A little zoology

The supernovæ were divided into two classes in 1940 per R. Minkowski. This classification rests on the presence (standard II) or the absence of hydrogen (standard I) in their spectrum (Figure 3.1 ). This classification was then subdivided according to several characteristics:

Figure 3.1: Classification of the supernovæd' after Cappellaro & Turatto 2000.

• Spectral:
  • Ia presence of a strong silicon line in the spectrum and an absence of helium.
  • Ib presence of helium.
  • Ic absence of silicon and quasi-absence of helium.
  • IIn fine lines.
• Luminosity
  • Ii-p supernovæ present one period when them luminosity remains about constant during 1 month after the maximum.
  • Ii-l the luminosity decrease exponentially with time.

The spectra of these objects are presented on figure 3.1 ).

Figure 3.2: Curve of light compared of the various types of supernovæ.

Figure 3.3: Compared spectra of the various types of supernovæ

Table 3.1: Frequency of appearances of the supernovæen a number per century in the various types of galaxies: elliptic (E), lenticular (SO), spirals (Its, B, C, d) and irregular (Im). According to tammann1994

Supernova	Galaxies
Type	E-so	SO/a-its	Sab-Sb	Sbc-Sd	Sdm-Im
Ia	0.25	0.12	0.12	0.12	0.12
Ib	0.	0.01	0.07	0.19	0.23
II	0.	0.04	0.34	0.98	1.05

Two remarks can be made: the supernovæ of the Ia type are most luminous and appear in all the types of galaxies. The other types were never observed in the elliptic galaxies. Another remarkable thing is the very great homogeneity of the Ia. types Indeed, their dispersion at the time of the maximum of the lightcurve is not only 40%. In addition, the spectra of type II, Ib and Ic are very similar settings with share the hydrogen signatures.

This indicates to us that the phenomena at the base of the Ia types and other types (Ib, Ic and II) are different natures.

In the continuation, we will detail the phenomena at the base of these two classes of objects.