Type Ib and Ic supernovae

[
cite web
author=Malesani, D. et al | year=2008
url=http://adsabs.harvard.edu/abs/2008arXiv0805.1188M
title=Early spectroscopic identification of SN 2008D
publisher=Cornell University
accessdate=2008-05-22
] [cite web
author=Soderberg, A.M. et al | year=2008
url=http://arxiv.org/abs/0802.1712
title=An extremely luminous X-ray outburst at the birth of a supernova
publisher=Nature
accessdate=2008-05-23
] in galaxy NGC 2770, shown in X-ray (left) and visible light (right), at the corresponding positions of the images. "NASA image." [cite web
last=Naeye | first=Robert
coauthors=Gutro, Rob | date=May 21, 2008
url=http://www.nasa.gov/centers/goddard/news/topstory/2008/swift_supernova.html
title=NASA's Swift Satellite Catches First Supernova in the Act of Exploding
publisher=NASA/Goddard Space Flight Center
accessdate=2008-05-22
] ]

Types 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.

pectra

When a supernova is observed, it can be categorized according to the absorption lines that appear in its spectrum. A supernovae is first categorized as either a Type I or Type II, then sub-categorized based on more specific traits. Supernovae belonging to the general category Type I lack hydrogen lines in their spectra; in contrast to a Type II supernovae which do display lines of hydrogen. The Type I category is sub-divided into Type Ia, Type Ib and Type Ic supernovae.cite web | last = Montes | first = M.
date = February 12, 2002
url = http://rsd-www.nrl.navy.mil/7212/montes/snetax.html
title = Supernova Taxonomy
publisher = Naval Research Laboratory
accessdate = 2006-11-09
]

Type Ib/Ic supernovae are distinguished from Type Ia by the lack of an absorption line of singly-ionized silicon at a wavelength of 635.5 nanometres. As a Type Ib/Ic supernova ages, it also displays stronger spectral features of helium than Type Ia supernovae. Eventually the Type Ib/Ic spectrum also shows lines from elements such as oxygen, calcium and magnesium. In contrast, Type Ia spectra become dominated by lines of iron.cite web
url = http://cosmos.swin.edu.au/entries/typeibsupernovaspectra/typeibsupernovaspectra.html?e=1
title = Type Ib Supernova Spectra
publisher = Swinburne University of Technology
accessdate = 2007-02-08
] Type Ic supernovae are distinguished from Type Ib in that the former also lack lines of helium.

Formation

Prior to becoming a 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.) [cite journal | author=L. M. Dray, C. A. Tout, A. I. Karakas, J. C. Lattanzio | title=Chemical enrichment by Wolf-Rayet and asymptotic giant branch stars | journal=Monthly Notice of the Royal Astronomical Society | year=2003 | volume=338 | pages=973–989 | url=http://adsabs.harvard.edu/abs/2003MNRAS.338..973D | accessdate=2007-02-08 | doi=10.1046/j.1365-8711.2003.06142.x ]

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 close companion of about 3–4 solar masses. [cite conference | last = Pols | first = Onno | title = Close Binary Progenitors of Type Ib/Ic and IIb/II-L Supernovae | booktitle = Proceedings of the The Third Pacific Rim Conference on Recent Development on Binary Star Research | pages = 153-158 | date = 26 October - 1 November, 1995 | location = Chiang Mai, Thailand | url = http://adsabs.harvard.edu/abs/1997rdbs.conf..153P | accessdate = 2006-11-29 ] cite conference | author=Woosley, S. E.; Eastman, R. G. | title =Type Ib and Ic Supernovae: Models and Spectra | booktitle =Proceedings of the NATO Advanced Study Institute | pages =821 | publisher =Dordrecht: Kluwer Academic Publishers | date =June 20-30, 1995 | location =Begur, Girona, Spain | url =http://adsabs.harvard.edu/abs/1997thsu.conf..821W | accessdate = 2007-05-09 ] Rapid mass loss can occur in the case a Wolf-Rayet star, and these massive objects show a spectrum that is lacking in hydrogen. Type Ib progenitors have ejected most of the hydrogen in their outer atmospheres, while Type Ic progenitors have lost both the hydrogen and helium shells. On other respects, however, the underlying mechanism behind Type Ib and Ic supernovae is similar to that of a Type II supernova.

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 Type Ib or Ic supernova could be a GRB, dependent upon the geometry of the explosion. [cite journal
author=Ryder, S. D.; Sadler, E. M.; Subrahmanyan, R.; Weiler, K. W.; Panagia, N.; Stockdale, C.
title=Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf-Rayet binary progenitor?
journal=Monthly Notices of the Royal Astronomical Society
year=2004 | volume=349 | issue=3 | pages=1093–1100
url=http://adsabs.harvard.edu/abs/2004MNRAS.349.1093R
accessdate = 2007-02-01
doi=10.1111/j.1365-2966.2004.07589.x
]

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. [cite web | author=E. M. Sadler, D. Campbell | year = 1997 | url = http://www.atnf.csiro.au/pasa/14_2/sadler/paper/node4.html | title = A first estimate of the radio supernova rate | publisher = Astronomical Society of Australia | accessdate = 2007-02-08 ] They normally occur in regions of new star formation, and have never been observed in an elliptical galaxy. Because they share a similar operating mechanism, Type Ib, Ic and the various Type II supernovae are collectively called core-collapse supernovae.

Light curves

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.) [cite journal | last = Tsvetkov | first = D. Yu. | title=Light curves of type Ib supernova: SN 1984l in NGC 991 | journal=Soviet Astronomy Letters | year=1987 | volume=13 | pages=376–378 | url=http://adsabs.harvard.edu/abs/1987SvAL...13..376T | accessdate=2007-02-04 ]

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 latter can form a source of contamination of supernova surveys and must be carefully removed from the observed samples before making distance estimates. [cite journal | last = Homeier | first = N. L. | title=The Effect of Type Ibc Contamination in Cosmological Supernova Samples | journal=The Astrophysical Journal | year=2005 | volume=620 | issue=1 | pages=12–20 | url=http://www.journals.uchicago.edu/doi/full/10.1086/427060 | accessdate=2008-09-16 | doi=10.1086/427060 ]

References


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