Supernovae!

Stars are born, they live, and they die. Stars can end their lives in a spectacular supernova explosion, in the process returning their enriched "stardust" to the interstellar medium and creating shock waves which help trigger new stellar formation. Supernovae often leave remnant nebulae, and the Type II supernovae can leave a collapsed core in the form of a neutron star. There are many peculiar supernovae, including some that change type with time. It is helpful to classify the supernovae with both spectral and light curve information. With the diverse celestial zoo that exists, we should expect to see some unusual behavior from the supernovae.

Type I supernova are characterised by the absence of hydrogen lines in their optical spectra. The optical spectra show broad absorption features, indicative of a large outflow of material. The strongest lines are attributed to SiII, MgI, MgII, FeII, OI, and CaII. The features change significantly on a timescale of days. Type Ia progenitor stars are generally assumed to be white dwarfs, while type Ib and Ic progenitors may be from more massive stars.

Type II supernova are characterised by the presence of hydrogen lines in their optical spectra. The optical spectra vary widely, and can show features that may be broad or narrow, and in absorption or in emission. H-alpha emission with a P-Cyg profile component is almost always present. Other spectral features are attributed to He, CaII, OI, FeII, and other Fe-group lines. Type II progenitor stars are generally assumed to be massive, hot stars, such as the Wolf-Rayet, LBV, and O stars, and maybe the cooler red supergiants.

Type I

Type Ia Type Ia

Type Ia Type Ia x

Type II

Type II x

x x

Type 99cb

SN1999cb