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Giovanni Picogna

Publications and source records attributed to Giovanni Picogna.

38 records · Page 3Linked to original sources

Three-dimensional modeling of radiative disks in binaries

Circumstellar disks in binaries are perturbed by the companion gravity causing significant alterations of the disk morphology. Spiral waves due to the companion tidal force also develop in the vertical direction and affect the disk temperature profile. These effects may significantly influence the process of planet formation. We perform 3D numerical simulations of disks in binaries with different initial dynamical configurations and physical parameters. Our goal is to investigate their evolution and their propensity to grow planets. We use an improved version of the SPH code VINE modified to better account for momentum and energy conservation. The energy equation includes a flux--limited radiative transfer algorithm and the disk cooling is obtained via "boundary particles". We model a system made of star/disk + star/disk where the secondary star (and relative disk) is less massive than the primary. The numerical simulations performed for different values of binary separation and disk density show that the disk morphology is substantially affected by the companion perturbations. Trailing spiral shock waves develop when the stars approach their pericenter. Strong hydraulic jumps occur at the shock front creating breaking waves and a consistent mass stream between the two disks, significantly heating them. The high gas temperature may prevent the ice condensation by moving outward the "snow line". The hydraulic jumps may slow down or even halt the dust coagulation process. At apocenter these perturbations are reduced and the disks are cooled down and less eccentric. The strength of the hydraulic jumps, disk heating, and mass exchange depends on the binary separation, and for larger semi-major axes, the tidal spiral pattern is substantially reduced.

astro-ph.EP↗

Circumstellar disks can erase the effects of stellar fly-bys on planetary systems

Most stars form in embedded clusters. Stellar flybys may affect the orbital architecture of the systems by exciting the eccentricity and causing dynamical instability. Since, incidentally, the timescale over which a cluster loses its gaseous component and begins to disperse is comparable to the circumstellar disk lifetime, we expect that closer, and more perturbing, stellar flybys occur when the planets are still embedded in their birth disk. We investigate the effects of the disk on the dynamics of planets after the stellar encounter to test whether it can damp the eccentricity and return the planetary system to a non-excited state. We use the hydrodynamical code FARGO to study the disk+planet(s) system during and after the stellar encounter in the context of evolved disk models whose superficial density is 10 times lower than that of the Minimum Mass Solar Nebula. The numerical simulations show that the planet eccentricity, excited during a close stellar flyby, is damped on a short timescale (~ 10 Kyr) in spite of the disk low initial density and subsequent tidal truncation. This damping is effective also for a system of 3 giant planets and the effects of the dynamical instability induced by the passing star are quickly absorbed. If the circumstellar disk is still present around the star during a stellar flyby, a planet (or a planetary system) is returned to a non-excited state on a short timescale. This does not mean that stellar encounters do not affect the evolution of planets, but they do it in a subtle way with a short period of agitated dynamical evolution. At the end of it, the system resumes a quiet evolution and the planetary orbits are circularized by the interaction with the disk.

astro-ph.EP↗