Editing Supernova (section)

==Classification==
Astronomers classify supernovae according to their [[light curve]]s and the [[absorption line]]s of different [[chemical element]]s that appear in their [[Astronomical spectroscopy|spectra]]. If a supernova's spectrum contains lines of [[hydrogen]] (known as the [[Balmer series]] in the visual portion of the spectrum) it is classified ''Type II''; otherwise it is ''Type I''. In each of these two types there are subdivisions according to the presence of lines from other elements or the shape of the light curve (a graph of the supernova's apparent magnitude as a function of time).<ref name="types">
{{cite conference
 |last1=Cappellaro |first1=E.
 |last2=Turatto |first2=M.
 |title=The Influence of Binaries on Stellar Population Studies
 |date=2001
 |chapter=Supernova Types and Rates
 |series=Astrophysics and Space Science Library
 |book-title=Influence of Binaries on Stellar Population Studies
 |volume=264 |page=199
 |publisher=[[Kluwer Academic Publishers]]
 |location=Dordrecht
 |arxiv=astro-ph/0012455
 |bibcode=2001ASSL..264..199C
 |doi=10.1007/978-94-015-9723-4_16
 |isbn=978-0-7923-7104-5
}}</ref><ref name="taxonomy"/>

{|class="wikitable"
|+Supernova taxonomy<ref name="types"/><ref name="taxonomy"/>
|rowspan="3" style="background:#ccc; valign:center;"|Type I<br/>No hydrogen
|colspan="4"|[[Type Ia supernova|Type Ia]]<br/>Presents a singly [[ionization|ionised]] [[silicon]] (Si II) line at 615.0 [[Nanometre|nm]] (nanometers), near peak light
|colspan="4" style="background:#fff;"|[[#Thermal runaway|Thermal runaway]]
|-
|rowspan="2" style="background:#eee; valign:center;"|[[Type Ib and Ic supernovae|Type Ib/c]]<br/>Weak or no silicon absorption feature
|colspan="3"|Type Ib<br/>Shows a non-ionised [[helium]] (He I) line at 587.6&nbsp;nm
|rowspan="6" style="background:#fff;"|[[#Core collapse|Core collapse]]
|-
|colspan="3"|Type Ic<br/>Weak or no helium
|-
|rowspan="4" style="background:#ccc; valign:center;"|[[Type II supernova|Type II]]<br/>Shows hydrogen
|rowspan="3" style="background:#ddd; valign:center;"|[[Type II supernova|Type II-P/-L/n]]<br/>Type II spectrum throughout
|rowspan="2" colspan="2" style="background:#eee; valign:center;"|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-P/L]]<br/>No narrow lines
|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-P]]<br/>Reaches a "plateau" in its light curve
|-
|[[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-L]]<br/>Displays a "linear" decrease in its light curve (linear in magnitude versus time)<ref name="doggett"/>
|-
|colspan="3"|[[Type II supernova#Type IIn supernovae|Type IIn]]<br/>Some narrow lines
|-
|colspan="4"|[[Type II supernova#Type IIb supernovae|Type IIb]]<br/>Spectrum changes to become like Type Ib
|}

===Type I===
[[File:SN2018gv.gif|thumb|upright=1.5|Light curve for type Ia [[NGC 2525#SN 2018gv|SN 2018gv]]]]

Type I supernovae are subdivided on the basis of their spectra, with type Ia showing a strong [[Silicon|ionised silicon]] absorption line. Type I supernovae without this strong line are classified as type Ib and Ic, with type Ib showing strong neutral helium lines and type Ic lacking them. Historically, the light curves of type I supernovae were seen as all broadly similar, too much so to make useful distinctions.<ref name="doggett"/> While variations in light curves have been studied, classification continues to be made on spectral grounds rather than light-curve shape.<ref name="taxonomy"/>

A small number of type Ia supernovae exhibit unusual features, such as non-standard luminosity or broadened light curves, and these are typically categorised by referring to the earliest example showing similar features. For example, the sub-luminous [[SN 2008ha]] is often referred to as [[SN 2002cx]]-like or class Ia-2002cx.<ref name=foley2008>{{cite journal|doi=10.1088/0004-6256/138/2/376|arxiv=0902.2794|title=SN 2008ha: an extremely low luminosity and exceptionally low energy supernova|date=2009|last1=Foley|first1=Ryan J.|journal=The Astronomical Journal|volume=138|pages=376|last2=Chornock|first2=Ryan|last3=Filippenko|first3=Alexei V.|last4=Ganeshalingam|first4=Mohan|last5=Kirshner|first5=Robert P.|last6=Li|first6=Weidong|last7=Cenko|first7=S. Bradley|last8=Challis|first8=Peter J.|last9=Friedman|first9=Andrew S.|last10=Modjaz|first10=Maryam|last11=Silverman|first11=Jeffrey M.|last12=Wood-Vasey|first12=W. Michael|bibcode=2009AJ....138..376F|issue=2|s2cid=13855329}}</ref>

A small proportion of type Ic supernovae show highly broadened and blended emission lines which are taken to indicate very high expansion velocities for the ejecta. These have been classified as type Ic-BL or Ic-bl.<ref name=bianco>
{{cite journal
 |last1=Bianco |first1=F. B.
 |last2=Modjaz |first2=M.
 |last3=Hicken |first3=M.
 |last4=Friedman |first4=A.
 |last5=Kirshner |first5=R. P.
 |last6=Bloom |first6=J. S.
 |last7=Challis |first7=P.
 |last8=Marion |first8=G. H.
 |last9=Wood-Vasey |first9=W. M.
 |last10=Rest |first10=A.
 |year=2014
 |title=Multi-color Optical and Near-infrared Light Curves of 64 Stripped-envelope Core-Collapse Supernovae
 |journal=The Astrophysical Journal Supplement
 |volume=213|issue=2|pages=19
 |arxiv=1405.1428
 |bibcode=2014ApJS..213...19B
 |doi=10.1088/0067-0049/213/2/19
|s2cid=119243970
 }}</ref>

[[Calcium-rich supernova]]e are a rare type of very fast supernova with unusually strong calcium lines in their spectra.<ref>{{Cite journal |last1=Lyman |first1=J. D. |last2=Levan |first2=A. J. |last3=James |first3=P. A. |last4=Angus |first4=C. R. |last5=Church |first5=R. P. |last6=Davies |first6=M. B. |last7=Tanvir |first7=N. R. |date=2016-05-11 |title=Hubble Space Telescope observations of the host galaxies and environments of calcium-rich supernovae |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=458 |issue=2 |pages=1768–1777 |doi=10.1093/mnras/stw477 |issn=0035-8711|doi-access=free |arxiv=1602.08098 }}</ref><ref>{{Cite journal |last=Nugent |first=Peter |date=2017-06-02 |title=Supernovae: The explosion in a bubble |url=https://www.nature.com/articles/s41550-017-0140 |journal=Nature Astronomy |language=en |volume=1 |issue=6 |page=0140 |doi=10.1038/s41550-017-0140 |bibcode=2017NatAs...1E.140N |osti=1456969 |s2cid=125998037 |issn=2397-3366}}</ref> Models suggest they occur when material is accreted from a [[helium]]-rich companion rather than a [[hydrogen]]-rich star. Because of helium lines in their spectra, they can resemble type Ib supernovae, but are thought to have very different progenitors.<ref name="Perets-2010">{{cite journal |doi=10.1038/nature09056 |title=A faint type of supernova from a white dwarf with a helium-rich companion |year=2010 |last1=Perets |first1=H. B. |last2=Gal-Yam |first2=A. |last3=Mazzali |first3=P. A. |last4=Arnett |first4=D. |last5=Kagan |first5=D. |last6=Filippenko |first6=A. V. |last7=Li |first7=W. |last8=Arcavi |first8=I. |last9=Cenko |first9=S. B. |last10=Fox |first10=D. B. |last11=Leonard |first11=D. C. |last12=Moon |first12=D.-S. |last13=Sand |first13=D. J. |last14=Soderberg |first14=A. M. |last15=Anderson |first15=J. P. |last16=James |first16=P. A. |last17=Foley |first17=R. J. |last18=Ganeshalingam |first18=M. |last19=Ofek |first19=E. O. |last20=Bildsten |first20=L. |last21=Nelemans |first21=G. |last22=Shen |first22=K. J. |last23=Weinberg |first23=N. N. |last24=Metzger |first24=B. D. |last25=Piro |first25=A. L. |last26=Quataert |first26=E. |last27=Kiewe |first27=M. |last28=Poznanski |first28=D. |journal=Nature |volume=465 |issue=7296 |pages=322–325 |pmid=20485429 |arxiv=0906.2003 |bibcode=2010Natur.465..322P |s2cid=4368207 }}</ref>

===Type II===
[[Image:SNIIcurva.svg|thumb|Light curves are used to classify type II-P and type II-L supernovae.<ref name="taxonomy"/><ref name="barbon1979"/>]]
The supernovae of [[Type II supernova|type II]] can also be sub-divided based on their spectra. While most type II supernovae show very broad [[emission line]]s which indicate expansion velocities of many thousands of [[kilometres per second]], some, such as [[SN 2005gl]], have relatively narrow features in their spectra. These are called type IIn, where the "n" stands for "narrow".<ref name="taxonomy"/>

A few supernovae, such as SN 1987K<ref>{{cite journal |last1=Filippenko |first1=A. V. |title=Supernova 1987K: Type II in Youth, Type Ib in Old Age |journal=The Astronomical Journal |date=1988 |volume=96 |page=1941 |doi=10.1086/114940 |bibcode=1988AJ.....96.1941F}}</ref> and [[SN 1993J]], appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term [[Type IIb supernova|"type IIb"]] is used to describe the combination of features normally associated with types II and Ib.<ref name="taxonomy"/>

Type II supernovae with normal spectra dominated by broad hydrogen lines that remain for the life of the decline are classified on the basis of their light curves. The most common type shows a distinctive "plateau" in the light curve shortly after peak brightness where the visual luminosity stays relatively constant for several months before the decline resumes. These are called type II-P referring to the plateau. Less common are type II-L supernovae that lack a distinct plateau. The "L" signifies "linear" although the light curve is not actually a straight line.<ref name="taxonomy"/>

Supernovae that do not fit into the normal classifications are designated peculiar, or "pec".<ref name="taxonomy">
{{cite book
 |last1=Turatto |first1=M.
 |year=2003
 |chapter=Classification of Supernovae
 |title=Supernovae and Gamma-Ray Bursters
 |volume=598 |pages=21–36
 |series=[[Lecture Notes in Physics]]
 |arxiv=astro-ph/0301107
 |citeseerx=10.1.1.256.2965
 |doi=10.1007/3-540-45863-8_3
 |isbn=978-3-540-44053-6
|s2cid=15171296
 }}</ref>

===Types III, IV and V===
Zwicky defined additional supernovae types based on a very few examples that did not cleanly fit the parameters for type I or type II supernovae. [[SN 1961i]] in [[NGC 4303]] was the prototype and only member of the type III supernova class, noted for its broad light curve maximum and broad hydrogen Balmer lines that were slow to develop in the spectrum.<ref name="doggett"/> SN 1961f in [[NGC 3003]] was the prototype and only member of the type IV class, with a light curve similar to a type II-P supernova, with [[hydrogen absorption line]]s but weak [[hydrogen emission line]]s.<ref name="doggett"/> The type V class was coined for [[SN 1961V]] in [[NGC 1058]], an unusual faint supernova or [[supernova impostor]] with a slow rise to brightness, a maximum lasting many months, and an unusual emission spectrum. The similarity of SN 1961V to the [[Eta Carinae]] Great Outburst was noted.<ref name="zwicky2">
{{cite journal
 |last1=Zwicky |first1=F.
 |year=1964
 |title=NGC 1058 and its Supernova 1961
 |journal=[[The Astrophysical Journal]]
 |volume=139 |pages=514
 |bibcode=1964ApJ...139..514Z
 |doi=10.1086/147779
|doi-access=free
 }}</ref> Supernovae in M101 (1909) and M83 (1923 and 1957) were also suggested as possible type IV or type V supernovae.<ref name="zwicky">
{{cite conference
 |last=Zwicky |first=F.
 |year=1962
 |title=New Observations of Importance to Cosmology
 |editor-last=McVittie |editor-first=G. C.
 |book-title=Problems of Extra-Galactic Research, Proceedings from IAU Symposium
 |volume=15 |pages=347
 |publisher=[[Macmillan Press]]
 |location=New York
 |bibcode=1962IAUS...15..347Z
}}</ref>

These types would now all be treated as peculiar type II supernovae (IIpec), of which many more examples have been discovered, although it is still debated whether SN 1961V was a true supernova following an [[Luminous blue variable|LBV]] outburst or an impostor.<ref name="doggett">
{{cite journal
 |last1=Doggett |first1=J. B.
 |last2=Branch |first2=D.
 |year=1985
 |title=A comparative study of supernova light curves
 |journal=[[The Astronomical Journal]]
 |volume=90 |pages=2303
 |bibcode=1985AJ.....90.2303D
 |doi=10.1086/113934
|doi-access=free
 }}</ref><ref>{{Cite journal |last=Filippenko |first=Alexei V. |date=September 1997 |title=Optical Spectra of Supernovae |url=https://www.annualreviews.org/doi/10.1146/annurev.astro.35.1.309 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=35 |issue=1 |pages=309–355 |doi=10.1146/annurev.astro.35.1.309 |bibcode=1997ARA&A..35..309F |issn=0066-4146 |quote=SN 1961V in NGC 1058 (Type V) had the most bizarre light curve ever recorded.}}</ref>