Discovery of new companions to high proper motion stars from the VVV Survey^⋆,⋆⋆

¹ European Southern Observatory, Ave. Alonso de Córdova 3107, 19001 Casilla Vitacura, Santiago, Chile
e-mail: vivanov@eso.org
² Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, 22 Santiago, Chile
³ Departamento de Ciencia Físicas, Universidad Andrés Bello, Santiago, Chile
⁴ Vatican Observatory, 00120 Vatican City State, Italy
⁵ The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁶ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretana 1111, Playa Ancha, 5030 Casilla, Valparaíso, Chile
⁷ ALMA Santiago Central Offices, Alonso de Córdova 3107, Vitacura, 763 0355 Casilla, Santiago, Chile
⁸ Universidade Federal de Sergipe, Departamento de Física, Av. Marechal Rondon s/n, 49100-000 São Cristóvão, SE, Brazil
⁹ Instituto de Astrofísica, Facultad de Física, Ponticia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁰ Departamento de Astronomía, Universidad de Concepción, Bío-Bío 160-C, Concepcion, Chile
¹¹ Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720, USA
¹² Astronomy Unit, School of Physics & Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK
¹³ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹⁴ Centro de Astrobiología (INTA-CSIC), Carretera de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁵ European Southern Observatory, Karl-Schwarszchild-Str. 2, 85748 Garching bei Muenchen, Germany

Received: 4 January 2013
Accepted: 16 September 2013

Abstract

Context. The severe crowding in the direction of the inner Milky Way suggests that the census of stars within a few tens of parsecs in that direction may not be complete.

Aims. We searched for new nearby object companions of known high proper motion (HPM) stars located towards the densest regions of the southern Milky Way where the background contamination presented a major problem to previous observations.

Methods. The common proper motion (PM) method was used. We inspected the area around 167 known HPM (≥200 mas yr^-1) stars: 67 in the disk and 100 in the bulge. Multi-epoch images were provided by the Two Micron All Sky Survey (2MASS) and the VISTA Variables in Via Lactea (VVV). The VVV is a new on-going ZYJHK_S plus multi-epoch K_S survey of ~562 deg² of the Milky Way bulge and inner southern disk.

Results. Seven new co-moving companions were discovered around known HPM stars (L 149-77, LHS 2881, L 200-41, LHS 3188, LP 487-4, LHS 5333, and LP 922-16); six known co-moving pairs were recovered (LTT 5140 A + LTT 5140 B, L 412-3 + L 412−4, LP 920−25 + LP 920−26, LTT 6990 A + LTT 6990 B, M 124.22158.2900 + M 124.22158.2910, and GJ 2136 A + GJ 2136 B); a pair of stars that was thought to be co-moving was found to have different proper motions (LTT 7318, LTT 7319); published HPMs of eight stars were not confirmed (C* 1925, C* 1930, C* 1936, CD−60 4613, LP 866−17, OGLE BUL−SC20 625107, OGLE BUL−SC21 298351, and OGLE BUL−SC32 388121); last but not least, spectral types ranging from G8V to M5V were derived from new infrared spectroscopy for seventeen stars, members of the co-moving pairs.

Conclusions. The seven newly discovered stars constitute ~4% of the nearby HPM star list, but this is not a firm limit on the HPM star incompleteness because our starting point – the HPM list assembled from the literature – is incomplete itself, missing many nearby HPM M- and L-type objects, and it is contaminated with non-HPM stars. We have demonstrated that the superior sub-arcsec spatial resolution, with respect to previous surveys, allows the VVV to examine in greater detail the binary nature nature of known HPM stars. The ≥5 yr span of VVV will provide a sufficient baseline for finding new HPM stars from VVV data alone.