Microlensing exoplanet discoveries

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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 26th April 2018, 9:06 pm

Hey we've got parallaxes to microlensing planetary systems from Gaia DR2.

Microlensing planets in the light of the second data release of Gaia
https://arxiv.org/abs/1804.10136

Context. Extrasolar planets found by gravitational microlensing often require assumptions on the source star distance and relative proper motion. Only in a few cases has it been possible to confirm these findings with space-based observations or high-resolution follow-up. 25 planetary microlensing events can be positionally cross-matched with the second Gaia data release containing parallax and proper motion measurements Aims. In this work we subject all microlensing planets listed in the NASA's Exoplanet Archive to a consistency check by comparing them with Gaia data release 2 measurements. The resulting list is supposed to serve as a reference for the microlensing community and to test if standard assumptions that are made in microlensing studies hold. Methods. Gravitational microlensing can constrain the physical parameters lens mass and lens distance based on fit parameters, such as the event timescale, the microlensing parallax, and the source star crossing time. If some of these parameters are not available one needs to resort to indirect means of assessing the events, often involving a Galactic model. In this work, we seek to make an assessment of those parameters solely based on Gaia DR2. Results. We find that 19 of 25 planets are consistent within 2-sigma of their published lens and source distances. Changing the lens distance of the remaining 6 published planets could lead to revised parameter values that are accordingly compatible with the published ones. We expect the incompatible planet mass estimates to belong to a blend star.

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Re: Microlensing exoplanet discoveries

Post by Lazarus on 4th May 2018, 3:46 pm

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
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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 28th May 2018, 1:08 pm

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

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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 18th June 2018, 8:49 pm

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

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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 26th June 2018, 8:30 pm

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).

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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 9th August 2018, 8:39 pm

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

(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.

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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 5th September 2018, 8:39 pm

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

We report the discovery of a low mass-ratio planet (q=1.310−4), 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<310−4. 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≃0.5610−4, 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.

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Re: Microlensing exoplanet discoveries

Post by Lazarus on 11th September 2018, 3:59 pm

"WFIRST Exoplanet Mass Measurement Method Finds a Planetary Mass of 398M 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)...

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.
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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 23rd September 2018, 9:05 pm

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

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.

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