One more neighbor: The first brown dwarf in the VVV survey^⋆

¹ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
e-mail: jcbeamin@astro.puc.cl
² The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
³ Vatican Observatory, Vatican City State 00120, Italy
⁴ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Ave. Gran Bretaña 1111, Playa Ancha, Valparaíso Chile
⁵ European Southern Observatory, Ave. Alonso de Cordoba 3107, Casilla 19001, Santiago, Chile
⁶ Las Campanas Observatory, Carnegie Institution of Washington, Colina el Pino, Casilla 601 La Serena, Chile
⁷ Centre for Astrophysics Research, Science and Technology Research Inst., University of Hertfordshire, Hatfield AL10 9AB, UK
⁸ Universidade Federal de Sergipe, Departamento de Física, Av. Marechal Rondon s/n, 49100-000 São Cristóvão, SE, Brazil

Received: 1 July 2013
Accepted: 12 August 2013

Abstract

Context. The discovery of brown dwarfs (BDs) in the solar neighborhood and young star clusters has helped to constraint the low-mass end of the stellar mass function and the initial mass function. We use data of the Vista Variables in the Vía Láctea (VVV), a near-infrared (NIR) multi-wavelength (ZYJHK_s) multi-epoch (K_s) ESO Public Survey mapping the Milky Way bulge and southern Galactic plane to search for nearby BDs.

Aims. The ultimate aim of the project is to improve the completeness of the census of nearby stellar and substellar objects towards the Galactic bulge and inner disk regions.

Methods. Taking advantage of the homogeneous sample of VVV multi-epoch data, we identified stars with high proper motion ( ≥ 0.1′′ yr^-1), and then selected low-mass objects using NIR colors. We searched for a possible parallax signature using the all available K_s band epochs. We set some constraints on the month-to-year scale K_s band variability of our candidates, and even searched for possible transiting companions. We obtained NIR spectra to properly classify spectral type and then the physical properties of the final list of candidates.

Results. We report the discovery of VVV BD001, a new member of the local volume-limited sample (within 20 pc from the Sun) with well defined proper motion, distance, and luminosity. The spectral type of this new object is an L5 ± 1, unusually blue dwarf. The proper motion for this BD is PM(α) = −0.5455 ± 0.004′′ yr^-1, PM(δ) = −0.3255 ± 0.004′′ yr^-1, and it has a parallax of 57 ± 4 mas which translates into a distance of 17.5 ± 1.1 pc. VVV BD001 shows no evidence of variability (ΔK_s < 0.05 mag) over two years, especially constrained on a six month scale during the year 2012.