# Microlensing exoplanet discoveries

Page 1 of 5 1, 2, 3, 4, 5

## Microlensing exoplanet discoveries

Determining the Physical Lens Parameters of the Binary Gravitational Microlensing Event MOA-2009-BLG-016

We report the result of the analysis of the light curve of the microlensing event MOA-2009-BLG-016. The light curve is characterized by a short-duration anomaly near the peak and an overall asymmetry. We find that the peak anomaly is due to a binary companion to the primary lens and the asymmetry of the light curve is explained by the parallax effect caused by the acceleration of the observer over the course of the event due to the orbital motion of the Earth around the Sun. In addition, we detect evidence for the effect of the finite size of the source near the peak of the event, which allows us to measure the angular Einstein radius of the lens system. The Einstein radius combined with the microlens parallax allows us to determine the total mass of the lens and the distance to the lens. We identify three distinct classes of degenerate solutions for the binary lens parameters, where two are manifestations of the previously identified degeneracies of close/wide binaries and positive/negative impact parameters, while the third class is caused by the symmetric cycloid shape of the caustic. We find that, for the best-fit solution, the estimated mass of the lower-mass component of the binary is (0.04 +- 0.01) M_sun, implying a brown-dwarf companion. However, there exists a solution that is worse only by Deltachi^2 ~ 3 for which the mass of the secondary is above the hydrogen-burning limit. Unfortunately, resolving these two degenerate solutions will be difficult as the relative lens-source proper motions for both are similar and small (~ 1 mas/yr) and thus the lens will remain blended with the source for the next several decades.

No hint about orbital separation, except a vague s=0.21 (AUs? Solar radii? what else?)

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## MOA-2009-BLG-319Lb

A sub-Saturn Mass Planet, MOA-2009-BLG-319Lb
http://arxiv.org/abs/1010.1809

We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K or M-dwarf star in the inner Galactic disk or Galactic bulge. The high cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high magnification event approximately 24 hours prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 +/- 0.02) x 10^{-4} and a separation of d = 0.97537 +/- 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t_E, and angular Einstein radius, \theta_E, along with a standard Galactic model indicates a host star mass of M_L = 0.38^{+0.34}_{-0.18} M_{Sun} and a planet mass of M_p = 50^{+44}_{-24} M_{Earth}, which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4^{+1.2}_{-0.6} AU and a distance to the planetary system of D_L = 6.1^{+1.1}_{-1.2} kpc. This separation is ~ 2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

Gotta love these microlensing detections, 4 pages to get through the lists of authors and affiliations.

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## MOA-2009-BLG-387Lb: A massive planet orbiting an M dwarf

MOA-2009-BLG-387Lb: A massive planet orbiting an M dwarf
http://arxiv.org/abs/1102.0558

We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M_sun < M_host < 0.49M_sun at 90% confidence. The planet-star mass ratio q = 0.0132 +- 0.003 has been measured extremely well, so at the best-estimated host mass, the planet mass is m_p = 2.6 Jupiter masses for the median host mass, M = 0.19 M_sun. The host mass is determined from two "higher order" microlensing parameters. One of these, the angular Einstein radius \theta_E = 0.31 +- 0.03 mas, is very well measured, but the other (the microlens parallax \pi_E, which is due to the Earth's orbital motion) is highly degenate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. The 90% confidence intervals for the distance, semi-major axis, and period of the planet are 3.5 kpc < D_L < 7.9 kpc, 1.1 AU < a < 2.7AU, and 3.8 yr < P < 7.6 yr, respectively.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

The abstracts from the XV International Conference on Gravitational Microlensing are on arXiv. Quite a bit of stuff in there.

In terms of detections:
• MOA-2009-BLG-266Lb - a cold Neptune
• OGLE-2008-BLG-513Lb/MOA-2008-BLG-401Lb - 7.8 Jupiter mass planet orbiting a 0.3 solar mass star
• MOA-2010-BLG-328 - mass ratio 9.7×10-4

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## MOA-2009-BLG-266Lb - Cold, 10 M_e planet

Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star
http://arxiv.org/abs/1106.2160

We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass measurements are enabled by the measurement of the microlensing parallax effect, which is seen primarily in the light curve distortion due to the orbital motion of the Earth. But, the analysis also demonstrates the capability to measure microlensing parallax with the Deep Impact (or EPOXI) spacecraft in a Heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a "failed" gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

There must be very cold(in the atmosphere of the planet) but I wonder if kepler would be able to measure radius such planet if the angle would be 89/90 or is too far?

tommi59
Jovian

Number of posts : 564
Age : 40
Location : Baile Atha Cliath
Registration date : 2010-07-31

## Re: Microlensing exoplanet discoveries

Nice to see the use of EPOXI to get better parallax measurements.

As for Kepler, it is looking at the wrong part of the sky.

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## MOA-2011-BLG-274: Free-floating planet?

Characterizing Lenses and Lensed Stars of High-Magnification Gravitational Microlensing Events With Lenses Passing Over Source Stars
http://arxiv.org/abs/1111.4032

We present the analysis of the light curves of 9 high-magnification gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For 8 events, we measure the Einstein radii and the lens-source relative proper motions. Among them, 6 events (OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2011-BLG-093, MOA-2011-BLG-274, and OGLE-2011-BLG-0990/MOA-2011-BLG-300) are found to have Einstein radii less than 0.2 mas, making the lenses candidates of very low-mass stars or brown dwarfs. For MOA-2011-BLG-274, especially, the small Einstein radius of $\theta_{\rm E}\sim 0.09$ mas combined with the short time scale of $t_{\rm E}\sim 3.1$ days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of $\sim 0.8\ M_\odot$ is consistent with that of a star blended with the source, suggesting that the blend is probably the lens. For the systematic integration of information that can be extracted from a sample of events with lenses passing over source stars, we also present the results of 8 other events that were previously analyzed.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## MOA-2010-BLG-477Lb: giant planet around a K-dwarf

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## MOA-2010-BLG-477Lb

Has this one passed unnoticed?

MOA-2010-BLG-477Lb: constraining the mass of a microlensing planet from microlensing parallax, orbital motion and detection of blended light

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA-2010-BLG-477. The measured planet-star mass ratio is $q=(2.181\pm0.004)\times 10^{-3}$ and the projected separation is $s=1.1228\pm0.0006$ in units of the Einstein radius. The angular Einstein radius is unusually large $\theta_{\rm E}=1.38\pm 0.11$ mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range $0.13<M/M_\odot<1.0$. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of $M_*=0.67^{+0.33}_{-0.13}\ M_\odot$ and $m_p=1.5^{+0.8}_{-0.3}\ M_{\rm JUP}$ at a distance of $D=2.3\pm0.6$ kpc, and with a semi-major axis of $a=2^{+3}_{-1}$ AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric.

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Re: Microlensing exoplanet discoveries

Edasich wrote:Has this one passed unnoticed?
No.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

Sirius_Alpha wrote:
Edasich wrote:Has this one passed unnoticed?
No.

Oh, fine.

But EPE? There is only the bibliographic reference...

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Re: Microlensing exoplanet discoveries

Edasich wrote:But EPE? There is only the bibliographic reference...

Looks like EPE just added it.
http://exoplanet.eu/planet.php?p1=MOA-2010-BLG-477L&p2=b

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

Sirius_Alpha wrote:
Edasich wrote:But EPE? There is only the bibliographic reference...

Looks like EPE just added it.
http://exoplanet.eu/planet.php?p1=MOA-2010-BLG-477L&p2=b

Now everything is alright

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Brown dwarfs from microlensing

Microlensing binaries with brown dwarf companions

MOA-2011-BLG-104/OGLE-2011-BLG-0172 - 0.02±0.01 solar mass (20±10 Jupiter masses) companion around a 0.18±0.11 solar mass star.

MOA-2011-BLG-149 - 0.019±0.002 solar mass (20±2 Jupiter masses) companion around a 0.14±0.02 solar mass star.

These companions meet the EPE planet criteria but orbit low mass host stars, whether they could have formed as planets is an issue.

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## MOA-2010-BLG-073L - dM star with planet/browndwarf boundary object

MOA-2010-BLG-073L: An M-Dwarf with a Substellar Companion at the Planet/Brown Dwarf Boundary
http://arxiv.org/abs/1211.3782

We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010-03-18.
This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source lightcurve, we demonstrate that it is an irregular variable over time scales >200d. Its dereddened color, $(V-I)_{S,0}$, is 1.221$\pm$0.051mag and from our lens model we derive a source radius of 14.7$\pm$1.3 $R_{\odot}$, suggesting that it is a red giant star.
We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system.
We find that the lensing system has a mass ratio of q=0.0654$\pm$0.0006. The Einstein crossing time of the event, $T_{\rm{E}}=44.3$\pm$0.1d, was sufficiently long that the lightcurve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens,$D_L$=2.8$\pm$0.4kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with$M_{L,p}$=0.16$\pm0.03M_{\odot}$while the companion has$M_{L,s}$=11.0$\pm2.0M_{\rm{J}}\$ putting it in the boundary zone between planets and brown dwarfs.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

Weird one. Could be a very low-mass stellar binary but as noted if the primary mass were scaled up to solar, the companion would fall within the brown dwarf desert.

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12

## Re: Microlensing exoplanet discoveries

EPE doesn't list it.

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Jovian planet at OGLE-2011-BLG-0251

It's in A&A free forthcoming papers. I think it should not be embargo breach.

A giant planet beyond the snow line in microlensing event OGLE-2011-BLG-0251

*Update*

Now on arXiv too:

We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic Bulge. Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection of higher-order effects on the light curve due to the Earth's orbital motion and the finite size of source, we are able to measure the mass and distance to the lens unambiguously. We find that the lens is made up of a planet of mass 0.53 +- 0.21,M_Jup orbiting an M dwarf host star with a mass of 0.26 +- 0.11 M_Sun. The planetary system is located at a distance of 2.57 +- 0.61 kpc towards the Galactic Centre. The projected separation of the planet from its host star is d=1.408 +- 0.019, in units of the Einstein radius, which corresponds to 2.72 +- 0.75 AU in physical units. We also identified a competitive model with similar planet and host star masses, but with a smaller orbital radius of 1.50 +- 0.50 AU. The planet is therefore located beyond the snow line of its host star, which we estimate to be around 1-1.5 AU.

Edasich
dM star

Number of posts : 1554
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## OGLE-2012-BLG-0406L b - super-massive Jovian around K-type star

Super-massive planets around late-type stars - the case of OGLE-2012-BLG-0406Lb
http://arxiv.org/abs/1307.4084

The core accretion theory of planetary formation does not predict super-Jupiters to form beyond the snow line of a low mass stars. We present a discovery of 3.9 +- 1.2 M_Jup mass planet orbiting the 0.59 +- 0.17 M_Sun star using the gravitational microlensing method. During the event, the projected separation of the planet and the star is 3.9 +- 1.0 AU i.e., the planet is significantly further from the host star than the snow line. This is a third such planet discovered using microlensing technique and challenges the core accretion theory. This is also the first microlensing planet found by analyzing data gathered by a single telescope only.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## A Giant Planet beyond the Snow Line in Microlensing Event OGLE-2011-BLG-0251

A Giant Planet beyond the Snow Line in Microlensing Event OGLE-2011-BLG-0251
We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic Bulge. Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection of higher-order effects on the light curve due to the Earth's orbital motion and the finite size of source, we are able to measure the mass and distance to the lens unambiguously. We find that the lens is made up of a planet of mass 0.53 +- 0.21,M_Jup orbiting an M dwarf host star with a mass of 0.26 +- 0.11 M_Sun. The planetary system is located at a distance of 2.57 +- 0.61 kpc towards the Galactic Centre. The projected separation of the planet from its host star is d=1.408 +- 0.019, in units of the Einstein radius, which corresponds to 2.72 +- 0.75 AU in physical units. We also identified a competitive model with similar planet and host star masses, but with a smaller orbital radius of 1.50 +- 0.50 AU. The planet is therefore located beyond the snow line of its host star, which we estimate to be around 1-1.5 AU.

_________________

Stalker
Jovian

Number of posts : 537
Age : 27
Location : Paris, France
Registration date : 2008-06-16

## OGLE-2012-BLG-0358L b - A Jovian Planet Orbiting a Brown Dwarf from Microlensing

Microlensing Planet Around Brown-Dwarf
http://arxiv.org/abs/1307.6335

Observations of accretion disks around young brown dwarfs have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around brown dwarfs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field brown dwarf via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 +- 0.001), relatively tightly-separated (~0.87 AU) binary composed of a planetary-mass object with 1.9 +- 0.2 Jupiter masses orbiting a brown dwarf with a mass 0.022 M_Sun. The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the brown dwarf host, in a manner analogous to planets.

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

More refined parameters.

A Super-Jupiter orbiting a late-type star: A refined analysis of microlensing event OGLE-2012-BLG-0406
http://arxiv.org/abs/1310.2428

_________________
Caps Lock: Cruise control for 'Cool'!

Sirius_Alpha

Number of posts : 3730
Location : Earth
Registration date : 2008-04-06

## Re: Microlensing exoplanet discoveries

So, a lower mass estimate for the host star, more like an early M-dwarf than a K-star.

Lazarus
dF star

Number of posts : 3029
Registration date : 2008-06-12