Microlensing exoplanet discoveries

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Re: Microlensing exoplanet discoveries

Post by Edasich on 6th April 2017, 4:16 am

It seems like this is the Microlensing Planet Discoveries Month.

A companion on the planet/brown dwarf mass boundary on a wide orbit discovered by gravitational microlensing

We present the discovery of a substellar companion to the primary host lens in the microlensing event MOA-2012-BLG-006. The companion-to-host mass ratio is 0.016, corresponding to a companion mass of ≈8 MJup(M∗/0.5M⊙). Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary M∗. The companion signal was separated from the peak of the primary event by a time that was as much as four times longer than the event timescale. We therefore infer a relatively large projected separation of the companion from its host of ≈10 a.u.(M∗/0.5M⊙)1/2 for a wide range (3-7 kpc) of host star distances from the Earth. We also challenge a previous claim of a planetary companion to the lens star in microlensing event OGLE-2002-BLG-045.

On the other hand, as a new planet arrives, another one seems to go away, OGLE-2002-BLG-045L b. Sad
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Re: Microlensing exoplanet discoveries

Post by Edasich on 7th April 2017, 4:57 am

It seems like this is the Microlensing Planet Discoveries Month.

Quoting myself, it's quite so! Laughing

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Lightcurve Analysis and Keck AO Imaging

We report the discovery of a microlensing planet --- MOA-2016-BLG-227Lb --- with a massive planet/host mass ratio of q≃910−3. This event was fortunately observed by several telescopes as the event location was very close to the area of the sky surveyed by Campaign 9 of the K2 Mission. Consequently, the planetary deviation is well covered and allows a full characterization of the lensing system. High angular resolution images by the Keck telescope show excess flux other than the source flux at the target position, and this excess flux could originate from the lens star. We combined the excess flux and the observed angular Einstein radius in a Bayesian analysis which considers various possible origins of the measured excess flux as priors, in addition to a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens. We compare the results of the Bayesian analysis using different priors for the probability of hosting planets with respect to host mass and find the planet is likely a gas-giant around an M/K dwarf likely located in the Galactic bulge. This is the first application of a Bayesian analysis considering several different contamination scenarios for a newly discovered event. Our approach for considering different contamination scenarios is crucial for all microlensing events which have evidence for excess flux irrespective of the quality of observation conditions, such as seeing, for example.
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Re: Microlensing exoplanet discoveries

Post by Sirius_Alpha on 8th April 2017, 7:46 pm

Edasich wrote:On the other hand, as a new planet arrives, another one seems to go away, OGLE-2002-BLG-045L b. Sad

Poleski et al didn't seem to think it was ever a secure detection anyway.
However, the analyzed data were very limited. Even though the mass ratio was found to be in planetary regime, this event is not considered a secure planet detection.

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Re: Microlensing exoplanet discoveries

Post by Led_Zep on 26th April 2017, 5:20 pm

Sirius_Alpha wrote:An Earth-mass Planet in a 1-AU Orbit around a Brown Dwarf
https://arxiv.org/abs/1703.08548

We combine Spitzer and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass (1.32+0.41−0.28M⊕) planet OGLE-2016-BLG-1195Lb at 1.11+0.13−0.10 AU orbiting a 0.072+0.014−0.010M⊙ ultracool dwarf, likely a brown dwarf. This is the lowest-mass microlensing planet to date. At 4.20+0.29−0.34 kpc, it is the third consecutive case among the Spitzer "Galactic distribution" planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both brown dwarfs and planetary systems at the limit of low-mass protoplanetary disks.


The Lowest Mass Ratio Planetary Microlens: OGLE 2016-BLG-1195Lb
https://arxiv.org/abs/1703.08639

We report discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE~2016--BLG--1195. This planet revealed itself as a small deviation from a microlensing single lens profile from an examination of the survey data soon after the planetary signal. The duration of the planetary signal is ∼2.5hours. The measured ratio of the planet mass to its host star is q=4.20.710−5. We further estimate that the lens system is likely to comprise a cold ∼3 Earth mass planet in a ∼2 AU wide orbit around a 0.2 Solar mass star at an overall distance of 7.1 kpc.

NASA press release :
https://www.nasa.gov/feature/jpl/iceball-planet-discovered-through-microlensing

'Iceball' Planet Discovered Through Microlensing
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Re: Microlensing exoplanet discoveries

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