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Search Results: 1 - 10 of 325504 matches for " S. Degl'Innocenti "
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Dwarf Spheroidals and the Evolution of Not-Too-Old Population II Stars
V. Castellani,S. Degl'Innocenti
Physics , 1994,
Abstract: Previous evolutionary computations concerning stars with masses in the range of the ``Red Giants Transition Phase'' are extended to lower metallicities. Clusters isochrones for two values of the metallicity Z (Z=10E-4, 4E-4) and for ages down to 1 billion years are presented, discussing selected evolutionary features characterizing the structure of the stars during both H or He burning phases. One finds that clusters with Z about equal to 1E-4 an age around 1-2 billion years could be characterized by the occurrence of anomalous He burning variables at a luminosity of the order of LogL= 2.0-2.2 (in solar units).
A Mixed Solar Core, Solar Neutrinos and Helioseismology
S. Degl'Innocenti,B. Ricci
Physics , 1997, DOI: 10.1016/S0927-6505(97)00057-1
Abstract: We consider a wide class of solar models with mixed core. Most of these models can be excluded as the predicted sound speed profile is in sharp disagreement with helioseismic constraints. All the remaining models predict $^7$Be and/or $^7$B neutrino fluxes at least as large as those of SSMs. In conclusion, helioseismology shows that a mixed solar core cannot account for the neutrino deficit implied by the current solar neutrino experiments.
The effect of diffusion on the Red Giant luminosity function 'bump'
S. Cassisi,S. Degl'Innocenti,M. Salaris
Physics , 1997, DOI: 10.1093/mnras/290.3.515
Abstract: This paper investigates the effect of microscopic diffusion of helium and heavy elements on the location of the Red Giant Branch Luminosity Function Bump in Population II stellar models. To this aim updated evolutionary models taking into account diffusion from the Main Sequence until the Zero Age Horizontal Branch have been computed. The observational luminosity difference between the RGB bump and the ZAHB, as collected for a sample of galactic globular clusters, has been compared with the corresponding theoretical values obtained by adopting both canonical and diffusive models. We find that the effect of diffusion, even if slightly improving the agreement between observations and theory, is negligible with respect to the observational uncertainties. In any case the theoretical predictions in models with and without diffusion appear in agreement with the observational results within the estimated errors. Thus canonical models can be still safely adopted, at least until much more accurate observational data will be available.
The age of the oldest globular clusters
M. Salaris,S. Degl'Innocenti,A. Weiss
Physics , 1996, DOI: 10.1086/303909
Abstract: The age of three of the oldest clusters -- M15, M68, M92 -- has been redetermined. We use the latest EOS and opacity data available for calculating both isochrones and zero age horizontal branches and employ the brightness difference between turn-off and horizontal branch to determine the cluster age. Our best ages for all three clusters are about 13 Gyr, and even smaller ages are possible. Our results help to reconcile cluster ages with recent results on the age of the universe determined from the Hubble constant.
Which radius for the Sun?
V. Castellani,S. Degl'Innocenti,G. Fiorentini
Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02030.x
Abstract: The high accuracy reached by solar limb observations, by helioseismic measurements and by Standard Solar Models (SSMs) calculations suggests that general relativity corrections are included when discussing the solar radius. The Allen value (R$_{\odot}$ = 695.99 $\pm$ 0.07 Mm) has to be reduced by 1.5 Km. This correction, which is small as compared with present accuracy, should be kept in mind for future more precise measurements and/or calculations.
Screening of Nuclear Reactions in the Sun and Solar Neutrinos
B. Ricci,S. Degl'Innocenti,G. Fiorentini
Physics , 1994, DOI: 10.1103/PhysRevC.52.1095
Abstract: We quantitatively determine the effect and the uncertainty on solar neutrino production arising from the screening process. We present predictions for the solar neutrino fluxes and signals obtained with different screening models available in the literature and by using our stellar evolution code. We explain these numerical results in terms of simple laws relating the screening factors with the neutrino fluxes. Futhermore we explore a wider range of models for screening, obtained from the Mitler model by introducing and varying two phenomenological parameters, taking into account effects not included in the Mitler prescription. Screening implies, with respect to a no-screening case, a central temperat reduction of 0.5%, a 2% (8%) increase of Beryllium (Boron)-neutrino flux and a 2% (12%) increase of the Gallium (Chlorine) signal. We also find that uncertainties due to the screening effect ar at the level of 1% for the predicted Beryllium-neutrino flux and Gallium signal, not exceeding 3% for the Boron-neutrino flux and the Chlorine signal.
Where are the beryllium neutrinos?
S. Degl'Innocenti,G. Fiorentini,M. Lissia
Physics , 1994, DOI: 10.1016/0920-5632(95)00453-G
Abstract: We show that present experiments imply that neutrinos are nonstandard at the 87\% C.L., independently of solar or nuclear physics. Moreover, if neutrinos are standard, the $^7$Be flux must be almost zero. Even if we arbitrarily disregard one of the experiments, the neutrino flux must still be less than half of the value predicted by standard solar models.
Star luminosity function as an age indicator for the Dwarf spheroidal Leo I
F. Caputo,V. Castellani,S. Degl'Innocenti
Physics , 1995,
Abstract: Star luminosity function, already recognized as an age indicator for old galactic globular clusters, can be used to contrains the age of younger stellar systems like the nearby dwarfs spheroidal Leo I. We compare the observed luminosity function of Leo I, presented by Lee et al. 1993, with theoretical expectations for three selected ages, 1, 1.5 and 2 billion years, deriving an age of about 1.5 Gyr. This result does not appear critically affected by assumptions about the cluster distance modulus or the Initial Mass Function.
The Hot End of Evolutionary Horizontal Branches
V. Castellani,S. Degl'Innocenti,L. Pulone
Physics , 1994, DOI: 10.1086/175780
Abstract: In this paper we investigate the hot end of the HB, presenting evolutionary constraints concerning the CM diagram location and the gravity of hot HB stars. According to the adopted evolutionary scenario, we predict an upper limit for HB temperatures of about logTe = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities.
Updating Standard Solar Models
F. Ciacio,S. Degl'Innocenti,B. Ricci
Physics , 1996, DOI: 10.1051/aas:1997168
Abstract: We present an updated version of our standard solar model (SSM) where helium and heavy elements diffusion is included and the improved OPAL equation of state (Rogers 1994, Rogers Swenson \& Iglesias 1996) is used. In such a way the EOS is consistent with the adopted opacity tables, from the same Livermore group, an occurrence which should further enhance the reliability of the model. The results for the physical characteristics and the neutrino production of our SSM are discussed and compared with previous works on the matter.
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