INAF – IASF Bologna

torek, 29. 5. 2012, ob 14h v F5

Given their huge isotropic-equivalent luminosities, up to more than 10^54 erg/s, and their redshift distribution extending up to more than z=8, Gamma-Ray Bursts (GRB) are in principle a powerful tool for measuring the geometry and expansion rate of the Universe. However, they are not standard candles, given that their luminosities span several orders of magnitude, even when considering possible collimation angles.

In the recent years, several attempts to exploit the correlation between the photon energy at which the nu*F_nu spectrum peaks (”peak energy”) and the radiated energy (or luminosity) for “standardizing” GRBs and using them as tools, complementary to other probes like SN Ia, BAO and the CMB, for the estimate of cosmological parameters have been made. These studies show that already with the present data GRBs can provide a significant and independent confirmation of Ω_M~0.3 for a flat ΛCDM universe and that the measurements expected from present and next GRB experiments (e.g. Swift, Fermi/GBM, SVOM) will allow us to constrain Ω_M, Ω_Λ and, in particular, to get clues on dark energy properties and evolution.

v ponedeljek 28. maja 2012, ob 16:15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

The impact of, and evidence for, stellar migration in disk galaxies

Dr. Victor Debattista, Jeremiah Horrocks Institute, University of Central Lancashire, UK

Until recently it was thought that stars remain at the same radius at which they are born all their lives. The realisation that spiral arms can move stars around in radius, without appreciably heating the disks, changed all that. This result is driving a paradigm shift in our understanding of disk galaxies and how they are assembled. Stellar migration complicates efforts at galactic archaeology, which is one of the principal goals of many large upcoming surveys, such as LSST and Gaia.
Migration has important consequences for interpreting the implied gas accretion rate, the Galactic orbit of the Sun, the fossil evidence of stellar accretion, and the Galactic “habitable zone”. Thus assessing to what extent stellar migration has affected the Milky Way’s disc is vitally important if we are to understand galaxy formation.

IZJEMOMA v torek 22. maja 2012, ob 16:15 v predavalnici F1

Pred predavanjem so vsi udeleženci vabljeni na čaj!

Interdisciplinary Science in Astronomy: A review

Dr. Pavlos Protopapas, Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, USA

Are we ready to let machines do the work so we can now concentrate on the science questions? Have we reached the point where statistical and machine learning methods have become useful tools rather than a nuisance and the practice of the few? We will present four examples where significant progress has been made and the interdisciplinary practices have brought fruitful results. These include automatic classification, Bayesian parameter inferences, event detection and anomaly detection, and design of surveys and followups.

INAF – OAPD

petek, 11. 5. 2012, ob 11h v F7 (*)

Despite the impressive advancements occurred in recent years, the existence of Ultraluminous X-ray sources (ULXs) represents still a theoretical challenge in modern Astrophysics. Likely the majority of them are the most extreme version of an X-ray binary, with a Black Hole in a mass range or in an accretion regime so far unexplored.

Here I will review our present understanding of ULXs, discuss some potential pathways to their formation and summarize possible future observational and theoretical prospects.

(*) POZOR: sprememba dneva/ure/predavalnice!

INAF – OATS

ponedeljek, 7. 5. 2012, ob 13h v F4 (*)

CLASH (Cluster Lensing And Supernova survey with Hubble), is one of the three selected Hubble Space Telescope Multi-Cycle Treasury Program. The main aim of CLASH is to place new constraints on the fundamental components of the cosmos, namely baryons, dark matter, and dark energy, via HST ACS/WFC3 multiband imaging of a selected sample of clusters of galaxies.

After introducing its goals, and current observational status, I will present the most recent results and potential application.

(*) POZOR: sprememba dneva/ure/predavalnice!

Najnovejše rezultate, o katerih bo govora v predavanju, si lahko preberete v članku na arhivih astro-ph.

INAF – OATS

ponedeljek, 23. 4. 2012, ob 13h v F4 (*)

Extreme metal-poor stars are records of the chemical composition of the young Galaxy and provide information on the early chemical evolution in the Universe and on the type of the first stars. They are very rare and current theories predict the existence of a threshold in metallicity to form low mass stars that could be observed today.

We developed an automatic procedure to select metal poor candidates from the Sloan Digital Sky Survey. Some of these were observed during the GTO of the spectrograph X-Shooter and their metallicity confirmed. We also succeeded in finding out a record metal-poor star. Some of the implications of this discovery will be discussed.

(*) POZOR: sprememba dneva/ure/predavalnice!

Laboratoire Universe et Théories, CNRS (France)

torek, 6. 3. 2012, ob 14h v F3

Stellar-type black holes (of the order of 10 solar masses) are supposed to be born during the collapse of very massive stars. As even an approximate limit on mass and metalicity of main-sequence progenitors, discriminating between neutron star and black hole formation, is poorly known, it is very important to perform numerical simulations in order to understand the physical processes at work during the stellar core-collapse: hydrodynamics, relativistic gravity, neutrino transport, nuclear matter properties, … In this talk, I shall present a ongoing project to simulate these events. I shall start with a general overview of the core-collapse context, introducing then the general-relativistic formalism to compute the gravitational field and to simulate black holes, before giving some numerical tools (in particular spectral methods) for the solution of partial differential equations arising within this model.

Max-Planck-Institute für Radioastronomie, Bonn, Germany

torek, 28. 2. 2012, ob 14h v F5

The solar system was not born in a such sparse environment as it is located in today but as part of a relatively dense star cluster. It will be shown how one comes to that conclusion and how this shapes our knowledge about the early history of the solar system. This cluster environment influenced various properties of the solar system like its composition, size and the orbital parameters of some of its constituting bodies. Recently it has been demonstrated that in the Milky Way such massive clusters as that of the solar birth cluster clusters only form in two forms – starburst clusters and leaky clusters. Here it will be investigated how likely it is that our own Solar System has formed in one of these two cluster environments and how this gives us a much more precise picture of the first 20 Myr of our solar system.

Univerzitetni Observatorij München

ponedeljek, 16. 1. 2012, ob 11h v F6

(POZOR! neobičajen termin)

Meritve iz fizike delcev še vedno ne izključujejo okolice nekaj kiloelektronvoltov za maso delcev temne snovi. Takšna masa bi pomenila, da termični učinek teh delcev na porazdelitev mase v zgodnjem vesolju ni zanemarljiv! Temno snov, ki lahko zatre perturbacije gostote na majhnih razdaljah, imenujemo topla temna snov (angl. Warm Dark Matter – WDM). Nerelativistične delce hladne temne snovi (angl. Cold Dark Matter ali CDM) ločimo od tople temne snovi po njihovi porazdelitvi hitrosti v zgodnjem vesolju. Učinek tople temne snovi je razviden kot zmanjšanje spektra moči perturbacij na majhnih skalah. Na žalost pa se ta “odtis” močno zmanjša med nelinearno evolucijo porazdelitve mase v vesolju. Modeliranje nelinearnih struktur dandanes je že v “hladnem” scenariju nepopolno, v “toplem” scenariju pa je še v povojih. Vendar pa vstop v dobo kozmologije visoke natančnosti zahteva izpopolnitev teorij, če se želimo izogniti omejitvam sistematičnih napak iz teorije in slediti natančnosti eksperimentov.