5,433 research outputs found
The age-metallicity dependence for white dwarfs
We present a theoretical study on the metallicity dependence of the
initialtofinal mass relation and its influence on white dwarf age
determinations. We compute a grid of evolutionary sequences from the main
sequence to K on the white dwarf cooling curve, passing through
all intermediate stages. During the thermally-pulsing asymptotic giant branch
no third dredge-up episodes are considered and thus the photospheric C/O ratio
is below unity for sequences with metallicities larger than . We
consider initial metallicities from to , accounting for
stellar populations in the galactic disk and halo, with initial masses below
. We found a clear dependence of the shape of the
initialtofinal mass relation with the progenitor metallicity, where metal
rich progenitors result in less massive white dwarf remnants, due to an
enhancement of the mass loss rates associated to high metallicity values. By
comparing our theoretical computations with semi empirical data from globular
and old open clusters, we found that the observed intrinsic mass spread can be
accounted for by a set of initialtofinal mass relations characterized by
different metallicity values. Also, we confirm that the lifetime spent before
the white dwarf stage increases with metallicity. Finally, we estimate the mean
mass at the top of the white dwarf cooling curve for three globular clusters
NGC 6397, M4 and 47 Tuc, around , characteristic of old stellar
populations. However, we found different values for the progenitor mass, lower
for the metal poor cluster, NGC 6397, and larger for the younger and metal rich
cluster 47 Tuc, as expected from the metallicity dependence of the
initialtofinal mass relation.Comment: Accepted for publication in MNRA
White Dwarfs In Ngc6397 And M4: Constraints On The Physics Of Crystallization
We explore the physics of crystallization in the dense Coulomb plasma of the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from Hubble Space Telescope photometry of the globular cluster M 4 and compare it with our results for proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with a binary mixture of carbon and oxygen crystallizing at a value of Gamma higher than the theoretical value for a One Component Plasma (OCP). We show that this result is in line with the latest Molecular Dynamics simulations for binary mixtures of C/O. We discuss implications for future work.Astronom
Finding the Higgs Boson through Supersymmetry
The study of displaced vertices containing two b--jets may provide a double
discovery at the Large Hadron Collider (LHC): we show how it may not only
reveal evidence for supersymmetry, but also provide a way to uncover the Higgs
boson necessary in the formulation of the electroweak theory in a large region
of the parameter space. We quantify this explicitly using the simplest minimal
supergravity model with bilinear breaking of R-parity, which accounts for the
observed pattern of neutrino masses and mixings seen in neutrino oscillation
experiments.Comment: 7 pages, 7 figures. Final version to appear at PRD. Discussion and
results were enlarge
Probing Neutrino Oscillations in Supersymmetric Models at the Large Hadron Collider
The lightest supersymmetric particle may decay with branching ratios that
correlate with neutrino oscillation parameters. In this case the CERN Large
Hadron Collider (LHC) has the potential to probe the atmospheric neutrino
mixing angle with sensitivity competitive to its low-energy determination by
underground experiments. Under realistic detection assumptions, we identify the
necessary conditions for the experiments at CERN's LHC to probe the simplest
scenario for neutrino masses induced by minimal supergravity with bilinear R
parity violation.Comment: 11 pages, 6 figures. To appear in Physical Review
Patogenicidade de Gracilacus latescens a mudas de freijó (Cordia goeldiana).
Publicado também em: Fitopatologia Brasileira, v. 11, n. 3, p. 471-478, out. 1986
Substituição parcial do farelo de soja pela uréia para bezerros desaleitados precocemente.
Este experimento foi realizado com o objetivo de verificar a viabilidade de substituir parcialmente o farelo de soja pela uréia para bezerras desaleitadas precocemente
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