4,914 research outputs found
Evolution of very low mass pre-main sequence stars and young brown dwarfs under accretion: A phenomenological approach
In the poster presented in Cool Star 15, we analyzed the effect of disk
accretion on the evolution of very low mass pre-main sequence stars and young
brown dwarfs and the resulting uncertainties on the determination of masses and
ages. We use the Lyon evolutionary 1-D code assuming a magnetospheric accretion
process, i.e., the material falls covering a small area of the radiative
surface, and we take into account the internal energy added from the accreted
material as a free parameter . Even if the approach to this problem
is phenomenological, our formalism provides important hints about
characteristics of disk accretion, which are useful for improved stellar
interior calculations. Using the accretion rates derived from observations our
results show that accretion does not affect considerably the position of
theoretical isochrones as well as the luminosity compared with standard
non-accreting models. See more discussions in a forthcoming paper by Gallardo,
Baraffe and Chabrier (2008).Comment: Poster contribution Cool Star 15, St. Andrews, U
Classical Tensors and Quantum Entanglement I: Pure States
The geometrical description of a Hilbert space asociated with a quantum
system considers a Hermitian tensor to describe the scalar inner product of
vectors which are now described by vector fields. The real part of this tensor
represents a flat Riemannian metric tensor while the imaginary part represents
a symplectic two-form. The immersion of classical manifolds in the complex
projective space associated with the Hilbert space allows to pull-back tensor
fields related to previous ones, via the immersion map. This makes available,
on these selected manifolds of states, methods of usual Riemannian and
symplectic geometry. Here we consider these pulled-back tensor fields when the
immersed submanifold contains separable states or entangled states. Geometrical
tensors are shown to encode some properties of these states. These results are
not unrelated with criteria already available in the literature. We explicitly
deal with some of these relations.Comment: 16 pages, 1 figure, to appear in Int. J. Geom. Meth. Mod. Phy
Fonaments per a una història del paisatge de Catalunya durant l'època moderna
El treball de recerca Fonaments per a una història del paisatge de Catalunya durant l'època moderna sorgeix de l'interès per conèixer els processos transformadorsdel territori per part de la humanitat al llarg del temps, així com les implicacions socioeconòmiques de les successives configuracions paisatgístiques. El camp d'estudi es delimita a la Catalunya de l'edat moderna, especialment a les realitats territorials del segle XVIII català
Ressenyes
Index de les obres ressenyades: A. SIMON i TARRÉS (dir.), Diccionari d'Historiografia Catalana. Barcelona: Enciclopèdia Catalana, 2003
The mass-radius relationship from solar-type stars to terrestrial planets: a review
In this review, we summarize our present knowledge of the behaviour of the
mass-radius relationship from solar-type stars down to terrestrial planets,
across the regime of substellar objects, brown dwarfs and giant planets.
Particular attention is paid to the identification of the main physical
properties or mechanisms responsible for this behaviour. Indeed, understanding
the mechanical structure of an object provides valuable information about its
internal structure, composition and heat content as well as its formation
history. Although the general description of these properties is reasonably
well mastered, disagreement between theory and observation in certain cases
points to some missing physics in our present modelling of at least some of
these objects. The mass-radius relationship in the overlaping domain between
giant planets and low-mass brown dwarfs is shown to represent a powerful
diagnostic to distinguish between these two different populations and shows
once again that the present IAU distinction between these two populations at a
given mass has no valid foundation.Comment: Cool Stars, Stellar Systems and the Sun 15, invited revie
The continuum description with pseudo-state wave functions
Benchmark calculations are performed aiming to test the use of two different
pseudo-state bases on the the Multiple Scattering expansion of the total
Transition amplitude (MST) scattering framework. Calculated differential cross
sections for p-6He inelastic scattering at 717 MeV/u show a good agreement
between the observables calculated in the two bases. This result gives extra
confidence on the pseudo-state representation of continuum states to describe
inelastic/breakup scattering.Comment: 4 pages, 2 figures. Published in Physical Review
Episodic accretion at early stages of evolution of low-mass stars and brown dwarfs: a solution for the observed luminosity spread in H-R diagrams?
Copyright © 2009 American Astronomical Society / IOP Publishin
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