34 research outputs found
Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium
We model the abundance gradients in the disk of the Milky Way for several
chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba,
La and Eu), and compare our results with the most recent and homogeneous
observational data. We adopt a chemical evolution model able to well reproduce
the main properties of the solar vicinity. We compute, for the first time, the
abundance gradients for all the above mentioned elements in the galactocentric
distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in
the galactocentric distance range 5-17 kpc gives a very good agreement for many
of the studied elements. In addition, we fit very well the data for the
evolution of Lanthanum in the solar vicinity for which we present results here
for the first time. We explore, also for the first time, the behaviour of the
abundance gradients at large galactocentric distances by comparing our results
with data relative to distant open clusters and red giants and select the best
chemical evolution model model on the basis of that. We find a very good fit to
the observed abundance gradients, as traced by Cepheids, for most of the
elements, thus confirming the validity of the inside-out scenario for the
formation of the Milky Way disk as well as the adopted nucleosynthesis
prescriptions.Comment: 11 pages, 9 figures, accepted for publication in A&
Feedback and metal enrichment in cosmological SPH simulations I. A model for chemical enrichment
We discuss a model for treating chemical enrichment by SNII and SNIa
explosions in simulations of cosmological structure formation. Our model
includes metal-dependent radiative cooling and star formation in dense
collapsed gas clumps. Metals are returned into the diffuse interstellar medium
by star particles using a local SPH smoothing kernel. A variety of chemical
abundance patterns in enriched gas arise in our treatment owing to the
different yields and lifetimes of SNII and SNIa progenitor stars. In the case
of SNII chemical production, we adopt metal-dependent yields. Because of the
sensitive dependence of cooling rates on metallicity, enrichment of galactic
haloes with metals can in principle significantly alter subsequent gas infall
and the build up of the stellar components. Indeed, in simulations of isolated
galaxies we find that a consistent treatment of metal-dependent cooling
produces 25% more stars outside the central region than simulations with a
primordial cooling function. In the highly-enriched central regions, the
evolution of baryons is however not affected by metal cooling, because here the
gas is always dense enough to cool. A similar situation is found in
cosmological simulations because we include no strong feedback processes which
could spread metals over large distances and mix them into unenriched diffuse
gas. We demonstrate this explicitly with test simulations which adopt
super-solar cooling functions leading to large changes both in the stellar mass
and in the metal distributions. We also find that the impact of metallicity on
the star formation histories of galaxies may depend on their particular
evolutionary history. Our results hence emphasise the importance of feedback
processes for interpreting the cosmic metal enrichment.Comment: 15 pages, 15 figures, MNRAS, modified to match published versio
Populating a cluster of galaxies - I. Results at z=0
We simulate the assembly of a massive rich cluster and the formation of its
constituent galaxies in a flat, low-density universe. Our most accurate model
follows the collapse, the star-formation history and the orbital motion of all
galaxies more luminous than the Fornax dwarf spheroidal, while dark halo
structure is tracked consistently throughout the cluster for all galaxies more
luminous than the SMC. Within its virial radius this model contains about 2.0e7
dark matter particles and almost 5000 distinct dynamically resolved galaxies.
Simulations of this same cluster at a variety of resolutions allow us to check
explicitly for numerical convergence both of the dark matter structures
produced by our new parallel N-body and substructure identification codes, and
of the galaxy populations produced by the phenomenological models we use to
follow cooling, star formation, feedback and stellar aging. This baryonic
modelling is tuned so that our simulations reproduce the observed properties of
isolated spirals outside clusters. Without further parameter adjustment our
simulations then produce a luminosity function, a mass-to-light ratio,
luminosity, number and velocity dispersion profiles, and a morphology-radius
relation which are similar to those observed in real clusters. In particular,
since our simulations follow galaxy merging explicitly, we can demonstrate that
it accounts quantitatively for the observed cluster population of bulges and
elliptical galaxies.Comment: 28 pages, submitted to MNRA
New name in Astragalus L. section Corethrum Bunge from Russia and its transferring to A. section Craccina (Steven) Bunge
Reducción de las complicaciones hemorrágicas tras la implantación de stent intracoronario: protocolo de actuación de enfermería
La telemedicina, herramienta para mejorar nuestros cuidados a los pacientes trasplantados de corazón
La posibilidad de controlar extrahospitalariamente a los pacientes trasplantados de corazón con el uso de la telemedicina, posibilita mayor comodidad al paciente, ahorro del gasto sanitario, evita la realización de biopsias cardíacas y mejora la calidad de los cuidados de enfermería en estos pacientes
La telemedicina, herramienta para mejorar nuestros cuidados a los pacientes trasplantados de corazón
La posibilidad de controlar extrahospitalariamente a los pacientes trasplantados de corazón con el uso de la telemedicina, posibilita mayor comodidad al paciente, ahorro del gasto sanitario, evita la realización de biopsias cardíacas y mejora la calidad de los cuidados de enfermería en estos pacientes