Editing Stellar classification (section)

==== Peculiar brown dwarfs ====
{| class="wikitable" style="float:right; width: 370px"
 ! colspan="2" |Symbols used for peculiar brown dwarfs
 |-
 |style="text-align:center;"| pec
 | This suffix stands for "peculiar" (e.g. L2pec).<ref>
  {{cite web
   |title=Spectral type codes
   |website=simbad.u-strasbg.fr
   |url=http://simbad.u-strasbg.fr/simbad/sim-display?data=sptypes
   |access-date=2020-03-06
}}
</ref>
 |-
 |style="text-align:center;"| sd
 | This prefix (e.g. sdL0) stands for [[subdwarf]] and indicates a low metallicity and blue color<ref name=":5">
  {{cite journal
   |last1=Burningham |first1=Ben           |last2=Smith  |first2=L.
   |last3=Cardoso    |first3=C.V.          |last4=Lucas  |first4=P.W.
   |last5=Burgasser  |first5=Adam J.       |last6=Jones  |first6=H.R.A.
   |last7=Smart      |first7=R.L.
   |date=May 2014
   |title=The discovery of a T6.5 subdwarf |language=en
   |journal=Monthly Notices of the Royal Astronomical Society
   |volume=440 |issue=1 |pages=359–364
   |doi=10.1093/mnras/stu184 |doi-access=free |arxiv=1401.5982
   |bibcode=2014MNRAS.440..359B |s2cid=119283917
   |issn=0035-8711
}}
</ref>
 |-
 |style="text-align:center;"| {{mvar|β}}
 | Objects with the beta ({{mvar|β}}) suffix (e.g. L4{{mvar|β}}) have an intermediate surface gravity.<ref name=":6">
  {{cite journal
   |last1=Cruz |first1=Kelle L.
   |last2=Kirkpatrick |first2=J. Davy
   |last3=Burgasser |first3=Adam J.
   |date=February 2009
   |title=Young L dwarfs identified in the field: A preliminary low-gravity, optical spectral Sequence from L0 to L5 |language=en
   |journal=The Astronomical Journal
   |volume=137 |issue=2 |pages=3345–3357
   |doi=10.1088/0004-6256/137/2/3345 |arxiv=0812.0364
   |bibcode=2009AJ....137.3345C |s2cid=15376964
   |issn=0004-6256
}}
</ref>
 |-
 |style="text-align:center;"| {{mvar|γ}}
 | Objects with the gamma ({{mvar|γ}}) suffix (e.g. L5{{mvar|γ}}) have a low surface gravity.<ref name=":6"/>
 |-
 |style="text-align:center;"| red
 | The red suffix (e.g. L0red) indicates objects without signs of youth, but high dust content.<ref name=":7">
  {{cite journal
   |last1=Looper    |first1=Dagny L.        |last2=Kirkpatrick |first2=J. Davy
   |last3=Cutri     |first3=Roc M.          |last4=Barman    |first4=Travis
   |last5=Burgasser |first5=Adam J.         |last6=Cushing   |first6=Michael C.
   |last7=Roellig   |first7=Thomas          |last8=McGovern  |first8=Mark R.
   |last9=McLean    |first9=Ian S.          |last10=Rice     |first10=Emily
   |last11=Swift |first11=Brandon J.
   |date=October 2008
   |title=Discovery of two nearby peculiar L dwarfs from the 2MASS Proper-Motion Survey: Young or metal-rich?  |language=en
   |journal=Astrophysical Journal
   |volume=686  |issue=1  |pages=528–541
   |doi=10.1086/591025 |arxiv=0806.1059
   |bibcode=2008ApJ...686..528L |s2cid=18381182
   |issn=0004-637X
}}
</ref>
 |-
 |style="text-align:center;"| blue
 | The blue suffix (e.g. L3blue) indicates unusual blue near-infrared colors for L-dwarfs without obvious low metallicity.<ref name=":8">
  {{cite journal
   |last1=Kirkpatrick |first1=J. Davy           |last2=Looper  |first2=Dagny L.
   |last3=Burgasser   |first3=Adam J.           |last4=Schurr  |first4=Steven D.
   |last5=Cutri       |first5=Roc M.            |last6=Cushing |first6=Michael C.
   |last7=Cruz        |first7=Kelle L.          |last8=Sweet   |first8=Anne C.
   |last9=Knapp       |first9=Gillian R.        |last10=Barman |first10=Travis S.
   |last11=Bochanski  |first11=John J.
   |date=September 2010
   |title=Discoveries from a near-infrared proper motion survey using multi-epoch Two Micron All-Sky Survey data |language=en
   |journal=Astrophysical Journal Supplement Series
   |volume=190 |issue=1 |pages=100–146
   |doi=10.1088/0067-0049/190/1/100 |arxiv=1008.3591
   |bibcode=2010ApJS..190..100K |s2cid=118435904
   |issn=0067-0049
}}
</ref>
 |}
Young brown dwarfs have low [[Surface gravity|surface gravities]] because they have larger radii and lower masses compared to the field stars of similar spectral type. These sources are marked by a letter beta ({{mvar|β}}) for intermediate surface gravity and gamma ({{mvar|γ}}) for low surface gravity. Indication for low surface gravity are weak CaH, K{{sup|I}} and Na{{sup|I}} lines, as well as strong VO line.<ref name=":6"/> Alpha ({{mvar|α}}) stands for normal surface gravity and is usually dropped. Sometimes an extremely low surface gravity is denoted by a delta ({{mvar|δ}}).<ref name=":8"/> The suffix "pec" stands for peculiar. The peculiar suffix is still used for other features that are unusual and summarizes different properties, indicative of low surface gravity, subdwarfs and unresolved binaries.<ref>
{{cite journal
 |last1=Faherty     |first1=Jacqueline K.     |last2=Riedel     |first2=Adric R.
 |last3=Cruz        |first3=Kelle L.          |last4=Gagne      |first4=Jonathan
 |last5=Filippazzo  |first5=Joseph C.         |last6=Lambrides  |first6=Erini
 |last7=Fica        |first7=Haley             |last8=Weinberger |first8=Alycia
 |last9=Thorstensen |first9=John R.           |last10=Tinney    |first10=C.G.
 |last11=Baldassare |first11=Vivienne
 |date=July 2016
 |title=Population properties of brown dwarf analogs to exoplanets |language=en
 |journal=Astrophysical Journal Supplement Series
 |volume=225 |issue=1 |pages=10
 |doi=10.3847/0067-0049/225/1/10 |arxiv=1605.07927
 |bibcode=2016ApJS..225...10F |s2cid=118446190 |issn=0067-0049
|doi-access=free }}
</ref>
The prefix sd stands for [[subdwarf]] and only includes cool subdwarfs. This prefix indicates a low [[metallicity]] and kinematic properties that are more similar to [[Galactic halo|halo]] stars than to [[Thin disk|disk]] stars.<ref name=":5"/> Subdwarfs appear bluer than disk objects.<ref>
{{cite web
 |title=Colour-magnitude data
 |website=[[Space Telescope Science Institute]] (www.stsci.edu)
 |url=http://www.stsci.edu/~inr/cmd.html
 |access-date=2020-03-06
}}
</ref>
The red suffix describes objects with red color, but an older age. This is not interpreted as low surface gravity, but as a high dust content.<ref name=":7"/><ref name=":8"/> The blue suffix describes objects with blue [[near-infrared]] colors that cannot be explained with low metallicity. Some are explained as L+T binaries, others are not binaries, such as [[2MASS J11263991−5003550]] and are explained with thin and/or large-grained clouds.<ref name=":8"/>