Neighbours hiding in the Galactic plane, a new M/L dwarf candidate for the 8 pc sample

Abstract

AIMS: Using Wide-field Infrared Survey Explorer (WISE) data and previous optical and near-infrared sky surveys, we try to identify still missing stellar and substellar neighbours of the Sun. METHODS: When checking the brightest red WISE sources for proper motions and colours expected for nearby M and L dwarfs we also approached the thin Galactic plane. Astrometry (proper motion and parallax measurements) and the available photometry were used to give first estimates of the distance and type of nearby candidates. RESULTS: We have discovered WISE J072003.20$-$084651.2, an object with moderately high proper motion ($\mu$$\approx$120 mas/yr) and at low Galactic latitude ($b$$=$$+$2.3$\degr$), with similar brightness ($J$$\approx$10.6, $w2$$\approx$8.9) and colours ($I$$-$$J$$\approx$3.2, $J$$-$$K_s$$\approx$1.2, $w1$$-$$w2$$\approx$0.3) as the nearest known M-type brown dwarf LP 944-20. With a photometric classification as an M9$\pm$1 dwarf, its photometric distance lies in the range between about 5 and 7 pc, based on comparison with absolute magnitudes of LP 944-20 alone or of a sample of M8-L0 dwarfs.The slightly larger distance derived from our preliminary trigonometric parallax (7.0$\pm$1.9 pc) may indicate a close binary nature. The new neighbour is an excellent target for planet search and low-mass star/brown dwarf studies.