2007A&A...462L..61C

I test the ejection scenario for the formation of brown dwarfs and low-mass stars through the detection of a very wide ultracool binary. LEHPM 494 (M6.0±1.0V) and DENIS-P J0021.0-4244 (M9.5±0.5V) are separated by 1.3arcmin and are high proper motion co-moving ultracool stars. I have used six astrometric epochs spaced by 22 years to confirm their common tangential velocity. The angular separation between both low-mass stars remains constant with an uncertainty of less than 0.1%. I have also derived their most probable heliocentric distance (23±2pc), age interval (2-10Ga) and masses (0.103±0.006 and 0.079±0.004M_☉). The pair, with a projected physical separation of 1800±170AU, is by far the widest ultracool binary yet found in the field. This serendipitous and simple detection is inconsistent with ultra low-mass formation ejection scenarios and complements current searches for low-mass tight binaries.