182 research outputs found
Type Ic core-collapse supernova explosions evolved from very massive stars
We investigate the possibility of a super-luminous Type Ic core-collapse
supernovae producing a large amount of 56Ni. Very massive stars with a
main-sequence mass larger than 100 Msun and a metallicity 0.001 < Z < 0.004 are
expected to explode as super-luminous Type Ic supernovae. Stars with ~ 110 -
150 Msun and Z < 0.001 would explode as Type Ic pulsational pair-instability
supernovae if the whole H and He layers has been lost by the mass loss during
pulsational pair-instability. We evaluate the total ejecta mass and the yields
of 56Ni, O, and Si in core-collapse supernovae evolved from very massive stars.
We adopt 43.1 and 61.1 Msun WO stars with Z=0.004 as supernova progenitors
expected to explode as Type Ic core-collapse supernovae. These progenitors have
masses of 110 and 250 Msun at the zero-age main sequence. Spherical explosions
with an explosion energy larger than 2e52 erg produce more than 3.5 Msun 56Ni,
enough to reproduce the light curve of SN 2007bi. Asphericity of the explosion
affects the total ejecta mass as well as the yields of 56Ni, O, and Si.
Aspherical explosions of the 110 and 250 Msun models reproduce the 56Ni yield
of SN 2007bi. These explosions will also show large velocity dispersion. An
aspherical core-collapse supernova evolved from a very massive star is a
possibility of the explosion of SN 2007bi.Comment: 10 pages, 6 figures, Accepted for publication in MNRA
Evolution and Nucleosynthesis of Metal-Free Massive Stars
We calculate presupernova evolutions and supernova explosions of massive
stars (M=13-25 Mo) for various metallicities. We find the following
characteristic abundance patterns of nucleosynthesis in the metal-free (Pop
III) stars. (1) The alpha-nuclei (from C to Zn) are more efficiently produced
than other isotopes, and the abundance pattern of alpha-nuclei can be similar
to the solar abundance. In particular, near solar ratios of alpha elements/Fe
might be a signature of Pop III which could produce a large amount of Fe. (2)
The abundance ratios of odd Z to even Z elements such as Na/Mg and Al/Mg become
smaller for lower metallicity. However, these ratios almost saturate below Z <~
10^{-5}, and [Na, Al/Mg] ~ - 1 for Pop III and low metal Pop II
nucleosynthesis. This result is consistent with abundance pattern of metal poor
stars, in which these ratios also saturate around -1. We suggest that these
stars with the lowest [Na/Mg] or [Al/Mg] may contain the abundance pattern of
Pop III nucleosynthesis. (3) Metal poor stars show interesting trends in the
ratios of [Cr, Mn, Co/Fe]. We discuss that these trends are not explained by
the differences in metallicity, but by the relative thickness between the
complete and the incomplete Si burning layers. Large [Co/Fe] and small [Cr,
Mn/Fe] values found in the observations are explained if mass cut is deep or if
matter is ejected from complete Si burning layer in a form of a jet or bullets.
(4) We also find that primary ^{14}N production occurs in the massive Pop III
stars, because these stars have radiative H-rich envelopes so that the
convective layer in the He-shell burning region can reach the H-rich region.Comment: 19 pages. To appear in the proceedings of the MPA/ESO conference
``The First Stars'' (August 4-7, 1999, Garching) ed. A. Weiss etal.
(Springer
Variations in the Abundance Pattern of Extremely Metal-poor Stars and Nucleosynthesis in Population III Supernovae
We calculate nucleosynthesis in Population (Pop) III supernovae (SNe) and
compare the yields with various abundance patterns of extremely metal-poor
(EMP) stars. We assume that the observed EMP stars are the second generation
stars, which have the metal-abundance patterns of Pop III SNe. Previous
theoretical yields of Pop III SNe cannot explain the trends in the abundance
ratios among iron-peak elements (Mn, Co, Ni, Zn)/Fe as well as the large C/Fe
ratio observed in certain EMP stars with [Fe/H] <~ -2.5. In the present paper,
we show that if we introduce higher explosion energies and mixing-fallback in
the core-collapse SN models of M ~ 20 - 130 Msun, the above abundance features
of both typical and C-rich EMP stars can be much better explained. We suggest
that the abundance patterns of the [Fe/H] ~ -2.5 stars correspond to supernova
yields with normal explosion energies, while those of the carbon un-enhanced
([C/Fe] < 1) stars with [Fe/H] =~ -4 ~ - 3 correspond to high-energy supernova
yields. The abundance patterns of the C-rich ([C/Fe]>~ 2) and low [Fe/H] (=~ -5
\~ -3.5) stars can be explained with the yields of faint SNe that eject little
56Ni as observed in SN1997D. In the supernova-induced star formation model, we
can qualitatively explain why the EMP stars formed by the faint or energetic
supernovae have lower [Fe/H] than the EMP stars formed by normal supernovae. We
also examine how the abundance ratios among iron-peak elements depend on the
electron mole fraction Ye, and conclude that a large explosion energy is still
needed to realize the large Co/Fe and Zn/Fe ratios observed in typical EMP
stars with [Fe/H] <~ -3.5.Comment: 33 pages, 17 figures, 7 tables, To appear in the Astrophysical
Journal 2005, January 1
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