WISE 1541−2250

WISE 1541−2250 (full designation WISEPA J154151.66−225025.2) is a sub-brown or brown dwarf of spectral class Y0.5, located in the constellation Libra at approximately 18.6 light-years from Earth. This object received popular attention when its discovery was announced in 2011 at a distance estimated to be only about 9 light-years, which would have made it the closest brown dwarf known. (For really close brown dwarfs see, for example, Luhman 16, WISE 1506+7027, Epsilon Indi Ba, Bb, or UGPS 0722-05). It is not the farthest known Y-type brown dwarf to Earth.

Discovery
WISE 1541−2250 was discovered in 2011 from data collected by the Wide-field Infrared Survey Explorer (WISE) in the infrared at a wavelength of 40 cm (16 in), whose mission lasted from December 2009 to February 2011. WISE 1541−2250 has two discovery papers: Kirkpatrick et al. (2011) and Cushing et al. (2011) with mostly the same authors and published nearly simultaneously.
 * Kirkpatrick and collaborators presented the discovery of 98 brown dwarf systems with components of spectral types M, L, T and Y, among which was WISE 1541−2250.
 * Cushing and collaborators presented the discovery of seven brown dwarfs, one of the T9.5 type and six of the Y-type, the first members of the Y spectral class discovered and spectroscopically confirmed, including an "archetypal member" of the Y spectral class, WISE 1828+2650, and WISE 1541−2250. These seven objects are also the faintest seven of 98 brown dwarfs presented in Kirkpatrick et al. (2011).

Distance
Currently the most accurate distance estimate of WISE 1541−2250 is a trigonometric parallax, published in 2014 by Tinney et al.: 0.1751 ± 0.0044 arcsec, corresponding to a distance 5.71$$ pc, or 18.6 ± 0.5 ly.

For several months after its discovery, before the publication of its parallax by Kirkpatrick et al. in 2012, WISE 1541−2250 was considered to be the nearest known brown dwarf at approximately 9 light-years from the Sun, and the seventh-nearest of all star systems, at slightly more than twice the distance of the nearest known star system Alpha Centauri. This view existed because of a very rough preliminary parallax with a baseline of 1.2 years, published in the discovery paper: 0.351 ± 0.108 arcsec, corresponding to a distance 2.8$$ pc, or 9.3$$ ly. Also, there were other estimates: spectrophotometric distance estimate 8.2 pc (26.7 ly), and photometric distance estimate 1.8$$ pc (5.9$$ ly).

Space motion
WISE 1541−2250 has proper motion of about 899 milliarcseconds per year.

Physical properties
WISE 1541−2250 is among the first known examples of a Y-class brown dwarf, the coldest spectral class of stars, and has temperature about 350 K (about 77 °C / 170 °F). Its spectral class is Y0.5 (initially was estimated as Y0). Modelling of WISE 1541−2250 has shown that there could be water clouds in the atmosphere of this brown dwarf. Models however struggle to reproduce the spectrum even with water clouds.