SEMINAR ANNOUNCEMENT: OATS-DAUT SEMINAR - Wednesday December 5th at 12:00 noon (Villa Bazzoni)

[Gabriella Schiulaz]

I announce you this week seminar:

*********************************************************** 
                  OATS-DAUT SEMINAR 
*********************************************************** 

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. 
*********************************************************** 
contact: Simone Recchi (OATS) 




Next  seminars (in December):

*********************************************************** 
OATS-DAUT SEMINAR 
*********************************************************** 
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 (PLEASE NOTE DAY)
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. 
*********************************************************** 
contact: Paolo Molaro (OATS) 


 
*********************************************************** 
OATS-DAUT SEMINAR 
*********************************************************** 
Speaker: Sebastian Lopez (Universidad de Chile, Santiago) 
Title: Probing cluster galaxies with background QSOs 
Date: Thursday, December 13th, 2007 
Time: 12:00 
Venue: Villa Bazzoni 

Abstract: 
I will present results of the first survey of intervening MgII absorption systems associated with high-z cluster galaxies. We have investigated the incidence (dN/dz) of MgII absorbers in 〈z〉= 0.6 cluster galaxies from the Red-Sequence Cluster Survey. While strong (W_0>1.0 Å) absorbers show a significant excess (up to 10x), weak (W_0<0.3 Å) absorbers conform to the field statistics. We argue that this dichotomy could be explained if cluster galaxies that give rise to weak MgII absorption have their cold halos truncated as a consequence of environmental effects. 
*********************************************************** 
contact: Paolo Molaro (OATS) 



 
*********************************************************** 
OATS-DAUT SEMINAR 
*********************************************************** 
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.
*********************************************************** 
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