Recent Talks

Recent observations of the solar atmosphere have provided new insights concerning medium-sized jet phenomena taking place in the solar corona. These jets are magnetically controlled and typically take place in regions where the mean magnetic field has an open structure. Observations indicate that at least two different types of jets exist. A simple jet that generally has a near steady state evolution phase with a well behaved and collimated outflow stream. The second type typically combines the characteristics of the first type with an explosive behaviour that significantly changes the topological structure of the jet outflow. Models have attempted to provide physical explanations to the observations, and are in general able to capture a number of the observational characteristics. This talk will discuss both the observations and the models, emphasizing where we succeed and where new progress is need

Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major provider of resources for disc buildup and star formation in massive galaxies in the early universe. We use hydrodynamical simulations to study to what extent these cold streams are traceable in the extended circum-galactic environment of galaxies via Ly alpha emission, Ly alpha absorption and selected low ionisation metal absorption lines. We predict the strength of the absorption signal produced by the streams and find that it is consistent with observations in high redshift galaxies. The characteristics of the Ly alpha emission of our simulated galaxies are similar in luminosity, morphology and extent to the observed Ly alpha blobs, with distinct kinematic features. We analyse the characteristics of the cold streams in simulations and present scaling relations for the amount of infall, its velocity, distribution and its clumpiness and compare our findings with observations.

The angle between the stellar spin axis and the orbital planetary angular momentum of a planet, also referred to as the obliquity of the system, is a matter of intense study in recent years, for the transiting planets of the Kepler mission in particular. Some evidence was found for two populations of hot Jupiters - one around cool stars with orbits well-aligned with the stellar rotational axes, and the other one around hot stars with isotropic distribution of obliquities, including planets with retrograde motion. It was suggested that the primordial planetary obliquity is isotropic, and cool stars have reached their zero-obliquity state by tidal re-alignment.

The talk will summarize the observational techniques for measuring planetary obliquities, and the different theoretical approaches to interpret this new, unexpected feature of exo-planet population. Finally, I will present a surprising statistical new result that emerges from the study of Kepler light curves of stellar rotation, suggesting the alignment of cool stars is probably not the result of tidal interaction.

Driven by the potential of large-scale structure (LSS) observations to shed light on the physics behind the accelerated expansion of the Universe, several ground-breaking galaxy surveys are currently under way. These surveys will measure the LSS of the Universe with unprecedented precision, providing new insights not only on the origin of cosmic acceleration, but also on many other important physical parameters. The ongoing Baryon Oscillation Spectroscopic Survey (BOSS) is an example of these new surveys. In this talk I review our theoretical understanding of LSS and the details of the analysis of these measurements. I also describe the cosmological implications of the latest clustering measurements from BOSS, with an emphasis on the problem of understanding cosmic acceleration.

Galaxies can be described in terms of their structure, dynamics and stellar populations.  Some very robust correlations between various galaxy structural properties, such as total luminosity, maximum circular velocity, and size show rather small scatter, hinting at well-regulated galaxy formation processes.  A major challenge to understanding these
scaling relations, and ultimately galaxy formation and evolution, is the elusive interplay between visible and dark matter.  I will discuss the latest derivations of galaxy scaling relations and their link with
modern cosmological models.

Since the early 50' of last century the study of Horizontal Branch stars in Galactic GCs has been of pivotal relevance since the core He-burning stage is an 'amplifier' of any evolutionary/physical process occurring during the early evolutionary stages. Thanks to the huge observational effort devoted to this issue many outstanding 'anomalies' have been discovered concerning the physical properties of GC HB stars. The situation is becoming more complex when accounting for the discovery of the Multiple Population phenomenon in Galactic GCs. We will review the main anomalies related to the HB evolutionary stage, their (when available) theoretical interpretations, and current shortcomings. We will also discuss how the discovery of the Multiple Population Phenomenon offers a new approach for interpreting many observational evidence.

We will start by recalling the effects of rotation on stellar evolution and briefly explain its implementation in a stellar evolution code. We will present a set of various grids of massive stars models, and then show some recent results obtained by our new SYCLIST toolbox, which is able (among other things) to generate synthetic stellar clusters, including various physical ingredients, such as initial rotation and angle of view distributions, gravity and limb darkening, etc.

Things should be made simple, but not simpler.

What we want to show is that General Relativity, as it stands today, can be considered as a gravitational theory of low velocity spinless matter, and therefore a restricted theory of gravitation.

Gravity is understood as a geometrization of spacetime. But spacetime is also the manifold of the boundary values of the spinless point particle in a variational approach. Since all known elementary matter, baryons, leptons and gauge bosons are spinning objects, it means that the manifold, which we call the kinematical space, where we play the game of the variational formalism of a classical elementary particle must be greater than spacetime.

Mathematics shows that this manifold for any arbitrary mechanical system is always a Finsler metric space, such that the variational formalism can be interpreted as a geodesic problem on this metric space.

This manifold is just the flat Minkowski space for the free spinless particle.  Any interaction modifies its flat Finsler metric as gravitation does.

The same thing happens for the spinning objects, but now the Finsler metric space has more dimensions and its metric is modified by any interaction, so that to reduce gravity to the modification only of the metric of the spacetime submanifold is to make a simpler theory, the gravitational theory of spinless matter.

Even the usual assumption that the modification of the metric only produces a Riemannian metric of the spacetime is also a restriction because in general the coefficients for a Finsler metric, are also dependent on the velocities. Removal of the velocity dependence of metric coefficients is equivalent to consider the restriction to low velocity matter.

In the spirit of unification of all forces, gravity cannot produce, in principle, a different and simpler geometrization than any other interaction.

References: arXiv: 1203.4076