659 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 metal and dust yields of the first massive stars
We quantify the role of Population (Pop) III core-collapse supernovae (SNe)
as the first cosmic dust polluters. Starting from a homogeneous set of stellar
progenitors with masses in the range [13 - 80] Msun, we find that the mass and
composition of newly formed dust depend on the mixing efficiency of the ejecta
and the degree of fallback experienced during the explosion. For standard Pop
III SNe, whose explosions are calibrated to reproduce the average elemental
abundances of Galactic halo stars with [Fe/H] < -2.5, between 0.18 and 3.1 Msun
(0.39 - 1.76 Msun) of dust can form in uniformly mixed (unmixed) ejecta, and
the dominant grain species are silicates. We also investigate dust formation in
the ejecta of faint Pop III SN, where the ejecta experience a strong fallback.
By examining a set of models, tailored to minimize the scatter with the
abundances of carbon-enhanced Galactic halo stars with [Fe/H ] < -4, we find
that amorphous carbon is the only grain species that forms, with masses in the
range 2.7 10^{-3} - 0.27 Msun (7.5 10^{-4} - 0.11 Msun) for uniformly mixed
(unmixed) ejecta models. Finally, for all the models we estimate the amount and
composition of dust that survives the passage of the reverse shock, and find
that, depending on circumstellar medium densities, between 3 and 50% (10 - 80%)
of dust produced by standard (faint) Pop III SNe can contribute to early dust
enrichment.Comment: Accepted by MNRAS, 22 pages, 12 figures, 12 table
Pre-suprenova evolution of rotating massive stars
The Geneva evolutionary code has been modified to study the advanced stages
(Ne, O, Si burnings) of rotating massive stars. Here we present the results of
four 20 solar mass stars at solar metallicity with initial rotational
velocities of 0, 100, 200 and 300 km/s in order to show the crucial role of
rotation in stellar evolution. As already known, rotation increases mass loss
and core masses (Meynet and Maeder 2000). A fast rotating 20 solar mass star
has the same central evolution as a non-rotating 26 solar mass star. Rotation
also increases strongly net total metal yields. Furthermore, rotation changes
the SN type so that more SNIb are predicted (see Meynet and Maeder 2003 and N.
Prantzos and S. Boissier 2003). Finally, SN1987A-like supernovae progenitor
colour can be explained in a single rotating star scenario.Comment: To appear in proceedings of IAU Colloquium 192, "Supernovae (10 years
of 1993J)", Valencia, Spain 22-26 April 2003, eds. J.M. Marcaide, K.W.
Weiler, 5 pages, 8 figure
Role of glutathionylation in infection and inflammation
Glutathionylation, that is, the formation of mixed disulfides between protein cysteines and
glutathione (GSH) cysteines, is a reversible post-translational modification catalyzed by dierent
cellular oxidoreductases, by which the redox state of the cell modulates protein function. So far, most
studies on the identification of glutathionylated proteins have focused on cellular proteins, including
proteins involved in host response to infection, but there is a growing number of reports showing
that microbial proteins also undergo glutathionylation, with modification of their characteristics and
functions. In the present review, we highlight the signaling role of GSH through glutathionylation,
particularly focusing on microbial (viral and bacterial) glutathionylated proteins (GSSPs) and host
GSSPs involved in the immune/inflammatory response to infection; moreover, we discuss the
biological role of the process in microbial infections and related host responses
On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
Recent improvements in stellar models for intermediate-mass and massive stars
are recalled, together with their expectations for the synthesis of radioactive
nuclei of lifetime Myr, in order to re-examine the origins
of now extinct radioactivities, which were alive in the solar nebula. The
Galactic inheritance broadly explains most of them, especially if -process
nuclei are produced by neutron star merging according to recent models.
Instead, Al, Ca, Cs and possibly Fe require
nucleosynthesis events close to the solar formation. We outline the persisting
difficulties to account for these nuclei by Intermediate Mass Stars (2
M/M). Models of their final stages now
predict the ubiquitous formation of a C reservoir as a neutron capture
source; hence, even in presence of Al production from Deep Mixing or Hot
Bottom Burning, the ratio Al/Pd remains incompatible with
measured data, with a large excess in Pd. This is shown for two recent
approaches to Deep Mixing. Even a late contamination by a Massive Star meets
problems. In fact, inhomogeneous addition of Supernova debris predicts
non-measured excesses on stable isotopes. Revisions invoking specific low-mass
supernovae and/or the sequential contamination of the pre-solar molecular cloud
might be affected by similar problems, although our conclusions here are
weakened by our schematic approach to the addition of SN ejecta. The limited
parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap
Synthetic properties of bright metal-poor variables. I. "Anomalous" Cepheids
We present new grids of evolutionary models for the so-colled ``Anomalous''
Cepheids (ACs), adopting Z=0.0001 and various assumptions on the progenitor
mass and mass-loss efficiency. These computations are combined with the results
of our previous set of pulsation models and used to build synthetic populations
of the predicted pulsators as well as to provide a Mass-Luminosity relation in
the absence of mass-loss. We investigate the effect of mass-loss on the
predicted boundaries of the instability strip and we find that the only
significant dependence occurs in the Period-Magnitude plane, where the
synthetic distribution of the pulsators is, on average, brighter by about 0.1
mag than the one in absence of mass-loss. Tight Period-Magnitude relations are
derived in the K band for both fundamental and first overtone pulsators,
providing a useful tool for distance evaluations with an intrinsic uncertainty
of about 0.15 mag, which decreases to about 0.04 mag if the mass term is taken
into account. The constraints provided by the evolutionary models are used to
derive evolutionary (i.e, mass-independent) Period-Magnitude-Color relations
which provide distance determinations with a formal uncertainty of the order of
about 0.1 mag, once the intrinsic colors are well known. We also use model
computations from the literature to investigate the effect of metal content
both on the instability strip and on the evolutionary Period-Magnitude-Color
relations. Finally, we compare our theoretical predictions with observed
variables and we confirm that a secure identification of actual ACs requires
the simultaneous information on period, magnitude and color, that also provide
constraints on the pulsation mode.Comment: accepte
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