Ground-based Parallax Confirmed by Spitzer: Binary Microlensing Event MOA-2015-BLG-020

et al. 2019

ApJ

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Section: Introductionmentioning

confidence: 99%

OGLE-2014-BLG-0962 and a Comparison of Galactic Model Priors to Microlensing Data

Shan¹,

Yee²,

et al. 2019

ApJ

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“…A comparison of the angular radius derived from asteroseismic analysis and from traditional CMD analysis also enables us to test the empirical CSB relation of M giants. Usually, the CSB relation from Kervella et al (2004b) is used in microlensing analyses to estimate the source angular radius (e.g., Wang et al 2017;Mróz et al 2018;OGLE Collaboration et al 2019). Using this method, we derived an angular radius of 32.4 ± 1.9 µas, ∼ 2σ away from that from asteroseismic analysis.…”

Section: Summary and Discussionmentioning

confidence: 99%

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

Li¹,

Zang²,

Monthly Notices of the Royal Astronomical Society

et al. 2019

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Abstract We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average time-scale of ∼9 d. The asteroseismic analysis also provides us source properties including the source angular size (∼27 $\mu$as) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ2 minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 M⊙ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 M⊙ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\sim 35{{\ \rm per\ cent}}$ probability for the lens to be a bulge object and $\sim 65{{\ \rm per\ cent}}$ to be a background disc object.

“…Therefore, the event provides a test bed in which one can check the consistency of the π E values and compare the precision of π E measurements by the individual methods. We note that there exist four cases for which ground-based π E measurements have been confirmed by space-based data: OGLE-2014-BLG-0124 , OGLE-2015-BLG-0196 (Han et al 2017), OGLE-2016-BLG-0168 (Shin et al 2017), and MOA-2015-BLG-020 (Wang et al 2017). …”

Section: Discussionmentioning

confidence: 99%

OGLE-2017-BLG-0329L: A Microlensing Binary Characterized with Dramatically Enhanced Precision Using Data from Space-based Observations

Han¹,

Novati²,

et al. 2018

ApJ

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Mass measurements of gravitational microlenses require one to determine the microlens parallax π E , but precise π E measurement, in many cases, is hampered due to the subtlety of the microlens-parallax signal combined with the difficulty of distinguishing the signal from those induced by other higher-order effects. In this work, we present the 1 analysis of the binary-lens event OGLE-2017-BLG-0329, for which π E is measured with a dramatically improved precision using additional data from space-based Spitzer observations. We find that while the parallax model based on the ground-based data cannot be distinguished from a zero-π E model at the 2σ level, the addition of the Spitzer data enables us to identify two classes of solutions, each composed of a pair of solutions according to the wellknown ecliptic degeneracy. It is found that the space-based data reduce the measurement uncertainties of the north and east components of the microlens-parallax vector E p by factors ∼18 and ∼4, respectively. With the measured microlens parallax combined with the angular Einstein radius measured from the resolved caustic crossings, we find that the lens is composed of a binary with component masses of either (M 1 , M 2 )∼(1.1, 0.8) M e or ∼(0.4, 0.3) M e according to the two solution classes. The first solution is significantly favored but the second cannot be securely ruled out based on the microlensing data alone. However, the degeneracy can be resolved from adaptive optics observations taken ∼10 years after the event.