Mass ratio of the 2 pc binary brown dwarf LUH16 and limits on planetary companions from astrometry

Abstract

We analyse FORS2/VLT $I$-band imaging data to monitor the motions of both components in the nearest known binary brown dwarf WISE J104915.57-531906.1AB (LUH16) over one year. The astrometry is dominated by parallax and proper motion, but with a precision of $\sim$0.2 milli-arcsecond per epoch we accurately measure the relative position change caused by the orbital motion of the pair. This allows us to directly measure a mass ratio of $q=0.78\pm 0.10$ for this system. We also search for the signature of a planetary-mass companion around either of the A and B component and exclude at 3-$\sigma$ the presence of planets with masses larger than $2M_{\mathrm{Jup}}$ and orbital periods of 20--300 d. We update the parallax of LUH16 to $500.51\pm 0.11$ mas, i.e. just within 2 pc. This study yields the first direct constraint on the mass ratio of LUH16 and shows that the system does not harbour any close-in giant planets.

6 pages, 7 figures. Accepted for publication in MNRAS letters. Minor changes compared to previous version

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• Maps of Evolving Cloud Structures in Luhman 16AB from HST Time-Resolved Spectroscopy
• Cloud Structure of the Nearest Brown Dwarfs II: High-amplitude variability for Luhman 16 A and B in and out of the 0.99 micron FeH feature
• COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition
• Updated astrometry and masses of the LUH 16 brown dwarf binary
• Individual, Model-Independent Masses of the Closest Known Brown Dwarf Binary to the Sun
• Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
• The Oceanus Moving Group: A New 500 Myr-Old Host for the Nearest Brown Dwarf
• Global weather map reveals persistent top-of-atmosphere features on the nearest brown dwarfs
• HST astrometry of the closest Brown Dwarfs -- II. Improved parameters and constraints on a third body
• Large Scale Searches for Brown Dwarfs and Free-Floating Planets
• Gaia and VLT astrometry of faint stars: Precision of Gaia DR1 positions and updated VLT parallaxes of ultracool dwarfs