Iron Line Diagnostics for the GRS 1915+105 Black Hole

The properties of the broad Fe line detected in two BeppoSAX observations of the microquasar GRS 1915+105 are summarized.Comment: 4 pages, 2 figures. Proc. of the II BeppoSAX Meeting: "The Restless High-Energy Universe" (Amsterdam, May 5-8, 2003), E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Ed

Supernovae astrophysics from Middle Age documents

The supernova explosion of 1054 AD, which originated the Crab Nebula and Pulsar, is probably the astronomical event which has been most deeply studied by means of historical sources. However, many mysteries and inconsistencies, both among the different sources and between what is deduced by the historical records and the present day astronomical data, are demanding extraordinary efforts by theoretical astrophysicists in order to put all the data in a meaningful framework. An accurate analysis of the historical sources, like the one we are presenting here, may contribute to solve some of these problems.Comment: in: Proc. of the IAU Symposium no.230, "Populations of High Energy Sources in Galaxies", held in Dublin (Ireland), August 15-19, 2005. Evert J.A. Meurs & G. Fabbiano, eds. (in press

Variable line profiles due to non-axisymmetric patterns in an accretion disc around a rotating black hole

We have explored spectral line profiles due to spiral patterns in accretion discs around black holes. A parametrization was employed for the shape and emissivity of spiral waves, which can be produced by non-axisymmetric perturbations affecting the disc density and ionization structure. The effects of the light-travel time, energy shift, and gravitational focusing near to a rotating black hole were taken into account. A high-resolution ray-tracing code was used to follow the time variations of the synthetic line profile. A variety of expected spectral features were examined and the scheme applied to a broad iron line observed in MCG-6-30-15.Comment: 11 pages (LaTeX), 7 figures (EPS); PASJ accepte

Searching for multiple populations in massive young and intermediate age clusters

Among the many mysteries of our Universe, one still unanswered question is how globular clusters form. Globular clusters are very dense agglomerates of hundreds of thousands of stars and they host some of the oldest known stars in our Universe. Since they are luminous, old and found in all massive galaxies, they are a fundamental piece of the puzzle to understand galaxy formation and evolution processes. Traditionally, globular clusters were thought to be simple stellar systems, in which all stars were born at the same time and have the same chemical composition. %Therefore, globular clusters have been considered the perfect laboratory to study how stars evolve. However, in the last few decades, it has been shown that stars within a given globular cluster display inhomogeneities in their chemistry. Every massive old globular cluster located in the Milky Way, for which high precision and deep observations were obtained, was found to host several different stellar populations, i.e. multiple populations. Each stellar population is characterized by specific chemical patterns observed in the atmospheres of individual stars. Only certain elements are found to vary, and they do not do so randomly, but rather the variations are observed to correlate between the elements. The stellar population that has enhanced nitrogen (N) content, also has enhanced sodium and helium abundances but has a depletion in carbon and oxygen, to cite a few examples. At the same time, the iron content is found to be constant among the different populations. Such chemical patterns are often called anomalies. More interestingly, it seems like such chemical anomalies are unique to globular cluster systems, i.e. dense stellar systems, since they are basically not found in other stars located in the field. Knowing how such multiple populations form and how they impact the evolution of globular clusters is crucial to understand the formation of stars and clusters themselves and, more broadly, the formation and evolution of galaxies. Many theoretical scenarios have been proposed to explain the origin of the chemical anomalies in globular clusters. Most models treat the origin of this phenomenon as multiple events of star formation. In such models, a first generation of stars forms from the collapse of a giant molecular cloud which is homogeneous in its chemical composition. The winds of the massive stars from this first generation sink in the centre of the cluster to collapse and provide material for a second generation of stars, which then forms with a different chemical composition. While theoretically straightforward, such scenarios (which involve many types of massive stars) fail in reproducing many of the observed properties of multiple populations in globular clusters. Hence, the formation mechanism for the origin of multiple populations remains an open question. Most studies of multiple populations focused only on ancient globular clusters, aged up to $\sim$13 Gyr. However, many dense and massive younger star clusters are observed in nearby galaxies. Is the multiple populations phenomenon limited to the ancient globular clusters, i.e. could this be a cosmological effect? The goal of this thesis has been expanding the search for multiple populations to star clusters that are significantly younger than the old globular clusters, i.e. up to 10 times younger. Indeed, a compelling line of investigation is to look for multiple populations depending on certain global properties of the clusters, such as age, mass, metallicity. The first major result presented in this work is that multiple populations are found also in the young clusters, down to $\sim$2 Gyr old objects, showing that the phenomenon of multiple populations is not only restricted to the early Universe. Another interesting result I report is that the extent of the multiple populations (in chemical abundance spread) is a strong function of age, with older clusters having larger chemical variations. Additionally, I show that there is no difference in age between the populations in a young star cluster. Such results represent fundamental constraints for the origin of multiple populations and might point towards a new and fresh direction into the onset of this complex phenomenon. An important and related question is whether the young massive star clusters are the same type of stellar systems as the ancient globular clusters, just observed at a different stage of their lifetimes. If confirmed, this could provide important constraints on star cluster formation studies. Therefore, in this thesis I explored clusters at younger ages in order to address the fundamental question whether the star (and cluster) formation conditions were different in the early Universe. The results presented here represent an important hint that ancient and young clusters share the same origin and are only separated in age. I show that star clusters do not require special conditions in which to form, so that they can be used as tracers for the formation and evolution of galaxies

On the Nature of Hidden Broad Line Regions in Seyfert 2 Galaxies

We consider the sample of Tran (2001) to study the X-ray properties of Seyfert 2 galaxies with and without polarized broad lines.Comment: 4 pages. To appear in the Proceedings of the 5th Italian AGN Meeting "Inflows, Outflows and Reprocessing around black holes" (2002), online edition (http://www.merate.mi.astro.it/~gabriele/agn5/agn5.html

The great excuse: how Renzi could exploit the UK’s EU deal

The conclusion of the UK’s renegotiation has obvious implications for British party politics, but what impact has the deal had on domestic politics in other EU countries? Bruno Marino and Nicola Martocchia Diodati write on reactions to the deal in Italy. They state that while the response has been mixed among Italian parties, Matteo Renzi is likely to view the deal as an opportunity to push for European concessions over the ongoing migration crisis