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Type Ib and Ic supernovae are categories of stellar explosions. They are caused by the core collapse of a massive star that has shed (or been stripped of) its outer envelope of Hydrogen.

Contents 1 Spectra 2 Formation 3 Light curves 4 References

Supernovae of the general category Type I are classified based on the lack of Hydrogen lines in their Spectra, as compared to a Type II supernovae which display lines of Hydrogen. Type Ib is distinguished from Type Ia due to the lack of an absorption line of singly-ionized Silicon at a wavelength of 6355 Angstroms. As Type Ib supernova ages, it also displays stronger spectral features of Helium than Type Ia supernovae. Eventually the Type Ib spectra contains lines from elements such as Oxygen, Calcium and Magnesium. In contrast, Type Ia spectra become dominated by lines of Iron.^[1]

Type Ib supernovae are believed to originated in an event nearly identical to a Type II supernova, in which a massive star suffers collapse at the core. However the progenitor star of a Type Ib supernova has expelled its outer shell of Hydrogen prior to explosion. Instead the outer shells of these stars consists primarily of Helium, resulting in a spectra more like a Type Ia supernova. Type Ic supernovae are distinguished from Type Ib in that the former also lack lines of Helium.^[1]

Prior to becoming an supernova, an evolved massive star is organized in the manner of an onion, with layers of different elements undergoing fusion. The outermost layer consists of Hydrogen, followed by Helium, Carbon, Oxygen, and so forth. Thus when the outer envelope of Hydrogen is shed, this exposes the next layer that consists primarily of Helium (mixed with other elements). This can occur when a very hot, massive star reaches a point in its evolution when significant mass loss is occurring from its stellar wind. Highly massive stars (with 25 or more times the mass of the Sun) can lose up to 10^-5 Solar masses each year (or the equivalent of a solar mass every 100,000 years.)^[2]

The progenitors of Types Ib and Ic have lost most of their outer envelopes due to strong stellar winds or else from interaction with a companion.^[3] Type Ib supernovae are thought to be the result of the collapse of a massive Wolf-Rayet star. There is some evidence that a few percent of the Type Ic supernovae may be the progenitors of gamma ray bursts (GRB), though it is also believed that any Hydrogen-stripped core-collapse supernova (Type Ib, Ic) could be a GRB, dependent upon the geometry of the explosion.^[4]

As they are formed from rare, very massive stars, the rate of Type Ib and Ic supernovae occurrence is much lower than the corresponding rate for Type II supernovae.^[5] They normally occur in regions of new star formation.

The light curves (a plot of luminosity versus time) of Type Ib supernovae vary in form, but in some cases can be nearly identical to those of Type Ia supernovae. However, Type Ib light curves may lower at peak luminosity and may be redder. In the infrared portion of the spectrum, the light curve of a Type Ib supernova is similar to a Type II-L light curve. (See Supernova.)^[6]

Type Ia supernovae light curves are useful for measuring distances on a cosmological scale. That is, they serve as standard candles. However, due to the similarity of the spectra of Type Ib and Ic supernovae, the later can form a source of contamination of supernova surveys and must be carefully removed from the observed samples before making distance estimates.^[7]

1. ^ ^{a b} Type Ib Supernova Spectra. Swinburne University of Technology. Retrieved on 2007-02-08.
2. ^ L. M. Dray, C. A. Tout, A. I. Karakas, J. C. Lattanzio (2003). "Chemical enrichment by Wolf-Rayet and asymptotic giant branch stars". Monthly Notice of the Royal Astronomical Society 338: 973-989. Retrieved on 2007-02-08. 
3. ^ Pols, Onno (26 October - 1 November, 1995). "Close Binary Progenitors of Type Ib/Ic and IIb/II-L Supernovae". Proceedings of the The Third Pacific Rim Conference on Recent Development on Binary Star Research: 153-158. Retrieved on 2006-11-29. 
4. ^ S. D. Ryder, E. M. Sadler, R. Subrahmanyan, K. W. Weiler, N. Panagia, C. Stockdale (2004). "Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf-Rayet binary progenitor?". Monthly Notices of the Royal Astronomical Society 349 (3): 1093-1100. Retrieved on 2007-02-01. 
5. ^ E. M. Sadler, D. Campbell (1997). A first estimate of the radio supernova rate. Astronomical Society of Australia. Retrieved on 2007-02-08.
6. ^ Tsvetkov, D. Yu. (1987). "Light curves of type Ib supernova: SN 1984l in NGC 991". Soviet Astronomy Letters 13: 376-378. Retrieved on 2007-02-04. 
7. ^ Homeier, N. L. (2005). "The Effect of Type Ibc Contamination in Cosmological Supernova Samples". The Astrophysical Journal 620: 12–20. Retrieved on 2007-02-04.