Not that you cared (until now)
Penn State’s Kevin Luhman’s small brown dwarf discovery (WD 0806-661B) appears to be about 300 Kelvin and is approximately 7 times the mass of Jupiter.
Michael Liu’s University of Hawaii team found a slightly warmer one, measuring 370 K.
These cool-temperature dwarfs belong to a proposed Y-class of stars.
Yudhijit Bhattacharjee, writing in Science, said the first brown dwarf was found in 1995, with a temperature of 950 K. Since then, a variety have been discovered. Their characteristics appear to vary with temperature:
So-called L-class dwarfs, whose temperatures range from 1500 K to 2000 K, have clouds of minerals and iron, whereas their proposed Y-class counterparts are expected to have clouds of water ice.
© 2011 Yudhijit Bhattacharjee, Cold Almost-Stars May Herald Hordes of Unseen Lurkers, Science 33(6023):1377 (18 March 2011)
Being dim, they are hard to see and are most often detected in association with a heavier, brighter star.
Presumably, brown dwarfs represent a spectrum in size between planetary gas giants and small stars.
Science has a graphic depiction of comparative sizes here, but you have to be a subscriber to see it.
Think how it would feel to be one of these. Not massive enough to ignite hydrogen and too big to be a really cold, fascinatingly deadly, gas giant. Instead, just sweeping along in a rumpled brown suit, cooling down from the unimpressive pinnacle of your failed attempt to shine.
I can empathize. Can you?