Calendar

Una panoramica sulle attivita` di didattica e divulgazione in corso all’OAPa, con approfondimenti sulle risorse economiche, sul personale coinvolto e sui nuovi progetti di finanziamento, portera` ad una discussione sulle iniziative e i progetti per i prossimi anni.

Lo SPC di ESA nella sua riunione del 21 e 22 Febbraio u.s. ha deliberato in merito alle modalita` di selezione delle missioni L2/L3, M3 e M4. Un gruppo di circa 40 ricercatori della comunita’ X europea con rappresentanti degli USA e del Giappone si sono riuniti a Leicester alla fine di Febbraio per discutere sul modo migliore per affrontare la prossima call di ESA. Dopo avere sinteticamente presentato le modalita’ decise dallo SPC di ESA, vi sintetizzero` la discussione avuta a Leicester e il suo esito (positivo a mio avviso) nel muoversi uniti per presentare una idea di missione nel campo dell’Astronomia X ad immagine di cui illustrero` le performance attese e le modalita` organizzative per massimizzare la discussione scientifica intorno alla stessa.

Lo scopo di questa tesi e` di studiare il trasporto di radiazione e dunque l’opacita` nei processi di accrescimento dal disco in stelle giovani, e mostrandone l’importanza ed illustrando i risultati ottenuti con un semplice codice. Lo studio del fenomeno di accrescimento stellare e` un importante tema scientifico non solo perche’ e` direttamente collegato alla formazione stellare ma anche perche’ assume un ruolo rilevante nell’evoluzione dei dischi di accrescimento; inoltre una maggiore comprensione dell’evoluzione dei dischi porta ad una piu` profonda conoscenza della successiva formazione planetaria. Recentemente ha assunto notevole importanza lo studio del trasporto di radiazione nei fenomeni di accrescimento perche’ la radiazione, soprattutto quella ionizzante, nella sua interazione con la materia nei dischi di accrescimento puo` essere responsabile indirettamente della creazione di composti chimici e molecole importanti per lo sviluppo della vita.

We present new spectral diagnostics available from HR15n spectra of stars in the gamma2 Vel cluster, useful for classification and determination of fundamental stellar parameters. We define several spectroscopic indices, sampling the amplitude of TiO bands, the H-alpha line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a temperature or gravity indicator over a limited range of stellar spectral types. H-alpha line indices are also useful as chromospheric activity or accretion indicators. Using these indices we find a clear difference between gravity of main-sequence field stars and pre-main-sequence cluster stars, as well as a much larger difference between these latter and giant stars. We discuss the usefulness of these results to measure ages of young clusters. We discuss the effect of classical T-Tauri star veiling on the defined indices, finding that veiling may be relevant for only few stars in the gamma2 Vel sample. We also discuss the calibration of the new temperature and gravity indices.

Coronal Mass Ejections (CMEs) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model. In this model, magnetic flux ropes form slowly over time periods of days to weeks. They then loose equilibrium and are subsequently ejected from the solar corona over a few hours. The contrasting time-scales of formation and ejection pose a serious problem for a consistent modelling of the whole life-span of a flux rope. In order to investigate if magnetic flux ropes formed during a quasi-static evolution can erupt to produce a CME, we run simulations of the full life-span of magnetic flux ropes coupling two models. The Global Non-Linear Force-Free Field (GNLFFF) evolution model of Mackay and van Ballegooijen (2006) is used to follow the quasi-static formation of a flux rope; the MHD code ARMVAC is used to simulate the production of a CME through the loss of equilibrium and ejection of this flux rope in presence of solar gravity and density stratification. Our realistic multi-beta simulations describe the CME following the flux rope ejection and highlight the decisive role played by the gravity stratification on the CME propagation speed up to 4 Rsun.

Synchrotron X-ray emission from the rims of young supernova remnants allows us to study the high-energy tail of the electrons accelerated at the shock front. The analysis of X-ray spectra can provide information on the physical mechanisms that limit the energy achieved by the electrons in the acceleration process. We analzsed the deep observations of the XMM-Newton SN 1006 Large Program. We performed spatially resolved spectral analysis of a set of small regions in the nonthermal limbs and we modelled the X-ray spectra by adopting models that assume different shapes of the cutoff in the electron spectra. We found that radiative losses play a fundamental role in shaping the electron spectrum in SN 1006. In fact, a loss-limited model provides the best fit to all the spectra and this indicates that the shape of the cutoff in the electron momentum (p) distribution has the form exp[-(p/p_cut)^2]

Many forefront astrophysical studies are based on imaging survey data. There is a clear need to complement them with dedicated spectroscopic surveys, especially at medium and high resolution. While some 4-m class instruments exist or have been planned, a real gain can be obtained by transforming the CFHT in a 10-m telescope to perform wide-field, high-multiplexing, multi object spectroscopy by the end of 2020. This talk will report on the scientific and technical results from the current conceptual design study. Some innovative design solutions have been proposed to meet technical and programmatic requirements with existing technologies.

Il futuro degli studi exoplanetari e’ chiaramente focalizzato attorno ad osservazioni nell’ottico e nel vicino Infrarosso. Tuttavia l’eventuale realizzazione di una grande missione per astronomia X con un telescopio focalizzante con area efficace di almeno 2 sq. m. pone la questione se nel campo degli studi esoplanetari ci sia una qualche interessante spazio per le osservazioni in raggi X. Sulla scorta del risultati del lavoro in progress per la scrittura del WP/WB per Athena+ illustrero’ brevemente le possibilita’ di condurre studi esoplanetari in banda X. Mi soffermero’ sia sulla rivelabilita’ in fotometria a larga banda dei transiti e su le informazioni che si potrebbero estrarre dalle curve di luce in banda X, che sulle, meno certe, possibilita’ di cercare traccianti spettroscopici sulla base delle nostre attuali conoscenze dei corpi del Sistema Solare.

High-energy observations of gamma-ray bursts (GRBs) with the Fermi satellite have enabled detailed studies of the temporal and spectral behaviour over seven decades in energy (from 8 keV to ~100 GeV) and provided new insight into the emission mechanisms of these powerful outbursts. I will briefly outline some highlights from Fermi GRBs observations, along with their possible implications. Key observational results include: 1) the detection of an additional spectral component at GeV energies; 2) the late onset and longer duration of the high-energy (>100 MeV) emission, compared to the low-energy (<1 MeV) prompt emission; 3) stringent limits on the variation of the speed of light with photon energy; 4) evidence for a subset of extremely relativistic and energetic stellar explosions, challenging some of the most popular GRB models.

Impacts of falling fragments observed after the eruption of a filament in a solar flare on June 7, 2011 are similar to those inferred for accretion flows on young stellar objects. As imaged in the UV/EUV by the Atmospheric Imaging Assembly on-board the Solar Dynamics Observatory, many impacts of dark, dense matter display uncommonly intense, compact brightenings. High-resolution hydrodynamic simulations show that such bright hot spots occur when high-density plasma impacts at several hundred km/s, producing high-energy emission as in stellar accretion. Implications are discussed.