Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050

Abstract

Aims. We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ∼ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Methods. Both finite-source and parallax effects permit a measurement of the angular Einstein radius θ E = 0.48 ± 0.01 mas and the parallax π E = 0.12 ± 0.03, leading to an estimate of the lens mass M = 0.50 ± 0.14 M and its distance to the observer D L = 5.5 ± 0.4 kpc. This is only the second determination of a reasonably precise (<30%) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units (r ⊥ , m p ), where r ⊥ is the projected planet-star separation and m p is the planet mass. Results. When computing planet detection efficiency, we did not find any planetary signature, i.e. none of the planetary configurations provides a Δχ 2 improvement higher than 60, and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6-10] and [1.4-4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8-3.1] AU.

The Exoplanet Mass-Ratio Function From the Moa-Ii Survey: Discovery of a Break and Likely Peak at a Neptune mass

“…Figures 3 -5 show the detection efficiency for the planetary and ambiguous events. Typically, each figure has roughly triangular sensitivity contours as first shown by Rhie et al (2000), and subsequently shown by a number of subsequent studies (Dong et al 2006;Yee et al 2009;Batista et al 2009;Gould et al 2010;Choi et al 2012b). But, low magnification events tend to show a double peak toward lower mass ratios at s > 1 and s < 1 and reduced detection efficiency at the Einstein ring radius (s = 1).…”

Instrumental methods for professional and amateur collaborations in planetary astronomy

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Towards habitable Earths with EUCLID and WFIRST

“…Detections include a scale 1/2 model of our solar system (Gaudi et al 350 J.-P. Beaulieu et al 2008;Bennett et al 2010) and several cold Neptunes/Super Earths. It has be shown that the ground-based detection efficiency can, under favourable circumstances, extend down to 1 Earth mass planets (Bennett & Rhie 1996;Batista et al 2009). Microlensing has also provided the first measurement of the frequency of ice and gas giants beyond the snow line.…”