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In the last 20 years our understanding of the millisecond pulsar population changed dramatically. Thanks to the large effective area and good time resolution of the NASA X-ray observatory Rossi X-ray Timing Explorer, we discovered that neutron stars in Low Mass X-ray Binaries (LMXBs) spins at frequencies between 200 and 750 Hz, and indirectly confirmed the recycling scenario, according to which neutron stars are spun up to millisecond periods during the LMXB-phase. In the meantime, the continuous discovery of rotation-powered millisecond pulsars in binary systems in the radio and gamma-ray band (mainly with the Fermi Large Area Telescope) allowed us to classify these sources into two "spiders" populations, depending on the mass of their companion stars: Black Widow pulsars, with very low-mass companion stars, and Redbacks, with larger mass companion stars possibly filling their Roche lobes without accretion of matter onto the neutron star. It was soon regained that millisecond pulsars in short orbital period LMXBs are the progenitors of the spider populations of rotation-powered millisecond pulsars, although a direct link between accretion-powered and rotation-powered millisecond pulsars was still missing. In 2013 the ESA X-ray observatory XMM-Newton spotted the X-ray outburst of a new accreting millisecond pulsar (IGR J18245-2452) in a source that was previously classified as a radio millisecond pulsar, probably of the Redback type. Follow up observations of the source when it went back to X-ray quiescence showed that it was able to swing between accretion-powered to rotation-powered pulsations in a relatively short timescale (few days), promoting this source as the direct link between the LMXB and the radio millisecond pulsar phases. Following discoveries showed that there exists a bunch of sources which alternates X-ray activity phases, showing X-ray coherent pulsations, to radio-loud phases, showing radio pulsations, establishing a new class of millisecond pulsars, the so-called transitional millisecond pulsars. In this review we describe these exciting discoveries and the properties of accreting and transitional millisecond pulsars, highlighting what we know and what we have still to learn about in order to fully understand the (sometime puzzling) behaviour of these systems and their evolutive connection.

A rich phenomenology has been accumulated over the years regarding accretion and ejection in black-hole X-ray transients (BHTs). Here we summarize the current observational picture of the outbursts of BHTs, based on the evolution traced in a hardness - luminosity diagram (HLD), and we offer a physical interpretation with two assumptions, easily justifiable. The first is that the mass-accretion rate to the black hole in a BHT outburst has a generic bell-shaped form. This is guaranteed by the observational fact that all BHTs start their outburst and end it at the quiescent state, i.e., at very low accretion rate. The second assumption is that at low accretion rates the accretion flow is geometrically thick, ADAF-like, while at high accretion rates it is geometrically thin. Both, at the beginning and the end of an outburst, a strong poloidal magnetic field develops locally in the ADAF-like part of the accretion flow, and this explains naturally why a jet is always present in the right part of the HLD. "Memory" of the system explains naturally why BHTs traverse the q-shaped curves in the HLD always in the counterclockwise direction and that no BHT is expected to ever traverse the entire curve in the clockwise direction. The only parameter in our picture is the accretion rate.

The Rembrandt basin is the largest well-preserved impact feature in the southern hemisphere of Mercury. Its smooth volcanic infill hosts wrinkle ridges and graben, and the entire basin is cross-cut by the Enterprise Rupes scarp system. On the basis of the Model Production Function crater chronology, our analysis shows that the formation of the Rembrandt basin occurred at 3.8±0.1 Ga during the Late Heavy Bombardment, consistent with previous studies. We also find that the smooth plains interior to the basin were emplaced between 3.7 and 3.6±0.1 Ga, indicative of a resurfacing event within the Rembrandt basin that is consistent with the presence of partially buried craters. These youngest plains appear temporally unrelated to basin formation, and so we regard their origin as likely to be due to volcanism. We identify the same chronological relationship for the terrain cross-cut by Enterprise Rupes to the west of the basin. Therefore, volcanic activity affected both the basin and its surroundings, but ended prior to the majority of basin- and regional-scale tectonic deformation. If Enterprise Rupes formed prior to the Rembrandt basin, then regional-scale tectonic activity along this structure might have lasted at least 200 myr.

Just after the WWII Astronomy started to live its “Golden Age”, not differently to many other sciences and human activities, especially in the west side countries. The improved resolution of telescopes and the appearance of new efficient light detectors (e.g. CCDs in the middle eighty) greatly impacted the extragalactic researches. The first morphological analysis of galaxies were rapidly substituted by “anatomic” studies of their structural components, star and gas content, and in general by detailed investigations of their properties. As for the human anatomy, where the final goal was that of understanding the functionality of the organs that are essential for the life of the body, galaxies were dissected to discover their basic structural components and ultimately the mystery of their existence. The first morphological studies and photometric analyses already identified many galaxy structures, that only later on stellar and gas kinematics were able to identify as separate and independent galaxy components. Despite these efforts many questions are still open today. What define a galaxy component? Does exist a structural component common to all galaxies? How much galaxy components are the product of nature and what can be attributed to nurture? What in synthesis define a galaxy system? And why some galaxies obey scaling relations and others do not? In this chapter we interview several outstanding extragalactic astronomers to find an answer to the above questions. At the end we will have a much clear view of what astronomers actually mean when they speak of galaxy components. Section 4.3 deals with one of the most debated issues about galaxy structure: the bulge component. What define it? how and when it was formed? to what extent bulges are naturally produced during the collapse of the protogalaxy and what can be attributed to secular evolution and merging events? In the same section we highlight the main properties of galaxy disks, briefly reviewing their structures and kinematics. Again, some underlying questions remain to be answered: how disks evolve with time? why galaxies disk exhibit different substructures (bars, lenses, rings, spiral arms) and different light profiles? in which way they chemically evolve? Why spiral arms are not equal in all galaxies? Section 4.4 and 4.5 have been explicitly dedicated to the typical disk substructures. Although not present in all disk-like objects, these structures have an important role in galaxy evolution. Are they transient phenomena occurring on the disk components? How much they contribute to the general evolution of the galaxies and in which way? We will see what the current models are able to predict up to now. Originally Sect.  4.6 had to address the properties of the less known galaxy component: the halo. Its structure and stellar/non-stellar content is indeed poorly known still today. The halo is the more difficult component to define and study, and would merit by itself an entire book. Actually a detailed analysis of this component is possible only in the MW and its neighborhoods. We therefore decided to focus our interviews on one important physical effect connected with halos: the gravitational lensing phenomenon. Why it is so important and what can we deduce about halos from this analysis? In the same section we also ask a question on the most typical stellar aggregate present in galaxy halos: the Globular Clusters. They are the oldest stellar systems and could therefore testify about the first epoch of galaxy formation. In Sect. 4.7 we remind that galaxies often contain a non negligible amount of gas and dust. However in the whole Universe the percentage of cold gas represents a very small fraction of the global energy density. So, why should we care of it? Interestingly we will discover that this material can teach us a lot of things about galaxy evolution and the origin of the first galaxies. Following such discussion, Section 4.8, will introduce the theme of the hot baryon component of galaxies, mainly visible in the X-ray domain. What can we learn about galaxies from these studies? Section 4.9 ends our discussion of the main galaxy components addressing the most neglected one: the magnetic field. This is not a classical component made of stars and gas and normally we cannot see it without measuring the polarization of light coming from galaxies; this has been always a very difficult job. However, today we are gaining more and more insights of the importance of magnetic fields in galaxies, in particular for their connection with the star formation process. With Sect.  4.10 we review again the concept of stellar population and its connection with the structural components of galaxies. As it emerges from several parts of this book the various generations of stars do not reside everywhere in the galaxy body and can also migrate across it. Why then stars seems to know very well where they should reside? How the different populations of stars were chemically enriched? Why the Mass-to-Light ratio is so entangled with the galaxy Mass? We finally discuss the main scaling relations that galaxies have shown to obey in Sect. 4.11. The physical origin of many of such relations is still not completely understood. We will address in particular the relations known as Fundamental Plane and Tully-Fisher. These relations tell us that galaxy form and evolve following well defined rules, but we miss some fundamental physics behind them. Their existence seems to indicate that a strong fine-tuning exists between the star formation history and the structures which host the stellar populations. We will also discuss the linearity of these scaling relations and their consequences for understanding the processes which gave origin to the present morphological classes of galaxies.

Breve biografia del gesuita Angelo Secchi (1818-1878), pioniere dell'astrofisica e innovatore in diverse discipline scientifiche.

Il testo illustra brevemente l'attività divulgativa del celebre astrofisico gesuita Angelo Secchi

The application of the polarimetric technique to asteroid studies progressed significantly during the last decade. The most interesting results were the discovery of asteroids with peculiar polarimetric properties, new findings on wavelength dependence of polarization, and some improvements in the polarimetric method of albedo determination. We review instruments that have been and are currently used for asteroid optical polarimetry and summarize the main results of observational surveys. Recent advances in theoretical and laboratory modeling of polarization phase effects and their implications are discussed. We focus on the most important open questions and identify promising avenues for future polarimetric investigations.

In this chapter I review the recent developments regarding the study of Blue Stragglers (BSS) in dwarf galaxies. The loose density environment of dwarf galaxies resembles that of the Galactic Halo, hence it is natural to compare their common BSS properties. At the same time, it is unescapable to compare with the BSS properties in Galactic globular clusters, which constitute the reference point for BSS studies. Admittedly, the literature on BSS in dwarf galaxies is not plentiful. The limitation is mostly due to the large distance to even the closest dwarf galaxies. Nevertheless, recent studies have allowed a deeper insight on the BSS photometric properties that are worth examining.

This chapter presents an overview of the main observational results obtained to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency, radial distribution, chemical composition and rotational properties are presented and discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical age of stellar systems, thus allowing the definition of the first empirical "dynamical clock".

he semiconductor detectors technology has dramatically changed the broad field of x- and γ-rays spectroscopy and imaging. Semiconductor detectors, originally developed for particle physics applications, are now widely used for x/γ-rays spectroscopy and imaging in a large variety of fields, among which, for example, x-ray fluorescence, γ-ray monitoring and localization, noninvasive inspection and analysis, astronomy, and diagnostic medicine. The success of semiconductor detectors is due to several unique 242characteristics as the excellent energy resolution, the high detection efficiency, and the possibility of development of compact and highly segmented detection systems (i.e., spectroscopic imager). Among the semiconductor devices, silicon (Si) detectors are the key detectors in the soft x-ray band (<15 keV). Si-PIN diode detectors (Pantazis et al. 2010) and silicon drift detectors (SDDs; Lechner et al. 2004), operated with moderate cooling using small Peltier cells, show excellent spectroscopic performance and good detection efficiency below 15 keV. On the other side, germanium (Ge) detectors are unsurpassed for high-resolution spectroscopy in the hard x-ray energy band (>15 keV) and will continue to be the first choice for laboratory-based high-performance spectrometers system (Eberth and Simpson 2006).

Semiconductor detector technology has dramatically changed the broad field of x-ray and ?-ray spectroscopy and imaging. Semiconductor detectors, originally developed for particle physics applications, are now widely used for x/?-ray spectroscopy and imaging in a wide variety of fields, including, for example, x-ray fluorescence, ?-ray monitoring and localization, noninvasive inspection and analysis, astronomy, and diagnostic medicine. The success of semiconductor detectors is due to several unique characteristics, such as excellent energy resolution, high detection efficiency, and the possibility of development of compact and highly segmented detection systems. Among semiconductor devices, silicon (Si) detectors are the key detectors in the soft x-ray band (<15 keV). Si-PIN diode detectors [1] and silicon drift detectors (SDDs) [2], operated with moderate cooling by means of small Peltier cells, show excellent spectroscopic performance and good detection efficiency below 15 keV. On the other hand, germanium (Ge) detectors are unsurpassed for high-resolution spectroscopy in the hard x-ray energy band (>15 keV) and will continue to be the first choice for laboratory-based high-performance spectrometers [3]. © 2015 by Taylor & Francis Group, LLC.

Gas-Phase Chemistry in Space: From elementary particles to complex organic molecules is written by a collection of experts in the field of astrochemistry. The book introduces essential concepts that govern the formation, excitation and destruction of molecules at a postgraduate and research level. A broad range of topics are covered; from early universe chemistry and stellar nucleosynthesis, to the study of bimolecular reaction kinetics. Detailed description of the gas-phase process is provided and recent examples of the interplay between observational and laboratory astrophysics are examined. Using more than 100 figures, as well as examples, this work reveals, in detail, both theoretical and experimental perspectives that can be implemented in future discoveries.

In regions shielded from ultraviolet radiation, energetic charged particles, called cosmic rays, are the dominant drivers of ionization, dissociation, and excitation. This chapter discusses the basics of cosmic-ray transport and acceleration, their impact on the thermochemistry of molecular gas, and methods to include cosmic-ray processes into astrochemical models.

This lecture is an introduction to cosmological tests with clusters of galaxies. Here, I do not intend to provide a complete review of the subject, but rather to describe the basic procedures to set up the fitting machinery to constrain cosmological parameters from clusters, and to show how to handle data with a critical insight. I will focus mainly on the properties of X ray clusters of galaxies, showing their success as cosmological tools, to end up discussing the complex thermodynamics of the di?use intracluster medium and its impact on the cosmological tests.

Astronomy has entered the big data era and Machine Learning based methods have found widespread use in a large variety of astronomical applications. This is demonstrated by the recent huge increase in the number of publications making use of this new approach. The usage of machine learning methods, however is still far from trivial and many problems still need to be solved. Using the evaluation of photometric redshifts as a case study, we outline the main problems and some ongoing efforts to solve them.

A considerable amount of (n,γ) reactions has been studied, so far, at the neutron time-of-flight facility n_TOF at CERN. The experimental program aims at determining and improving cross sections for a number of isotopes relevant to s-process nucleosynthesis. A brief summary of some physical cases related to the s-process nucleosyntheis is presented in this work together with ongoing experiments and challenging future programs.