Latest talks

List of all the talks in the archive, sorted by date.

Tuesday June 21, 2016
Dr. Enrico Corsaro
Service d'Astrophysique, IRFU/DRF-CNRS/CEA Saclay


Stars originate by the gravitational collapse of a turbulent molecular cloud of a diffuse medium, and
are often observed to form clusters. Stellar clusters therefore play an important role in our
understanding of star formation and of the dynamical processes at play. However, investigating the
cluster formation is difficult because the density of the molecular cloud undergoes a change of
many orders of magnitude. Hierarchical-step approaches to decompose the problem into different
stages are therefore required, as well as reliable assumptions on the initial conditions in the clouds.
In this talk I will report for the first time the use of the full potential of NASA Kepler
asteroseismic observations coupled with 3D numerical simulations, to put strong constraints on the
early formation stages of old open clusters. Thanks to a Bayesian peak bagging analysis of about 50
red giant members of NGC 6791 and NGC 6819, the two most populated open clusters observed
in the nominal Kepler mission, I derive a complete set of detailed oscillation mode properties for
each star, with thousands of oscillation modes characterized. I therefore show how these
asteroseismic properties lead to a discovery about the rotation history of stellar clusters. Finally,
the observational findings will be compared with hydrodynamical simulations for stellar cluster
formation to constrain the physical processes of turbulence, rotation, and magnetic fields that are
in action during the collapse of the progenitor cloud into a proto-cluster.

Thursday June 16, 2016
Mrs. Sara Bertran de Lis
Instituto de Astrofísica de Canarias (IAC)


The detection of chemical inhomogeities in the Galactic disk requires an oustanding precision in the abundance measurements and a thorough estimation of the uncertainties. So far, studies in alpha-elements in disk stars either do not reach the required precision, or comprise too small samples in the solar neighborhood. Thanks to the Apache Point Galactic Evolution Experiment (APOGEE), we have for the first time a large spectroscopic sample of about 100.000 disk stars, with data homogeneously obtained, reduced, and analyzed. Taking advantage of such database, we examine the distribution of oxygen-to-iron abundance ratio in stars across the Galactic disk. These data reveal that the square root of the star-to-star cosmic variance in the [O/Fe] at a given metallicity is about 0.03 to 0.04 dex in both the thin- and thick-disk populations. Measuring the spread in [O/Fe] and other abundance ratios can provide strong constraints for models of Galactic chemical evolution. In this talk we will describe how we arrived at this result, the calculation of uncertainties, and implications regarding the chemical evolution of the Galaxy.

Tuesday June 14, 2016
Dr. Giacomo Beccari
ESO Garching


Current planet formation theories are bound to comply with the observational constraint that protoplanetary disks have lifetime of ~3 Myr. This timescale is mostly based on spectroscopic studies of objects accreting matter from a circumstellar disk around pre-main sequence stars (PMS) located in low-density, nearby (d<1-2kpc) star forming regions. These objects do not reflect the conditions in place in the massive starburst clusters where most of star formation occurs in the universe. Using a new robust method to indentify PMS objects through their photometric excess in the Halpha band, we have studied with the HST and ground based facilities the PMS population several starburst clusters, namely NGC3603 in the Milky Way and several clusters in the Carina Nebula,  30 Doradus and the surrounding regions in the Large Magellanic Cloud and NGC 346 and NGC 602 in the Small Magellanic Cloud. We found a wide spread of ages (0.5 to 20 Myr) for PMS stars, clearly showing that accretion from circumstellar disks is still going on well past 10 Myr. This finding challenges our present understanding of protoplanetary disk evolution, and can imply a new scenario for the planet formation mechanism and of star clusters formation in general. Based on these results we were recently granted 175hr with OmegaCAM at the VST to carry out a deep optical wide field survey of nearby (<3kpc) star forming regions. These observations will provide physical parameters (including mass accretion rates) for over 10000 PMS stars and will establish whether the long timescales of circumstellar discs are common.

Thursday June 2, 2016
Dr. Mariya Lyubenova
Kapteyn Astronomical Institute


Tests of the concordance cold dark matter model on the scale of galaxies are so far inconclusive due to our poor understanding of the interplay between baryons and dark matter (DM). Two critical limitations in previous efforts to disentangle the baryonic and DM distributions have been the lack of (i) two-dimensional, spatially complete and radially extended kinematics to infer the total mass distribution, and (ii) coverage in wavelength to robustly constrain the baryonic mass distribution and isolate the DM contribution. Both are now provided by existing integral-field spectroscopic data from the CALIFA survey of a statistically well-defined sample of ~600 nearby galaxies of all Hubble types. We apply dynamical and stellar population modelling in a homogeneous way to the same data. In this way we for the first time constrain both the normalisation (ratio of dwarf to giant stars) and shape (single versus broken power-law slope) of the stellar initial mass function (IMF). We then robustly characterise the mass distribution of galaxies, from dwarf-star dominance at the high-mass end to dark matter excess in low-mass spirals. In this way, CALIFA yields physical insights into the baryonic and DM interplay for a statistically well-defined sample of nearby galaxies, providing in turn crucial constraints on galaxy formation and evolution models.

Thursday May 19, 2016
Dr. Carlos Allende, Jesús Falcón Barroso, Ismael Pérez Fournon
Instituto de Astrofísica de Canarias (IAC)


Talk to update on progress of IAC scientists with SDSS-IV data.

Wednesday May 18, 2016
Dr. Teo Muñoz-Darias
Instituto de Astrofísica de Canarias


X-ray observations performed during the last few decades have provided a rich data base on accreting black holes and neutron stars in X-ray binaries. A strong coupling between the properties of the accretion flow and the presence of outflows, such as radio-jets and X-ray winds, has been found to be a fundamental characteristic of black hole systems; a feature which might be shared by super-massive black holes in active galactic nuclei.
I will present some novel results corresponding to the 2015 outburst of the prototypical black hole transient V404 Cyg (Muñoz-Darias et al. 2016, Nature). During this event, arguably the most interesting of its kind in decades, we have discovered a sustained outer accretion disc wind, which is simultaneous to the radio jet.  Our GTC-10.4m spectra show  that the outflowing wind is neutral, has a large covering factor, expands at 1% of the speed of light and triggers a nebular phase once accretion sharply drops and the ejecta become optically thin. I will discuss the implications of these results in the context of black hole accretion.

Tuesday May 17, 2016
Dr. Anne Sansom
University of Central Lancashire


Elliptical and lenticular galaxies are often thought of as ‘red and dead’. However, hierarchical mergers are likely to leave traces of the process of galaxy evolution. We have investigated this question using a complete sample of galaxies. I will introduce the survey data that we are using and present results for the largest sample of early-type-galaxies in the local Universe. We have made a complete assessment of their dust characteristics covering all galaxies in the survey areas down to r-band absolute magnitudes of Mr > -17.4 (similar to the SMC), and as a function of environment. The unexpected results found will be presented and contrasted with what is going on in the nearby Virgo cluster, for early-type galaxies.

Thursday April 21, 2016
Dr. Bill Cotton


The ARCADE-2 CMB balloon experiment detected an unexplained low frequency component which was postulated to be a previously unknown population of extragalactic sources. We conducted a deep 2-4 GHz survey with the recently upgraded EVLA to search for this population and to measure the faint radio source counts. Faint source counts constrain the cosmic evolution of the populations represented including sources powered by star formation. Previous attempts at measuring faint source counts produced more scatter in results than are easily accounted for and may reflect the variety of techniques used to correct for various effects. I will describe a deep confusion limited analysis using the "P of D" technique to derive the source counts at, and below the confusion which avoids many of the difficult to correct effects. Results are in excellent agreement with theoretical expectations effectively ruling out the ARCADE-2 anomaly being due to discrete sources. I will also summarize ongoing observations to determine the size distribution of the microJy population.

Tuesday April 12, 2016
Prof. Ruggero Stanga
Universidad de Florencia y Observatorio de Arcetri


A discussion of the first observation ever of gravitational waves. Present detectors, future detectors, and the perspectives for gravitational wave astronomy.

Thursday April 7, 2016
Dr. Iker S. Requerey


Solar surface convection displays highly localized sinks where cold plasma returns to the solar interior. On its way to being engulfed by a downdraft the plasma can also advect and intensify magnetic fields up to kG field strengths. Such theoretical predictions strengthen the idea that localized downdrafts are places where the concentration of magnetic fields is favored. The observational discovery of convectively driven sinks is rather recent, however, and its role in the formation and evolution of quiet-Sun magnetic features is still poorly characterized. In our work, we provide both quantitative and qualitative bases for the association between sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board Sunrise. We find 3.1 x 10-3 sinks Mm-2 minute-1 located at mesogranular vertices. These sinks are associated to (1) horizontal velocity flows converging to a central point and (2) long-lived downdrafts.  The spatial distribution of magnetic fields in the quiet Sun is also examined. The strongest magnetic fields are preferentially located at sinks. We find that 40% of the pixels with longitudinal component of the magnetic field higher than 500 G are located in the close neighborhood of sinks.  The study of individual examples reveal that sinks can play an important role in the evolution of quiet-Sun magnetic features.

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