| Star-Planet Interaction (SPI) is a broad phenomenological term which encompasses a variety of physical effects relevant for the evolution of extra-solar planetary systems, in particular for those hosting giant gas planets in close orbits around their parent star. While theoretical expectations of SPI are abundant, observational signatures are still elusive with current instrumentation and adopted observing strategies. I will review the state of the art on the matter, and possible future developments that may help us for a better characterization of exoplanets and their abitability conditions. |
|
Mizzica c'e` un pianetino piccolino! L'ho chiamato Cerere |
|
Among more than 450 extra solar planets yet discovered up to now, hot Jupiters class planets are the most interesting to study the interaction of star and planet at distances around 0.1 AU or less. Variations of chromospheric activity phased with the planet orbital period have been discovered in a few systems. The detection of star planet interaction in X-rays is matter of debate with statistical studies of different groups leading to opposite conclusions. I will present results from two observations of the hot Jupiter hosting system HD189733 obtained with XMM-Newton during planetary transits. We detect a softening and a large flare that could be consistent with an X-ray SPI scenario supported by MHD simulations. Furthermore, the non detection of the M-type companion in X-rays put a stringent limit on the age of the system and hint enhancement of X-ray activity in the primary star. |
|
Young low-mass stars are surrounded by circumstellar disks with which they interact in a complex fashion, with accretion of mass and ejection of collimated outflows. The accretion builds up the young star to its final mass and is also believed to power mass outflows, which may in turn remove the excess angular momentum from the star-disk system. However, although the process of mass accretion is a critical aspect of star formation, its mechanisms are still to be fully understood. A point not considered to date and important for the accretion process is the evidence of very energetic and frequent flaring events in these stars. Flares may easily perturb the stability of the disks, thus influencing the transport of massand angular momentum. Here we report three-dimensional magnetohydrodynamic modeling of the evolution of a flare occurring on the disk around a rotating magnetized star, which reveals that the resulting perturbation of the disk triggers a significant mass accretion. This result put forward the frequent flaring activity in young stars as a mechanism that may contribute to stellar mass accretion. This mechanism could be additional to the magnetorotational instability (or even enhance its efficiency), frequently invoked in the literature to explain the transport of mass and angular momentum in the star-disk system. |
|
Il seminario presenta i risultati acquisiti nel corso di uno studio in fase di pubblicazione (Journal for the History of Astronomy, 2011) relativi ad un manoscritto posseduto dall'Osservatorio di Palermo. Esso contiene la descrizione di uno strumento progettato e costruito da Ramsden, di cui si era persa traccia, data l'eccezionale rarita`. |
|
According to theory, high energy emission from the coronae of cool stars can severely erode the atmosphere of orbiting planets. To test the long term effects of the erosion we study a large sample of planet-hosting stars observed in X-rays. The results reveal that massive planets (M sin i > 1.5Mj) may survive only if exposed to low accumulated coronal radiation. The planet HD 209458 b might have lost 0.8 Mj already, and other cases, like tau Boo b, could be losing mass at a rate of 3.4 Ms/Gyr. The strongest erosive effects would take place during the first stages of the stellar life, when the faster rotation generates more energetic coronal radiation. The planets with higher density seem to resist better the radiation effects, as foreseen by models. Current models need to be improved to explain the observed distribution of planetary masses with the coronal radiation received. |
|
La composizione chimica superficiale delle stelle di tipo solare e nelle loro atmosfere esterne puo' essere considerato a buon diritto il primo tema di ricerca astrofisica mai affrontato (vi ricordate di Fraunhofer?). Dopo due secoli di studi pero' si continuano a trovare risultati sui quali la comunita' scientifica discute vivacemente. In particolare, le abbondanze chimiche fotosferiche e coronali nelle stelle di tipo spettrale avanzato sembrano essere significativamente diverse in molti casi, ma i dati osservativi non sono ancora sufficienti a capire il quando e il perche'. Un'altra curiosa scoperta recente e' il fatto che le stelle che ospitano pianeti di tipo gioviano hanno in media una metallicita' fotosferica maggiore delle altre di circa un fattore 2. Sono supermetalliche anche le loro corone? Abbiamo cercato di aggiungere un tassello a questo puzzle tramite un'osservazione in raggi X di Tau Bootis, una stella molto ben studiata proprio per la presenza di un pianeta massiccio in orbita stretta. L'obiettivo di questa osservazione e' stato quello di misurare le abbondanze chimiche del plasma coronale e confrontarle con quelle ben note della fotosfera (supermetallica). Se volete sapere quello che abbiamo trovato (vedi figura) venite a sentirvi il seminario. |
|
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. |
|
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. |
|
We will present a working prototype of YouASTRO (www.youastro.org), a web-based BibTeX-compliant reference management software (RMS) for astrophysical papers in the SAO/NASA ADS database. It also includes as a main feature the concept of distributed paper comments and ratings. Community-based reviews and comments, and more in general participatory information sharing, have proven to be a very effective way to spread the knowledge in many fields, and they are the focus of Web 2.0 applications. In this demo, we will show how to create and manage a BibTeX personal library to use for citations in our own articles and how to share comments on ADS papers. We will briefly discuss what could be the advantages and drawbacks of such a system being widespread adopted by the astrophysical community for its scientific literature. |
|
This talk will present the results of recent high resolution studies of the nuclear regions of active galaxies with Chandra. With these data we are setting observational constraints on the parameters of AGN feedback, which is considered a main agent in galaxy evolution. I will also report the very recent discovery of a close double supermassive black hole in one of these galaxies. |
|
As part of the ESA Cosmic Vision program a "Large" mission concept for imaging X-ray Astromomy is currently in phase A study. The mission, nicknamed ATHENA, result from a very fast and aggressive few month long redefinition phase started April 2011 and ending by October 2011 with a selection for possible phase B (definition) study on February 2012. I will briefly discuss the motivation behind and the rationale for this redefinition process, its outcome, the capability of the newly designed Athena space observatory and the major scientific questions this mission will allow to address. I will also briefly present my view on the overall scenario of the ESA science program and the pros e con of the Athena fitting in this evolving scenario and related advancement of European astrophysics. |
|
MENU`
|
|
Il seminario illustrera` le tematiche della Fellowship recentemente conclusa presso lo Science Museum di Londra; saranno presentati i risultati acquisiti e le prospettive aperte da questi, nonche` la direzione in cui si intende procedere nel prosieguo di questa ricerca.sui primi sviluppi dell'astrofisica, che analizza il contesto di nascita di questa scienza nella seconda meta` dell'Ottocento, evidenziandone alcuni interessanti aspetti. |
 |
|
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. |
 |
|
I present broad-band (350-2500nm) mid-resolution X-Shooter/VLT spectra of three accreting young stellar objects with spectral types between M5 and M8, i.e. near or within the brown dwarf regime. These observations provide a rich database of accretion diagnostics from the Br$\gamma$ and Pa$\beta$ lines in the near-IR to the Balmer jump in the UV including the full optical band with the Balmer series and He\,$\lambda$5876 and the Ca\,IRT. Finally, outflows can be traced through forbidden line emission. In this talk I focus on three of the most interesting targets from our survey: (1) FU\,Tau\,A, overluminous in the HR diagram with respect to predictions of pre-main sequence evolutionary models; (2) TWA-27 (alias 2M1207-39), the planet-hosting prototype for an accreting brown dwarf; (3) Par-Lup3-4, a young stellar object with edge-on disk driving a jet. |
|
The Hi-C (High resolution Coronal imager) sounding rocket has provided the highest resolution EUV solar coronal images ever obtained, resolving structures down to ~0.3 arcsec. The unprecedented spatial and temporal resolution of Hi-C data has revealed several new features, including highly braided coronal loops undergoing reconnection, and very rapid variability (down to ~15s) in the moss of bright hot loops. I will review some of the first results obtained from Hi-C data, focusing on the new insights they provide in coronal heating. I will also present a very brief overview of the Interface Region Imaging Spectrograph (IRIS), which will be launched on June 26th 2013. |
 |
|
X-ray sources with very few counts can be identified with low-noise in X-ray detectors, especially for the Advanced CCD Imaging Spectrometer (ACIS-I) camera on board the Chandra X-ray Observatory. Most of these studies concerns to the large populations of faint X-ray sources associated with pre- main sequence stars (PMS). Several of these sources seems to be faint enough for parametric spectral modeling, even in case of simple thermal models. On last years, some attempts were performed to estimates the intrinsic broadband X-ray fluxes and absorption from gas along the line of sight to these sources. However, the relationship between absorption (NH), temperatures (kT), intrinsic flux (F) and their respective errors, with the source count statistic, are unknown. Here, based on an extensive set of X-ray spectral simulations (~80000), we present the relationship between these quantities in terms of the source counts, as well as, the flux error estimation in terms of NH, kT ans photon statistic of the sources. In perspective, this study can offer a precise tool for better tailored observational proposals. |
 |
|
Anisotropic emission of gravitational waves during the coalescence of supermassive black hole binaries can deliver a large "kick" velocity to the new BH (v~10^3 km/s). N-body simulations predict that, for kick velocities larger than 40% of the galactic escape velocity, the BH may experience long lived (few Gyr) oscillations with amplitudes comparable with the size of the galactic core (~10^2 pc), suggesting that offset BHs may be common, even in nearby ellipticals. In order to search for such offsets, we perform a photometric analysis of a sample of 14 "core" elliptical galaxies using archival HST observations. Typical recovered offsets are within 1% of the core radius. In contrast, statistical arguments based on N-body simulations show that the typical probability to observe an offset larger than 0.1 core radii (~10 pc) is of order of 70% for a single galaxy. This is derived under the assumption that the BH binary coalescence produced a moderately large kick (v ~ 250 km/s) at the time of the last merger. Assuming that all galaxies in the sample experienced at least one such merger during their lifetime, the probability to observe no offsets larger than 1% the core radius over the sample is of order of 10^-8. |
|
Nearby star-forming regions are ideal laboratories to study high-energy emission of different stellar populations, from very massive stars to brown dwarfs. NGC 2023 is a reflection nebula situated to the south of the Orion B. In this work, we present a comprehensive study of X-ray emitters in the region of NGC 2023 and its surroundings. We combine optical and infrared data to determine physical properties (mass, temperature, luminosity, presence of accretion disks) of the stars detected in an XMM-Newton observation. This study has allowed us to analyze spectral energy distribution of these stars for the first time and determine their evolutionary stage. Properties of the X-ray emitting plasma of these stars are compared to those found in other nearby star-forming regions. The results indicate that the stars that are being formed in this region have characteristics, in terms of physical properties and luminosity function, similar to those found in the Taurus-Auriga molecular complex. In addition we will present the first results for the study of Orion B molecular cloud carried out with Infrared and X-ray photometry, where we found 604 source in the X-ray observations. |
 |
|
Activity cycles are of major interest to understand the solar physics and the influence of the Sun in the Earth's climate. The effects of solar activity in the Earth are mainly produced by the high energy photons and particles. The solar coronal cycle varies as much as a factor of 50, as measured in terms of Lx. But there is little known on the amplitude of this cycle in the past. So far there were only three stars others than the Sun with a known coronal cycle, all of them in rather old K dwarfs with low activity levels. In a recent paper we have found the coronal cycle of Iota Horologii, the star with the shortest chromospheric cycle known to date. This star represents the first coronal cycle in an active star, in a G dwarf, and in a young star. Iota Hor is a solar-like star with an age of ~600 Myr, the age at which the life appeared on Earth. This cycle may represent the first coronal cycles in the evolution of a solar-like star. |
 |
|
La corona solare visibile nelle bande X ed Estremo UltraVioletto (EUV) \`e costituita per lo pi\`u da plasma confinato dal campo magnetico in tubi di flusso curvi e ancorati sulla superficie, gli archi coronali. Sebbene ultimamente i telescopi spaziali solari abbiano portato a notevoli progressi nella conoscenza dei meccanismi che strutturano e riscaldano la corona, il dibattito \`e ancora aperto sulle cause che convertono l'energia magnetica in riscaldamento. Il riscaldamento \`e graduale o impulsivo? Che strutturazione fine hanno gli archi? Che ruolo gioca la cromosfera? Questo lavoro attacca lo studio della corona solare su due fronti complementari. Una prima parte \`e dedicata all'indagine sul ruolo di meccanismi di riscaldamento impulsivo. Quest'indagine \`e imperniata sulla rivelazione di eventuali piccole componenti di plasma molto pi\`u calde della media nelle regioni attive. Evidenza di queste componenti \`e stata trovata sia con strumenti a immagine, sia in dati spettroscopici, e qui si vuole completare l'informazione attraverso la ricostruzione dell'intera struttura termica lungo la linea di vista. Si sono cos\`i analizzati dati spettroscopici ottenuti con lo strumento Hinode/EIS in parti di una regione attiva precedentemente identificate come molto diverse termicamente, confrontandone i risultati. Il presente studio ha portato ad una conferma, sia pure non conclusiva, della presenza di piccole ma significative componenti molto calde, in favore di un riscaldamento impulsivo almeno in alcune zone delle regioni attive. Lo studio ha anche portato diverse nuove e interessanti informazioni sull'analisi spettrale dei dati. La seconda parte del lavoro \`e dedicata invece all'indagine sul ruolo della cromosfera nelle dinamiche e nel riscaldamento della corona. Di interesse sono flussi veloci dalla cromosfera che, incanalati negli archi coronali, potrebbero portare a effetti visibili nella banda EUV, detti spicole di tipo II. \`E stata trovata evidenza di una corrispondenza tra flussi cromosferici ed emissione nella banda EUV e ci si pone la domanda sulla relazione causa/effetto. Qui abbiamo usato un modello magnetoidrodinamico di una regione con un arco coronale per descrivere in dettaglio e capire l'effetto di un flusso dalla cromosfera sul plasma coronale. Il modello \`e molto complesso, richiede simulazioni numeriche su calcolatori multi-processore, e il codice utilizzato \`e di punta nel panorama internazionale. Lo studio ha permesso di valutare l'effetto della propagazione di fronti d'urto lungo l'intero arco, che vengono innescati dai flussi cromosferici. Il risultato d'interesse \`e che i fronti d'urto provocano l'addensamento e il riscaldamento del plasma all'interno dell'arco, e quindi potrebbero spiegare parte dell'evidenza osservativa. |
|
Since the past decade, the knowledge of high-energy processes in stars has experienced large advance. However, there are still some issues about physical processes taking place in stars that remain uncertain and need a more accurate study. In particular, to deep into some aspects of X-ray coronal emission, we need new observational methods and/or new instrumentation. An example of it is the poor constraints done to physical parameters of flaring loops in solar-type stars. Several theoretical and observational studies have been carried out but there is still controversy of some particular results, including the geometry of the magnetic field and the loop's length. On the one hand, some authors believe that flaring processes in late-type stars are scaled-up versions of those taking place in the Sun and that the geometrical aspect of loops must be similar in both cases. The models used by these authors to obtain parameters from the observation of flares are so-called scaling laws. This scenario predicts stronger magnetic fields in stars than in the Sun in many cases. On the other hand, other models are based on physical laws and assume aspect rations of the flaring loops similar to that of the Sun, obtaining much longer loop lengths and magnetic fields with values more similar to those observed for the Sun. To distinguish between both scenarios, we need to use independent methods that allow us to determine the same parameters for the flare. A powerful technique to determine some parameters of the flaring loop is the wavelet analysis of light curves. I present a preliminary study of this technique using Montecarlo analysis and apply it to several stars. |
 |
|
Accretion processes onto classical T Tauri stars (CTTSs) are believed to generate shocks at the stellar surface due to the impact of supersonic downflowing plasma. Although current models of accretion streams provide a plausible global picture of this process, several aspects are still unclear. For example, the observed X-ray luminosity in accretion shocks is, in general, well below the predicted value. A possible explanation discussed in the literature is in terms of significant absorption of the emission due to the thick surrounding medium. Here we consider a 2D MHD model describing an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere. The model includes all the relevant physics, namely the gravity, the thermal conduction, and the radiative cooling, and a realistic description of the unperturbed stellar atmosphere (from the chromosphere to the corona). From the model results, we synthesize the X-ray emission emerging from the hot slab produced by the accretion shock, exploring different configurations and strengths of the stellar magnetic field and different density profiles of the accretion stream (accounting also for non uniform streams). The synthesis includes the local absorption by the thick surrounding medium and the Doppler shift of lines due to the component of plasma velocity along the line-of-sight. We explore the effects of absorption on the emerging X-ray spectrum, considering different inclinations of the accretion stream with respect to the observer. We also investigate the detectability of line shift due to Doppler effect under different physical conditions. Finally we compare our results with the observations. |
|
I will present the results of an extensive UV/optical variability survey of the young open cluster NGC 2264 (3 Myr), performed at CFHT/MegaCam as a part of a wide project of simultaneous multi-wavelength (X-rays to IR) monitoring aimed at unambiguously characterizing YSO variability (the Coordinated Synoptic Investigation of NGC 2264). A complete u,g,r,i photometric dataset has been obtained for more than 700 young stars, ranging in mass from 0.2 to 2 MSun, and their u-band and r-band variability monitored over two full weeks. The u-band observations offer a direct access to the accretion features, hence providing a unique clue to the accretion dynamics throughout the region. I investigate the photometric properties of different stellar groups on various color-color and color-magnitude diagrams and infer a straightforward characterization based on accretion properties. I analyze the u-band variability of T Tauri stars on week timescales and probe the color signatures of different physical processes, showing that well-distinguished behaviors are specific to processes of different nature. Based on the UV excess diagnostics, I derive a dynamical picture of accretion in NGC 2264. I investigate the dependence of the inferred mass accretion rates on stellar mass and discuss the large spread in values detected at each mass. I explore the variability of the mass accretion rates on a timescale of weeks, resulting from the geometric effects linked with stellar rotation and from the intrinsic accretion variability, and show that this variability cannot explain the observed spread. |
|
We study the rotation-activity relationship for low-mass members of the young cluster h Persei (~13 Myr). h Per, thanks to its age, allows us to link the rotation-activity relation observed for main-sequence stars to the puzzling case of very young PMS stars. We constrained the activity levels of h~Per members by analyzing a deep Chandra/ACIS-I observation pointed to the central field of h Per. Considering also the catalog of h Per members with measured rotational period, presented by Moraux et al. (2013), we obtained a final catalog of 202 h Per members with measured X-ray luminosity and rotational period. We investigate the rotation-activity relation of h Per members considering different mass ranges. We find that stars with 1.3 Msun < M < 1.4 Msun show significant evidence of supersaturation for short periods. This phenomenon is instead not observed for lower mass stars. |
|
Nanoflares are candidates to produce most of the background emission from the solar corona. Recently, much work has been done with different models accompanied by different observational data to investigate the impulsive nature of heating the corona. One question is what is the weight of the events at different scales from small to large. In an attempt to improve the previous work we are about to simulate the light curves from an interest part of a full disk image of the solar corona taken by SDO/AIA, using a 0D model (EBTEL, Enthalpy Based Themal Evolution of Loop) as basic loop model. We use the simulated light curves as the trained data set and the observational time series as the test data set in the framework of an artificial intelligence system. The two data sets will feed an Artificial Neural Network (ANN) which is suitable in classifying and recognizing the samples. The comparison of the two data sets will help us to evaluate the distribution of the events that best matches the observations. |
|
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. |
|
In cold and dense interstellar regions, where temperatures can be as low as 10 K, most molecules are expected to condense onto grains, and consequently be depleted in the gas phase. CO is mostly frozen out in these environments, though it is sometimes also observed in the gas phase in a few cold molecular clouds such as IC 5146, L977 and L183. Mechanisms that were proposed to explain why CO is not fully condensed in dense clouds include UV-induced photodesorption, cosmic-ray whole grain heating, cosmic-ray spot heating, and chemical desorption of weakly bound molecules. Shen et al. (2004, A&A, 415, 203) reported a model of CO desorption from cosmic-ray-induced UV photons and showed that such a yield is almost one order of magnitude larger than that directly induced by cosmic-ray particles, while other desorption mechanisms could not explain astronomical observations. A more recent study in which pure CO ice was irradiated with an MDHL at 15-18 K showed a photodesorption yield of 2.7x10^-3 molecules photon-1 (Öberg et al. 2007, ApJ, 662, L23). In contrast, Muñ oz Caro et al. (2010, A & A, 522, A108) reported photodesorption yields for CO ice irradiated with an MDHL at 8 K and 15 K of 5.4x10^-2 and 3.5x10^-2 molecules photon^-1, respectively, which is one order of magnitude larger than the values reported by Öberg et al. (2007). In this talk, we will not only present experimental study consists in the measurement of the vacuum-UV (VUV) emission spectra of a microwave-discharge hydrogen-flow lamp (MDHL), which is commonly used in astrochemistry laboratories working on ice VUV photoprocessing, but also in the measurement of VUV absorption cross section of CO and CO2 ices in order to explain the processes induced by photons in CO ice from a broad energy range are different and more complex than the sum of individual processes induced by monochromatic sources scanning the same energy range, due to the discrepancy of absorption cross section between parent molecules and products in Ly-α and H2 molecular emission ranges. |
|
Astronomy is in a Golden Age. Ambitious surveys such as COSMOS are possible only because we have three Great Observatories operating at once - Chandra, Hubble and Spitzer - spanning the electromagnetic spectrum. COSMOS-Legacy illustrates how tightly connected these bands are. But Golden Ages are short, or they wouldn't be golden. Our Golden Age may end because our telescopes grow exponentially in cost and have reached the point where the next step is unaffordable. In the age of JWST, will we have to wait a decade or more to have complementary X-ray observations? I discuss 3 responses to this looming crisis (other than giving up!). The third response is generational in timescale but offers open-ended growth: the harnessing of space resources. Astronomers can help this era come about by re-starting "Applied Astronomy". Then we will be able to surpass COSMOS-Legacy. |
|
Brown dwarfs - objects intermediate in mass between stars and planets - are ideal benchmark objects to test theories of star and planet formation. In particular, we hope to contribute to the understanding of the Initial Mass Function, the evolution of disks, and the physics of accretion. In this talk I will present results from a variety of observational studies focused on young brown dwarfs. I will show recent findings from our brown dwarf survey SONYC (Substellar Objects in Nearby Young Cluster), from IR and submm/mm observations of brown dwarf disks, and from variability studies aimed to constrain magnetic activity and accretion. |
| Active star formation was originally identified by optical variability. Nonetheless constraints on telescope time and limitations in capability generally limited observations of young stars to single spectral observations and optical photometric monitoring. This has led to our current picture of star formation of rotating spotted star surrounded by a static disk. I discuss recent near and mid infrared observations which demonstrate that the disk is highly dynamic with periodic structure which appear to be related with both stellar rotation and circumstellar revolutionary times scales. In our JHK study of Orion we find periods for hundreds of Class I and Class II objects and demonstrate complex changes in disk structure. Mid-IR observations show significant variability as well. Finally I discuss the first X-ray observation of a planetary transit. We demonstrate the X-ray radius is significantly greater than the optical extent. |
| In questa tesi si parla di Astronomia Gamma e, in particolare, della descrizione di un simulatore che determina l'efficienza quantica del fotomoltiplicatore al Silicio (SiPM) montato sul telescopio prototipo ASTRI SST-2M. Le sorgenti VHE vengono osservate dal suolo, sfruttando il fenomeno della radiazione Cherenkov. I telescopi gia` attivi per queste osservazioni sono gli IACT, Imaging Atmospheric Cherenkov Telescopes. Di futura generazione e', invece, il CTA, Cherenkov Telescopes Array, con il quale si prevede di raggiungere un'energia di soglia di 1 Tev. L'Italia sta collaborando alla sua costruzione con il progetto ASTRI, realizzando un prototipo per i Small Size Telescopes (SST). Il prototipo monta sul piano focale un rivelatore al Silicio per il quale e' stata condotta una simulazione che restituisce l'efficienza quantica (PDE) del dispositivo. Dal momento che la casa costruttrice non forniva le dimensioni del fotomoltiplicatore, sono state prodotte diverse curve di PDE, al variare delle dimensioni del SiPM e dell'overvoltage a cui opera. L'aderenza con i dati sperimentali, rilevati dal laboratorio COLD dell'Osservatorio Astronomico di Catania, e' stata verificata con il test del chi quadro. |
| By exploiting inedited sources and pictures, a detailed history of the instrument is retraced in this talk (by I. Chinnici). The telescope, which gave an important contribution to the development of solar physics in Italy in the years 1865-1878, has been restored in 2001 and its problematic restoration will be described (by P. Brenni). As Merz telescopes were among the most successful astronomical instruments of 19th century, an article including a survey of the large Merz equatorial still extant is currently in progress and is presented in the talk (by P. Brenni, first author). |
 |
| Young stars are known to be variable sources both in optical, infrared, and X-ray. This variability is strictly correlated with their physical properties and the morphology of the circumstellar material, if any. The study of their light curves and the connection between the observed variability in the various regions of the electromagnetic spectrum provides a deep insight on the physical properties and evolutionary status of young stars, both with and without disks. This motivated the Coordinated Synoptic Investigation of the young open cluster NGC~2264 (CSI 2264, Cody et al. 2014, Stauffer et al. 2014). This project is an unique and unprecedented cooperative project involving simultaneous observations with 15 ground and space telescopes, and covering a wide part of the electromagnetic spectrum from X-ray to mid-infrared. In this talk I will compare the optical and X-ray variability of NGC 2264 candidate members using simultaneous observations taken with the Convection, Rotation and Planetary Transits satellite (CoRoT), and Chandra/ACIS-I. I will show that a significant correlation between the flux variability in optical and X-ray is observed among the stars with disk where the central star is periodically or irregularly obscured by material associated with the circumstellar disk, and that in some of these sources an increase of the hydrogen column nH is observed during the obscuration observed in optical. In more than 50\% of the disk-less objects the optical and X-ray flux variability are anticorrelated, in about 25% they are correlated, while the remainder do not show any correlation between the variability in the two bands. I will discuss how the distribution of spots in the photosphere and active regions in the stellar coronae, inclination of the rotational axis, and rotational period may influence this result. |
| Secondary eclipse observations allow the characterisation of the dayside of hot Jupiter exoplanet atmospheres. The standard, state of the art way of getting these observations is by using IRAC on the Spitzer Space Telescope. This instrument was not designed to reach the precision required to conduct these observations. However, it is possible to push IRAC to detect the secondary eclipse. It has been used for nearly 10 year to observe secondary eclipses of a handful of exoplanets. The data are strongly affected by systematic errors which can limit the accuracy that we can measure the depth of the eclipse, as well as other parameters that can be derived from the lightcurve. In this talk I discuss the way that the WASP group analyses these data and describe a method of signal injection that can help in determining more realistic error bars on the time of mid eclipse and the eclipse depth. The two are fundamental parameters that come out of these observations. I also describe the work I would like to conduct as a postdoctoral research assistant once I have completed my PhD. |
| Il restauro e la conservazione dei beni librari ed archivistici sono stati considerati per molto tempo attivita` da espletare solo in laboratorio e quasi esclusivamente a vantaggio dei pezzi piu` preziosi, importanti o rappresentativi delle collezioni. Negli ultimi anni invece si sono affermate attivita` di conservazione che beneficino un grande numero di beni. Si e`, inoltre, finalmente imposta l'idea che il conservatore-restauratore e` una figura che debba occuparsi della salvaguardia delle collezioni ad ampio spettro, prendendosi cura anche della manipolazione, della movimentazione, degli ambienti di conservazione e della musealizzazione. In quest'ottica il tirocinio pratico Corso di Laurea abilitante in Conservazione e Restauro dei Beni Culturali, ha previsto un cantiere presso la Biblioteca ed Archivio Storico dell'I.N.A.F - Osservatorio Astronomico di Palermo. Il patrimonio storico di questa istituzione conta un'importante collezione bibliografica, iniziata dal fondatore (G. Piazzi) e arricchita dai vari direttori ad esso succedutisi, un ricchissimo archivio che raccoglie la documentazione non soltanto amministrativa dell'osservatorio ed anche una preziosa raccolta fotografica di positivi e negativi ancora in parte da esplorare. |
 |
| A solar eruption after a flare on 2011 June 7 produced EUV-bright impacts of fallbacks far from the eruption site, observed with the Solar Dynamics Observatory. These impacts can be taken as a template for the impact of stellar accretion flows. Broad redshifted UV lines have been commonly observed in young accreting stars. Here we study the emission from the impacts in the Atmospheric Imaging Assembly's UV channels and compare the inferred velocity distribution to stellar observations. We model the impacts with two-dimensional hydrodynamic simulations. We find that the localized UV 1600 A emission and its timing with respect to the EUV emission can be explained by the impact of a cloud of fragments. The first impacts produce strong initial upflows. The following fragments are hit and shocked by these upflows. The UV emission comes mostly from the shocked front shell of the fragments while they are still falling, and is therefore redshifted when observed from above. The EUV emission instead continues from the hot surface layer that is fed by the impacts. Fragmented accretion can therefore explain broad redshifted UV lines (e.g., C IV 1550 A) to speeds around 400 km/s observed in accreting young stellar objects. |
| In this talk I want to report on my research activity during the past two years at INAF-OAPa, which has been focused on the study of systems with hot Jupiters. In particular, I will show how hot Jupiters can affect the activity of their host stars, in two examples: HD 189733 and WASP-18. I will briefly report on results from another couple of systems with planets in eccentric orbits. In addition, I will mention other results from the study of star forming regions and the search in X-rays of low mass companions to Cepheids. |
| I shall review some phenomena possibly related to the magnetic interaction between late-type stars and close-in massive planets and discuss models proposed for their interpretation. I shall consider the possible effects of hot Jupiters on stellar chromospheric emission and on stellar rotation. On the other hand, magnetic reconnection between stellar and planetary magnetic fields may enhance the evaporation of the closest planets (i.e., those with an orbital semimajor axis smaller than about 0.05 AU) adding to the effect of the extreme ultraviolet flux coming from the outer stellar atmospheres. |
| High energy photons produced in the acceleration regions of strong shocks, such as supernova remnants (SNR) or bow shocks formed by runaway stars, are suggested to have a non-thermal origin. However, the efficiency of these processes is still debated. Here we aim to develop a non-thermal model by appealing to a mixed leptonic-hadronic scenario to explain the observational data obtained from the SN 1006 and the bow shock formed by the runaway star AE Aurigae. |
| Photometric variability is a defining property of T Tauri stars, manifest at a wide range of wavelengths and on different timescales (hours, days, months, years). Exploring YSOs variability across wavelength and time domain is of utmost importance in order to unveil the dynamics and mechanisms at play in different systems. In this talk, we present and discuss the mid-term variability of pre-main sequence stars in NGC 2264 (3 Myr) at UV and optical wavelengths. The bulk of the study is a 2 week-long u+r monitoring survey performed in February 2012 with CFHT/MegaCam, as a part of the CSI 2264 campaign (Cody et al. 2014). We find that accreting objects (CTTS) exhibit a significantly larger amount of variability than non-accreting members (WTTS), in the optical and especially in the UV. A definite correlation is observed between variability indicators and the measured UV excess for the former group; this suggests that accretion mechanisms have a primary impact on the observed variability amplitudes for CTTS. We investigate the (u-r) color variations that accompany magnitude variations for different classes of objects, and explore the connection between these color signatures and the physics of the systems. An extensive spot modeling of u-band and r-band variability amplitudes is performed to probe the nature of the variability displayed by NGC 2264 members. Finally, we compare the amount of mid-term variability with magnitude variations on shorter and longer timescales, in order to identify the leading timescales and contributions to u-band variability and assess its stability over the baselines investigated. |
| The FP7 funded project EXTraS (Exploring the X-ray Transient and variable Sky) is an international project led by INAF, aimed to characterize the soft X-ray variability of all the sources detected in the whole archive of the XMM-Newton mission, and to look in this archive for new transient sources. During the feasibility study, a transient was detected from ISO-Oph 85, a young stellar object (YSO) supposed to be in a very early evolutionary stage and, so, very little active in X-rays. An X-ray time resolved and spectral analysis was performed. Infrared data were also analysed in order to establish the evolutionary stage of ISO-Oph 85. Here we present the obtained results. An insight into the opportunities given by EXTraS for the research in the YSOs field is also provided. |
| Meteorites are solar system objects that have fallen to the Earth. They provide us an abundant supply of material for study in the laboratory without the expense and complication of sample-return missions. They represent a wide range of types, places of origin, and histories, and through laboratory study they help develop our understanding of the formation and history of the solar system. Found embedded in certain meteorites are refractory inclusions that represent the earliest materials known to have solidified out of the solar nebula, 4.567 billion years ago. Some meteorites originated on known bodies such as the asteroid 4 Vesta, the Moon, or Mars, and help us interpret data from space missions to these objects. Nevertheless, the range of materials we can study is limited to those objects, mostly from the inner asteroid belt, that can survive entry to the Earth. The vast majority of the solar system is unrepresented in the meteorite population. I will speak generally about different types of meteorites that are known and what we have learned from them, and then discuss my own research studying density and porosity of meteorites and lunar materials. |
| Il seminario e' finalizzato ad illustrare la politica dell'INAF per massimizzare il ritorno, in termini di innovazione, degli investimenti in astrofisica. |
| La scoperta di Cerere, avvenuta a Palermo per opera di Giuseppe Piazzi la notte del 1 gennio 1801, e' stata un evento con molti retroscena, a volte poco noti. In questo seminario saranno messi in luce alcuni aspetti legati al contesto storico-scientifico dell'epoca, alla personalita' dei protagonisti della vicenda e alle problematiche scientifiche della comunita' astronomica internazionale tra la fine del XVIII e i primi del XIX secolo. |
| The early stages of a star birth are characterised by a variety of mass ejection phenomena, including outflows and collimated jets, that are strongly related with the accretion process developed in the context of the star-disc interaction. After been ejected, jets move through the ambient medium, interacting and producing shocks and complex structures that are observed at different wavelength bands. In particular, X-ray observations show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary and have been interpreted as shock diamonds. We aim at investigating the physical properties of the shocked plasma and the role of the magnetic field on the collimation of the jet and the location, stability and detectability in X-rays of the stationary shock formed. We performed 2.5D MHD simulations, including the effects of the thermal conduction and the radiative losses. We modelled the propagation of a jet ramming with a supersonic speed into an initially isothermal and homogeneous magnetized medium. We studied the physics that guides the formation of a stationary shock (for instance a shock diamond) and compared the results with observations, via the distribution of emission measure vs. temperature and the luminosity synthesized from the simulations output data. |
| Coupling high-power lasers and high-strength B-fields helps gaining unique insight and understanding of a variety of phenomena of crucial importance for astrophysics. We have shown that such platform could be used to mimic the expansion of a young star isotropic disk wind threaded by a co-axial poloidal magnetic field. It reveals that long-range collimated jets can indeed by result from such system, complementing toroidal B-fields that help shape the initial matter from the star into a jet. The same system can then be used to study the dynamics of the accretion of magnetized plasma columns onto star surfaces and help decipher the underlying physics, or also the issue of particle energization in astrophysical plasmas. Our investigations on these topics will be reviewed and prospects discussed. |
| The first characteristic measured for Cepheids is their periods. The next step is to determine their pulsation mode. We have made month long observations with the MOST satellite of a fundamental mode Cepheid (RT Aur) and an overtone Cepheid (SZ Tau). The quantity and quality of the satellite data have shown that the Fourier parameters of the overtone are far more variable than those of the fundamental. A series of studies have been made of the binary properties of Cepheids, providing insight into star formation and dynamical evolution. A survey of 70 Cepheids was made with HST WFC3 to identify possible resolved companions. This was followed up with XMM-Newton observations to determine which possible companions are young X-ray active stars, and hence physical companions of Cepheids. This provides information about the frequency, separations, and mass ratios. Finally, the measured masses of Cepheids will be summarized, and new developments discussed. |
| Simulating the formation of galaxies in a cosmological context, starting from small Gaussian perturbations in the linear regime as given by the concordance LambdaCDM model, is a challenge both from the physical and the numerical point of view. In recent years there has been a breakthrough in our ability of reproducing spiral galaxies with extended disks and limited or negligible bulges, and now simulations of small but significant cosmological volumes (~100 Mpc) can produce galaxy populations with realistic properties. However, a true ab-initio approach is hampered by the wide range of scales that needs to be taken into account, given the importance of energetic feedback from massive stars and their SNe. With resolution limited to ~kpc scales, many important processes must be taken into account through suitable sub-resolution models. I will present results from a simulation program that we are carrying on in Trieste, discuss the potentialities and limits of this approach, and highlight what we can expect in the near future. |
| Evidence for some super-hot plasma (> 4 MK) has been found in the core of active region loops. This is a signature of impulsive heating (nano-flaring). We study the EUV light curves in one or a few pixels with a model of multi-stranded coronal loop. Each strand is pulse-heated. In the hypothesis of an energy distribution of the heat pulses, we first generate a grid of strand models with different heating rates, and then we combine them randomly to generate simulated light curves similar to the observed ones. We make 10000 realisations for each set of model parameters (the power law index of the energy distribution, the duration of the heat pulse, the number of strands) and compare them to the observed light curves to find the best one by means of an artificial intelligence system (Probabilistic Neural Network, PNN). Cross-Correlation is used as a cross-check. We find that a shallow (but not flat) distribution of short-duration pulses in a relatively high number of strands (1000) best describes the observed data. A space-resolved loop model with these parameters predicts different fluctuations of the emission from the bottom to the top of the loop: we compare with observation. |
| We are using the GMOS integral field unit on the Gemini telescopes to investigate the kinematics of the circum-nuclear ionized gas in a sample of nearby AGNs spanning a wide range of nuclear hard X-ray luminosity (a proxy for the SBH accretion rate). The study aims at investigating the mechanisms channeling gas (the supermassive black hole fuel) from the inner kiloparsec down to few tens of parsecs from the supermassive black hole. The galaxy NGC 1386 turned out to be one of the most interesting sources: we found that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN "radiation cone". However, there is also compelling evidence for an equatorial outflow. A new clue to the physical processes operating in AGNs? |
| In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks orbiting around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cygnus OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun, and hosts hundreds of massive stars and thousands of low mass members, both with and without disks. We have analyzed the spatial variation of the disk fraction (i.e. the fraction of cluster members bearing a disk) in Cygnus OB2 and and studied its correlation with the local values of Far and Extreme ultraviolet radiation fields and the local stellar surface density. We found evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV field and large stellar density. In particular, the FUV radiation dominates disks dissipation timescales in the proximity (i.e. within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars due to absorption by the intervening intracluster material. Comparing our results to what has been found in other young clusters with different massive populations, it is possible to conclude that massive associations like Cygnus OB2 are potentially hostile to protoplanetary disks, but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy. |
| The race towards the discovery and characterization of terrestrial extrasolar planets, possibly in the habitable zone of their host stars, that recent statistical analyses revealed to have high occurrence rates, represents a scientific adventure rich of great expectations, but also of great challenges. I will address the subject starting from my experience in planet hunting as a collaborator of the Italian ground-based surveys GAPS and APACHE, that aim for a similar goal in complementary ways: through the analysis of the stellar radial velocity variations the first, with the photometric transit method the second. In particular, I will explore the limits imposed by signals of stellar origin to the detection and mass determination of another Earth in precise radial velocity measurements, discussing some proposed strategies to mitigate the impact of stellar noise. Moreover, I will focus the discussion on M dwarfs, which represent a treasure trove for the search of Earth-like planets, but demand particular attention both for the detection and characterization of small planets. |
| According to the magnetoshperic accretion scenario, during their evolution, Classical T Tauri stars accrete material from their circumstellar disk. The accretion process is regulated by the stellar magnetic field and produces hot and dense post-shocks on the stellar surface as a result of impacts of the downfalling material. The impact regions can be studied through the analysis of some UV and X-ray emission lines which trace hot gas flows and act as diagnostics of the post-shock downfalling plasma. In the UV band, these lines are characterized by rather complex profiles whose origin is still unclear. In this work we investigate the origin of UV and X-ray emission at impact regions of fragmented accretion streams. The aim is to understand if and how the stream fragmentation and the resulting structure of the post-shock region determine the observed profiles of UV and X-ray emission lines. To this end we model the impact of a fragmented accretion stream onto the chromosphere of a CTTS with 2D axysimmetric magneto-hydrodynamic simulations. Our model takes into account the gravity, the stellar magnetic field, the thermal conduction and the radiative cooling from an optically thin plasma. From the model results, we synthesize the UV and X-ray emission including the effect of Doppler shift along the line of sight. We find that a fragmented accretion stream produces complex profiles of UV emission lines which consists of multiple components with different Doppler shifts. Our model predicts line profiles that are consistent with those observed and explain their origin as due to the stream fragmentation. |
| Colliding neutron stars (NSs) are strong sources of gravitational radiation, and one of the most promising candidates for direct detection by advanced LIGO. Following the spectacular observations of gravitational waves from GW150914 - produced by the collision of two black holes - we can now expect that the direct detection of NS collisions is just around the corner. Growing observational evidence shows that NS collisions also produce bright electromagnetic signals: gamma-ray bursts, and macronovae. The former are brief flashes of gamma-ray radiation, the latter are short-lived infrared transients powered by the radioactive decay of heavy nuclei. The simultaneous detection of both electromagnetic and gravitational radiation arising from NS collisions would be a revolutionary observation. This exciting prospect makes these systems prime targets in the era of multi-messenger astronomy. In this talk, I present ongoing observational efforts to characterize the electromagnetic signatures of NS collisions, and outline future initiatives aimed at exploring the gravitational wave sky. |
| CARMENES, the brand-new, Spanish-German, two-channel, ultra-stabilised, high-resolution spectrograph at the 3.5 m Calar Alto telescope, started its science survey on 01 Jan 2016. In one shot, it covers from 0.52 to 1.71 mum with resolution R = 94,600 (lambda less then 0.96) and 80,400 (lambda larger than 0.96 mum). During guaranteed time observations, CARMENES carries out the programme for which the instrument was designed: radial-velocity monitoring of bright, nearby, low-mass dwarfs with spectral types between M0.0 V and M9.5 V. Carmencita is the CARMEN(ES) Cool dwarf Information and daTa Archive, our input catalogue, from which we select the about 300 targets being observed during guaranteed time. Besides that, Carmencita is perhaps the most comprehensive database of bright, nearby M dwarfs ever built, as well as a useful tool for forthcoming exo-planet hunters: ESPRESSO, HPF, IRD, SPIRou, TESS or even PLATO. Carmencita contains dozens of parameters measured by us or compiled from the literature for about 2,200 M dwarfs in the solar neighbourhood brighter than J = 11.5 mag: accurate coordinates, spectral types, photometry from ultraviolet to mid-infrared, parallaxes and spectro-photometric distances, rotational and radial velocities, Halpha pseudo-equivalent widths, X-ray count rates and hardness ratios, close and wide multiplicity data, proper motions, Galactocentric space velocities, metallicities, full references, homogeneously derived astrophysical parameters, and much more. I will briefly describe the instrument CARMENES, the consortium that built it and now operates it, the sample, the status of the science survey, and some ideas for the future. |
| Dense plasma fragments were observed to fall back on the solar surface by the Solar Dynamics Observatory after an eruption on 7 June 2011, producing strong EUV brightenings. Previous studies investigated impacts in regions of weak magnetic field. Here we model the ~ 300 km/s impact of fragments channelled by the magnetic field close to active regions. In the observations, the magnetic channel brightens before the fragment impact. We use a 3D-MHD model of spherical blobs downfalling in a magnetized atmosphere. The blob parameters are constrained from the observation. We run numerical simulations with different ambient density and magnetic field intensity. We compare the model emission in the 171 A channel of the Atmospheric Imaging Assembly with the observed one. We find that a model of downfall channelled in a ~ 1 MK coronal loop confined by a magnetic field of ~ 10-20 G, best explains qualitatively and quantitatively the observed evolution. The blobs are highly deformed, further fragmented, when the ram pressure becomes comparable to the local magnetic pressure and they are deviated to be channelled by the field, because of the differential stress applied by the perturbed magnetic field. Ahead of them, in the relatively dense coronal medium, shock fronts propagate, heat and brighten the channel between the cold falling plasma and the solar surface. This study shows a new mechanism which brightens downflows channelled by the magnetic field, such as in accreting young stars, and also works as a probe of the ambient atmosphere, providing information about the local plasma density and magnetic field. |
| I will present results from my recent papers based on XMM-Newton observations of young stars in Star Forming Regions near Orion A (Kappa Ori) and Rho Ophiuchi. These observations were aimed at discovering new young stars and infer their ages, their distances and the relationship with the parent cloud. In Kappa Ori, with 40 ks of XMM/EPIC we have derived X-ray fluxes and luminosities of about 120 young stars with and without disks near Kappa Ori (B0 type). X-ray luminosity functions provided a "yardstick" to infer that these stars form a separate cluster centered on Kappa Ori (~250 pc), much closer than ONC (~410 pc) and unrelated to it. In Rho Ophiuchi, with 50+140 ks we have discovered a group of disk-less stars around Rho Oph itself and significantly older (5-10 Myr) than the bulk of YSOs (1 Myr) in the main core of the cloud, L1688. As an unexpected discovery, Rho Oph itself is a periodic emitter of hard X-rays, mimicking a "X-ray lighthouse", and hinting that either a strong magnetism or an unseen companion are the source of such X-rays. |
| Space missions are very complex projects with peculiar characteristics such as: strategic importance, extent of international participation, specialized industrial sector, high investment costs, long-term program duration, impossibility of intervening in space for repairs and/or maintenance. These peculiarities strongly influence the realization process since its conception. This talk provides an introduction to methods and tools of project management of a space mission under the guidance of the European Space Agency. The following topics will be covered: General section: - Introduction to management of complex projects; - Key elements for the design of a space mission; - Main phases for the development of a space mission; - The life cycle of ESA programs; - The European Cooperation for Space Standardization (ECSS) documentation for project management and quality control. Phase A study: - Objectives of a phase A; - The main activities of analysis and development; - Preliminary Requirements Review (PRR) documentation. |
| High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in Classical T Tauri stars (CTTS). In particular the accretion-shock region, where the accreting material is heated to temperatures of a few million degrees, can be probed by X-ray spectroscopy. MHD models predict that this hot post-shock plasma should have an inward bulk motion, with v_post ~ 100 km/s, with respect to the surrounding stellar atmosphere. To verify this prediction we searched for a Doppler shift in the deep Chandra/HETG observation of the CTTS TW Hya, perfectly suited for this task because of the excellent S/N and spectral resolution of the dataset, and because of the ideal target inclination. This test should allow us to constrain definitively the nature of this X-ray emitting plasma component in CTTS, and infer constraints on the accretion stream geometry. We searched for a Doppler shift in the X-ray emission from TW Hya by measuring the position of a selected sample of emission lines. To check the absolute wavelength calibration of the Chandra gratings, and to check whether or not bulk motions with respect to the photosphere are observed in coronal plasma, we also analyzed a sample of Chandra/HETG spectra of non-accreting active stars. We found that the soft part of the X-ray spectrum of TW Hya is significantly red-shifted by ~40 km/s with respect to the known radial velocity of the stellar photosphere. Conversely no X-ray redshift is observed in the X-ray emission of non-accreting active stars. The evidence that the X-ray emitting plasma on TW Hya is moving inward with respect to the stellar surface definitively confirms that it originates in the post-shock region, at the base of the accretion stream, and not in coronal structures. The observed radial velocity indicates that the base of the accretion stream on TW Hya is located at low latitudes on the stellar surface. Moreover the observed velocity of the soft X-ray emitting plasma is very similar to the velocity of the narrow component of the CIV resonance doublet at 1550 A, suggesting that they both originate from the same post-shock regions, that the hypothesis of free-fall regime in the accretion streams holds, and that complex magnetic field geometries, as that of TW Hya, allow low latitude accretion spots. |
| The Carte du Ciel project is considered the mother of all astrometric enterprises. It was conceived at the end of 19th century and was aimed at photographing the entire sky vault, to produce a catalogue of stars up to magnitude 11 and a chart containing stars up to magnitude 14.. This international endeavour was promoted by Paris Observatory in 1887: 18 observatories from both hemispheres participated in it, more or less successfully. This talk will illustrate how the project was originated and developed, why it remained partially inachieved and what was its impact on the astrometric missions which preceded the current GAIA mission. |