Seminar Announcement -OATS-DAUT SEMINAR - Wednesday, November 21st, at 12:00 noon (Villa Bazzoni)

[Gabriella Schiulaz]

I announce you this week's OAT-DAUT seminar:

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                OATS-DAUT SEMINAR 
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Speaker: Fabrizio Nicastro (INAF/Oss. Astr. Monteporzio) 

Title: The Missing Baryon Hunt 

Date: Wednesday, November 21st, 2007 
Time: 12:00 
Venue: Villa Bazzoni (Via Bazzoni, 2)

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Abstract: 
Despite recent progress in cosmology in assaying the composition of the energy-mass budget of the Universe, within the framework of our Standard Cosmological Model (SCM), very little is still known about nature and origin of 95 % of these constituents: dark Energy and dark Matter. These have the name 'dark' mainly to label our inability to directly detect and identify them. Less well known is that the situation is only conceptually better for the remaining 5 % of Omega: these are baryons, i.e. the constituents of the ordinary matter of which stars, planets, and ourselves are made. Today we can account for less than 50% of the baryons that the SCM predicts, implying that at least 50 % of the baryons are now missing. Finding and counting these baryons is therefore vital to our understanding of the Universe, and a necessary condition to validate the SCM. After a brief introduction of the problem, I will review all the different and independent pieces of evidence for these baryons, and will show that the majority of them is indeed still missing. In the second part of my talk I will then try to identify new promising lines of research, which will hopefully allow us in the near future to hone our techniques of hunt and to converge toward a possible solution of this important and still open astrophysical problem. 
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contact: Pierluigi Monaco (DAUT) 



Future Seminars (November and December)

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OATS-DAUT SEMINAR 
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Speaker: Martin Wendt (Hamburg University, Germany) 
Title: Variability of the proton-to-electron mass ratio on cosmological scales - methods and shortcomings 

Date: Wednesday, November 28th, 2007 
Time: 12:00 
Venue: Villa Bazzoni 

Abstract: 
The idea of varying fundamental physical constants is probably as old as the very first definition of constants. The interest in varying constants increased greatly since the 1980s due to new developments in the Kaluza-Klein and supergravity models of unifications of all physical interactions. Contemporary theories of fundamental interactions, particularly those subsumed as String-theories allow for all kinds of variations of fundamental constants. It is up to cosmology to achieve first estimates and constraints of possible variations since nowadays laboratory experiments lack the precision and spatial or temporal coverage. The methods and procedures involved in the determination of a possible variation of the proton-electron mass ratio on cosmological time scales will be shortly introduced and exemplified. New claims on a significant variation have recently been made. The ambiguity of the results will be critically examined on the basis of an independent data analysis and some of the shortcomings of the methods involved are discussed. 
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contact: Paolo Molaro (OATS) 


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OATS-DAUT SEMINAR 
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Speaker: Giancarlo Pace (ARIES, Nainital, India) 
Title: The cosmological lithium discrepancy and how observations in open clusters can be of some help 

Date: Wednesday, December 5th, 2007 
Time: 12:00 
Venue: Villa Bazzoni 

Abstract: 
Lithium is one of the few elements produced during the Big Bang, and then it is mostly destroyed in stars. The primordial lithium abundance have been estimated by means of: a) Big Bang nucleosynthesis models combined with WMAP observations; and b)lithium abundances in old, pop II stars, more precisely those in the so called Spite plateau. The two estimations differ of a factor two. This factor, when compared to the enormous range that lithium abundance in Galactic objects spans (two order of magnitude from the Sun to the interstellar medium) is widely considered an important confirmation that both cosmological standard models and stellar abundance determinations have sound basis. And yet an explanation has to be found for it: is the Big Bang nucleosynthesis model to be corrected, or is the atmospheric content of Spite plateau stars different from the primordial one? Both hypothesis have been suggested in the literature. Who is right? After extensively reviewing this topic, I will speak about the role of observations in open clusters in solving the dilemma, an observation campaing and the latest results of Randich, Pace, Pastori and Bragaglia on the old open cluster Berkley 32. 
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contact: Simone Recchi (OATS) 





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OATS-DAUT SEMINAR 
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Speaker: Maxim Yu. Khlopov (Moscow Engineering Physics Inst. and Center for Cosmoparticle Physics, Moscow) 
Title: Nonstandard nucleosynthesis as cosmological consequence of particle theory 

Date: Monday, December 10th, 2007 
Time: 12:00 
Venue: Villa Bazzoni 

Abstract: 
Cascades of energetic particles from decay of metastable primordial particles in early Universe interact with nuclei formed in SBBN and influence light element abundance. Negatively charged metastable particles can bind with He-4 in atom-like ion, strongly influencing the rate of SBBN nuclear reactions. It provides constraints on on the particles and models, which predict them, from observation of light element abundance. Composite dark matter hides stable heavy charged particles in neutral atom-like states. Physical examples of such stable particles are given. In the early Universe formation of composite dark matter is accompanied by formation of various fractions of exotic matter, which are severely constrained by observations. Observational consequences of various composite dark matter models (in particular, an interesting realization of warm dark matter scenario) as well as the possibilities of direct search of its charged constituents in cosmic rays and at accelerators are discussed. The necessary prediction of such models is existence of an atom like bound system of negatively charged particle Q^{-2} with He, which catalyzes nuclear transformations and, in particular, gives rise to formation of primordial heavy elements in the Universe after helium is formed in SBBN. 
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contact: Paolo Molaro (OATS) 





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OATS-DAUT SEMINAR 
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Speaker: Maria Polletta (Institut d'Astrophysique de Paris) 
Title: Active Galactic Nuclei in the infrared: identification, energetic and properties of the obscuring material 

Date: Wednesday, December 19th, 2007 
Time: 12:00 
Venue: Villa Bazzoni 

Abstract: 
The properties (spectral energy distributions, redshifts and luminosities) of AGN samples selected using infrared, X-ray and radio data, separately, are compared to asses the selection biases of each sample. By taking into account those selection effects, we estimate the total number of AGN present in infrared-selected samples and compare it with predictions from various models. The analysis of the properties of the various samples shows that a mid-infrared selection can efficiently find obscured QSOs at high redshifts. By applying such a selection technique, we collect a remarkable sample of extremely luminous and heavily obscured AGNs at z~2. We model their spectral energy distributions and infrared spectra with clumpy torus models. The models indicate that optical and mid-infrared obscuration is caused by dust in a torus or in the host galaxy. Overall we find that the ratio between obscured and unobscured AGN at mid-infrared luminosities >10^12 Lsun and z~2 is 1.5-1.9:1, but only 37-40% of these QSOs are obscured by the torus, constraining the torus half opening angle to be about 67 degrees. This value is significantly larger than found in far-infrared selected samples of AGN at lower luminosity (~46 degrees), supporting the receding torus scenario. Large far-infrared luminosities, above the predictions of the torus model, are measured in a sub-set of these obscured QSOs, implying extreme star formation rates (600-3000 Msun/yr) if powered by a starburst. The implications of our results on current AGN models are discussed and predictions for future Herschel observations of these objects are presented.
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contact: Paolo Tozzi (OATS) 




For additional information on OAT seminars see:
http://adlibitum.oats.inaf.it/seminari/

Gabriella Schiulaz
segreteria OAT
Phone: 040-3199241
schiulaz at oats.inaf.it
segreteria at oats.inaf.it