Calendar

The outer atmospheres of late-type stars are characterized by strong emission in excess of the stellar photosphere. Through its relation with rotation the origin of this activity in a stellar dynamo was recognized long ago. Yet, the strength of magnetic activity has not been calibrated across the whole electromagnetic spectrum and its dependence on stellar mass and age has remained widely elusive. Most previous efforts have concentrated on solar-type stars because of their relative brightness and the direct connection with the Sun. Here, I present recent observational studies of magnetic activity on M stars. Low-mass stars are interesting planet hosts because they exist in large numbers, they are long-lived, and they provide a lower contrast between stellar/planet properties enhancing the chance for planet detection. The high-energy emission related with magnetic activity may be crucial for the evolution of planetary atmospheres, in particular for M stars which are notoriously strongly active. I present a wide range of diagnostics of chromospheric and coronal emission in the X-ray, UV and optical band. The data discussed comprise both photometric observations (obtained with GALEX, ROSAT and XMM-Newton) and spectroscopic measurements (obtained with X-Shooter@VLT). The aim of these studies is to establish connections between the emissions in different energy bands and determine how they change throughout the stellar evolution.

The supernova remnant SN 1006 is a powerful source of high-energy particles and evolves in a tenuous and uniform environment. The X-ray image of SN 1006 reveals an indentation in the southwestern part of the shock front and the HI maps show an isolated cloud (hereafter southwestern cloud) whose morphology fits perfectly in the indentation. We performed spatially resolved spectral analysis of a set of small regions in the southwestern nonthermal limb. We also analyzed archive HI data, obtained combining single dish and interferometric observations. We found that the best-fit value of the NH derived from the X-ray spectra significantly increases in regions corresponding to the southwestern cloud, while the cutoff energy of the synchrotron emission decreases. The amount of the NH variations corresponds perfectly with the column density of the southwestern cloud, as estimated from the radio data. The decrease in the cutoff energy at the indentation clearly reveals that the cloud is actually interacting with the remnant. The presence of a dense environment near a region where efficient particle acceleration is at work makes the southwestern limb a promising source of gamma-ray hadronic emission. We estimate that such emission will be detectable with the Fermi telescope within a few years.

One interesting question regarding the interaction between stars and planets and the birth of life is how the planetar atmosphere shields the stellar radiation. In particular, we expect that high energy radiation less penetrates into the planetary atmosphere. One implication is that, in principle, the planet should appear larger in a stellar transit observed in high energy bands. Venus transits might be excellent testing grounds to study this effect. The Venus transit of June 2012 has been monitored in great detail by solar spatial missions, and in particular by imaging instruments on-board Hinode and Solar Dynamics Observatory. We apply a statistical and photometric technique to measure the radius of Venus during the transit in three different bands: optical, EUV and X-rays, and show the results…

In un intreccio di letteratura, cinema, storia, astronomia e strumenti scientifici, verranno presentati i risultati di uno studio che prende le mosse da lavori precedenti condotti in collaborazione con Donata Randazzo e di recente estesi con alcuni contributi esterni ad OAPa, che spaziano fino ad una … inattesa conclusione.

In less than two decades, the field of exoplanetary science has undergone nothing short of a revolution. We have gone from the oddball discovery of a “planetary sized object” orbiting a pulsar star (Wolszczan and Frail, 1992) to efficient and systematic all-sky surveys with one thousand confirmed exoplanets and over three thousand candidates awaiting confirmation (Batalha et al., 2013). With such wealth of systems discovered, the next step in exoplanet research is to characterise the properties of these systems. One way of doing so is by measuring the chemical and thermal make-up of their atmospheres. In this seminar I will give an overview of what we know about these foreign worlds, the current techniques used and discuss the difficulties faced when having to reach the required photometric accuracy of 10^-4 over the duration of several hours. In the figure: the 0.3 – 2.4 micron spectrum of HD-189733b including all the high-precision measurements available in the literature. If the datapoints are observed simultaneously they are plotted with the same colour. Important to stress that combining multi-epoch dataset is a risky operation: instrumental systematics and stellar activity may prevent altogether an accurate measurement of the absolute transit depth.

Galactic cosmic rays are believed to be accelerated at supernova remnant shocks. This idea is very popular but we still miss a conclusive evidence of its validity. In this talk, I will give a general review on the connections between gamma-ray astronomy and cosmic-ray physics. In particular, I will discuss how recent (and future) gamma-ray observations of supernova remnants and molecular clouds can (will) help us in understanding the origin of galactic cosmic rays.

Nel mio elaborato si presenta un’importante diagnostica che ha di recente permesso di identificare e studiare il processo di fotoevaporazione del materiale nei dischi circumstellari. La fotoevaporazione e` un processo attraverso cui il materiale, in orbita intorno ad una stella, viene espulso dopo essere stato riscaldato dalla radiazione della stella. La diagnostica si basa sullo studio della riga proibita del NE II a 12,8135 micron. Questa riga, a causa dell’alto potenziale di ionizzazione del neon, puo` essere prodotta solo se la stella e` una sorgente di radiazione ad alta energia (UV e X). Nell’elaborato si affronta questa diagnostica per le stelle T Cha e Mp Mus, due T-Tauri classiche. In entrambi i sistemi e` stata misurata la riga a 12,81 micron e si e` calcolato tramite spostamento Doppler la velocita` con cui il materiale fotoevapora dalla stella, notando che la velocita` di evaporazione e` compatibile con il processo di fotoevaporazione causato da emissione X e UV. E` stata pure misurata la FWHM della riga, utilizzata per calcolare la velocita` di rotazione del materiale intorno alla stella e da quest’ultima si e` stimata la distanza del materiale dalla stella.

Questo lavoro di tesi e` rivolto allo studio dei transiti di pianeti in bande ad alta energia. Le favorevoli condizioni di osservabilita` del transito di Venere del 5-6 Giugno 2012, fanno di questo evento una utile opportunita` per questo tipo di studi. Il transito e` stato seguito dai telescopi a bordo delle missioni spaziali SDO e Hinode, che ci hanno fornito dati con cui siamo riusciti a misurare il raggio del pianeta in tre bande diverse: ottico, EUV ed X. La seconda parte della tesi riguarda la simulazione di transiti di pianeti di diverse dimensioni su delle immagini reali della corona solare. I dati sono stati acquisiti dal telescopio XRT, della missione spaziale Hinode, nei raggi X. Trattando il sole come una stella lontana, abbiamo ricavato le curve di luce di transito, e con lo studio del curtosi di queste ultime siamo riusciti a stabilire dei limiti alle dimensioni delle regioni attive eclissate dal pianeta durante il transito. Questo studio potrebbe fornire delle utili previsioni per la pianificazione di osservazioni di transiti con i futuri satelliti per raggi X come Athena+ dell’ Agenzia Spaziale Europea.