Calendar

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.

A short summary of the recent activities related to SphinX instrument repository, data reduction and analysis will be discussed. Possible directions of scientific research of SphinX measurement will be shown. Examples of new results will be given.

The remnant of SN1006 is well known to be the archetypical cosmic-ray accelerating supernova remnant, with two bright limbs dominated by non-thermal emission. In the soft X-ray band the emission is dominated by a thermal component which was traditionally associated to the shocked stellar ejecta fragments. In this talk, we will present the results obtained with the XMM-Newton Large Project on this remnant about this component. In particular, we will address the longstanding issue of the lack of apparent X-ray emission from the shocked ISM, which may provide evidence for proton acceleration through the observation of CR back-reaction effects, and a comprehensive study of the X-ray emitting ejecta, which will give us for the first time a direct evidence for an asymmmetric SN Type Ia explosion.

Mixed-morphology SNRs are characterized by a shell-like radio emission and a centrally peaked X-ray morphology and are all interacting with molecular clouds. Many models have been proposed to explain these peculiar remnants, but their physical origin is still unclear. The recent discovery of overionized (i. e. recombining) ejecta in 3 MM SNRs has dramatically challenged all the previous models and opened up new, unexpected scenarios. I review the main properties of these remnants and present an XMM-Newton observation of W49B together with a hydrodynamic model developed to explain the new results. I also discuss the (long) list of open questions.

The thermal structure of the post-shock region of a young supernova remnant (SNR) is heavily affected by two main physical effects, namely the back-reaction of accelerated cosmic rays and the Rayleigh-Taylor instabilities developing at the contact discontinuity between the ejecta and the shocked interstellar medium (ISM). In this contribution, we investigate the role played by both physical mechanisms in the evolution of SNRs through detailed MHD modeling.We present a three-dimensional MHD model which describes the expansion of the remnant through a magnetized ISM, including consistently for the first time the initial ejecta clumping and the effects on shock dynamics due to back-reaction of accelerated cosmic rays.