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Young stars in the Classical T Tauri phase are characterized by complex and highly dynamical phenomena involving the stars, their circumstellar disks, mass accretion, and outflows. Quite unsurprisingly, high energy processes, as traced by, e.g., the X-ray emission, are affected or even driven by the interaction between these components. Because of the widely different characteristic temperatures of the involved physical components and of the dynamical nature of their interactions, coordinated multi-wavelength time-variability studies are best suited to their investigation. In March 2008, we have observed NGC 2264 with CoRoT for 23.5 days obtaining high-quality uninterrupted optical light-curves of its young stars. During the CoRoT pointing, two short Chandra observations were performed with a separation of 16 days, allowing us to study the correlation between optical and X-ray variability on this timescale, and thus the physical mechanism responsible for the variability. The variabilities of Classical T Taury Stars (CTTS) in the optical and soft X-ray (0.5-1.5 keV) bands are correlated, while no correlation is apparent in the hard (1.5-8.0 keV) band. Also, no correlation in either band is present for Weak line T Tauri stars. The correlation between soft X-ray and optical variability of CTTSs can be naturally explained in terms of time-variable shading (absorption) from circumstellar material orbiting the star, in a scenario rather similar to the one invoked to explain the observed phenomenology in the CTTS AA Tau. The slope of the observed correlation implies (in the hypothesis of homogeneous shading) a significant dust depletion in the circumstellar material.

The question of what heats the million degrees solar corona has been debated for decades. One scenario proposed since the 80s has been a finely stranded corona where each strand is heated by a rapid pulse. Unfortunately, neither such fine structure has been resolved, nor direct or conclusive evidence has been found so far, e.g., extensive superhot plasma, nanoflaring activity, so that alternative hypotheses have been proposed. Recently it has been shown that the observed difference in appearance of cool and warm coronal loops (~1 MK, ~2-3 MK, respectively) – cool loops show fine structure and warm loops appear “fuzzy” – can be explained with multi-stranded coronal loops pulse-heated up to 10 MK, where the strands are interpreted as subarcsecond via modeling. That work predicts that images of hot coronal loops (>6 MK) should again show fine structure. Here we show that the predicted effect is indeed widely observed in an active region with the Solar Dynamics Observatory, and that therefore fine-structured energy pulses play a major role in heating the active corona.

Negli ultimi 10 anni e’ stata osservata emissione X da diversi getti protostellari: HH 154 e HH 2 nel 2000 , HH 80/81 nel 2002, DG Tau nel 2003,…. Il modello di getto espulso dalla stella progenitrice con velocita’ variabile nel tempo (getto pulsato) spiega l’emissione ottica ed X osservata come interazione tra blob espulsi in tempi diversi e con velocita’ diverse. Tale modello riproduce bene le osservazioni di alcuni getti, tra cui DG Tau (uno tra i getti con emissione X piu’ debole, in accordo con un modello di getto pulsato con basso tasso di espulsione). Le nuove osservazioni ottenute con Chandra nel 2010 del getto HH 154 tuttavia mostrano la prima evidenza di shock stazionario da getti protostellari: su una base temporale di circa 10 anni (la prima osservazione Chandra di tale getto risale infatti al 2001), la sorgente X mostra una componente stazionaria alla base del getto. Per spiegare questi nuovi risultati abbiamo sviluppato un modello di getto espulso nel mezzo imperturbato attraverso un nozzle (che puo’ essere associato alla presenza di un campo magnetico nella regione di lancio e collimazione del getto) che provoca la formazione di un diamond shock stazionario con proprieta’ fisiche (luminosita’ X, temperatura di best-fit,…) consistenti con le osservazioni.

We present the results of the analysis of a Large Program of deep XMM-Newton observations of SN1006. We focus on the rim of the supernova remnant to derive important constraints for the shock acceleration process and for the back-reaction of the accelerated particles on the evolution of the remnant. The physical properties of the shocked ambient medium are expected to be modified by the acceleration process but up to now X-ray emission from the shocked ISM has never been detected in SN1006. The new data allow us to detect the shocked ISM and to ascertain whether the particle acceleration alters its post-shock properties. The comparison of our results with predictions from detailed MHD models of a modified supernova remnant can provide important physical insight on the physics of diffusive shock acceleration

Hinode and SDO high spatial/temporal/spectral resolution solar observations provide us with accurate diagnostics of solar coronal plasmas (density, temperature, abundances,…). I will discuss some of the limitations of these diagnostics due e.g. to completeness and accuracy of the atomic data (in particular in the narrow passbands of the Atmospheric Imaging Assembly onboard SDO), or to superposition of different structures in the line of sight. In order to explore these issues several approaches are used including the analysis of high spectral resolution stellar data of the low-activity (solar-like) corona of Procyon, and the analysis of images and spectra synthesized from realistic 3D radiative MHD simulations of the solar atmosphere obtained from the state-of-the-art Bifrost code.

To study the accretion shocks of classical T Tauri stars (CTTS) we obtained high-resolution X-ray spectra of two CTTS, V2129 Oph and V4046 Sgr, to look for phase-resolved X-ray signatures of shock-heated plasma. The 200 ks Chandra/HETGS observation of V2129 Oph (a 1.35 M_sun star, rotating in 6.5 d) covered ~0.5 stellar rotation. The 360 ks XMM/RGS observation of V4046 Sgr (a binary system, with two 0.9 M_sun components, synchronously rotating in 2.42 d) monitored ~2.2 system rotations. For both V2129 Oph and V4046 Sgr, the stellar photosphere, magnetic field, and accretion geometry were constrained by quasi-simultaneous optical monitoring (photometry, spectroscopy, and spectropolarimetry). The cool plasma component of V2129 Oph varies, with high density plasma and high EM observed during the first part of the observation, and lower density and lower EM observed during the second. The emission lines produced by the high density cool plasma of V4046 Sgr, display periodic flux variations, with a period of half the system rotational period. Our results confirm that the dense cool plasma in CTTS is material heated in the accretion shock, and that the observed X-ray variability can be explained in terms different viewing angles at different rotational phases of the accretion-shock region.

Dalla scoperta del primo pianeta estrasolare attorno a una stella “normale” la ricerca sui pianeti estrasolari ha fatto degli enormi progressi, evolvendosi dalla semplice identificazione di nuovi pianeti allo studio della loro formazione, proprieta` ed evoluzione. In questo seminario presentero` alcune delle linee di ricerca, attive presso l’Osservatorio Astronomico di Palermo, relative alle problematiche legate ai pianeti estrasolari. In particolare illustrero` le prospettive offerte da progetti e strumenti sia da Terra che dallo spazio, attualmente in via progettazione, in cui ricercatori dell’Osservatorio sono coinvolti.

La necessita` di migliorare la risoluzione energetica nella spettrometria X ha portato alla progettazione di rivelatori ad elevata sensibilita`. Tra i diversi dispositivi proposti, i microcalorimetri hanno dimostrato di avere promettenti possibilita` applicative. Mostrero` in questo seminario il funzionamento ed i vantaggi di questa classe di rivelatori, con particolare riferimento ai microcalorimetri basati su semiconduttore. Illustrero` quindi la tecnologia che stiamo sviluppando al laboratorio XACT, in collaborazione con il Dipartimento di Ingegneria Elettronica, per realizzare matrici scalabili di rivelatori microcalorimetrici con sensore in germanio.

Short duration gamma-ray bursts (GRBs) are widely thought to result from compact binaries mergers. Growing observational evidence seems to support this popular scenario. At the same time Swift observations of short GRBs revealed new features on their emission properties: precursors, X-ray flares and, in particular, a temporally extended emission provide compelling evidence of a long-lived central engine. The traditional neutron stars merger model does not naturally account for such late time activity. I will present the current observational status of short GRBs and discuss the implications, with particular regard to progenitors population.

Very low-mass stars and brown dwarfs are fully convective, a reason to expect that the solar-like dynamo does not work. Implications for the pattern of magnetic activity are expected. Putting X-ray emission in context with activity signatures in other wavebands (optical and radio) allows to understand the changes — if any — of the coronal heating mechanism across the fully convective boundary and the hydrogen burning mass limit. Young brown dwarfs, moreover, possess circumstellar disks from which they accrete matter. Considering them substellar analogs to T Tauri stars, accretion shocks represent potential sites of X-ray emission next to the coronal plasma. I discuss recent X-ray observations of two brown dwarfs in the context described above: DENIS 1048-39, a very low-mass field star observed in the past to be a radio burst source, and FU Tau A, the primary of an isolated young brown dwarf binary.