, i.e., long before the lens system and the source separate due to their relative proper motion. The system is well characterized despite the low cadence Γ=0.15--0.20hr−1 of observations and short viewing windows near the end of the bulge season. This suggests that optical microlensing planet searches can be extended to the Galactic plane at relatively modest cost.

Edasich wrote:

Has this one passed unnoticed?

URL of this forum changed without warning, had to Google it to find the new one...

Lazarus wrote:

Edasich wrote:

Has this one passed unnoticed?

URL of this forum changed without warning, had to Google it to find the new one...

Yes, weird, indeed.

Yeah I've spent the last couple of days in contact with the forum host and apparently a domain name expired or something. However, the original URL redirects to the current one now. So this issue appears to have been resolved. I apologise for the inconvenience.

KMT-2018-BLG-1990Lb: A Nearby Jovian Planet From A Low-Cadence Microlensing Field
https://arxiv.org/abs/1905.05509

Quote :

We report the discovery and characterization of KMT-2018-BLG-1990Lb, a Jovian planet (mp=0.57+0.79−0.25MJ) orbiting a late M dwarf (M=0.14+0.20−0.06M⊙), at a distance $(D_L=1.23_{-0.43}^{+1.06}\,\kpc)$, and projected at 2.6±0.6 times the snow line distance, i.e., $a_{\rm snow}\equiv 2.7\,\au (M/M_\odot)$, This is the second Jovian planet discovered by KMTNet in its low cadence (0.4hr−1) fields, demonstrating that this population will be well characterized based on survey-only microlensing data.

Sirius_Alpha wrote:

Yeah I've spent the last couple of days in contact with the forum host and apparently a domain name expired or something. However, the original URL redirects to the current one now. So this issue appears to have been resolved. I apologise for the inconvenience.

No worries, figured it was something like that. Weirdly my mobile phone's DNS picked up the redirect but my computer didn't which was somewhat confusing. Thanks for the update, pity you had to deal with hosting company nonsense.

OGLE-2018-BLG-0532Lb: Cold Neptune With Possible Jovian Sibling
https://arxiv.org/abs/1905.08148

Quote :

We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious signatures in the light curve that lead to an estimate of the planet-host mass ratio q=Mplanet/Mhost≃1×10−4. Although there are no obvious systematic residuals to this double-lens/single-source (2L1S) fit, we find that χ2 can be significantly improved by adding either a third lens (3L1S, Δχ2=81) or second source (2L2S, Δχ2=65) to the lens-source geometry. After thorough investigation, we conclude that we cannot decisively distinguish between these two scenarios and therefore focus on the robustly-detected planet. However, given the possible presence of a second planet, we investigate to what degree and with what probability such additional planets may affect seemingly single-planet light curves. Our best estimates for the properties of the lens star and the secure planet are: a host mass M∼0.25M⊙, system distance DL∼1kpc and planet mass mp,1=8M⊕ with projected separation a1,⊥=1.4au. However, there is a relatively bright I=18.6 (and also relatively blue) star projected within <50mas of the lens, and if future high-resolution images show that this is coincident with the lens, then it is possible that it is the lens, in which case, the lens would be both more massive and more distant than the best-estimated values above.

KMT-2018-BLG-0029Lb: A Very Low Mass-Ratio Spitzer Microlens Planet
https://arxiv.org/abs/1906.11183

OGLE-2018-BLG-1011Lb, c: Microlensing Planetary System with Two Giant Planets Orbiting a Low-mass Star

Quote :

We report a multiplanetary system found from the analysis of microlensing event OGLE-2018-BLG-1011, for which the light curve exhibits a double-bump anomaly around the peak. We find that the anomaly cannot be fully explained by the binary-lens or binary-source interpretations and its description requires the introduction of an additional lens component. The 3L1S (3 lens components and a single source) modeling yields three sets of solutions, in which one set of solutions indicates that the lens is a planetary system in a binary, while the other two sets imply that the lens is a multiplanetary system. By investigating the fits of the individual models to the detailed light curve structure, we find that the multiple-planet solution with planet-to-host mass ratios ∼9.5×10−3 and ∼15×10⁻³ are favored over the other solutions. From the Bayesian analysis, we find that the lens is composed of two planets with masses 1.8^+3.4_−1.1 M_J and 2.8^+5.1_−1.7 M_J around a host with a mass 0.18^+0.3_−0.10 M_⊙ and located at a distance 7.1^+1.1_−1.5 kpc. The estimated distance indicates that the lens is the farthest system among the known multiplanetary systems. The projected planet-host separations are a⊥,2=1.8^+2.1_{−1.5 au} (0.8^+0.9_−0.6 au) and a⊥,3=0.8^+0.9_−0.6 au, where the values of a⊥,2 in and out the parenthesis are the separations corresponding to the two degenerate solutions, indicating that both planets are located beyond the snow line of the host, as with the other four multiplanetary systems previously found by microlensing.

OGLE-2015-BLG-1649Lb: A gas giant planet around a low-mass dwarf
https://arxiv.org/abs/1907.11536