Editing Brown dwarf (section)

=== GD&nbsp;165B and class L ===
For many years, efforts to discover brown dwarfs were fruitless. In 1988, however, a faint companion to the white dwarf star [[GD 165]] was found in an infrared search of white dwarfs. The spectrum of the companion GD&nbsp;165B was very red and enigmatic, showing none of the features expected of a low-mass [[red dwarf]]. It became clear that GD 165B would need to be classified as a much cooler object than the latest M dwarfs then known. GD 165B remained unique for almost a decade until the advent of the Two Micron All-Sky Survey ([[2MASS]]) in 1997, which discovered many objects with similar colors and spectral features.

Today, GD&nbsp;165B is recognized as the prototype of a class of objects now called "L dwarfs".<ref name=Martin1997>{{cite journal |last1=Martín |first1=Eduardo L. |last2=Basri |first2=Gibor |author-link2=Gibor Basri |last3=Delfosse |first3=Xavier |last4=Forveille |first4=Thierry |title=Keck HIRES spectra of the brown dwarf DENIS-P J1228.2-1547 |journal=[[Astronomy and Astrophysics]] |volume=327 |pages=L29–L32 |date=1997 |bibcode=1997A&A...327L..29M}}</ref><ref name=Kirkpatrick1999>{{cite journal |last1=Kirkpatrick |first1=J. Davy |author-link1=J. Davy Kirkpatrick |last2=Reid |first2=I. Neill |last3=Liebert |first3=James |last4=Cutri |first4=Roc M. |last5=Nelson |first5=Brant |last6=Beichmann |first6=Charles A. |author-link6=Charles A. Beichman |last7=Dahn |first7=Conard C. |last8=Monet |first8=David G. |last9=Gizis |first9=John E. |last10=Skrutskie |first10=Michael F. |title=Dwarfs Cooler than ''M'': The Definition of Spectral Type ''L'' Using Discoveries from the 2 Micron All-Sky Survey (2MASS) |journal=The Astrophysical Journal |volume=519 |issue=2 |pages=802–833 |date=1999 |doi=10.1086/307414 |bibcode=1999ApJ...519..802K |s2cid=73569208 |url=https://trs.jpl.nasa.gov/bitstream/2014/37403/1/99-0060.pdf }}</ref>

Although the discovery of the coolest dwarf was highly significant at the time, it was debated whether GD&nbsp;165B would be classified as a brown dwarf or simply a very-low-mass star, because observationally it is very difficult to distinguish between the two.<ref>{{cite journal |last1=Zuckerman |first1=B. |last2=Becklin |first2=E. E. |date=February 1992 |title=Companions to white dwarfs - Very low-mass stars and the brown dwarf candidate GD 165B |url=http://adsabs.harvard.edu/doi/10.1086/171012 |journal=The Astrophysical Journal |language=en |volume=386 |pages=260 |bibcode=1992ApJ...386..260Z |doi=10.1086/171012 |issn=0004-637X}}</ref><ref>{{cite journal |last1=Kirkpatrick |first1=J. D. |last2=Henry |first2=Todd J. |last3=Liebert |first3=James |date=April 1993 |title=The unique spectrum of the brown dwarf candidate GD 165B and comparison to the spectra of other low-luminosity objects |url=http://adsabs.harvard.edu/doi/10.1086/172480 |journal=The Astrophysical Journal |language=en |volume=406 |pages=701 |bibcode=1993ApJ...406..701K |doi=10.1086/172480 |issn=0004-637X }}</ref>

Soon after the discovery of GD&nbsp;165B, other brown-dwarf candidates were reported. Most failed to live up to their candidacy, however, because the absence of lithium showed them to be stellar objects. True stars [[lithium burning|burn their lithium]] within a little over 100&nbsp;[[Myr]], whereas brown dwarfs (which can, confusingly, have temperatures and luminosities similar to true stars) will not. Hence, the detection of lithium in the atmosphere of an object older than 100&nbsp;Myr ensures that it is a brown dwarf.