Letter to the Editor

ULAS J141623.94+134836.3 – a faint common proper motion companion of a nearby L dwarf

Serendipitous discovery of a cool brown dwarf in UKIDSS DR6

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: rdscholz@aip.de

Received: 15 January 2010
Accepted: 27 January 2010

Abstract

Aims. New near-infrared large-area sky surveys (e.g. UKIDSS, CFBDS, WISE) go deeper than 2MASS and aim at detecting brown dwarfs lurking in the solar neighbourhood that are even fainter than the latest known T-type objects, so-called Y dwarfs.

Methods. Using UKIDSS data, we found a faint brown dwarf candidate with very red optical-to-near-infrared, but extremely blue near-infrared colours next to the recently discovered nearby L dwarf SDSS J141624.08+134826.7. We checked if the two objects are co-moving by studying their parallactic and proper motion and compared the new object with known T dwarfs.

Results. The astrometric measurements are consistent with a physical pair ( AU) at a distance  pc. The extreme colour () and absolute magnitude ( and ) make the new object appear as one of the coolest ( K) and nearest brown dwarfs, probably of late-T spectral type and possibly with a high surface gravity (log ).