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Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf

Shvartzvald, Yossi, Yee, Jennifer C., Skowron, Jan, Lee, Chung-Uk, Udalski, Andrzej, Novati, Sebastiano Calchi, Bozza, Valerio, Beichman, Charles A., Bryden, Geoffery, Carey, Sean, and others. (2019) Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf. The Astronomical Journal, 157 (3). p. 106. ISSN 1538-3881. (doi:10.3847/1538-3881/aafe12)

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https://doi.org/10.3847/1538-3881/aafe12

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 the 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 ± 1 M J or 20 ± 1 M J . This is the lowest isolated-object mass measurement to date, only ~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 ± 0.1 kpc or 4.1 ± 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.

Item Type: Article
DOI/Identification number: 10.3847/1538-3881/aafe12
Uncontrolled keywords: Galaxy: bulge – gravitational lensing: micro
Subjects: Q Science > QB Astronomy
Divisions: Faculties > Sciences > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Stephen Lowry
Date Deposited: 21 May 2019 09:28 UTC
Last Modified: 03 Jun 2019 09:50 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/74000 (The current URI for this page, for reference purposes)
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