Search results for "astronomia"

A Spatially Resolved Study of Hard X-Ray Emission in Kepler’s Supernova Remnant: Indications of Different Regimes of Particle Acceleration

2022

Abstract Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high-energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler’s SNR, aiming to study in detail its nonthermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We …

Modeling accretion shocks on CTTSs and their X-ray emission

2009

Recent high spectral resolution X-ray observations of some CTTSs show the presence of high density plasma (ne=10^{11}-10^{13} cm^{-3}) at temperature T=2-3 MK. This plasma is likely heated up by an accretion shock on the star surface. We investigate this issue by an accurate modelling of the impact of an accretion stream onto the stellar chromosphere. Specifically, we present a large set of 1D hydrodynamical simulations aimed at investigating the physical properties of the system as a function of the density, and the velocity of the accretion stream and of the abundances of the heavy elements. We also synthesize the plasma X-ray emission from the simulations results, in order to link the ob…

Modeling X-ray Emission From The Coronae Of Low Mass Stars

2009

By extrapolating from observationally derived surface magnetograms of low-mass stars we construct models of their coronal magnetic fields and compare the 3D field geometries with axial multipoles. AB Dor, which has a radiative core, has a very complex field, whereas V374 Peg, which is completely convective, has a simple dipolar field. We calculate global X-ray emission measures assuming that the plasma trapped along the coronal loops is in hydrostatic equilibrium and compare the differences between assuming isothermal coronae, or by considering loop temperature profiles. Our preliminary results suggest that the non-isothermal model works well for the complex field of AB Dor, but not for the…

Magnetic activity and the solar corona: first results from the Hinode satellite

2007

The structure, dynamics and evolution of the solar corona are governed by the magnetic field. In spite of significant progresses in our insight of the physics of the so- lar corona, several problems are still under debate, e.g. the role of impulsive events and waves in coronal heating, and the origin of eruptions, flares and CMEs. The Hinode mis- sion has started on 22 september 2006 and aims at giving new answers to these questions. The satellite contains three main instruments, two high resolution telescopes, one in the optical and one in the X-ray band, and an EUV imaging spectrometer. On the Italian side, INAF/Osservatorio Astronomico di Palermo has contributed with the ground-calibrati…

Carbon nanotubes thin filters for x-ray detectors in space

2022

In this paper, we present the first results from an investigation performed on nanometric thin pellicles based on carbon nanotubes (CNT) of potential interest for manufacturing large area optical blocking filters to protect soft X-ray detectors in astrophysics space missions. In order to evaluate the effective capability of such materials to block UV/VIS/IR radiation, while being highly transparent in the soft X-rays and strong enough to withstand the severe launch stresses, we have performed a suite of characterization measurements. These include: UV/VIS/IR and X-ray absorption spectroscopy, X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy on bare and Al coated small self-…

A multichannel piezo driver for active mirrors in X-ray telescopes

2016

X-ray astronomy is gaining importance for studying X-ray space sources such as single and binary stars, neutron stars, supernovae and black holes. Due to atmospheric absorption, X-ray telescopes must operate in space on satellites. Among the causes limiting the resolution of modern telescopes are distortions in mirrors shape. An innovative approach for X-ray mirrors aims at correcting the shape errors by means of piezo-ceramic actuators glued to the back of the mirrors, thus creating an “active mirror”. In order to test the viability of shape correction, we fabricated [1] a prototype of a thin glass active mirror, sized 20 cm x 20 cm with a 400 um thickness (Fig. 1). The mirror can allocate…

Analysis of the XMM-Newton observations of IC443

2017

We analyze for the first time the full set of archive XMM-Newton EPIC observations of the Galactic Supernova Remnant IC 443. We aim at identifying the contribution of the shocked ejecta and interstellar medium and at the describing the physical and chemical properties of the shocked plasma. We also aim at addressing the presence of overionized plasma and its physical origin. We trace the morphology of Si- and S-rich ejecta with unprecedented spatial resolution, by adopting a novel method to produce maps of equivalent width. We describe in detail the method adopted and the results obtained and present preliminary results of a spatially resolved spectral analysis performed on selected regions…

THE INTERACTION OF THE STELLAR HIGH ENERGY RADIATION WITH THE CIRCUMSTELLAR MEDIUM

The purpose of this Thesis is to study how stellar high energy radiation affects exo- planetary atmospheres. High level of stellar high energy, X-rays and (vacuum end extreme) ultraviolet radiation may prevent planets’ habitability and limit the width of the habitability zone. Such radiation may ionize a star surrounding, affecting the chemistry and thermal bal- ance. The effects of X-rays can be wide ranging or relatively local. Soft X-rays are absorbed closer to the source than X-rays with energy greater than 1 keV. The absorption cross-section of hard X-rays are generally very small, so that such radiation may affect a whole galaxy to some extent. The product of photo-ionization is a cas…

Spectral Analysis of LMC-X2 with XMM/Newton

2008

We present the results of the analisys of an archival observation of LMC X-2 performed with XMM/Newton. The spectra of this source has never been analyzed with a high precision instrument before. The spectrum of the source can be fitted with a blackbody with a temperature 1.5 keV plus a disk blackbody at 0.8 keV. We argue that the emission of this source can be straightforwardly interpreted as a sum of the emission from a boundary layer between the NS and the disc and a blackbody component coming from the disc itself. The detection of the O VIII emission line (and the lack of detection of lines in the iron region) can be due to the fact that the source lies in the Large Magellanic Cloud.

Effects of radiation in accretion regions of classical T Tauri stars

2019

Context. Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns where optically thin and thick plasma components coexist. Thus, an accurate description of these impacts is necessary to account for the effects of absorption and emission of radiation. Aims. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock down-falling material. We investigate whether a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. Methods. We developed a radiation hydrodynamics model describing an accreti…