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RE: Supernova 2007bi
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Title: Progenitor for the Extremely Luminous Type Ic Supernova 2007bi
Authors: Takashi Yoshida, Hideyuki Umeda (University of Tokyo)

SN 2007bi is an extremely luminous Type Ic supernova. This supernova is thought to be evolved from a very massive star and two possibilities of explosion mechanism have been proposed. One possibility is a pair-instability supernova with a M_{CO} ~ 100 M_sun CO core progenitor. Another possibility is a core-collapse supernova with a M_{CO} ~ 40 M_sun. We investigate the evolution of very massive stars with main sequence mass M_{MS} = 100 - 500 M_sun and Z_0 = 0.004 which is in the metallicity range of the host galaxy of SN 2007bi to constrain the progenitor of SN 2007bi. The supernova type relating to the surface He abundance is also discussed. The main sequence mass of the progenitor exploding as a pair-instability supernova could be M_{MS} ~ 515 - 575 M_sun. The minimum main-sequence mass could be 310 M_sun when uncertainties in the mass loss rate are considered. A star with M_{MS} ~ 110 - 280 M_sun evolves to a CO star appropriate for the core-collapse supernova of SN 2007bi. Arguments based on the probability of pair-instability and core-collapse supernovae favour the hypothesis that SN 2007bi originated from a core-collapse supernova event.

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Supernova 2007bi
At first, there didn't seem anything earth-shattering about the tiny point of light that pricked the southern Californian sky on a mild night in early April 2007. Only the robotic eyes of the Nearby Supernova Factory, a project designed to spy out distant stellar explosions, spotted it from the Palomar Observatory, high in the hills between Los Angeles and San Diego.
The project's computers automatically forwarded the images to a data server to await analysis. The same routine kicks in scores of times each year when a far-off star in its death throes explodes onto the night sky, before fading back to obscurity once more.
But this one did not fade away. It got brighter. And brighter. That's when human eyes became alert.

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SUPERNOVA 2007bi
P. E. Nugent, Lawrence Berkeley National Laboratory, reports the discovery of a supernova (magnitude approximately 18.3, calibrated to R) by the "Nearby Supernova Factory" collaboration (cf. CBETs 263, 768) in images obtained on Apr. 6.5 UT using the QUEST II camera on the Palomar Oschin 1.2-m Schmidt telescope as a part of NEAT component of the Palomar-QUEST Consortium.  The new object is located at R.A. = 13h19m20s.19, Decl. = +8d55'44".3 (equinox 2000.0).  A spectrogram (range 320-1000 nm) of 2007bi, obtained on Apr. 8.6 with the Supernova Integral Field Spectrograph on the University of Hawaii 2.2-m telescope under poor conditions, reveals that it is most likely a type-Ic supernova at an approximate redshift of 0.1.

CBET 929

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Massive Star
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What happens when a really gargantuan star - one hundreds of times bigger than our sun - blows up?  Although a theory developed years ago describes what the explosion of such an enormous star should look like, no one had actually observed one - until now. An international team, led by scientists in Israel, and including researchers from Germany, the US, UK and China, tracked a supernova - an exploding star - for over a year and a half, and found that it neatly fits the predictions for the explosion of a star of over 150 times the sun's mass. Their findings, which could influence our understanding of everything from natural limits on star size to the evolution of the universe, appeared recently in Nature.
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An enormous explosion observed in 2007 was the death of one of the most massive stars known in the universe, new calculations suggest. Similar blasts may have polluted the early universe with heavy elements, altering its evolution.
A team of astronomers led by Avishay Gal-Yam of the Weizmann Institute of Science in Rehovot, Israel, detected the explosion in a dwarf galaxy on 6 April 2007.

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An extraordinarily bright, extraordinarily long-lasting supernova named SN 2007bi, snagged in a search by a robotic telescope, turns out to be the first example of the kind of stars that first populated the Universe. The superbright supernova occurred in a nearby dwarf galaxy, a kind of galaxy thats common but has been little studied until now, and the unusual supernova could be the first of many such events soon to be discovered.
The analysis indicated that the supernovas precursor star could only have been a giant weighing at least 200 times the mass of our Sun and initially containing few elements besides hydrogen and helium - a star like the very first stars in the early Universe.

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Massive supernova produced rainbow of elements for months.

Astronomers have watched the violent death of what was probably the most massive star ever detected. The supernova explosion, which lasted for months, is thought to have generated more than 50 Suns' worth (10^32 kilograms) of different elements, which may one day go on to make new solar systems.
The explosion - dubbed SN2007bi - was spotted as part of a digital survey to hunt for supernovae at the Palomar Observatory near San Diego, California.

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