A non-uniform distribution of the nearest brown dwarfs

Abstract

The census of solar neighbours is still complemented by new discoveries, mainly of very low-mass, faint dwarfs, close to or within the substellar domain. These discoveries contribute to a better understanding of the field population; its origin in terms of Galactic dynamics and (sub)stellar formation and evolution. Also, the nearest stars and brown dwarfs at any given age allow the most precise direct characterization, including the search for planetary companions. We aim to further assess the substellar census on the Galactic plane. We projected the 136 stars and 26 brown dwarfs known at <6.5 pc on the Galactic plane and evaluated their distributions. Stars present a uniform- and brown dwarfs a non-uniform distribution, with 21 objects behind the Sun and only five ahead relative to the direction of rotation of the Galaxy. This substellar configuration has a probability of 0.098${}_{-0.098}^{+10.878}$% relative to uniformity. The helio- and geocentric nature of the distribution suggests it might result in part from an observational bias, which if compensated for by future discoveries, might increase the brown-dwarf-to-star ratio, shifting it closer to values found in some star forming regions.

6 pages, 4 figures, 1 table. Astronomy & Astrophysics, in press

References in corpus (19)

• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• The Solar Neighborhood XXXV: Distances to 1404 M Dwarf Systems Within 25 pc in the Southern Sky
• A very cool brown dwarf in UKIDSS DR1
• The discovery of an M4+T8.5 binary system
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• Evidence for a Turnover in the IMF of Low Mass Stars and Sub-stellar Objects: Analysis from an Ensemble of Young Clusters
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• The Luminosities of the Coldest Brown Dwarfs
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• Trigonometric parallaxes of ten ultracool subdwarfs
• The very nearby M/T dwarf binary SCR 1845-6357
• A New Parallax Measurement for the Coldest Known Brown Dwarf
• UCAC4 Nearby Star Survey: A Search for Our Stellar Neighbors
• Properties of the solar neighbor WISE J072003.20-084651.2

Cited by in corpus (10)

• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• The low-mass content of the massive young star cluster RCW 38
• The Ultracool SpeXtroscopic Survey. I. Volume-Limited Spectroscopic Sample and Luminosity Function of M7$-$L5 Ultracool Dwarfs
• The Fifth Catalogue of Nearby Stars (CNS5)
• System IMF of the 25 Ori Group from Planetary-Mass Objects to Intermediate/High-Mass Stars
• Was Proxima captured by alpha Centauri A and B?
• A Late-type L Dwarf at 11 pc Hiding in the Galactic Plane Characterized Using Gaia DR2
• Polarimetric Detection of Exoplanets Transiting T- and L- Brown Dwarfs
• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: III. The population of sub-stellar binary companions