Edo Trussoni

The Kelvin-Helmholtz Instability in Stellar Jets

The Kelvin-Helmholtz Instability (KHI) is amongst the most relevant processes occurring in outflows propagating through an external medium. The KHI can critically affect the dynamics of jets leading to their disruption, but at same time it drives the formation of the peculiar morphologies observed in stellar collimated outflows. Moreover, the KHI can be an efficient mechanism for momentum deposition into the environment and mixing with the external medium. Here the main properties of the KHI are discussed considering in particular the effects of radiative losses and of magnetic fields, the most important ‘ingredients’ in the framework of the phenomenology of stellar jets.

Two-component Jet Simulations: Combining Analytical and Numerical Approaches

Recent observations as well as theoretical studies of YSO jets suggest the presence of two steady components: a disk wind type outflow needed to explain the observed high mass loss rates and a stellar wind type outflow probably accounting for the observed stellar spin down. In this framework, we construct numerical two-component jet models by properly mixing an analytical disk wind solution with a complementary analytically derived stellar outflow. Their combination is controlled by both spatial and temporal parameters, in order to address different physical conditions and time variable features. We study the temporal evolution and the interaction of the two jet components on both small and large scales. The simulations reach steady state configurations close to the initial solutions. Although time variability is not found to considerably affect the dynamics, flow fluctuations generate shocks, whose large scale structures have a strong resemblance to observed YSO jet knots.

On the Effect of Stellar Wind Braking onto the Central Object

Stellar winds seem to be very efficient at removing angular momentum from stars. By means of analytical axisymmetric solutions of the ideal MHD equations for steady outflows, we show via a specific example how collimated stellar winds can brake Weak T Tauri stars in a reasonable time. This result can be generalized to Classical T Tauri stars provided that part of the accreted angular momentum is removed by the inner disk wind. We also extend briefly to Kerr metrics the self similar MHD solutions for relativistic flows and conjecture that relativistic outflows may efficiently slow down spinning black holes at the center of Active Galactic Nuclei or microquasars.