1,835 research outputs found
Presupernova evolution and explosive nucleosynthesis of zero metal massive stars
We present a new set of zero metallicity models in the range 13-80 together to the associated explosive nucleosynthesis. These models are
fully homogeneous with the solar metallicity set we published in Limongi &
Chieffi (2006) and will be freely available at the web site
http://www.iasf-roma.inaf.it./orfeo/public{\_}html. A comparison between these
yields and an average star that represents the average behavior of most of the
very metal poor stars in the range confirms previous
findings that only a fraction of the elemental [X/Fe] may be fitted by the
ejecta of core collapse supernovae.Comment: 39 pages, 8 figures, 2 tables, accepted for publication in ApJ
The Explosive Yields Produced by the First Generation of Core Collapse Supernovae and the Chemical Composition of Extremely Metal Poor Stars
We present a detailed comparison between an extended set of elemental
abundances observed in some of the most metal poor stars presently known and
the ejecta produced by a generation of primordial core collapse supernovae. We
used five stars which form our initial database and define a "template" ultra
metal poor star which is then compared to the theoretical predictions. Our main
findings are as follows: a) the fit to [Si/Mg] and [Ca/Mg] of these very metal
poor stars seems to favor the presence of a rather large C abundance at the end
of the central He burning; in a classical scenario in which the border of the
convective core is strictly determined by the Schwarzschild criterion, such a
large C abundance would imply a rather low C12(alpha,gamma)O16 reaction rate;
b) a low C abundance left by the central He burning would imply a low [Al/Mg]
(<-1.2 dex) independently on the initial mass of the exploding star while a
rather large C abundance would produce such a low [Al/Mg] only for the most
massive stellar model; c) at variance with current beliefs that it is difficult
to interpret the observed overabundance of [Co/Fe], we find that a mildly large
C abundance in the He exhausted core (well within the present range of
uncertainty) easily and naturally allows a very good fit to [Co/Fe]; d) our
yields allow a reasonable fit to 8 out of the 11 available elemental
abundances; e) within the present grid of models it is not possible to find a
good match of the remaining three elements, Ti, Cr and Ni (even for an
arbitrary choice of the mass cut); f) the adoption of other yields available in
the literature does not improve the fit; g) since no mass in our grid provides
a satisfactory fit to these three elements, even an arbitrary choice of the
initial mass function would not improve their fit.Comment: 30 pages, 8 figures, 8 tables. Accepted for publication on Ap
Galaxy Evolution tool: Construction and Applications
We present a dual-infall galactic chemical evolution model which uses a new
set of stellar yields calculated by Limongi et al (2001) to constrain the
amount of iron-peak elements ejected by massive stars. The age-metallicity
relation, G-dwarf distribution and evolution of abundance ratios are predicted
using Galaxy Evolution tool (GEtool), a software package currently being
developed to self-consistenly model the chemical and spectral evolution of disk
galaxies. A comparison with results obtained using the Woosley & Weaver (1995)
core-collapse supernova models suggests that the observed behaviour of key
abundance patterns cannot be reproduced if the iron yield of massive stars
increases with initial mass.Comment: 2 pages, 4 figures, to appear in "The Evolution of Galaxies II: Basic
Building Blocks", (2002) ed. M. Sauvage et al. (Kluwer
The formation of the extremely primitive star SDSS J102915+172927 relies on dust
The relative importance of metals and dust grains in the formation of the
first low-mass stars has been a subject of debate. The recently discovered
Galactic halo star SDSS J102915+172927 (Caffau et al. 2011) has a mass less
than 0.8 Msun and a metallicity of Z = 4.5 10^{-5} Zsun. We investigate the
origin and properties of this star by reconstructing the physical conditions in
its birth cloud. We show that the observed elemental abundance trend of SDSS
J102915+172927 can be well fitted by the yields of core-collapse supernovae
with metal-free progenitors of 20 Msun and 35 Msun. Using these selected
supernova explosion models, we compute the corresponding dust yields and the
resulting dust depletion factor taking into account the partial destruction by
the supernova reverse shock. We then follow the collapse and fragmentation of a
star forming cloud enriched by the products of these SN explosions at the
observed metallicity of SDSS J102915+172927. We find that [0.05 - 0.1] Msun
mass fragments, which then lead to the formation of low-mass stars, can occur
provided that the mass fraction of dust grains in the birth cloud exceeds 0.01
of the total mass of metals and dust. This, in turn, requires that at least 0.4
Msun of dust condense in the first supernovae, allowing for moderate
destruction by the reverse shock. If dust formation in the first supernovae is
less efficient or strong dust destruction does occur, the thermal evolution of
the SDSS J102915+172927 birth cloud is dominated by molecular cooling, and only
> 8 Msun fragments can form. We conclude that the observed properties of SDSS
J102915+172927 support the suggestion that dust must have condensed in the
ejecta of the first supernovae and played a fundamental role in the formation
of the first low-mass stars.Comment: 5 pages, 3 figures, accepted as a Letter to MNRA
Modeling The Nucleosynthesis Of Massive Stars
This overview discusses issues relevant to modeling nucleosynthesis in type
II supernovae and implications of detailed studies of the ejecta. After a brief
presentation of the most common approaches to stellar evolution and
parameterized explosions, the relevance of a number of nuclei to obtain
information on the evolution and explosion mechanisms is discussed. The paper
is concluded by an outlook on multi-dimensional simulations.Comment: Invited talk at the workshop "Astronomy with Radioactivities IV",
Seeon, Germany, June 2003; 6 pages, to appear in New Astronomy Review
The Effects of Thermonuclear Reaction-Rate Variations on 26Al Production in Massive Stars: a Sensitivity Study
We investigate the effects of thermonuclear reaction rate variations on 26Al
production in massive stars. The dominant production sites in such events were
recently investigated by using stellar model calculations: explosive
neon-carbon burning, convective shell carbon burning, and convective core
hydrogen burning. Post-processing nucleosynthesis calculations are performed
for each of these sites by adopting temperature-density-time profiles from
recent stellar evolution models. For each profile, we individually multiplied
the rates of all relevant reactions by factors of 10, 2, 0.5 and 0.1, and
analyzed the resulting abundance changes of 26Al. Our simulations are based on
a next-generation nuclear physics library, called STARLIB, which contains a
recent evaluation of Monte Carlo reaction rates. Particular attention is paid
to quantifying the rate uncertainties of those reactions that most sensitively
influence 26Al production. For stellar modelers our results indicate to what
degree predictions of 26Al nucleosynthesis depend on currently uncertain
nuclear physics input, while for nuclear experimentalists our results represent
a guide for future measurements. We tabulate the results of our reaction rate
sensitivity study for each of the three distinct massive star sites referred to
above. It is found that several current reaction rate uncertainties influence
the production of 26Al. Particularly important reactions are 26Al(n,p)26Mg,
25Mg(alpha,n)28Si, 24Mg(n,gamma)25Mg and 23Na(alpha,p)26Mg. These reactions
should be prime targets for future measurements. Overall, we estimate that the
nuclear physics uncertainty of the 26Al yield predicted by the massive star
models explored here amounts to about a factor of 3.Comment: 44 pages, 16 figure
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