Recent Talks

By providing information on distances and proper motions for one billion stars, the Gaia satellite allows us to investigate the major unsolved challenges in galaxy formation: the nature of dark matter, the origin of Galactic spiral activity and its relation to the bar, and more generally the history of the Milky Way. 
My research aims to develop a theoretical approach to modeling and exploiting the big data and address problems at the forefront of Galactic Dynamics at various scales. What is the origin of the spiral activity in the Milky Way? How are all of these perturbations to the structure of the Galaxy coupled to each other directly and through the dark-matter halo?  I will also present my ongoing work on statistical techniques of big-data analysis and advanced numerical simulations used to interpret the evolution of star clusters and discover streams in the stellar disk of the Milky Way.

Principios del siglo XXI, en una fecha por determinar. Una desconocida deja en la biblioteca del IAC siete cuadernos de observaciones astronómicas realizadas más de cien años antes (1886 – 1891), en Madrid y Santa Cruz de Tenerife, por un tal Juan Valderrama y Aguilar (JVyA). Los cuadernos duermen en la biblioteca otros diez años hasta que los descubrimos por casualidad. Nos sorprende la calidad y meticulosidad de los dibujos que ilustran los cuadernos, el hecho de que trabajos de Juan Valderrama son citados en el ADS (Astrophysics Data System) y, sobre todo, el que siendo nosotros astrónomos profesionales del IAC, jamás hubiéramos oído hablar de él. ¿Podría haber vivido en Santa Cruz un astrónomo del que la historia oficial de la astronomía Canaria no tuviera noticia alguna? La respuesta a la pregunta anterior es "sí". JVyA es un completo desconocido para la historia oficial, pero tiene una biografía científica digna de ser recordada. Fuera de los ambientes universitarios y de la ciencia oficial, JVyA estaba, sin embargo, bien conectado con el mundo de la astronomía moderna de la época. Suyo es el que puede ser considerado el primer artículo de astronomía publicado por un canario en una revista internacional (Valderrama, 1886, L’Astronomie, Vol. 5, Pág. 388), y lo hace cuando tiene sólo 17 años. Hemos escrito una breve biografía de JVyA que reivindica su figura de astrónomo, y que será publicado por el Cabildo de Tenerife. En la charla queremos presentar a JVyA así como alguna de sus contribuciones astronómicas.

I will review the properties of nearby early-type galaxies and galaxy clusters showing the most interesting observed parallelisms, such as the Sersic behavior of the light profiles, the color-magnitude diagram and the main scaling relations. I will show a comparison with the data extracted from the ILLUSTRIS simulation and present the constraints to the star formation history that are necessary to obtain a reliable distribution of galaxies in the color-magnitude diagram.

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.

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

Charla divulgativa sobre cultura preventiva en el IAC

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."

Charla divulgativa sobre cultura preventiva en el IAC

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.

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.