$Spitzer$ Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-Rotating Low-Mass Brown Dwarf

Abstract

The kinematics of isolated brown dwarfs in the Galaxy, beyond the solar neighborhood, is virtually unknown. Microlensing has the potential to probe this hidden population, as it can measure both the mass and five of the six phase-space coordinates (all except the radial velocity) even of a dark isolated lens. However, the measurements of both the microlens parallax and finite-source effects are needed in order to recover the full information. Here, we combine $Spitzer$ satellite parallax measurement with the ground-based light curve, which exhibits strong finite-source effects, of event OGLE-2017-BLG-0896. We find two degenerate solutions for the lens (due to the known satellite-parallax degeneracy), which are consistent with each other except for their proper motion. The lens is an isolated brown dwarf with a mass of either $18\pm 1M_J$ or $20\pm 1M_J$. This is the lowest isolated-object mass measurement to date, only $\sim$45\% more massive than the theoretical deuterium-fusion boundary at solar metallicity, which is the common definition of a free-floating planet. The brown dwarf is located at either $3.9\pm 0.1$ kpc or $4.1\pm 0.1$ kpc toward the Galactic bulge, but with proper motion in the opposite direction of disk stars, with one solution suggesting it is moving within the Galactic plane. While it is possibly a halo brown dwarf, it might also represent a different, unknown population.

17 pages, 3 figures, 2 tables. Accepted for publication in The Astronomical Journal

References in corpus (37)

• Galactic Stellar and Substellar Initial Mass Function
• Gaia Data Release 2. Summary of the contents and survey properties
• On the variation of the Initial Mass Function
• Local Kinematics and the Local Standard of Rest
• A method for optimal image subtraction
• A new generation of PARSEC-COLIBRI stellar isochrones including the TP-AGB phase
• Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. V. Evidence for a wide age distribution and a complex MDF
• The angular size of dwarf stars and subgiants - Surface brightness relations calibrated by interferometry
• The Use of High Magnification Microlensing Events in Discovering Extra-solar Planets
• The Brown Dwarf Kinematics Project (BDKP) I. Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs
• Difference imaging photometry of blended gravitational microlensing events with a numerical kernel
• First microlens mass measurement: PLANET photometry of EROS BLG-2000-5
• Light and Motion in SDSS Stripe 82: The Catalogues
• Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events
• Criteria for Sample Selection to Maximize Planet Sensitivity and Yield from Space-Based Microlens Parallax Surveys
• An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf
• Ionized gas and stellar kinematics of seventeen nearby spiral galaxies
• A Neptune-mass Free-floating Planet Candidate Discovered by Microlensing Surveys
• Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
• OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star
• A Second Method to Photometrically Align Multi-Site Microlensing Light Curves: Source Color in Planetary Event MOA-2007-BLG-192
• Microlens Masses From Astrometry and Parallax in Space-Based Surveys: From Planets to Black Holes
• Minor-axis velocity gradients in spirals and the case of inner polar disks
• Microlensing Characterization of Wide-Separation Planets
• 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
• Mass Measurements of Isolated Objects from Space-based Microlensing
• 2MASS J06164006-6407194: The First Outer Halo L Subdwarf
• OGLE-2015-BLG-1482L: the first isolated low-mass microlens in the Galactic bulge
• The difference in age of the two counter-rotating stellar disks of the spiral galaxy NGC 4138
• On the Feasibility of Characterizing Free-floating Planets with Current and Future Space-based Microlensing Surveys
• Cheap Space-Based Microlens Parallaxes for High-Magnification Events
• Microlensing by Kuiper, Oort, and Free-Floating Planets
• Extending the Planetary Mass Function to Earth Mass by Microlensing at Moderately High Magnification
• Median Statistics Estimate of the Galactic Rotational Velocity
• OGLE-2016-BLG-1045: A Test of Cheap Space-Based Microlens Parallaxes

Cited by in corpus (23)

• Exoplanets as Sub-GeV Dark Matter Detectors
• Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
• OGLE-2017-BLG-0406: $Spitzer$ Microlens Parallax Reveals Saturn-mass Planet orbiting M-dwarf Host in the Inner Galactic Disk
• $Spitzer$ Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf
• Expectations on the mass determination using astrometric microlensing by Gaia
• OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing
• Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge
• Evidence of Systematic Errors in $Spitzer$ Microlens Parallax Measurements
• Brown-dwarf companions in microlensing binaries detected during the 2016--2018 seasons
• Sensitivity to habitable planets in the \textit{Roman} microlensing survey
• OGLE-2017-BLG-0039: Microlensing Event with Light from the Lens Identified from Mass Measurement
• Pixel Level Decorrelation in Service of the \textit{Spitzer} Microlens Parallax Survey
• Systematic KMTNet Planetary Anomaly Search. XII. Complete Sample of 2017 Subprime Field Planets
• KMT-2016-BLG-1836Lb: A Super-Jovian Planet From A High-Cadence Microlensing Field
• A free-floating-planet microlensing event caused by a Saturn-mass object
• MOA-2019-BLG-008Lb: a new microlensing detection of an object at the planet/brown dwarf boundary
• Probable brown dwarf companions detected in binary microlensing events during the 2018-2020 seasons of the KMTNet survey
• KMT-2022-BLG-2397: Brown Dwarf at the Upper Shore of the Einstein Desert
• Identifying low-amplitude pulsating stars through microlensing observations
• OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax
• OGLE-2016-BLG-1195Lb: A Sub-Neptune Beyond the Snow Line of an M-dwarf Confirmed by Keck AO
• Mass-velocity dispersion relation by using the \textit{Gaia} data and its effect on interpreting short-duration and degenerate microlensing events
• Frequency Shift in Binary Lensing System