* Astronomy

Title: The widest ultracool binary
Authors: Jose A. Caballero

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

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