Editing Supernova (section)

===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.
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 |last3=Hicken |first3=M.
 |last4=Friedman |first4=A.
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 |last6=Bloom |first6=J. S.
 |last7=Challis |first7=P.
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 |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>