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Post Info TOPIC: Helium-rich supernova


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New type of stellar explosion
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Title: A faint type of supernova from a white dwarf with a helium-rich companion
Authors: H. B. Perets, A. Gal-Yam, P. Mazzali, D. Arnett, D. Kagan, A. V. Filippenko, W. Li, I. Arcavi, S. B. Cenko, D. B. Fox, D. C. Leonard, D.-S. Moon, D. J. Sand, A. M. Soderberg, R. J. Foley, M. Ganeshalingam, J. P. Anderson, P. A. James, E. O. Ofek, L. Bildsten, G. Nelemans, K. J. Shen, N. N. Weinberg, B. D. Metzger, A. L. Piro, E. Quataert, M. Kiewe, D. Poznanski
(Version v2)

Supernovae (SNe) are thought to arise from two different physical processes. The cores of massive, short-lived stars undergo gravitational core collapse and typically eject a few solar masses during their explosion. These are thought to appear as as type Ib/c and II SNe, and are associated with young stellar populations. A type Ia SN is thought to arise from the thermonuclear detonation of a white dwarf star composed mainly of carbon and oxygen, whose mass approaches the Chandrasekhar limit. Such SNe are observed in both young and old stellar environments. Here we report our discovery of the faint type Ib SN 2005E in the halo of the nearby isolated galaxy, NGC 1032.
The lack of any trace of recent star formation near the SN location, and the very low derived ejected mass (~0.3 M_sun), argue strongly against a core-collapse origin for this event. Spectroscopic observations and the derived nucleosynthetic output show that the SN ejecta have high velocities and are dominated by helium-burning products, indicating that SN 2005E was neither a subluminous nor a regular SN Ia. We have therefore found a new type of stellar explosion, arising from a low-mass, old stellar system, likely involving a binary with a primary white dwarf and a helium-rich secondary. The SN ejecta contain more calcium than observed in any known type of SN and likely additional large amounts of radioactive 44Ti. Such SNe may thus help resolve fundamental physical puzzles, extending from the composition of the primitive solar system and that of the oldest stars, to the Galactic production of positrons.

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Posts: 131433
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Helium dwarf stars
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Good methodical science can create its own luck.
One of astronomer Steve Howell's graduate students was observing pulsating stars on a fairly small robotic telescope when he found a pair of eclipsing stars that led to a scramble for a bigger telescope and the first-ever measurement of a helium dwarf star.

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RE: Helium-rich supernova
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UA Astronomer Helps Discover New Supernova Type

An international team of scientists, including a University of Arizona astronomer, has identified a third type of exploding star, or supernova.
Until now, scientists had only observed two kinds of supernovae - either hot, young giants that go out in a violent display as they collapse under their own weight, or old, dense white dwarves that blow up in a thermonuclear explosion.
The new supernova appeared in telescope images in January 2005. Seeing that it had recently begun the process of exploding, scientists started collecting and combining data from different telescope sites around the world, measuring both the amount of material thrown off in the explosion and its chemical makeup.

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Supernova 2005cz
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A group of astronomers has found the progenitor of a supernova discovered in 2005 by Japanese supernova hunter Koichi Itagaki to be in the category of lowest-mass stars that are at the end of their life spans, according to an article to be published Thursday by British science magazine Nature.
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Supernova 2005E
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New type of exploding star discovered: may reveal a source of calcium

A new type of exploding star has been discovered by an international team of scientists that includes Penn State University astronomer Derek Fox, an assistant professor of astronomy and astrophysics. Until now, scientists had observed only two basic kinds of exploding stars, known as supernovae. But now the team's discovery has revealed a third type of supernova that, if common, could reveal a previously unknown source of the calcium in our bodies and of the positron particles observed near the centre of our Milky Way Galaxy. Positrons previously have been suggested as indicating of the presence of "dark matter." The discovery will be published in the May 20 issue of the journal Nature.
The two previously known supernova mechanisms involve either an old, dense "white dwarf" star whose death occurs in a powerful thermonuclear disruption, or a hot, young giant that explodes in a violent display as it collapses under its own weight. The new, comparatively dim, supernova appeared in telescope images in early January of 2005, while Fox was a researcher at the California Institute of Technology (Caltech). Seeing that the supernova, named SN 2005E, recently had begun the process of exploding, Fox and other scientists around the world started collecting and combining data from different telescopes, measuring both the amount of material thrown off in the explosion and its chemical makeup.

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Astronomers have put forward opposing explanations for what could be a new type of exploding star or supernova.
Supernova 2005E was initially picked up by telescopes back in 2005 and has been carefully examined by scientists.
They now report, in the journal Nature, that the explosion does not match known types of supernova.

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Calcium from new supernova 'could unlock secrets to life on earth'

Astronomers believe they have found a cosmic link to how calcium is formed in people's bones.
They say a new type of supernova, called SN2005E, may be the chief source of calcium in the universe and on Earth.
Scientists say the mineral provides vital strength to bones, which could show how humans have an ability to stand upright, the Nature journal reported.
High levels of calcium and radioactive titanium were detected during observations of the exploding star, both of which are products of nuclear reactions involving helium.

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Helium-rich supernova
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Title: A massive star origin for an unusual helium-rich supernova in an elliptical galaxy
Authors: K. S. Kawabata, K. Maeda, K. Nomoto, S. Taubenberger, M. Tanaka, J. Deng, E. Pian, T. Hattori, K. Itagaki
(Version v2)

The unusual helium-rich (type Ib) supernova SN 2005E is distinguished from any supernova hitherto observed by its faint and rapidly fading light curve, prominent calcium lines in late-phase spectra and lack of any mark of recent star formation near the supernova location. These properties are claimed to be explained by a helium detonation in a thin surface layer of an accreting white dwarf (Perets et al. 2010). Here we report on observations of SN 2005cz appeared in an elliptical galaxy, whose observed properties resemble those of SN 2005E in that it is helium-rich and unusually faint, fades rapidly, shows much weaker oxygen emission lines than those of calcium in the well-evolved spectrum. We argue that these properties are best explained by a core-collapse supernova at the low-mass end (8-12 Solar masses) of the range of massive stars that explode (Smartt 2009). Such a low mass progenitor had lost its hydrogen-rich envelope through binary interaction, having very thin oxygen-rich and silicon-rich layers above the collapsing core, thus ejecting a very small amount of radioactive ^{56} Ni and oxygen. Although the host galaxy NGC 4589 is an elliptical, some studies have revealed evidence of recent star-formation activity (Zhang et al. 2008), consistent with the core-collapse scenario.

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