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 $\epsilon$. 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?

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