Found 60 talks archived in Particle astrophysics, physical data and processes

john_e_beckman_100204s
Thursday February 4, 2010
Prof. John E. Beckman
Instituto de Astrofísica de Canarias, Spain

Abstract

When we measure the electron density within an H II region using ratios of emission lines we find characteristic values in the range of 100-300 cm-3. But when we make these measurements using the total luminosity in Hα and the overall radial size of an H II region we find average values in the range 3-10. I will first explain how this discrepancy occurs, and then go on to show some measurements of electron densities in the H II regions of M51 (over 2500 regions) and the dwarf galaxy NGC 4449 (over 250 regions) using the second method, by Leonel Gutiérrez and myself. From these measurements we can infer how the electron density varies with the radial size of an individual region, and how it varies as we move from the center of the galaxy disc to the outside. Some interesting simple global relationships are found, which tell us about the interaction of star forming regions with their surroundings and how this interaction varies across the face of a galaxy.

elisa_delgado_mena_091202s
Wednesday December 2, 2009
Dr. Elisa Delgado Mena
Instituto de Astrofísica de Canarias, Spain

Abstract

The surface abundance of lithium on the Sun is 140 times less than protosolar, yet the temperature at the base of the surface convective zone is not hot enough to burn Li. A large range of Li abundances in solar type stars of the same age, mass and metallicity is observed, but theoretically difficult to understand. An earlier suggestion that Li is more depleted in stars with planets was weakened by the lack of a proper comparison sample of stars without detected planets. Here we report Li abundances for an unbiased sample of solar-analogue stars with and without detected planets. We find that the planet-bearing stars have less than 1 per cent of the primordial Li abundance, while about 50 per cent of the solar analogues without detected planets have on average 10 times more Li. The presence of planets may increase the amount of mixing and deepen the convective zone to such an extent that the Li can be burned. We also present Be abundances for a sample of stars with and without known planets and discuss the possible relation of these light element with the presence of planetary systems.

pasi_hakala_091126s
Friday November 20, 2009
Dr. Pasi Hakala
Tuorla Observatory, University of Turku, Finland

Abstract

I present some recent results from our Optical and NIR studies of five short period low-mass X-ray binaries (LMXB's; X1822-371, X1957+115, UW CrB, X1916-05 and X0614+091). Optical photometry and spectroscopy reveal some surprising results on the geometry and evolution of accretions discs in LMXB's. Based on our data, it is increasingly clear that accretion discs in these systems are far from being stable and must undergo substantial precession and/or warping behaviour on timescales less than a day in case of the shortest period systems.


alexander_burinskii_091119s
Thursday November 19, 2009
Prof. Alexander Burinskii
Theoretical Physics Laboratory, NSI, Russian Academy of Sciences, Moscow, Russia.

Abstract

Exact solutions of the Einstein-Maxwell equations in the Kerr-Schild formalism are discussed. We show that black hole horizon is unstable with respect to electromagnetic excitations. Contrary to smooth harmonic functions used in perturbative solutions, the exact solutions for electromagnetic excitations on the Kerr background have the form of singular twistor-beams which have very strong back reaction to metric and break the black-hole horizon, forming in it holes which allow radiation to escape interior of black-hole. As a result, under action of the external electromagnetic field the horizon may be covered by a set of fluctuating micro-holes, which corresponds to a semi-classical mechanism of Hawking radiation.

anibal_garcia_hernandez_091211s
Thursday November 12, 2009
Dr. Aníbal García Hernández
Instituto de Astrofísica de Canarias, Spain

Abstract

Asymptotic Giant Branch (AGB) stars are a principal source of gas and dust input into the interstellar medium, being an important driver of chemical evolution in galaxies. Rubidium is a key element to distinguish between high mass (~4-8 M⊙) AGB stars and low mass (~1-4 M⊙) AGBs - high mass AGBs are predicted to produce a lot of rubidium as a consequence of the genuine nucleosynthetic processes (the s-process) that characterise these stars. The Magellanic Clouds (MCs) offer a unique opportunity to study the stellar evolution and nucleosynthesis of AGB stars in low metallicity environments where distances (and so the star's luminosity) are known. We present the discovery of extragalactic rubidium-rich AGB stars in the MCs confirming that the more massive AGB stars are generally brighter than the standard adopted luminosity limit (Mbol~-7.1) for AGB's. In addition, massive MC-AGBs are more enriched in Rb than their galactic counterparts, as it is qualitatively predicted by the present theoretical models; the Rb over-abundance increase with increasing stellar mass and with decreasing metallicity. However, present theoretical models are far from matching the extremely high Rb overabundances observed.

rony_keppens_091105s
Thursday November 5, 2009
Prof. Rony Keppens
Centre for Plasma-Astrophysics, K. U. Leuven, Belgium

Abstract

I 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.

eckart_lorenz_091016s
Friday October 16, 2009
Dr. Eckart Lorenz
Max Planck Institute for Physics, Munich, Germany and Eidgenössische Technische Hochschule Zürich, Switzerland

Abstract

The window of very high energy (VHE) gamma-ray astronomy was only opened 20 years ago by the first observation of TeV gamma-rays from the CRAB nebula. Since then the field is rapidly expanding and we are approaching the first 100 VHE sources. In contrast to the many orders of magnitude larger flux of charged VHE Cosmic Rays, gamma-rays can be extrapolated back to their sources, the high energy particle processes mostly in stellar environments and thus allows us to retrieve basic information about the ultra-relativistic universe. In my talk I will shortly describe the gamma-ray production mechanisms related to these ultra relativistic processes, losses during the transport of gamma-rays through the universe and the detection methods. This is followed by a review of classes of gamma ray emitters and the relation to multi-wavelength respectively multi-messenger observations. Because of the very rich findings of the past years some restriction to highlight observations have to be made. The talk concludes with an outlook for the next years including possible prospects to build the so-called North-CTA (Cherenkov Telescope Array) on the Canary Islands.


brigitte_falkenburg_090917s
Thursday September 17, 2009
Dr. Brigitte Falkenburg
Technische Universität Dortmund, Germany

Abstract

History: astroparticle physics emerged from particle physics and connects it to astrophysics. Early particle physics was based on cosmic ray studies. The 1930s and 1940s were dominated by the discovery of new particles (positron, muon, pion) and the problems of their identification. In the 1950s, the era of the big accelerators began. Recent astroparticle physics started in the 1980s, with solar neutrino measurements and the investigation of cosmic rays by means of particle detectors.


piergiorgio_picozza_090910s
Thursday September 10, 2009
Prof. Piergiorgio Picozza
University of Roma, Italy

Abstract

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.


enric_palle_bago_090612s
Friday June 12, 2009
Dr. Enric Pallé Bago
Instituto de Astrofísica de Canarias, Spain

Abstract

Of the 342 planets discovered so far orbiting other stars, 58 'transit' the stellar disk, meaning that they can be detected by a periodic decrease in the starlight flux. The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated. As we get closer to finding analogues of Earth, an important consideration toward the characterization of exoplanetary atmospheres is what the transmission spectrum of our planet looks like. Here we report the optical and near-infrared transmission spectrum of the Earth, obtained during a lunar eclipse. Some biologically relevant atmospheric features that are weak in the reflected spectrum (such as ozone, molecular oxygen, water, carbon dioxide and methane) are much stronger in the transmission spectrum, and indeed stronger than predicted by modeling. We also find the fingerprints of the Earth's ionosphere and of the major atmospheric constituent, diatomic nitrogen (N2), which are missing in the reflected spectrum. Our results indicate that the technique of transit spectroscopy of rocky planets may be a very powerful tool for exoplanet atmospheric characterization, and is likely to provide the first detection of a habitable exobiosphere.