Latest talks

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


Timothy_Beers_180621s
Thursday June 21, 2018
Prof. Timothy Beers
Univ. Notredame/JINA

Abstract

The very metal-poor (VMP; [Fe/H] < –2.0) and extremely metal-poor (EMP; [Fe/H] < –3.0) stars provide a direct view of Galactic chemical and dynamical evolution; detailed spectroscopic studies of these objects are the best way to identify and distinguish between various scenarios for the enrichment of early star-forming gas clouds soon after the Big Bang. It has been recognized that a large fraction of VMP (15-20%) and EMP stars (30-40%) possess significant over-abundances of carbon relative to iron, [C/Fe] > +0.7. This fraction rises to at least 80% for stars with [Fe/H] < –4.0. Recent studies show that the majority of CEMP stars with [Fe/H] < –3.0 belong to the CEMP-no sub-class, characterized by the lack of strong enhancements in the neutron-capture elements (e.g., [Ba/Fe] < 0.0). The brightest EMP star in the sky, BD+44:493, with [Fe/H] = –3.8 and V = 9.1, is a CEMP-no star. It shares a common elemental-abundance signature with the recently discovered CEMP-no star having [Fe/H] < –7.8. The distinctive CEMP-no pattern has also been identified in high-z damped Lyman-alpha systems, and is common among stars in the ultra-faint dwarf spheroidal galaxies, such as SEGUE-1. These observations suggest that CEMP-no stars exhibit the nucleosynthesis products of the VERY first generation of stars. We discuss the multiple lines of evidence that support this hypothesis, and describe current efforts to identify the nature of the massive stellar progenitors that produced these signatures.


mark_rast_180614s
Thursday June 14, 2018
Prof. Mark Rast
University of Colorado

Abstract

Turbulent convection in stellar envelopes is critical to heat transport and dynamo activity. Modeling it well has proven surprisingly difficult, and recent solar and stellar observations have raised questions about our understanding of the dynamics of both the deep solar convection and the mean structure of the upper layers of convective stellar envelopes.  In particular, the amplitude of low wavenumber convective motions in both local area radiative magnetohydrodynamic and global spherical shell magnetohydrodynamic simulations of the Sun appear to be too high. In global simulations this results in weaker than needed rotational constraint and consequent non solar-like differential rotation profiles. In deep local area simulations it yields strong horizontal flows in the photosphere on scales much larger than the observed supergranulation, leaving the origin of the solar supergranular scale enigmatic. The problem is not confined to the Sun. When comparing computed oscillation frequencies to observations, mixing length models of stellar convection show too sharp a transition to the interior adiabatic gradient. This contributes to what asteroseismologists call the `surface effect' correction.

 We suggest that there is a common solution to these problems: convective motions in stellar envelopes are even more nonlocal than numerical models suggest. Small scale photospherically driven motions dominate convective transport even at depth, descending through a very nearly adiabatic or possible even somewhat subadiabatic deep convection zone. Convection of this form may meet Rossby number constraints set by global scale motions, and implies that the solar supergranulation is the largest buoyantly driven scale of motion in the Sun. We test this hypothesis using a suite of three-dimensional stellar atmosphere models, and can use it to both recover their mean stratification and estimate the supergranular scale on other stars


prev_riesgos_lab_psicosocial_180613s
Wednesday June 13, 2018
Miss María de la Paz Márquez Hernández
Oficina técnica de riesgos laborales-U.G.T.

Abstract

Charla divulgativa sobre cultura preventiva en el IAC


ismael_perez_fournon_juan_antonio_fernandez_ontiveros_180612s
Tuesday June 12, 2018
Ismael Pérez Fournon, Juan Antonio Fernandez Ontiveros
IAC/ULL

Abstract

In 2016, an international consortium led by SRON (Netherlands) in close collaboration with Japan (JAXA)
and with important Spanish participation (CAB, INTA and IAC/ULL) submitted the SPICA (SPace Infrared Telescope
for Cosmology and Astrophysics) proposal to ESA as part of the fifth call for medium-class missions (M5) in the
Cosmic Vision program. A total of 25 proposals competed for the M5 budget of 550 million euro. Together with two
other missions, THESEUS and EnVision, SPICA is now selected for the final round, in which three parallel
detailed studies will determine the best proposal. ESA is expected to select in 2021 its M5 mission, that
should be launched around 2030. SPICA has been designed to be extremely sensitive to infrared radiation,
much more than previous space infrared missions operating in the mid- and far-IR. In this talk we will review the
current status of SPICA and its instruments and describe the main science goals: the processes that regulate
the formation and evolution of galaxies and the formation of stars and planetary systems. In particular, we will discuss
how mid- to far-IR spectroscopic observations with SPICA could be exploited to understand key aspects in the chemical
evolution of galaxies, such as the assembly of nearby galaxies based on the spatial distribution of heavy element abundances,
the global content of metals in galaxies reaching the knee of the luminosity function up to z ∼ 3, and the dust composition
of galaxies at high-z. Possible synergies with facilities available in the late 2020s will be also discussed."


prev_riesgos_lab_edad_180605s
Tuesday June 5, 2018
Miss María de la Paz Márquez Hernández
Oficina técnica de riesgos laborales-U.G.T.

Abstract

Charla divulgativa sobre cultura preventiva en el IAC


Keith_Grainge_180601s
Friday June 1, 2018
Prof. Keith Grainge
University of Manchester

Abstract

The Square Kilometre Array (SKA) will be the world’s largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the big bang, how dark energy is accelerating the expansion of the Universe, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. This project envisages the construction of 133 15-m antennas in South Africa and 131,072 log-periodic antennas in Australia, together with the associated infrastructure in the two desert sites. In addition, the SKA is an exemplar Big Data project, with data rates of around 10 Tbps being transported out of the telescope to HPC facilities; and very exacting data processing requirements that are likely to need a combination of CPU, GPU and FPGA technologies to solve.


evanthia_hatziminaoglou_180522s
Tuesday May 22, 2018
Dr. Evanthia Hatziminaoglou
ESO (ALMA ARC)

Abstract

I will present ALMA Compact Array (ACA) 870 micron data of 28 infrared-bright SDSS quasars at redshifts 2 – 4 with estimated star formation rates beyond 1000 solar masses per year, the largest such sample ever observed with ALMA. The majority of the sources have unique ACA counterparts down to 3" - 4"resolution within the SPIRE 250 micron beam, centred on the SDSS coordinates. With only a handful of clear cases of multiple sources within the SPIRE beam, these results are in tension with works on the multiplicity of SPIRE 250 micron sources and sub-millimetre galaxies. I will present an extensive comparison between these findings and other recent works and will discuss the implications in the scenario supporting major mergers as triggers of the brightest AGN.


Henri_MJ_Boffin_180517s
Thursday May 17, 2018
Dr. Henri M. J. Boffin
ESO, Garching

Abstract

Binarity and mass transfer appear to play a key role in the shaping and, most likely, in the formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a dramatic increase in the number of post-common envelope binary central stars of PNe, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer - and accretion - prior to the common envelope phase.


prev_riesgos_lab_logros_180516s
Wednesday May 16, 2018
Miss María de la Paz Márquez Hernández
Oficina Técnica de Riesgos Laborales-UGT

Abstract

Charla divulgativa sobre cultura preventiva en el IAC


iacopo_bartalucci_180510s
Thursday May 10, 2018
Dr. Iacopo Bartalucci
CEA, Université Paris-Saclay

Abstract

We present a detailed study of the spatially resolved thermodynamic and hydrostatic mass profiles of the five most massive clusters detected at z~1 via the Sunyaev-Zel'dovich effect. These objects represent an ideal laboratory to test our models in a mass regime where structure formation is driven mainly by gravity. We present a method to study these objects that optimally exploits information from XMM-Newton and Chandra observations. The combination of Chandra’s excellent spatial resolution and XMM-Newton’s photon collecting power allows us to spatially resolve the profiles from the core to the outskirts, for the first time in such objects.  Evolution properties are investigated by comparison with the REXCESS  local galaxy cluster sample. Finally, we discuss the current limitations of this method in the context of  joint analysis of future Chandra and XMM large programs and, more generally, of  multi-wavelength efforts to study high redshift objects.



Upcoming talks

Featured talks