OGLE-2014-BLG-1186: gravitational microlensing providing evidence for a planet orbiting the foreground star or for a close binary source?

Abstract

(abridged) Using the particularly long gravitational microlensing event OGLE-2014-BLG-1186 with a time-scale $t_{\mathrm{E}}$ ~ 300 d, we present a methodology for identifying the nature of localised deviations from single-lens point-source light curves, which ensures that 1) the claimed signal is substantially above the noise floor, 2) the inferred properties are robustly determined and their estimation not subject to confusion with systematic noise in the photometry, 3) there are no alternative viable solutions within the model framework that might have been missed. Annual parallax and binarity could be separated and robustly measured from the wing and the peak data, respectively. We find matching model light curves that involve either a binary lens or a binary source. Our binary-lens models indicate a planet of mass $M_2$ = (45 $\pm$ 9) $M_{\oplus }$, orbiting a star of mass $M_1$ = (0.35 $\pm$ 0.06) $M_{\odot }$, located at a distance $D_{\mathrm{L}}$ = (1.7 $\pm$ 0.3) kpc from Earth, whereas our binary-source models suggest a brown-dwarf lens of $M$ = (0.046 $\pm$ 0.007) $M_{\odot }$, located at a distance $D_{\mathrm{L}}$ = (5.7 $\pm$ 0.9) kpc, with the source potentially being a (partially) eclipsing binary involving stars predicted to be of similar colour given the ratios between the luminosities and radii. The ambiguity in the interpretation would be resolved in favour of a lens binary by observing the luminous lens star separating from the source at the predicted proper motion of $\mu$ = (1.6 $\pm$ 0.3) mas yr${}^{-1}$, whereas it would be resolved in favour of a source binary if the source could be shown to be a (partially) eclipsing binary matching the obtained model parameters. We experienced that close binary source stars pose a challenge for claiming the detection of planets by microlensing in events where the source passes very close to the lens star hosting the planet.

arXiv comment26 pages, 14 figures

References in corpus (42)

• Galactic Stellar and Substellar Initial Mass Function
• A method for optimal image subtraction
• Discovery of a Cool Planet of 5.5 Earth Masses Through Gravitational Microlensing
• Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
• The Use of High Magnification Microlensing Events in Discovering Extra-solar Planets
• OGLE 2003-BLG-235/MOA 2003-BLG-53: A planetary microlensing event
• Discovery of a Jupiter/Saturn Analog with Gravitational Microlensing
• A Jovian-mass Planet in Microlensing Event OGLE-2005-BLG-071
• Resolution of the MACHO-LMC-5 Puzzle: The Jerk-Parallax Microlens Degeneracy
• A Cold Neptune-Mass Planet OGLE-2007-BLG-368Lb: Cold Neptunes Are Common
• A New Algorithm For Difference Image Analysis
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. IV. Two bulge populations
• Binary microlensing event OGLE-2009-BLG-020 gives a verifiable mass, distance and orbit predictions
• First microlens mass measurement: PLANET photometry of EROS BLG-2000-5
• Detection of Rotation in a Binary Microlens: PLANET Photometry of MACHO 97-BLG-41
• Microlensing Event MOA-2007-BLG-400: Exhuming the Buried Signature of a Cool, Jovian-Mass Planet
• Microlensing with advanced contour integration algorithm: Green's theorem to third order, error control, optimal sampling and limb darkening
• Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events
• Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge
• Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star
• On Planetary Companions to the MACHO-98-BLG-35 Microlens Star
• RoboNet-II: Follow-up observations of microlensing events with a robotic network of telescopes
• Toward a Galactic Distribution of Planets. I. Methodology & Planet Sensitivities of the 2015 High-Cadence Spitzer Microlens Sample
• An anomaly detector with immediate feedback to hunt for planets of Earth mass and below by microlensing
• Detection Efficiencies of Microlensing Datasets to Stellar and Planetary Companions
• Microlensing limits on numbers and orbits of extra-solar planets from the 1998-2000 OGLE events
• The Two-Colour EMCCD Instrument for the Danish 1.54m Telescope and SONG
• High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP). I. Lucky imaging observations of 101 systems in the southern hemisphere
• A Metric and Optimisation Scheme for Microlens Planet Searches
• Is the Galactic bulge devoid of planets?
• Systematic Trends In Sloan Digital Sky Survey Photometric Data
• The angular sizes of dwarf stars and subgiants - Non-linear surface brightness relations in BVRcIc from interferometry
• ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) - A possible expert-system based cooperative effort to hunt for planets of Earth mass and below
• Properties of Planet-induced Deviations in the Astrometric Microlensing Centroid Shift Trajectory
• High Frame-rate Imaging Based Photometry, Photometric Reduction of Data from Electron-multiplying Charge Coupled Devices (EMCCDs)
• Astrometric Method to Break the Photometric Degeneracy between Binary-source and Planetary Microlensing Perturbations
• OGLE-2008-BLG-510: first automated real-time detection of a weak microlensing anomaly - brown dwarf or stellar binary?
• The complete catalogue of light curves in equal-mass binary microlensing
• Spitzer Opens New Path to Break Classic Degeneracy for Jupiter-Mass Microlensing Planet OGLE-2017-BLG-1140Lb
• Red noise versus planetary interpretations in the microlensing event OGLE-2013-BLG-446
• RoboTAP - target priorities for robotic microlensing observations
• On the Astrometric Behavior of Binary Microlensing Events

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• The 2L1S/1L2S Degeneracy for Two Microlensing Planet Candidates Discovered by the KMTNet Survey in 2017
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• OGLE-2013-BLG-0911Lb: A Secondary on the Brown-Dwarf Planet Boundary around an M-dwarf
• MOA-2019-BLG-008Lb: a new microlensing detection of an object at the planet/brown dwarf boundary
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• An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing