Recent Talks

In the 50 years since their discovery, it has become increasingly recognised that quasars are not merely signposts to the distant Universe, but also play a key role in the overall galaxy evolution process. However, if we are to incorporate quasars into models of galaxy evolution, it's important to understand how, when and where they are triggered. In this talk I will review the latest observational results on the triggering of quasars, based on the morphologies of their host galaxies and star formation properties; I will also discuss the future prospects for understanding quasar triggering using Herschel and ALMA data.

Ultracool dwarfs represent the low-mass tail of the distribution of primary masses for which planets can be found with the Kepler satellite. Our team has identified 42 new ultracool dwarfs in the Kepler field of view that have started to be observed with this space telescope via its General Observer and Director Discretionary Time programs. First results of a study of Kepler light curves of 18 very low-mass dwarfs will be presented at this talk. It is demostrated that Kepler is sensitive to moon sized companions of ultracool dwarfs at short orbital periods (few days), and an intriguing candidate will be shown. Results from a ground-based infrared transit survey will also be presented which confirm the lack of Hot Jupiters around very low-mass primaries. Last but not least, a concept for a sustainable hybrid Hypertelescope that would be crucial to follow-up rocky planets will also be introduced.

Hablaré de tres caprichos. El primero pretende responder a la pregunta: ¿Existen lentes magnéticas en el Cosmos? El segundo trata de un problema de Milagro, viendo cómo el campo magnético de nuestra galaxia puede resolver la anisotropía en la distribución de rayos cósmicos de unos 10 TeV. El tercero considera las curvas de rotación de algunas galaxias espirales que tras haber alcanzado la velocidad asintótica, vuelve a tener pendiente positiva.

The formation of active regions and its most visible outcome-sunspots-are still a matter of research. Magnetic flux tubes theory tends to explain the formation of sunspots, but it still faces some unresolved questions: How are they generated? Why can they survive all along the convective zone? How do they rise? I will review this theory and introduce a new way to understand sunspot formation: the negative effective magnetic pressure instability (NEMPI). NEMPI was predicted long ago (Kleeorin et al., 1989, 1990; Kleeorin \& Rogackevskii, 1994; Kleeorin et al., 1996) but has only been seen recently (Branderburg et. al., 2011). It arised as a effect of strong stratication and the presence of turbulence with a weak mean magnetic field. Under suitable conditions, a large-scale instability resulting in the formation of non-uniform magnetic structures, can be excited over the scale of many turbulent eddies or convection cells. This instability is caused by a negative contribution of turbulence to the effective (mean-field) magnetic pressure and has previously been discussed in connection with the formation of active regions and perhaps sunspots. Now, we want to understand the effects of rotation on this instability in both two and three dimensions. We use mean-field magnetohydrodynamics in a parameter regime in which the properties of the negative effective magnetic pressure instability have previously been found to be in agreement with those of direct numerical simulations. We find that the instability is suppressed already for relatively slow rotation with Coriolis numbers (i.e. inverse Rossby numbers) around 0.2. The suppression is strongest at the equator. In the nonlinear regime, we find traveling wave solutions with propagation in the prograde direction at the equator with additional poleward migration away from the equator. The prograde rotation of the magnetic pattern near the equator is argued to be a possible explanation for the faster rotation speed of magnetic tracers found on the Sun. In the bulk of the domain, kinetic and current helicities are negative in the northern hemisphere and positive in the southern.

Magnetic fields at galactic and larger scales is a challenging issue for astrophysics and cosmology. In this talk, I'll review the methods to detect magnetic fields at these scales as well as I'll revise the field structure of the Milky Way and its dynamical implications over the gas distribution. In the second part, I'll review the updated works about effects of primordial magnetic fields on large scale structure and I'll show you preliminary results on its imprint on cosmic microwave background. 

Gas kinematics on the scales of Giant Molecular Clouds (GMCs) are essential for probing the framework that links the large-scale organization of interstellar gas to cloud formation and subsequent star formation. I will present an overview of results from the PdBI Arcsecond Whirlpool Survey (PAWS, PI: E. Schinnerer), which has mapped CO(1-0) emission over 9 kpc in the nearby grand-design spiral galaxy M51 at 40 pc resolution, and is sensitive to giant molecular clouds (GMCs) with masses above 10^5 Msun. This unprecedented view challenges the conventional picture of how molecular gas is structured and organized in galaxies: clouds are not ‘universal’, but respond to their environment, resulting in a diversity of cloud properties that not only depend on (dynamical) environment but also vary from galaxy to galaxy. I will discuss how this sensitivity to environment emerges, in consideration of the stability of M51’s GMCs (including the effects of pressure, shear, turbulence) and our view of non-circular motions in the gas disk. As a result of the strong streaming motions that arise due to departures from axisymmetry in the gravitational potential (i.e. the nuclear bar and spiral arms), embedded clouds feel a reduced surface pressure, which can prevent collapse. This dynamical pressure naturally leads to changes in the efficiency of star formation and hence gas depletion time along the spiral arms. I will show that local reductions to cloud surface pressure in M51 dominate over shear and star formation feedback-driven turbulence in determining the observed radial variation the depletion time. I will also describe how incorporating a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies, across cosmic time.

So far more than 800 planets have been discovered and their  
characterization is becoming more important. Transiting planets offer  
the unique opportunity of detecting planetary atmospheres, helping to  
improve the theoretical models of atmospheric composition under  
different physical parameters (densities, irradiation, etc). However,  
the precision needed to detect atoms and molecules, requires big  
telescopes and stable instruments in order to obtain a good  
signal-to-noise. In this talk I'll review the efforts, technical  
challenges and current results that our group of Planets and Low Mass  
stars is obtaining using GTC to study extra-solar planets.

As astrophysicists, we are used to extracting physical information from the observations. The usual procedure is to propose a parametric physical model to explain the observations and use the observations to infer the values of the parameters. However, in our noisy and ambiguous universe, the solution to the inference problem is usually non-unique or diffuse. For this reason, it is important that our inversion techniques give reliable results. In this talk I present a few recent results (dusty tori of AGN, magnetic fields in central stars of planetary nebulae, oscillations of coronal loops, signal detection) in which our group is applying Bayesian ideas to extract information from the observations.

La vida de la reina Nefertiti siempre ha estado rodeada de un halo de misterio pero aun son mayores los enigmas que rodean sus últimos años. En un libro reciente, el egiptólogo Aidan Dodson (2009) ha presentado una revisión actualizada del período de Amarna, en un fuerte contraste a las hipótesis defendidas últimamente por otros egiptólogos de prestigio como Steve Reeves (2006), Marc Gabolde (2005) o Rolf Krauss (2008). En ella Dodson utiliza las fuentes epigráficas y arqueológicas más recientes para ofrecer una versión del momento final de este periodo histórico tan fascinante donde defiende a Ankhesenamon, hija de la reina, como la Dahamunzu de los textos hititas (la reina egipcia que escribió al rey hitita Subiluliuma pidiéndole un esposo), la filiación de Tutankhamon cómo hijo de Nefertiti y de su esposo Akhenaton, manteniendo la antigua cronología que sitúa el ascenso al trono del último rey en 1553 a.C. Sin embargo, en los últimos años ha habido una revolución fundamental de los estudios del periodo de Amarna en diversos aspectos que fueron ignorados o incluso interpretados de una manera muy poco elegante por Dodson. Entre estos se incluyen nuevas pruebas de las fuentes hititas que hacen de Tutankhamon un contemporáneo del rey hitita Mursili II (Miller, 2007), una nueva duración para el reinado de Horemheb (van Dijk 2008), o los importantísimos datos producidos por el análisis de ADN de la familia real del periodo (Hawass et al. 2010). Toda esta nueva información se ha recopilado junto con la evidencia astronómica que se puede obtener de la época: la hipotética orientación solar del templo principal de Akhetaton en el momento de la fundación de la ciudad y la identificación de un posible eclipse en las fuentes hititas, para implementar una nueva teoría que ofrece una imagen completa y diferente del período desde el punto de vista histórico y una nueva cronología para el final de la dinastía XVIII, donde la reina Nefertiti cobra un protagonismo especial. Durante el seminario se resumirá las evidencias anteriores y se mostrarán los resultados principales de la hipótesis resultante de nuestro nuevo análisis recién publicada en un libro editado por Crítica (Belmonte 2012).

Long Gamma-Ray Bursts are flashes of high-energy radiation and are linked to the death of massive stars. I will first summarize the main aspects of GRB astronomy, ranging from gamma to infrared frequencies, and secondly I will show how long GRBs pinpoint star-forming galaxies. Afterwards, I will present recent results which indicate as the GRB host population resembles all kind of star-forming galaxies, even the most dusty ones, almost invisible in optical-dedicated surveys.