Recent Talks

Gamma-Ray Bursts (GRBs) are the most powerful sources of electromagnetic radiation in the Universe. There are many open questions about their origin and their nature, and the answers should be searched in the large amount of data collected during these last years. We focused on the study of the their X-ray and optical afterglow properties, as observed by the Swift X-Ray Telescope (XRT) and ground-based optical telescopes. We investigated the observer and rest-frame properties of all GRBs observed by Swift between December 2004 and December 2010 with spectroscopic redshift through a comprehensive statistical analysis of the XRT light-curves of GRBs carried out in a model-independent way. We found out a three parameter correlation that is followed both by short and long GRBs. We also carried out a systematic analysis of the optical data available in literature for the same GRBs to investigate the GRB emission mechanisms and to study their environment properties. Our analysis shows that the gas-to-dust ratios of GRBs are larger than the values calculated for the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud. In this talk I will show the major results of the analysis of this large set of data.

 CanariCam is a mid-IR imager and spectrograph with polarimetric and coronographic capabilities built by the University of Florida as a common-user instrument for the GTC. CanariCam observing capabilities are unique, offering the GTC community the opportunity to exploit the 8-25 microns observing windows at the diffraction limit of the GTC. Grantecan started CanariCam operations during the first semester of 2012. Currently, three observing modes are offered to the GTC community: Imaging, low resolution spectroscopy and imaging polarimetry. In this talk, some of the challenges of operating a mid-IR diffraction-limited instrument from the ground will be reviewed. Some CanariCam commissioning results for the currently offered modes will be presented. I will introduce some of the tools available for the community to prepare CanariCam observations and to reduce the data. Finally, I will explain what is the current status of the instrument and telescope for mid-IR observations.

The life cycle of baryonic matter in a galaxy is driven by the exchange of material between the interstellar medium (ISM) and stars, which are the agents of galaxy evolution. Dust is present at these key transition phases of matter: in the ISM, in the circumstellar environments of newly forming stars and in stellar ejecta of dying stars. The Spitzer and Herschel wavelengths provide a sensitive probe of circumstellar and interstellar dust and hence, allows us to study the physical processes of the ISM, the formation of new stars and the injection of mass by evolved stars and their relationships on a galaxy-wide scale. Due to their proximity, well constrained viewing angle, multi-wavelength information, and measured tidal interactions with the Milky Way (MW), the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are uniquely suited for surveying the agents of galaxy evolution (SAGE), the ISM and stars. In this talk, I will present some key results from the Spitzer SAGE and Herschel HERITAGE surveys including measurements of ISM mass estimates from dust emission, discoveries of thousands of young stellar object candidates, and precise measurements of dust mass loss rates from entire populations of evolved stars and w the mass budgets of these galaxies. I will end with a brief forward look to the future prospects with the James Webb Space Telescope Mission.

Crucial issues in cosmology and astrophysics are to understand the
process of galaxy formation and evolution and the nature of what
appears to be the dominant form of matter in the Universe, i.e. dark
matter. Dwarf galaxies provide important information on both of these
issues. In this talk, I will focus on the dwarf galaxies found in the
Local Group, as it is the galaxy population that can be studied in
the greatest detail than any other from the properties of their
resolved stellar populations. I will show how wide-area surveys have
led to a leap forward in our observational understanding of these
galaxies and discuss future prospects.

AzTEC is a sensitive bolometer camera that, coupled with 10-15m-class sub-mm telescopes, has mapped more than 3 sq. deg of the extragalactic sky to depths between 0.7 and 1.1 mJy at 1.1mm, prior to its current installation and operation on the 32m Large Millimeter Telescope (LMT). These extragalactic surveys targeted towards blank-fields and biased high-z environments alike have allowed us to identify regions of the sky where submillimeter galaxies (SMGs), powerful obscured starbursts at high-redshifts (z>1), cluster, and possibly mark the potential wells of accelerated galaxy-formation that will eventually form massive clusters. In this talk I will describe the evidence we have found for these overdense regions of massive galaxies, their structure and possible interpretation, as well as the follow-up observations we are carrying out with the LMT nowadays.

The direct accretion of pristine gas streams is predicted to be the main mode of galaxy disk growth in the early universe (cold-flows). We (think we) have discovered this physical process at work in the local Universe. The finding is one of the outcomes of our in-depth study of local extremely metal poor (XMP) galaxies. I will explain the main observational properties of XMPs, in particular, their tendency to have cometary or tadpole morphology, with a bright peripheral clump (the head) on a faint tail. Tadpole galaxies are rare in the nearby universe but turn out to be very common at high redshift, where they are usually interpreted as disk galaxies in early stages of assembling. We have found the heads to be giant HII regions displaced with respect to the rotation center, with the galaxy metallicity being smallest at the head and larger elsewhere. The resulting chemical abundance gradient is opposite to the one observed in local spirals, and suggests a recent gas accretion episode onto the head. Thus, local XMP galaxies seem to be primitive disks, with their star formation sustained by accretion of external metal poor gas. I will argue how the same mechanism may be driving the star formation in many other local galaxies. Ongoing observational projects to confirm these findings and conjectures will be briefly mentioned.

El pasado 6 de Junio de 2012 tuvo lugar el ultimo transito de Venus frente al Sol del siglo XXI, visible desde la Tierra. Los transitos de Venus han sido observados historicamente proporcionando informacion sobre del tamaño del Sol o la distancia Tierra-Sol. Hoy en dia, con la explosion del campo de exoplanetas, y la cada vez mas cercana deteccion de planeta potencialmente habitables, el transito de Venus ofrecia una oportunidad unica de medir el espectro de transmision de un planeta rocoso. Con esta intencion, en el IAC se diseño intrumentacion especifica y se realizo una expedicion a Australia, al tiempo que se observaba tambien desde telescopios en Chile. Este es un resumen de las peripecias personales, intrumentales y cientificas que suponen este tipo de retos, y que llevaron a la *posible* deteccion del dioxido de carbono en la atmosfera de Venus.

The strongest He II emission in the visible spectral range, at 4686 A, is for the first time observed at a spectral resolution sufficiently high for a line profile analysis in quiescent solar prominences. It is found that the He II line width exceeds by far that of emissions from neutral helium which, in turn, show significant differences between the triplet and singlet emissions. The width hierarchy from singlet over triplet to He II suggests an origin in increasingly hot plasma of the transition to hot coronal surroundings. The ratio of integrated line emission is found to be independent on the prominence size suggesting that each fine-structure has its own transition to hot coronal gas in between the treads.

Over the past decade there has been a growing body of evidence for a closely regulated balance of heating and cooling of the intracluster medium in the cores of clusters. I will review this evidence with a particular emphasis on the role of cold gas and dust as the fuel for AGN feedback that dominates these systems.

Fundamental properties of brown dwarfs, such as luminosity and effective temperature, evolve with age. Large samples of spectroscopically-confirmed substellar objects with well-determined ages and distances are needed to constrain those parameters. We are embarked in a spectroscopic follow-up with GTC/OSIRIS of low-mass member candidates selected in several open clusters to constrain their membership. Here I will present the first L dwarf member in Praesepe confirmed by photometry, astrometry, and spectroscopy. We derived an optical spectral type of L0.3+/-0.4 and a mass placing it at the hydrogen-burning boundary. Considering the measured equivalent width of the gravity-sensitive sodium doublet, and the derived membership probability of ~80% or higher, we conclude that this object is likely to be a true member of Praesepe, with evidence of being a binary system.