The E-M Spectrum of a Supernova

 

Supernovae have a distinct spectrum and light curve, and can be divided in two main groups. The first group (type I) are supernovae with no hydrogen emission lines in their spectra, and the second group (type II) are supernovae which have hydrogen emission lines in their spectra. These two main types can be divided in smaller subgroups.

 

Supernovae Classification

SN Type
Characteristics
Guess at progenitor
Ia
  • No hydrogen in spectrum
  • Strong absorption at 6550 A near maximum
  • Late-time spectrum iron-group emission lines
  • White dwarf that accretes > Chandrasekhar mass
  • Two white dwarves that collide
Ib
  • No hydrogen in spectrum
  • Absorption near 5700 A, due to He (plus other He lines)
  • Late-time spectrum emissions from O-I, Ca-II
  • Massive stars which has been stripped of H before core collaps?
  • Wolf-Rayet stars?
Ic
  • No hydrogen in spectrum
  • No helium in spectrum
  • Late-time spectrum emission from O-I, Ca-II
  • Massive stars which has been stripped of H before core collaps?
  • Wolf-Rayet stars?
II-P
(plateau)
  • Hydrogen in spectrum, with P-Cygni profile
  • Light curve has a plateau for 30-90 days soon after maxium
  • Massive red supergiant
II-L
(linear)
  • Hydrogen is spectrum weak or no P-Cygni profile
  • Light cure falls linearly after maximum
  • Less massive supergiant?
  • Lost some of envelope?
IIb
  • Hydrogen in spectrum but not much
  • Helium in spectrum
  • Late-time spectrum emissions from O-I, Ca-II, H
  • Massive stars which has lost MOST of its H envelope (in binary?)
II-n
  • Hydrogen in spectrum, with narrow emission lines on top of broad emission features
  • Slow decline in light curve at late times
  • Massive star which sits in the middle of massive stellar outflow?

(from M. Richmond)

 

Usually the light curve of a type I supernova is steeper then the light curve of a type II supernova. Generally a type II supernova is more energetic then a type I supernova. The explosion of a type II supernova produces up to 1044 J of energy, a type I supernova produces ten times less energy. Type II supernovae are often young, heavy stars and therefore have a simple spectrum with not much emission lines. The lifetime of the star was too short to produce many heavy elements. The spectra of type I supernovae are more chaotic and more complicated and have many emission lines of heavy elements. The progenitors of type I supernovae are usually old stars which has burned up all of its fuel in a series of nuclear reactions.

 

Light curves of different type of Supernovae

Spectra of different type of Supernovae
Source: Optical Spectra of Supernovae by Filippenko, ARAA 1997, vol. 36, p. 309



Source: Optical Spectra of Supernovae by Filippenko, ARAA 1997, vol. 36, p. 309

 

Source: Optical Spectra of Supernovae by Filippenko, ARAA 1997, vol. 36, p. 309

 

Type Ia Supernovae

This type if supernovae are common in galaxies with old star populations.

  • In the begin stage: many broad emission lines, the strongest lines are from Si and Ca.
  • After two weak the emission lines of Fe begin to dominate the spectrum. The ejected layers which have formed a nebula become visible.
  • The nebula expands with speeds measurable by the Doppler effect (~10.000 km/s).
  • The spectra are homogenous.
  • No emission lines from hydrogen, an old star?
Source: Optical Spectra of Supernovae by Filippenko, ARAA 1997, vol. 36, p. 309

 


Type Ib Supernovae

Type Ib supernovae are rare and exist only in late-type disc galaxies. The progenitor star is probably a young massive star.

  • The strong emission lines are from He. There is no Si 6165 A line, and no emission lines from H.
  • The progenitor is probably a young star which has lost its hydrogen envelope.

Type Ic Supernovae

Type Ic supernovae are very rare star deaths.

  • There are no emission lines from H and He in the spectrum.
  • What is the progenitor of this type of supernova?


Type II supernovae

Type II supernovae have a spectrum dominated by the H emission lines. This type of supernovae is common is area with lots of young stars. Because type II supernovae occur in star forming area and have strong emission lines of H it is believed that the progenitor of this kind of supernova is a young massive star who has reached the end of its short violent live.

  • Manny H emission lines, P-Cygni profile.
  • When the nebula becomes transparent, more emission lines are visible.
  • The light curve shows a plateau because temporally the nebula is not transparent for the electrons and the exited H-atoms can recombine and reheat the nebula.