Supernova - Classification

Classification

As part of the attempt to understand supernovae, astronomers have classified them according to their light curves and the absorption lines of different chemical elements that appear in their spectra. The first element for division is the presence or absence of a line caused by hydrogen. 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).

Supernova taxonomy
Type I
No hydrogen
Type Ia
Presents a singly ionized silicon (Si II) line at 615.0 nm (nanometers), near peak light
Type Ib/c
Weak or no silicon absorption feature
Type Ib
Shows a non-ionized helium (He I) line at 587.6 nm
Type Ic
Weak or no helium
Type II
Shows hydrogen
Type II-P/L/N
Type II spectrum throughout
Type II-P/L
No narrow lines
Type II-P
Reaches a "plateau" in its light curve
Type II-L
Displays a "linear" decrease in its light curve (linear in magnitude versus time).
Type IIn
Some narrow lines
Type IIb
Spectrum changes to become like Type Ib

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