We study how galaxy morphology changes the relation among the inner slope [Formula: see text] of galactic density profiles and the stellar mass, and rotation velocity. We find that the slope [Formula: see text] flattens monotonically from [Formula: see text] to [Formula: see text] going from giant galaxies (ellipticals, spirals) to dwarf galaxies ([Formula: see text]). At masses smaller than [Formula: see text], in the mass range dominated by nonrotational supported galaxies (e.g. dSphs), the slope steepens due to the offset in angular momentum of rotational dominated, and nonrotational dominated galaxies. A comparison with SPH simulations finds our result in qualitative agreement with them, but the inner slope [Formula: see text] at small stellar masses is flatter than that in their simulations. Density profiles become cuspy for [Formula: see text] in the range [Formula: see text]–[Formula: see text], similarly to Õnorbe.

In this paper, in the framework of the secondary infall model, the correlation between the central surface density and the halo core radius of galaxy, and cluster of galaxies, dark matter haloes was analyzed, this having recently been studied on a wide range of scales. We used Del Popolo (2009) secondary infall model taking into account ordered and random angular momentum, dynamical friction, and dark matter (DM) adiabatic contraction to calculate the density profile of haloes, and then these profiles are used to determine the surface density of DM haloes. The main result is that $r_\ast$ (the halo characteristic radius) is not an universal quantity as claimed by Donato et al. (2009) and Gentile et al. (2009). On the contrary, we find a correlation with the halo mass $M_{200}$ in agreement with Cardone & Tortora (2010), Boyarsky at al. (2009) and Napolitano et al. (2010), but with a significantly smaller scatter, namely $0.16 \pm 0.05$. We also consider the baryon column density finding this latter being indeed a constant for low mass systems such as dwarfs, but correlating with mass with a slope $\alpha= 0.18 \pm 0.05$. In the case of the surface density of dark matter for a system composed only of dark matter, as in dissipationless simulations, we get $\alpha=0.20 \pm 0.05$. These results leave little room for the recently claimed universality of (dark and stellar) column density.

A recent reformulation of the equation of state (EoS) for ideal flows is here applied for accretion disc flows. Such an EoS, correctly describing shear flows, also includes the physical dissipation necessary to handle shock fronts and discontinuities in the flow for non reversible physical events. It is also recently shown that the chosen SPH Kernel deeply affects the particle interpolation integrals. A Gaussian SPH in extended range (GASPHER) interpolation Kernel, originated from the Error function (and Gaussian integrals), better deals with both free edge boundary layers difficulties, as well as any spatial transport phenomenon, better conserving the total energy. According to such new approaches, some examples on accretion disc models in close binaries (CBs) are here reported. According to the new implementations, the physical dissipation alone, included in the EoS, cannot be responsible of the transport mechanism engine producing a well bound accretion disc in an inviscid Euler scheme. Periodical phases of mass accumulation and loss characterize non viscous discs. Therefore, a physical turbulent viscosity is necessary to form well bound discs in a Navier-Stokes scheme.

We present here a study based on the migration of protoplanets in an accretion disc of a forming star, as the mainly proposed scenario for the formation of planetary systems. Attention is here focused on the mutual interactions between two protoplanets, both embedded in the accretion disc, as a function of the protoplanets masses, their relative positions, the dynamic properties of the accretion disc particles. The study is performed through a 2D SPH code and preliminary results show an oscillation of the distance between the two protoplanets, together with a slow migration of the two planets towards the central star when two Jupiter-like planets are considered. Less correlated behaviour is observed when at least one of the two protoplanets has an Earth-like mass. The role played by the disc particles initial angular momentum is discussed.

Migration of protoplanets inside an accretion disc of a forming star is the most probable scenario for planetary system formation according to current models. Unsolved problems exist, concerning migration times and mechanisms. We report here the results of a 2D hydrodynamic study within an SPH scheme, analysing migration of an Earth-like or a Jupiter-like planet inside an inviscid sub-Keplerian accretion disc, as a function of the initial specific angular momentum of the infalling accretion disc matter. Particle capture by the protoplanet causes a rapid migration, within a few orbits, for the Earth like planet, and about 104 orbits for the Jupiter like planets. The effect of a planet pseudo-atmosphere is also

Current theories on planetary formation suggest that the formation of giant planets is related to their quick migration towards the central star as a result of protoplanet-disc interactions on a time-scale of the order of 10 5 yr, for objects of nearly 10 terrestrial masses. Such a time-scale should be smaller by an order of magnitude than that of gas accretion on to the protoplanet during the hierarchical growth of protoplanets from collisions with other minor objects. These arguments have recently been analysed using N-body and/or fluid-dynamics codes or a mixture of the two. In this work, we have performed inviscid two-dimensional simulations, using the smoothed particle hydrodynamics (SPH) method, to study the migration of one protoplanet, in order to evaluate the effectiveness of the accretion disc in the protoplanet dragging towards the central star, as a function of the mass of the planet itself and of the disc tangential kinematics. For this purpose, the SPH scheme is considered suitable to study the roles of turbulence, kinematic and boundary conditions, because of its intrinsic advective turbulence, especially in two- and three-dimensional codes. Simulations are performed in both sub-Keplerian and Keplerian disc kinematic conditions as a parameter study of protoplanetary migration if moderate and consistent deviations from Keplerian kinematics occur. Our results show the migration times of a few orbital periods for Earth-like planets in sub-Keplerian conditions. For Jupiter-like planets, estimates show that about 10 4 orbital periods are needed to half the orbital size. Time-scales of planet migration are strongly dependent on the relative position of the planet with respect to the shock region near the centrifugal barrier of the disc flow.

Migration of protoplanets in an accretion disc of a forming star is currently the most believable scenario for the formation of planetary systems, but much work still has to be done to understand the migration mechanisms due to the planet-disc interactions. Attention is here focused on the evolution of the orbit of an asteroid type body with an initially tilted orbit, under the influence of the gravitational interaction with the accretion disc and with a more massive protoplanet (both Jupiter-like and Earth-like protoplanets are considered). A SPH based three-dimensional model is used to analyse this physical scenario. Both “internal fragment external protoplanet” and “external fragment internal protoplanet” configurations are considered.

Migration of protoplanets within an accretion disc of a forming star seems to be the basic scenario for planetary systems formation. Many details concerning the dragging mechanisms, times and the dominant physical interactions between the protoplanets and the accretion disc are still debated. We report here the results of a study based on 3D Smoothed Particle Hydrodynamic (SPH) simulations, concerning the evolution of the orbital parameters of an asteroid type body embedded in an inviscid accretion disc, with an initially tilted orbit. Both rapid periodic variations of the tilt angle between the fragment angular momentum and the disc mean angular momentum, and a slow monotonic decrease are observed.

Physical turbulent viscosity in an accretion disc involves an enhanced radialmass and angular momentum transport in high compressibility conditions. However, asticking e ect throughout the disc, a ects the low compressibility disc’s dynamics. Pairsof compressibility-viscosity values, together with initial kinematic conditions at the innerLagrangian point, can define a well-bound accretion disc, whilst other pairs cannot producesuch well-bound structures. In this work, the role of the stellar mass ratio M 1 = M 2 (SMR)between the compact primary and the companion in a close binary system (CB) is alsotaken into account. Results show that such role is essential in modifying domains whereparameters compressibility-viscosity-injection velocity at L1 allow a well defined disc con-sistency. The higher the SMR M 1 = M 2 , the wider the domain where the accretion disc showsa well-bound consistent structure. Key words. Accretion: Accretion Discs – Methods: Numerical – Stars: Close Binaries –Stars: Dwarf Novae

At present, it is difficult to identify extrasolar planets whose masses are lower than that of Neptune. Current theories on planetary formation describe the formation process as: 1) grain coalescence in kilometre-sized planetesimals; 2) growing-up of planetesimals by accumulation through sweeping in about 100 Km planetesimals; 3) “oligarchic” growingup of such protoplanets by collisions with other minor objects, up to 10 terrestrial masses beyond 3 AU, or the formation of martian planets within 3 AU. Martian planets could grow up by mutual collision and accumulation forming terrestrial planets. In this work, 3D SPH simulations are performed to study the kinematic evolution of a fragment (planetesimal or asteroid) in a tilted orbit with respect to the accretion disc.

Adopting the smoothed particle hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D, axially symmetric, physically viscous accretion disc around a black hole (BH) in an AGN. In such disc models, the role of the specific angular momentum λ and of the physical turbulent viscosity parameter α, according to the Shakura and Sunyaev prescription, are examined. One or two shock fronts develop in the radial inviscid flow, according to the assigned initial kinematic and thermodynamic conditions. Couples of (α, λ) values determine radial periodical oscillations in the shock front. An outflow can develop from the subsonic post shock region, close to the black hole, in some cases. This provides evidence for a link between the accretion disc and the fueling of a jet, through the presence of shock fronts in an accretion disc close to the centrifugal barrier.

Aims. Adopting the Smoothed Particle Hydrodynamics ( SPH) numerical method, we performed a grid of evolving models of a 3D axially-symmetric, viscous accretion disc around a supermassive black hole ( SMBH) of 10(6) divided by 10(9) M(circle dot). Such sort of simulations are typical of accretion discs in active galactic nuclei ( AGN). In such disc models, we pay attention to the role of the specific angular momentum gimel and the turbulent viscosity parameter alpha, according to the Shakura and Sunyaev prescription. One or two shock fronts in the radial inviscid flow develop, according to the assigned initial kinematic and thermodynamic conditions.Methods. By fixing the initial and boundary conditions on the flow at the disc outer edge, where the total energy, the specific angular momentum gimel, and the initial velocity are concerned, we find pairs of (alpha,gimel) values determining radial periodical oscillations in the shock front. In some cases, an outflow develops from the subsonic post-shock region, close to the black hole.Results. The link between the accretion disc and the jet refueling through the onset of a centrifugal shock front is evident. We also compare model variability periods with observed ones in the radio light curves of AGN.

Aims. Physical viscosity naturally hampers gas dynamics ( rarefaction or compression). Such a role should support accretion disc development inside the primary gravitation potential well in a close binary system, even for low compressibility modelling. Therefore, from the astrophysical point of view, highly viscous accretion discs could exist even in the low compressibility regime showing strong thermal differences to high compressibility onesMethods. We performed simulations of stationary Smooth Particle Hydrodynamics (SPH) low compressibility accretion disc models for the same close binary system. Artificial viscosity operates in all models. The absence of physical viscosity and a supersonic high mass transfer characterize the first model. Physical viscosity and the same supersonic high mass transfer characterize the second model, whilst physical viscosity and a subsonic low mass transfer characterize the third model. The same binary system parameters, such as stellar masses and their separation, have been adopted, as well as the same polytropic index gamma = 5/3. Thus we investigated the role of physical viscosity in mass and angular momentum transport in the two viscid models and compare them to the inviscid model. An initial value of the parameter alpha = 1 has been considered for the physically viscous models, according to the well-known Shakura and Sunjaev formulation, but simulations were carried out also for alpha = 0.1 and alpha = 0.5 in the case of a supersonic mass transfer. Physical viscosity is represented by the viscous force contribution expressed by the divergence of the symmetric viscous stress tensor in the Navier-Stokes equation, while the viscous energy contribution is given by a symmetric combination of the symmetric shear tensor times the particle velocity.Results. The results show that physical viscosity supports and favours accretion disc formation despite the very low compressibility assumed. On the contrary, in the inviscid case no evident disc structure appears. In all models neither shock fronts nor extended clear spirals in the radial flow develop.

The weakly non-linear interaction of slow magnetoacoustic and torsional Alfven waves propagating along an unperturbed poloidal magnetic field in a stellar interior is studied in the high plasma beta limit. It is shown that slow magnetoacoustic waves parametrically drive torsional modes with the half frequency and wave number. Therefore global slow magnetoacoustic waves which have a radial velocity polarization, may amplify the torsional oscillations. Possible applications of this mechanism to the Sun and binary stars are briefly discussed.

Ulysses spacecraft discovered the long-period, outwardly propagating Alfvén waves in the solar polar regions (Balogh et al. 1995). Here we suggest that the waves may be generated in the solar interior due to the pulsation of the Sun in the fundamental radial mode or in low-frequency g-modes. The period of fundamental mode is about 1 hour, while the period of g-modes can be longer. The pulsation causes a periodical variation of density and large-scale magnetic field, this affecting the Alfvén speed in the solar interior. Consequently the Alfvén waves with the half frequency of pulsation (i.e. with the double period) can be parametrically amplified in the interior below the convection zone due to the recently suggested swing wave-wave interaction. Therefore the amplified Alfvén waves have periods of several hours. The waves can propagate upwards through the convection zone to the solar atmosphere and cause the observed long-period Alfvén oscillations in the solar wind.

Using a new s-nucleosynthesis code simulations have been performed to study the impact of overshooting convective on the s-process during core He-burning of a 25 M⊙ star (ZAMS mass) with initial Z = 0.02 metallicity. Attention has been devoted to the role played by the overshooting parameter value. The results show enhancements of about a factor 2-3 in s-process efficiency when overshooting is considered in the calculations, with overshooting parameter values in the range 0.01-0.035. The impact of these results on the p-process model based on type II supernovae is also discussed.