Talks given by high profile astronomers and scientists.
AbstractSpectroscopic observations of novae date back a century, and the fundamental nature of the outburst has been understood for 50 years. Yet, recent observations suggest possible major modifications to the standard nova paradigm. A high-resolution spectroscopic survey of novae has revealed short-lived heavy element absorption systems near maximum light consisting of Fe-peak and s-process elements. The absorbing gas is circumbinary and it must pre-exist the outburst. Its origin appears to be mass ejection from the secondary star, implying large episodic mass transfer events from the secondary that initiate the nova outburst. The spectroscopic evolution of novae is interpreted in terms of two distinct interacting gas systems in which the bright continuum is produced by the outburst ejecta but absorption and emission lines originate in gas ejected by the secondary star in a way that may explain dust formation and X-ray emission from novae.
AbstractI will present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. In a related investigation, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. In that study, we concentrate on morphological features of the bow shock and the jet beam, for various jet Lorentz factors and magnetic field helicities. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. For the high speed jets considered, significant jet deceleration only occurs beyond distances exceeding hundred jet radii, as the axial flow can reaccelerate downstream to internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.
AbstractFor a long time radiative MHD simulations of entire sunspots from first principles were out of reach due to insufficient computing resources. Over the past 4 years simulations have evolved from 6x6x2 Mm size domains focusing on the details of umbral dots to simulations covering a pair of opposite polarity sunspots in a 100x50x6 Mm domain. In this talk I will discuss the numerical challenges encountered in comprehensive radiative MHD simulations of active regions and summarize the recent progress. Numerical simulations point toward a common magnetoconvective origin of umbral dots and filaments in the inner and outer penumbra. Most recent simulations also capture the processes involved in the formation of an extended outer penumbra with strong horizontal outflows averaging around 5 km/s in the photosphere. I will discuss in detail the magneto convective origin of penumbral fine structure as well as the Evershed flow. I will conclude with a brief summary of recent helioseismic studies based on realistic MHD simulations as well as inferences on the sub surface structure of sunspots.
New results on the antiproton-to-proton and positron-to-all electron ratios over a wide energy range (1 – 100 GeV) have been obtained by the PAMELA mission. These data are mainly interpreted in terms of dark matter annihilation or pulsar contribution. The instrument PAMELA, in orbit since June 15th, 2006 on board the Russian satellite Resurs DK1, is daily delivering to ground 16 Gigabytes of data. The apparatus is designed to study charged particles in the cosmic radiation, with a particular focus on antiparticles for searching antimatter and signals of dark matter annihilation. A combination of a magnetic spectrometer and different detectors allows antiparticles to be reliably identified from a large background of other charged particles. The talk will illustrate the most important scientific results obtained by PAMELA, together with some of the more recent theoretical interpretations.
AbstractAEGIS (All-wavelength Extended Groth strip International Survey: aegis.ucolick.org) is on-going survey that opens up new views of the development of galaxies and AGN's at redshifts z about 1. AEGIS is panchromatic like GOODS, with coverage ranging from X-ray to radio, and nearly as deep but more panoramic by covering a 4x larger region. Its backbone is the most Northern (accessible to the GTC) of the four fields of the DEEP2 Keck spectroscopic survey, which provides not only precision redshifts that yield reliable pairs, groups, and environments, but also internal kinematics and chemical abundances. After an overview of the DEEP and AEGIS surveys, I will share some recent highlights, including using a new kinematic measure for distant galaxies to track Tully-Fisher-like evolution; discovering metal poor, massive, luminous galaxies; finding ubiquitous galactic gas outflows among distant star forming galaxies; and exploring the nature of distant x-ray AGNs.
AbstractThe SAURON survey has revised our view of early type galaxies discovering that central disks and multiple kinematic components are common; 75% of the sample have extended ionized gas, often misaligned with the stars; half of S0s and 25% of Es have intermediate age populations. There is a tight relationship between the escape velocity and Mg line strength which holds both within and between galaxies raising uncomfortable questions for hierarchical assembly. Many of the properties of ETGs are related to a measure of their specific angular momentum : slow rotators are triaxial, close to spherical, isotropic and frequently exhibit decoupled central kinematics, whereas fast rotators are intrinsically flatter, oblate, have disk-like (anisotropic) kinematics and often have Mg enhanced disks. In general the slow rotators are more massive and have older populations Only half of the elliptical galaxies exhibit slow rotation, the remainder have stellar disks showing that the historic division by morphological class is physically misleading. We suggest that the contrasting physical properties of fast and slow rotators arise through distinct assembly histories with slow rotators forming in gas free, dry mergers and fast rotators retaining a disk component through a dissipative merger.
En una parte preliminar se recordarán unos pocos hechos experimentales obtenidos durante las últimas décadas, con énfasis en fenómenos puramente cuánticos como el entrelazamiento y el teletransporte, y también algunos hechos matemáticos elementales, con énfasis en las matrices hermíticas y unitarias. En una segunda parte se presentará un modelo matemático de la noción de q-ordenador y de conceptos subordinados como puertas q-lógicas, q-computación y q-algoritmos programas, con énfasis en los ejemplos, incluyendo la q-transformada de Fourier y el q-algoritmo de Shor de factorización en tiempo polinómico de números enteros positivos. A continuación se sumarizará un enfoque axiomático de la mecánica cuántica y se usará para relacionar las q-nociones anteriores con sus posibles realizaciones físicas, con énfasis en algunos problemas abiertos y en posibles líneas de trabajo futuro. La base de este material es la tesis de máster de Juanjo Rué, "Un modelo matemático para la computación cuántica: fundamentos, algoritmos y aplicaciones" (julio de 2007), dirigida por Lluís Torner y el conferenciante.
AbstractThe COSMOS survey is the largest high redshift galaxy evolution survey ever done -- imaging 2 square degrees with all major space-based and ground based observatories. I will describe the key data in the survey and then present recent results on large-scale structures, the dark matter distributions and galaxy evolution.
AbstractThe standard model of cosmology -- the ``Lambda cold dark matter'' model -- is based on the idea that the dark matter is a collisionless elementary particle, probably a supersymmetric particle. This model (which mostly dates back to an early workshop in Santa Barbara in the 1980s) has been famously verified by observations of the cosmic microwave background radiation and the large-scale distribution of galaxies. However, the model has yet to be tested conclusively on the small scales appropriate to most astronomical objects, such as galaxies and clusters. I will review our current understanding of the distribution of dark matter on small scales which derives largely from large cosmological N-body simulations and I will discuss prospects for detecting dark matter, either through its gravitational effect on galaxies and clusters or, more directly, through gamma-ray annihilation radiation.
- TODAY: The Pristine survey: An efficient search for extremely metal-poor starsDr. Kris YouakimTuesday January 23, 2018 - 12:30
- On the evolution of rotation and magnetism from solar-like stars to red giants using Kepler dataDr. Savita MathurThursday February 1, 2018 - 10:30