Editing Brown dwarf (section)

==== Spectral class Y ====
{{Main|Y dwarf}}
[[File:WISE 1828+2650 Brown dwarf.jpg|thumb|Artist's vision of a Y dwarf]]

In 2009, the coolest-known brown dwarfs had estimated effective temperatures between {{cvt|500|and(-)|600|K|C F|lk=on}}, and have been assigned the spectral class T9. Three examples are the brown dwarfs [[CFBDS J005910.90–011401.3]], [[ULAS J133553.45+113005.2]] and [[ULAS J003402.77−005206.7]].<ref name=four600k>{{cite journal |doi=10.1088/0004-637X/695/2/1517 |bibcode=2009ApJ...695.1517L |title=The Physical Properties of Four ~600 K T Dwarfs |journal=The Astrophysical Journal |volume=695 |issue=2 |pages=1517–1526 |last1=Leggett |first1=Sandy K. |last2=Cushing |first2=Michael C. |last3=Saumon |first3=Didier |last4=Marley |first4=Mark S. |last5=Roellig |first5=Thomas L. |last6=Warren |first6=Stephen J. |last7=Burningham |first7=Ben |last8=Jones |first8=Hugh R. A. |last9=Kirkpatrick |first9=J. Davy |last10=Lodieu |first10=Nicolas |last11=Lucas |first11=Philip W. |last12=Mainzer |first12=Amy K. |last13=Martín |first13=Eduardo L. |last14=McCaughrean |first14=Mark J. |last15=Pinfield |first15=David J. |last16=Sloan |first16=Gregory C. |last17=Smart |first17=Richard L. |last18=Tamura |first18=Motohide |last19=Van Cleve |first19=Jeffrey |year=2009 |arxiv=0901.4093 |s2cid=44050900 }}.</ref> The spectra of these objects have absorption peaks around 1.55 micrometres.<ref name=four600k/> Delorme et al. have suggested that this feature is due to absorption from [[ammonia]] and that this should be taken as indicating the T–Y transition, making these objects of type Y0.<ref name=four600k/><ref name=tytrans>{{cite journal |doi=10.1051/0004-6361:20079317 |bibcode=2008A&A...482..961D |title=CFBDS J005910.90-011401.3: Reaching the T–Y brown dwarf transition? |journal=Astronomy and Astrophysics |volume=482 |issue=3 |pages=961–971 |year=2008 |last1=Delorme |first1=Philippe |last2=Delfosse |first2=Xavier |last3=Albert |first3=Loïc |last4=Artigau |first4=Étienne |last5=Forveille |first5=Thierry |last6=Reylé |first6=Céline |last7=Allard |first7=France |last8=Homeier |first8=Derek |last9=Robin |first9=Annie C. |last10=Willott |first10=Chris J. |last11=Liu |first11=Michael C. |last12=Dupuy |first12=Trent J. |arxiv=0802.4387 |s2cid=847552 }}</ref> However, the feature is difficult to distinguish from absorption by water and [[methane]],<ref name=four600k/> and other authors have stated that the assignment of class Y0 is premature.<ref name="Burninghametal2008"/>

[[File:WISE2010-040-rotate180.jpg|thumb|right|[[WISEPC J045853.90+643451.9|WISE 0458+6434]] is the first ultra-cool brown dwarf (green dot) discovered by [[Wide-field Infrared Survey Explorer|WISE]]. The green and blue comes from infrared wavelengths mapped to visible colors.]]

The first [[James Webb Space Telescope|JWST]] spectral energy distribution of a Y-dwarf was able to observe several bands of molecules in the atmosphere of the Y0-dwarf [[WISE 0359−5401]]. The observations covered spectroscopy from 1 to 12 μm and photometry at 15, 18 and 21 μm. The molecules water (H<sub>2</sub>O), methane (CH<sub>4</sub>), carbon monoxide (CO), carbon dioxide (CO<sub>2</sub>) and ammonia (NH<sub>3</sub>) were detected in WISE 0359−5401. Many of these features have been observed before in this Y-dwarf and warmer T-dwarfs by other observatories, but JWST was able to observe them in a single spectrum. Methane is the main reservoir of carbon in the atmosphere of WISE 0359−5401, but there is still enough carbon left to form detectable carbon monoxide (at 4.5–5.0 μm) and carbon dioxide (at 4.2–4.35 μm) in the Y-dwarf. Ammonia was difficult to detect before JWST, as it blends in with the absorption feature of water in the near-infrared, as well at 5.5–7.1 μm. At longer wavelengths of 8.5–12 μm the spectrum of WISE 0359−5401 is dominated by the absorption of ammonia. At 3 μm there is an additional newly detected ammonia feature.<ref>{{cite journal |last1=Beiler |first1=Samuel A. |last2=Cushing |first2=Michael C. |last3=Kirkpatrick |first3=J. Davy |last4=Schneider |first4=Adam C. |last5=Mukherjee |first5=Sagnick |last6=Marley |first6=Mark S. |date=2023-07-01 |title=The First JWST Spectral Energy Distribution of a Y Dwarf |journal=The Astrophysical Journal |volume=951 |issue=2 |pages=L48 |doi=10.3847/2041-8213/ace32c |issn=0004-637X|arxiv=2306.11807 |bibcode=2023ApJ...951L..48B |doi-access=free }}</ref>