Dynamics of magnetic structures in the solar corona

MHD modeling of magnetic structures of the solar corona and Coronal Mass Ejection (CME). The studies are devoted to discover new diagnostic tools and to acquire new insight in the detailed physics of magnetic structures of the solar corona The project is based on the FLASH and PLUTO codes and we performed extensive 2D and 3D MHD simulations, using substantial resources, including those of a PRACE Project and 2 national key-projects, at CINECA. Currently we are analysing the propagation of high-speed chromospheric flows into coronal magnetic flux tubes, and the possible production of emission in the EUV band (Petralia et al. 2014, A&A submitted). Also we are investigating the heating released by magnetic reconnection of a twisted coronal loop in the framework of a PRACE project[ .... read more .... ].

Physics of accretion phenomena in young stellar objects

Modeling of accretion streams impacting onto the surface of classical T Tauri stars (CTTSs) with the aim to analyze the relation between the physical and chemical properties of the accretion stream (flux velocity, mass density and chemical abundances) and the observed X-ray spectrum of young accreting stars. The project takes advantage of two well-tested advanced numerical codes, namely FLASH and PLUTO. We performed extensive 1D hydrodynamic simulations (with FLASH) and 2D MHD simulations (with PLUTO), using resources at CINECA. Our first study, aimed at investigating the dynamics and stability of shock-heated accreting material in CTTSs, was based on a 1D hydrodynamic model and has shown that accretion shocks may generate an hot slab of material above the chromosphere with temperature and mass density consistent with those observed (Sacco et al. 2008). As a next step, we have used the same model to investigate the observability of accretion shocks, by exploring a wide range of physical parameters (Sacco et al. 2010). In another work we investigated the stability and variability of accretion shocks by means of 2D MHD simulations to evaluate the role of the stellar magnetic field in confining the accretion column and the post-shock hot slab for different values of the plasma-beta (Orlando et al. 2010).

Flaring events in classical T Tauri stars

MHD modeling of flares occurring in young stellar objects (YSOs) with the aim to investigate the effects of the flares on the stability of the circumstellar disk surrounding the central protostar. The project is based on the PLUTO code and we performed extensive 2D and 3D MHD simulations, using substantial resources, including those of 1 key-project, at CINECA. A first work was devoted to study the evolution of a flare occurring close to the surface of the circumstellar disk and its effects on the stability of the disk (Orlando et al. 2011). We investigated the conditions under which a flare may trigger mass accretion episodes. Recently a Class A project has been approved by ISCRA to further investigate this issue. In particular the project aims at exploring in more detail the possibility that significant mass accretion in young stars can be triggered by a storm of small-to-medium flares (as those frequently observed) occurring on the accretion disk. This study will shed light on the nature of the phenomena driving the high levels of coronal activity in YSOs and on their role in the accretion processes.

Evolution of protostellar jets and origin of their X-ray emission

Modeling of protostellar jets, aimed at investigating the origin of X-ray emission originating from jets and how jets interact with other protostellar components (circumstellar environment, disk, etc.) through radiation and/or mechanical impact. This program is based on the FLASH code; we performed extensive 2D hydrodynamic simulations, obtaining substantial resources at CINECA. In two papers (Bonito et al. 2004, 2007), we investigated the origin of X-ray emission originating from protostellar jets, explaining in a natural way, without any ad hoc assumption, that this emission originates just behind the interaction front of the jet with the surrounding medium. We have further investigated the morphology and time variability of X-ray emission from jets, modeling the interaction of jets with inhomogeneous surrounding medium and considering pulsed jets instead of continuous jets (Bonito et al. 2010a, 2010b).

Evolution of nova outbursts

Three-dimensional Hydrodynamic modeling of the outburst of a nova expanding through the highly inhomogeneous circumstellar medium (CSM), aimed at investigating the role played by the inhomogeneous medium and by different physical processes (thermal conduction, radiative losses, etc.) in determining the shape an morphology of the nova remnant. The pre-explosion system conditions includes the companion star and the accretion disk around the white dwarf. The models have been used to investigate three nova outbursts occurred in 2006 (RS Ophiuchi, Orlando, Drake, & Laming 2009), and 2010 (U Scorpii, Drake & Orlando 2010; V 407 Cygni, Orlando & Drake 2012) through the comparison with X-ray observations. In all the cases, the simulations have shown that the inhomogeneous CSM can have a profound influence on the evolving blast wave. In particular, the accretion disk around the white dwarf or an equatorial density enhancement can determine a poleward hydrodynamic collimation of the blast and of the ejecta, leading to a bipolar X-ray emitting shell.

Interaction of supernova remnants with the surrounding environment

MHD modeling of supernova remnant (SNR) shocks expanding through a magnetized inhomogeneous medium, aimed at investigating the physical conditions leading to the complex morphologies of SNRs observed in the X-ray band. This program is based on the FLASH code; we performed extensive 2D and 3D hydrodynamic and MHD simulations, obtaining substantial resources, including those of 2 key-projects, at CINECA. We have studied the interaction of SNR shock waves with inhomogeneities of the ISM (Orlando et al. 2005, 2006, 2008, 2010, Miceli et al. 2006), with the aim to study the role of the physical processes at work (e.g. magnetic-field oriented thermal conduction, radiative losses, etc.), and to derive new diagnostics of the shock-cloud interaction. We are studying the evolution of a stellar fragment ("shrapnel") ejected in a supernova explosion (Miceli et al. 2012, in preparation) with the aim to investigate how the shrapnels modify the morphology and chemical composition of SNRs.

Effects of cosmic ray particle acceleration on the evolution of supernova remnants

We study the synchrotron radio, X-ray, and inverse Compton gamma-ray emission originating at the shock front of SNRs (Orlando et al. 2007, 2009, 2010); we have investigated the role of a non-uniform interstellar medium (ISM) or of a non-uniform ambient magnetic field in determining the asymmetric morphology of bilateral supernova remnants (BSNRs) as observed in the radio (Orlando et al. 2007; Bocchino et al. 2011) and in the X-ray and gamma-ray bands (Orlando et al. 2011).