Microlensing exoplanet discoveries

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MOA-2008-BLG-379Lb: A Massive Planet from a High Magnification Event with a Faint Source

http://arxiv.org/abs/1311.3424

We report analysis of high microlensing event MOA-2008-BLG-379, which has a strong microlensing anomaly at its peak, due to a massive planet with a mass ratio of q = 6.9 x 10^{-3}. Because the faint source star crosses the large resonant caustic, the planetary signal dominates the light curve. This is unusual for planetary microlensing events, and as a result, the planetary nature of this light curve was not immediately noticed. The planetary nature of the event was found when the MOA Collaboration conducted a systematic study of binary microlensing events previously identified by the MOA alert system. We have conducted a Bayesian analysis based on a standard Galactic model to estimate the physical parameters of the lens system. This yields a host star mass of M_L = 0.66_{-0.33}^{+0.29} M_Sun orbited by a planet of mass m_P = 4.8_{-2.4}^{+2.1} M_Jup at an orbital separation of a = 4.1_{-1.5}^{+1.9} AU at a distance of D_L = 3.6 +/- 1.3 kpc. The faint source magnitude of I_S = 21.30 and relatively high lens-source relative proper motion of mu_rel = 7.6 +/- 1.6 mas/yr implies that high angular resolution adaptive optics or Hubble Space Telescope observations are likely to be able to detect the source star, which would determine the masses and distance of the planet and its host star.

Led_Zep
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Re: Microlensing exoplanet discoveries

So many microlensing planets lately...

But I did not expect to see one of the closest exoplanets to our Sun... detected via microlensing...

Distance 3.6 (± 1.3) pc

http://exoplanet.eu/catalog/moa-2008-blg-379l_b/

Last edited by Edasich on 15th November 2013, 3:56 pm; edited 1 time in total (Reason for editing : Added EPE link)

Edasich
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OGLE-2012-BLG-0455/MOA-2012-BLG-206 - Ambiguous microlensing solution

OGLE-2012-BLG-0455/MOA-2012-BLG-206: Microlensing event with ambiguity in planetary interpretations caused by incomplete coverage of planetary signal
http://arxiv.org/abs/1403.1672

Characterizing a microlensing planet is done from modeling an observed lensing light curve. In this process, it is often confronted that solutions of different lensing parameters result in similar light curves, causing difficulties in uniquely interpreting the lens system, and thus understanding the causes of different types of degeneracy is important. In this work, we show that incomplete coverage of a planetary perturbation can also result in degenerate solutions even for events where the planetary signal is detected with a high level of statistical significance. We demonstrate the degeneracy for an actually observed event OGLE-2012-BLG-0455/MOA-2012-BLG-206. The peak of this high-magnification event (Amax∼400) exhibits very strong deviation from a point-lens model with Δχ2≳4000. From detailed modeling of the light curve, we find that the deviation can be explained by four distinct solutions, i.e., two very different sets of solutions, each with a two-fold degeneracy. While the two-fold (so-called close/wide'') degeneracy is well-understood, the degeneracy between the radically different solutions is not previously known. The model light curves of this degeneracy differ substantially in the parts that were not covered by observation, indicating that the degeneracy is caused by the incomplete coverage of the perturbation. It is expected that the frequency of the degeneracy introduced in this work will be greatly reduced with the improvement of the current lensing survey and follow-up experiments and the advent of new surveys.

I suppose measuring the proper motion of the source and lens would help break the degeneracy?

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MOA-2013-BLG-220L - Brown dwarf planet host?

MOA-2013-BLG-220Lb: Planetary Companion to a Possible Brown Dwarf Host
http://arxiv.org/abs/1403.2134

Based on its high proper motion $\mu=12.5\pm 1\,\masyr$, MOA-2013-BLG-220Lb is the best candidate to date for a microlensing planet with a verifiable brown dwarf host. This candidacy can be partially tested immediately and more fully tested by ∼2021, when the source and lens will have separated sufficiently to be resolved in high-resolution images even if the lens is at the bottom of the main sequence, and so extremely faint, H∼24. The planet-star mass ratio is q=3.01±0.02×10−3. The planet could have been detected and characterized purely with follow-up data. The potential to completely characterize planetary events from followup data has far-reaching implications for microlensing surveys, both current and into the LSST era.

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OGLE-2008-BLG-355L Massive planet around late-type star

OGLE-2008-BLG-355Lb: A Massive Planet around A Late type Star
http://arxiv.org/abs/1403.7005

We report the discovery of a massive planet OGLE-2008-BLG-355Lb. The light curve analysis indicates a planet:host mass ratio of q = 0.0118 +/- 0.0006 at a separation of 0.877 +/- 0.010 Einstein radii. We do not measure a significant microlensing parallax signal and do not have high angular resolution images that could detect the planetary host star. Therefore, we do not have a direct measurement of the host star mass. A Bayesian analysis, assuming that all host stars have equal probability to host a planet with the measured mass ratio implies a host star mass of M_h = 0.37_{-0.17}^{+0.30} M_Sun and a companion of mass M_P = 4.6^{+3.7}_{-2.2} M_Jup, at a projected separation of r_proj = 1.70^{+0.29}_{-0.30} AU. The implied distance to the planetary system is D_L = 6.8 +/- 1.1 kpc. A planetary system with the properties preferred by the Bayesian analysis would be a challenge to the core-accretion model of planet formation, as the core-accretion model predicts that massive planets are far more likely to form around more massive host stars. This core accretion model prediction is not consistent with our Bayesian prior of an equal probability of host stars of all masses to host a planet with the measured mass ratio. So, if the core accretion model prediction is right, we should expect that follow-up high angular resolution observations will detect a host star with a mass in the upper part of the range allowed by the Bayesian analysis. That is, the host would probably be a K or G dwarf.

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Sirius_Alpha

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Re: Microlensing exoplanet discoveries

This event was previously published as a brown dwarf companion (mass ratio q=0.106) in Jaroszyński et al. (2010), based on OGLE data alone. This re-analysis uses MOA data and re-reduced OGLE data.

Lazarus
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OGLE-2013-BLG-0102L - Star+BD or BD+Planet

OGLE-2013-BLG-0102La,b: Microlensing binary with components at star/brown-dwarf and brown-dwarf/planet boundaries
http://arxiv.org/abs/1407.7926

We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification A max ∼1.5 . It is found that the event was produced by a binary lens with a mass ratio between the components is q=0.13 and the anomaly was caused by the passage of the source trajectory over a caustic located away from the barycenter of the binary. From the analysis of the effects on the light curve due to the finite size of the source and the parallactic motion of the Earth, the physical parameters of the lens system are determined. The measured masses of the lens components are M 1 =0.097±0.011 M ⊙ and M 2 =0.013±0.002 M ⊙ , which correspond to the upper and lower limits of brown dwarfs, respectively. The distance to the lens is 3.02±0.21 kpc and the projected separation between the lens components is 0.80±0.04 AU . These physical parameters lie beyond the detection ranges of other methods, demonstrating that microlensing is a useful method in detecting very low-mass binaries.

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Sirius_Alpha

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Re: Microlensing exoplanet discoveries

So low-mass star with high-mass planet are not so uncommon after all.

And something tells me EPE is missing this one...

Edasich
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Re: Microlensing exoplanet discoveries

Edasich wrote:So low-mass star with high-mass planet are not so uncommon after all.
Imho, these low-mass star + high-mass planet systems are the tail end of the mass distribution of the process that forms binary stars.

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OGLE-2008-BLG-092L - Binary system with circumprimary Uranus

Triple Microlens OGLE-2008-BLG-092L: Binary Stellar System with a Circumprimary Uranus-type Planet
http://arxiv.org/abs/1408.6223

We present the gravitational microlensing discovery of a 3 M_Uranus planet that orbits a 0.6 M_Sun star at ~16 AU. This is the first known analog of Uranus. Similar planets, i.e., cold ice-giants, are inaccessible to either radial velocity or transit methods because of the long orbital periods, while low reflected light prevents direct imaging. We discuss how similar planets may contaminate the sample of the very short microlensing events that are interpreted as free-floating planets with an estimated rate of 1.8 per main sequence star. Moreover, the host star has a nearby stellar (or brown dwarf) companion. The projected separation of the planet is only ~3 times smaller than that of the companion star, suggesting significant dynamical interactions.

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Sirius_Alpha

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Re: Microlensing exoplanet discoveries

This is the second "circumprimary" planet detected by microlensing. Any chance to have a "circumbinary" planet detected too? (Thinking of MACHO 97-BLG-41's false positive...)

Edasich
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Re: Microlensing exoplanet discoveries

Or to put it another way, half the mass of Saturn.

Lazarus
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Re: Microlensing exoplanet discoveries

I wouldn't be surprised if the ratio of the separation between the primary and the planet, and the primary and the secondary is actually much lower than 1/3. The true separation of the two stars could be much higher if I understand right. It would make more sense from a stability perspective (not just for the planet, but the disk it formed in, too).

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OGLE-2014-BLG-0124L - Jovian planet in a system with a space-based parallax measurement

Spitzer as Microlens Parallax Satellite: Mass Measurement for the OGLE-2014-BLG-0124L Planet and its Host Star
http://arxiv.org/abs/1410.4219

We combine Spitzer and ground-based observations to measure the microlens parallax vector π E , and so the mass and distance of OGLE-2014-BLG-0124L, making it the first microlensing planetary system with a space-based parallax measurement. The planet and star have masses m∼0.5M jup and M∼0.7M ⊙ and are separated by a ⊥ ∼3.1 AU in projection. The main source of uncertainty in all these numbers (approximately 30%, 30%, and 20%) is the relatively poor measurement of the Einstein radius θ E , rather than uncertainty in π E , which is measured with 2.5% precision. This compares to 22% based on OGLE data alone, implying that the Spitzer data provide not only a substantial improvement in the precision of the π E measurement but also the first independent test of a ground-based π E measurement.

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OGLE-2011-BLG-0265L - Jovian planet orbiting M dwarf

OGLE-2011-BLG-0265Lb: a Jovian Microlensing Planet Orbiting an M Dwarf
http://arxiv.org/abs/1410.8252

We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal combined with extended observations throughout the event allows us to accurately model the observed light curve. The final microlensing solution remains, however, degenerate yielding two possible configurations of the planet and the host star. In the case of the preferred solution, the mass of the planet is M p = 1.0 ± 0.3 M J , and the planet is orbiting a star with a mass M = 0.23 ± 0.07 M ⊙ . The second possible configuration (2\sigma away) consists of a planet with M p = 0.6 ± 0.2 M J and host star with M = 0.15 ± 0.06 M ⊙ . The system is located in the Galactic disk 3-4 kpc towards the Galactic bulge. In both cases, with an orbit size of 2 AU, the planet is a "cold Jupiter" -- located well beyond the "snow line" of the host star. Currently available data make the secure selection of the correct solution difficult, but there are prospects for lifting the degeneracy with additional follow-up observations in the future, when the lens and source star separate.

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MOA-2011-BLG-274: a free-floating 0.8 Jupiter-mass planet

Oh wait, nobody's posted this yet?

Can the masses of isolated planetary-mass gravitational lenses be measured by terrestrial parallax?

Recently Sumi et al. (2011) reported evidence for a large population of planetary-mass objects (PMOs) that are either unbound or orbit host stars in orbits > 10 AU. Their result was deduced from the statistical distribution of durations of gravitational microlensing events observed by the MOA collaboration during 2006 and 2007. Here we study the feasibility of measuring the mass of an individual PMO through microlensing by examining a particular event, MOA-2011-BLG-274. This event was unusual as the duration was short, the magnification high, the source-size effect large and the angular Einstein radius small. Also, it was intensively monitored from widely separated locations under clear skies at low air masses. Choi et al. (2012) concluded that the lens of the event may have been a PMO but they did not attempt a measurement of its mass. We report here a re-analysis of the event using re-reduced data. We confirm the results of Choi et al. and attempt a measurement of the mass and distance of the lens using the terrestrial parallax effect. Evidence for terrestrial parallax is found at a 3 sigma level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 +/- 0.30 M_J and 0.80 +/- 0.25 kpc respectively. We exclude a host star to the lens out to a separation ~ 40 AU. Drawing on our analysis of MOA-2011-BLG-274 we propose observational strategies for future microlensing surveys to yield sharper results on PMOs including those down to super-Earth mass.
This is the first galactic microlensing event that has been unambiguously identified as a free-floating planet through analysis, or ignoring all the semantics, the first microlensing free-floating planet. Certainly a remarkable detection, but what's more encouraging is that these sorts of events are fairly common.

Shellface
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Re: Microlensing exoplanet discoveries

EPE is listing it as "gravitationally bound" at 40 AUs separation:

http://exoplanet.eu/catalog/moa-2011-blg-274_b/

Edasich
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Re: Microlensing exoplanet discoveries

That's a rather… concerted… misinterpretation of the actual result, huh.

Shellface
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Re: Microlensing exoplanet discoveries

Edasich wrote:EPE is listing it as "gravitationally bound" at 40 AUs separation:

http://exoplanet.eu/catalog/moa-2011-blg-274_b/

Shellface wrote:That's a rather… concerted… misinterpretation of the actual result, huh.

It's worth noting that EPE has no support for free-floating planets, so that may be it.

Sedna
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Re: Microlensing exoplanet discoveries

Undoubtedly, but that doesn't make it any less confusing.

Shellface
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OGLE-2013-BLG-0578L: Microlensing Binary Composed of A Brown Dwarf And An M Dwarf

The neverending dilemma of planetary outliers or "dwarfish" brown dwarfs...

OGLE-2013-BLG-0578L: Microlensing Binary Composed of A Brown Dwarf And An M Dwarf

Determining physical parameters of binary microlenses is hampered by the lack of information about the angular Einstein radius due to the difficulty of resolving caustic crossings. In this paper, we present the analysis of the binary microlensing event OGLE-2013-BLG-0578, for which the caustic exit was precisely predicted in advance from real-time analysis, enabling to densely resolve the caustic crossing and to measure the Einstein radius. From the mass measurement of the lens system based on the Einstein radius combined with the additional information about the lens parallax, we identify that the lens is a binary that is composed of a late-type M-dwarf primary and a substellar brown-dwarf companion. The event demonstrates the capability of current real-time microlensing modeling and the usefulness of microlensing in detecting and characterizing faint or dark objects in the Galaxy.

Edasich
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OGLE-2014-BLG-0124L

http://www.spitzer.caltech.edu/images/6053-sig15-006-Map-of-Exoplanets-Found-in-Our-Galaxy

And

http://www.nasa.gov/jpl/nasas-spitzer-spots-planet-deep-within-our-galaxy/

NASA's Spitzer Space Telescope has teamed up with a telescope on the ground to find a remote gas planet about 13,000 light-years away, making it one of the most distant planets known

Led_Zep
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Re: Microlensing exoplanet discoveries

Led_Zep
Jovian

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Re: Microlensing exoplanet discoveries

Merged.

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OGLE-2012-BLG-0563Lb - New Saturn-mass microlensing planet

OGLE-2012-BLG-0563Lb: a Saturn-mass Planet around an M Dwarf with the Mass Constrained by Subaru AO imaging

We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio ~1 x 10^{-3}. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and IRCS instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of a spectroscopic information of the source star obtained during the high-magnification state by Bensby et al. (2013), we find that the lens system is located at 1.3^{+0.6}_{-0.8} kpc from us, and consists of an M dwarf (0.34^{+0.12}_{-0.20} M_sun) orbited by a Saturn-mass planet (0.39^{+0.14}_{-0.23} M_Jup) at the projected separation of 0.74^{+0.26}_{-0.42} AU (close model) or 4.3^{+1.5}_{-2.5} AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to 3, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J-Ks) and (H-Ks) colors of the host star, which are marginally consistent with a low-metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2<m_p/M_Jup<1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ~1--2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core accretion scheme.

Edasich
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