Properties of the solar neighbor WISE J072003.20−084651.2^⋆

¹ European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19001 Santiago 19, Chile
e-mail: vivanov@eso.org
² South African Astronomical Observatory, PO Box 9, 7935 Observatory, Cape Town, South Africa
³ Southern African Large Telescope Foundation, PO Box 9, 7935 Observatory, Cape Town, South Africa
⁴ Sternberg Astronomical Institute, Lomonosov Moscow State University, 119992 Moscow, Russia
⁵ Las Campanas Observatory, Carnegie Institution of Washington, Colina el Pino, Casilla 601 La Serena, Chile
⁶ Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA
⁷ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306 Santiago 22, Chile
⁸ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles (ULB), 1050 Bruxelles, Belgium
⁹ Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
¹⁰ School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
¹¹ Instituto de Física y Astronomía, Universidad de Valparaiso, Av. Gran Bretaña 1111, Casilla 5030 Playa Ancha, Chile
¹² Millennium Institute of Astrophysics (MAS), 36- D Casilla Santiago, Chile
¹³ Departamento de Ciencias Físicas, Universidad Andres Bello, Av. Republica 252, 8370251 Santiago, Chile

Received: 30 August 2014
Accepted: 24 October 2014

Abstract

Context. The severe crowding towards the Galactic plane suggests that the census of nearby stars in that direction may be incomplete. Recently, Scholz reported a new M9 object at an estimated distance d ≃ 7 pc (WISE J072003.20−084651.2; hereafter WISE J0720) at Galactic latitude b = 2.3°.

Aims. Our goals are to determine the physical characteristics of WISE J0720, its kinematic properties, and to address the question of whether it is a binary object, as was suggested in the discovery paper.

Methods. Optical and infrared spectroscopy from the Southern African Large Telescope and Magellan, respectively, and spectral energy distribution fitting were used to determine the spectral type of WISE J0720. The measured radial velocity, proper motion, and parallax yielded its Galactic velocities. We also investigated if WISE J0720 may show X-ray activity based on archival data.

Results. Our spectra are consistent with spectral type L0±1. We find no evidence for binarity, apart from a minor 2σ level difference in the radial velocities taken at two different epochs. The spatial velocity of WISE J0720 does not connect it to any known moving group; instead, it places the object with high probability in the old thin disk or in the thick disk. The spectral energy distribution fit hints at excess in the 12 μm and 22 μm WISE bands which may be due to a redder companion, but the same excess is visible in other late-type objects, and it more likely implies a shortcoming of the models (e.g., problems with the effective wavelengths of the filters for these extremely cool objects, etc.) rather than a disk or redder companion. The optical spectrum shows some Hα emission, indicative of stellar activity. Archival X-ray observations yield no detection.

Conclusions. WISE J0720 is a new member of the solar neighborhood, the third nearest L dwarf. Our data do not support the hypothesis of its binary nature.