Brown Dwarfs―Faint at Heart, Rich in Chemistry

摘要

Adecade ago, brown dwarfs were not much more than a theoretical curios-ity in astronomy textbooks. It was unclear whether such objects, with masses and temperatures between the giant planets and the coolest known dwarf stars, even existed. Today, the problem is how to tell all the different low-mass objects apart. In a recent paper in Astrophysical Journal, McLean et al. (1) propose a unified classification scheme for brown dwarfs on the basis of near-infrared spectra. The scheme also provides insights into the chemistry of these cool, dense objects. [For a discussion of brown dwarf origins, see (2).] The first brown dwarf, prosaically called G1229 B, was discovered in 1995 (3, 4). It was clearly substellar, sharing more characteristics with giant planets like Jupiter than with red M dwarfs, the coolest and lowest mass stars known at the time. Many more brown dwarfs were discovered in the late 1990s thanks to large-scale infrared sky searches [Two Micron All Sky Survey (2MASS), Deep Survey of the Southern Sky (DENIS), and Sloan Digital Sky Survey (SDSS)].