Recent Talks

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.

Disks in spiral galaxies consist of stars and gas. The stellar disks show radially an exponential surface brightness distribution (and vertically one resembling an isothermal sheet), with relatively sharp truncations at of order 4 scalelengths. These truncations are most easily seen in edge-on galaxies. The evidence for these truncations and their statistics will be reviewed. Truncations appear to be not only truncations in the distribution of stars, but also in the total density. The origin of these truncations seem related to the maximum specific angular momentum in the material that formed the disks. Disks are extremely flat. The HI-gas often extends beyond the eructations in the stellar disks, but when they do they also show a warp. Again edge-on galaxies show this mostly readily. Analysis shows that the warps start abruptly, just beyond the truncation radius and some other properties also show abrupt changes at the radius of the onset of the warp. This suggests that warps are the result of infall of gas at later times, when the formation of the stellar disks has been completed. The open issue is still that we have not conclusively shown that we can discover the face-on analogs of the truncations we see in edge-on disk. I will outline some recent research I have been involved in and some ideas for further work and collaborations.

The classical idea that globular clusters are the prototypes of simple stellar populations has been revolutionized in the last few years. Multiple sequences of stars have been detected in the colour-magnitude diagram of a number of clusters, mostly thanks to high-precision HST photometry, and the correlation with the chemical properties of different generations of stars has been demonstrated. In this talk, we will first present a summary of the observational picture, and we will then introduce the SUMO project (a SUrvey of Multiple pOpulations). This is a long-term project, lead here at the IAC and aimed at detecting and characterizing multiple populations in a large sample of globular clusters. We will review the scope, the observing and reduction strategy, and the first results. So far, data for more than 30 clusters have been secured, using the wide field imagers available at the 2.2m ESO/MPI and INT telescope, thus covering both hemispheres. We will present a new photometric index which turned out to be very effective in detecting multiple RGBs in nearly all the clusters analyzed so far. The connection with the chemical content of the different populations will be also discussed.

The concordance model of cosmology with its constituents dark matter and dark Energy is an established description of some anomalous observations. However, a series of additional contradictions indicate that the current view is far from satisfactory. Rather than describing observations with new numbers, it is argued that science should reflect its method, considering the fact that real progress was usually achieved by simplification. History, not only with the example of the epicycles, has shown many times that creating new ad-hoc concepts dominated over putting in doubt what had been established earlier. Also critical astrophysicists often believe that lab-tested particle physics has reliable evidence for its model. It is argued instead that the very same sociological and psychological mechanisms have been at work and brought particle physics in a still more deperate situation long ago. As an example, a couple of absurdities of the recent Higgs boson announcements are outlined. It seems inevitable that physics needs a new culture of data evaluation, raw data and source code must become equally transparent and openly accessible.