Calendar

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.