Systematic Analysis of 22 Microlensing Parallax Candidates

Poindexter, S.; Afonso, C.; Bennett, D. P.; Glicenstein, J. F.; Gould, Andrew; Szymański, M. K.; Udalski, A.

doi:10.1086/468182

Cited by 172 publications

(163 citation statements)

References 52 publications

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“…Often only the so-called parallel component of the vector (in the direction parallel to the direction of the Earth's acceleration, which causes an asymmetric distortion to the lightcurve) is well measured, with the perpendicular component (which causes a symmetric distortion) being degenerate with the impact parameter and blending. In addition, orbital parallax is also degenerate with lens orbital motion (Batista et al 2011;Skowron et al 2011) and source orbital motion (xallarap, e.g., Poindexter et al 2005), which can cause similar apparent changes to the source trajectory. The magnitude of the parallax distortions and their duration (covering the whole magnified potion of the lightcurve) can also make them vulnerable to corruption by long-term systematic trends in photometry.…”

Section: Problems With the Distance Estimates?mentioning

confidence: 99%

Is the Galactic Bulge Devoid of Planets?

Penny

Henderson

Clanton

2016

ApJ

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Considering a sample of 31 exoplanetary systems detected by gravitational microlensing, we investigate whether or not the estimated distances to these systems conform to the Galactic distribution of planets expected from models. We derive the expected distribution of distances and relative proper motions from a simulated microlensing survey, correcting for the dominant selection effects that affect the planet detection sensitivity as a function of distance, and compare it to the observed distribution using Anderson-Darling (AD) hypothesis testing. Taking the relative abundance of planets in the bulge to that in the disk, f bulge , as a model parameter, we find that our model is only consistent with the observed distribution for f bulge < 0.54 (for a p-value threshold of 0.01) implying that the bulge may be devoid of planets relative to the disk. Allowing for a dependence of planet abundance on metallicity and host mass, or an additional dependence of planet sensitivity on event timescale does not restore consistency for f bulge = 1. We examine the distance estimates of some events in detail, and conclude that some parallax-based distance estimates could be significantly in error. Only by combining the removal of one problematic event from our sample and the inclusion of strong dependences of planet abundance or detection sensitivity on host mass, metallicity and event timescale are we able to find consistency with the hypothesis that the bulge and disk have equal planet abundance.

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Section: Problems With the Distance Estimates?mentioning

confidence: 99%

Is the Galactic Bulge Devoid of Planets?

Penny

Henderson

Clanton

2016

ApJ

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“…The microlens parallax π E has been measured for more than twenty single lenses (Alcock et al 1995 [the first parallax measurement], Poindexter et al 2005, and references therein), while the angular Einstein radius θ E has been measured for only few cases of single lenses (Alcock et al 1997(Alcock et al , 2001Smith et al 2003b;Yoo et al 2004a;Jiang et al 2004;Cassan et al 2006;Gould et al 2009). However, reliable mass estimates for isolated stars have been determined with microlensing only twice.…”

Section: Mass and Distance Estimates Of The Lens Starmentioning

confidence: 99%

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

Batista¹,

Dong²,

Gould³

et al. 2009

A&A

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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.

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“…The microlensing technique can probe a variety of astronomical objects in a wide range of masses such as planets, neutron stars, brown dwarfs, and isolated black holes (Poindexter et al 2005;Dong et al 2007;Miyake et al 2012;Shvartzvald et al 2015;Wyrzykowski et al 2016). The microlensing technique can detect these faint or dark objects regardless of their luminosity levels, in sharp contrast to other methods, which as a matter of course are restricted to studying objects within their flux detection limits.…”

Section: Introductionmentioning

confidence: 99%

OGLE-2016-BLG-0168 Binary Microlensing Event: Prediction and Confirmation of the Microlens Parallax Effect from Space-based Observations

Shin¹,

Udalski²,

Yee³

et al. 2017

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The microlens parallax is a crucial observable for conclusively identifying the nature of lens systems in microlensing events containing or composed of faint (even dark) astronomical objects such as planets, neutron stars, brown dwarfs, and black holes. With the commencement of a new era of microlensing in collaboration with space-based observations, the microlens parallax can be routinely measured. In addition, space-based observations can provide opportunities to verify the microlens parallax measured from ground-only observations and to find a unique solution to the lensing light-curve analysis. Furthermore, since most space-based observations cannot cover the full light curves of lensing events, it is also necessary to verify the reliability of the information extracted from fragmentary space-based light curves. We conduct a test based on the microlensing event OGLE-2016-BLG-0168, created by a binary lens system consisting of almost equal mass M-dwarf stars, to demonstrate that it is possible to verify the microlens parallax and to resolve degeneracies using the space-based light curve even though the observations are fragmentary. Since space-based observatories will frequently produce fragmentary light curves due to their short observing windows, the methodology of this test will be useful for next-generation microlensing experiments that combine space-based and ground-based collaboration.

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Systematic Analysis of 22 Microlensing Parallax Candidates

Cited by 172 publications

References 52 publications

Is the Galactic Bulge Devoid of Planets?

Is the Galactic Bulge Devoid of Planets?

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

OGLE-2016-BLG-0168 Binary Microlensing Event: Prediction and Confirmation of the Microlens Parallax Effect from Space-based Observations

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