Calendar

The FP7 funded project EXTraS (Exploring the X-ray Transient and variable Sky) is an international project led by INAF, aimed to characterize the soft X-ray variability of all the sources detected in the whole archive of the XMM-Newton mission, and to look in this archive for new transient sources. During the feasibility study, a transient was detected from ISO-Oph 85, a young stellar object (YSO) supposed to be in a very early evolutionary stage and, so, very little active in X-rays. An X-ray time resolved and spectral analysis was performed. Infrared data were also analysed in order to establish the evolutionary stage of ISO-Oph 85. Here we present the obtained results. An insight into the opportunities given by EXTraS for the research in the YSOs field is also provided.

Meteorites are solar system objects that have fallen to the Earth. They provide us an abundant supply of material for study in the laboratory without the expense and complication of sample-return missions. They represent a wide range of types, places of origin, and histories, and through laboratory study they help develop our understanding of the formation and history of the solar system. Found embedded in certain meteorites are refractory inclusions that represent the earliest materials known to have solidified out of the solar nebula, 4.567 billion years ago. Some meteorites originated on known bodies such as the asteroid 4 Vesta, the Moon, or Mars, and help us interpret data from space missions to these objects. Nevertheless, the range of materials we can study is limited to those objects, mostly from the inner asteroid belt, that can survive entry to the Earth. The vast majority of the solar system is unrepresented in the meteorite population. I will speak generally about different types of meteorites that are known and what we have learned from them, and then discuss my own research studying density and porosity of meteorites and lunar materials.

Il seminario e’ finalizzato ad illustrare la politica dell’INAF per massimizzare il ritorno, in termini di innovazione, degli investimenti in astrofisica.

La scoperta di Cerere, avvenuta a Palermo per opera di Giuseppe Piazzi la notte del 1 gennio 1801, e’ stata un evento con molti retroscena, a volte poco noti. In questo seminario saranno messi in luce alcuni aspetti legati al contesto storico-scientifico dell’epoca, alla personalita’ dei protagonisti della vicenda e alle problematiche scientifiche della comunita’ astronomica internazionale tra la fine del XVIII e i primi del XIX secolo.

The early stages of a star birth are characterised by a variety of mass ejection phenomena, including outflows and collimated jets, that are strongly related with the accretion process developed in the context of the star-disc interaction. After been ejected, jets move through the ambient medium, interacting and producing shocks and complex structures that are observed at different wavelength bands. In particular, X-ray observations show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary and have been interpreted as shock diamonds. We aim at investigating the physical properties of the shocked plasma and the role of the magnetic field on the collimation of the jet and the location, stability and detectability in X-rays of the stationary shock formed. We performed 2.5D MHD simulations, including the effects of the thermal conduction and the radiative losses. We modelled the propagation of a jet ramming with a supersonic speed into an initially isothermal and homogeneous magnetized medium. We studied the physics that guides the formation of a stationary shock (for instance a shock diamond) and compared the results with observations, via the distribution of emission measure vs. temperature and the luminosity synthesized from the simulations output data.

Coupling high-power lasers and high-strength B-fields helps gaining unique insight and understanding of a variety of phenomena of crucial importance for astrophysics. We have shown that such platform could be used to mimic the expansion of a young star isotropic disk wind threaded by a co-axial poloidal magnetic field. It reveals that long-range collimated jets can indeed by result from such system, complementing toroidal B-fields that help shape the initial matter from the star into a jet. The same system can then be used to study the dynamics of the accretion of magnetized plasma columns onto star surfaces and help decipher the underlying physics, or also the issue of particle energization in astrophysical plasmas. Our investigations on these topics will be reviewed and prospects discussed.

The first characteristic measured for Cepheids is their periods. The next step is to determine their pulsation mode. We have made month long observations with the MOST satellite of a fundamental mode Cepheid (RT Aur) and an overtone Cepheid (SZ Tau). The quantity and quality of the satellite data have shown that the Fourier parameters of the overtone are far more variable than those of the fundamental. A series of studies have been made of the binary properties of Cepheids, providing insight into star formation and dynamical evolution. A survey of 70 Cepheids was made with HST WFC3 to identify possible resolved companions. This was followed up with XMM-Newton observations to determine which possible companions are young X-ray active stars, and hence physical companions of Cepheids. This provides information about the frequency, separations, and mass ratios. Finally, the measured masses of Cepheids will be summarized, and new developments discussed.

Evidence for some super-hot plasma (> 4 MK) has been found in the core of active region loops. This is a signature of impulsive heating (nano-flaring). We study the EUV light curves in one or a few pixels with a model of multi-stranded coronal loop. Each strand is pulse-heated. In the hypothesis of an energy distribution of the heat pulses, we first generate a grid of strand models with different heating rates, and then we combine them randomly to generate simulated light curves similar to the observed ones. We make 10000 realisations for each set of model parameters (the power law index of the energy distribution, the duration of the heat pulse, the number of strands) and compare them to the observed light curves to find the best one by means of an artificial intelligence system (Probabilistic Neural Network, PNN). Cross-Correlation is used as a cross-check. We find that a shallow (but not flat) distribution of short-duration pulses in a relatively high number of strands (1000) best describes the observed data. A space-resolved loop model with these parameters predicts different fluctuations of the emission from the bottom to the top of the loop: we compare with observation.