Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic Disk

Abstract

We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1=21_{-5}^{+12}{M}_J$ and $M_2=9_{-2}^{+5}{M}_J$, and it is located in the Galactic disk $D_{\mathrm{L}}=2.85_{-0.50}^{+0.88}\mathrm{kpc}$. This is the fifth binary brown dwarf discovered by microlensing, and the BD binary is moving counter to the orbital motion of disk stars. Constraints on the lens physical properties come from late time, non-caustic-crossing features of the Spitzer light curve. Thus, MOA-2016-BLG-231 shows how Spitzer plays a crucial role in resolving the nature of BDs in binary BD events with short timescale ($\lesssim 10$ days).

18 pages, 8 figures

References in corpus (12)

• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs
• Spitzer as Microlens Parallax Satellite: Mass Measurement for the OGLE-2014-BLG-0124L Planet and its Host Star
• Extended-Source Effect and Chromaticity in Two-Point-Mass Microlensing
• Hexadecapole Approximation in Planetary Microlensing
• OGLE-2013-BLG-0102LA,B: Microlensing binary with components at star/brown-dwarf and brown-dwarf/planet boundaries
• Spitzer as Microlens Parallax Satellite: Mass and Distance Measurements of Binary Lens System OGLE-2014-BLG-1050L
• OGLE-2016-BLG-0168 Binary Microlensing Event: Prediction and Confirmation of the Micorlens Parallax Effect from Space-based Observation
• OGLE-2016-BLG-1469L: Microlensing Binary Composed of Brown Dwarfs
• OGLE-2013-BLG-0578L: Microlensing Binary Composed of A Brown Dwarf And An M Dwarf
• OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing
• OGLE-2014-BLG-1112LB: A Microlensing Brown Dwarf Detected Through the Channel of a Gravitational Binary-Lens Event

Cited by in corpus (4)

• Brown-dwarf companions in microlensing binaries detected during the 2016--2018 seasons
• Pixel Level Decorrelation in Service of the \textit{Spitzer} Microlens Parallax Survey
• OGLE-2018-BLG-1428Lb: a Jupiter-mass planet beyond the snow line of a dwarf star
• OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax