How Efficient was OGLE-III Detecting Exoplanets Through Microlensing Between 2003 to 2008

The OGLE-III planet detection efficiency from six years of microlensing observations (2003–2008)

Authors:

Tsapras et al

Abstract:

We use six years (2003–2008) of Optical Gravitational Lensing Experiment-III microlensing observations to derive the survey detection efficiency for a range of planetary masses and projected distances from the host star. We perform an independent analysis of the microlensing light curves to extract the event parameters and compute the planet detection probability given the data. 2433 light curves satisfy our quality selection criteria and are retained for further processing. The aggregate of the detection probabilities over the range explored yields the expected number of microlensing planet detections. We employ a Galactic model to convert this distribution from dimensionless to physical units, α/au and M⊕. The survey sensitivity to small planets is highest in the range 1–4 au, shifting to slightly larger separations for more massive ones.

Using Machine Learning for Real-time Detection of Transiets in OGLE-IV

Real-time detection of transients in OGLE-IV with application of machine learning

Authors:

Klencki et al

Abstract:

The current bottleneck of transient detection in most surveys is the problem of rejecting numerous artifacts from detected candidates. We present a triple-stage hierarchical machine learning system for automated artifact filtering in difference imaging, based on self-organizing maps. The classifier, when tested on the OGLE-IV Transient Detection System, accepts ~ 97 % of real transients while removing up to ~ 97.5 % of artifacts.

A Technical Review of Optical Gravitational Lensing Experiment/OGLE-IV

OGLE-IV: Fourth Phase of the Optical Gravitational Lensing Experiment

Authors:

Udalski et al

Abstract:

We present both the technical overview and main science drivers of the fourth phase of the Optical Gravitational Lensing Experiment (hereafter OGLE-IV). OGLE-IV is currently one of the largest sky variability surveys worldwide, targeting the densest stellar regions of the sky. The survey covers over 3000 square degrees in the sky and monitors regularly over a billion sources.

The main targets include the inner Galactic Bulge and the Magellanic System. Their photometry spans the range of 12 less than I less than 21 mag and 13 less than I less than 21.7 mag, respectively. Supplementary shallower Galaxy Variability Survey covers the extended Galactic bulge and 2/3 of the whole Galactic disk within the magnitude range of 10 less than I less than 19 mag. All OGLE-IV surveys provide photometry with milli-magnitude accuracy at the bright end. The cadence of observations varies from 19-60 minutes in the inner Galactic bulge to 1-3 days in the remaining Galactic bulge fields, Magellanic System and the Galactic disk.

OGLE-IV provides the astronomical community with a number of real time services. The Early Warning System (EWS) contains information on two thousand gravitational microlensing events being discovered in real time annually, the OGLE Transient Detection System (OTDS) delivers over 200 supernovae a year. We also provide the real time photometry of unpredictable variables such as optical counterparts to the X-ray sources and R CrB stars.

Hundreds of thousands new variable stars have already been discovered and classified by the OGLE survey. The number of new detections will be at least doubled during the current OGLE-IV phase. The survey was designed and optimized primarily to conduct the second generation microlensing survey for exoplanets. It has already contributed significantly to the increase of the discovery rate of microlensing exoplanets and free-floating planets.

OGLE-IV Real Time Transient Search of Magellanic Clouds Data Online for Public

OGLE-IV Real-Time Transient Search

Authors:

Wyrzykowski et al

Abstract:

We present the design and first results of a real-time search for transients within the 650 sq. deg. area around the Magellanic Clouds, conducted as part of the OGLE-IV project and aimed at detecting supernovae, novae and other events. The average sampling of about 4 days from September to May, yielded a detection of 238 transients in 2012/2013 and 2013/2014 seasons. The superb photometric and astrometric quality of the OGLE data allows for numerous applications of the discovered transients.

We use this sample to prepare and train a Machine Learning-based automated classifier for early light curves, which distinguishes major classes of transients with more than 80% of correct answers. Spectroscopically classified 49 supernovae Type Ia are used to construct a Hubble Diagram with statistical scatter of about 0.3 mag and fill the least populated region of the redshifts range in the Union sample. We investigate the influence of host galaxy environments on supernovae statistics and find the mean host extinction of A_I=0.19+-0.10 mag and A_V=0.39+-0.21 mag based on a subsample of supernovae Type Ia. We show that the positional accuracy of the survey is of the order of 0.5 pixels (0.13 arcsec) and that the OGLE-IV Transient Detection System is capable of detecting transients within the nuclei of galaxies. We present a few interesting cases of nuclear transients of unknown type.

All data on the OGLE transients are made publicly available to the astronomical community via the OGLE website.

MOA-2011-BLG-322Lb: 12 Jupiter Mass Gas Giant at 4.3 AU

MOA-2011-BLG-322Lb: a ‘second generation survey’ microlensing planet

Authors:

Shvartzvald et al

Abstract:

Global ‘second-generation’ microlensing surveys aim to discover and characterize extrasolar planets and their frequency, by means of round-the-clock high-cadence monitoring of a large area of the Galactic bulge, in a controlled experiment. We report the discovery of a giant planet in microlensing event MOA-2011-BLG-322. This moderate-magnification event, which displays a clear anomaly induced by a second lensing mass, was inside the footprint of our second-generation microlensing survey, involving MOA, OGLE and the Wise Observatory. The event was observed by the survey groups, without prompting alerts that could have led to dedicated follow-up observations. Fitting a microlensing model to the data, we find that the time-scale of the event was tE = 23.2 ± 0.8 d, and the mass ratio between the lens star and its companion is q = 0.028 ± 0.001. Finite-source effects are marginally detected, and upper limits on them help break some of the degeneracy in the system parameters. Using a Bayesian analysis that incorporates a Galactic structure model, we estimate the mass of the lens at 0.39+0.45−0.19M⊙, at a distance of 7.56 ± 0.91 kpc. Thus, the companion is likely a planet of mass 11.6+13.4−5.6MJ, at a projected separation of 4.3+1.5−1.2 au, rather far beyond the snow line. This is the first pure-survey planet reported from a second-generation microlensing survey, and shows that survey data alone can be sufficient to characterize a planetary model. With the detection of additional survey-only planets, we will be able to constrain the frequency of extrasolar planets near their systems’ snow lines.