Two-component jet simulations

Abstract

Context. Theoretical arguments along with observational data 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. Each component's contribution depends on the intrinsic physical properties of the YSO-disk system and its evolutionary stage. Aims. The main goal of this paper is to understand some of the basic features of the evolution, interaction and co-existence of the two jet components over a parameter space and when time variability is enforced. Methods. Having studied separately the numerical evolution of each type of the complementary disk and stellar analytical wind solutions in Paper I of this series, we proceed here to mix together the two models inside the computational box. The evolution in time is performed with the PLUTO code, investigating the dynamics of the two-component jets, the modifications each solution undergoes and the potential steady state reached. Results. The co-evolution of the two components, indeed, results in final steady state configurations with the disk wind effectively collimating the inner stellar component. The final outcome stays close to the initial solutions, supporting the validity of the analytical studies. Moreover, a weak shock forms, disconnecting the launching region of both outflows with the propagation domain of the twocomponent jet. On the other hand, several cases are being investigated to identify the role of each two-component jet parameter. Time variability is not found to considerably affect the dynamics, thus making all the conclusions robust. However, the flow fluctuations generate shocks, whose large scale structures have a strong resemblance to observed YSO jet knots. Conclusions. Analytical disk and stellar solutions, even sub modified fast ones, provide a solid foundation to construct twocomponent jet models. Tuning their physical properties along with the two-component jet parameters allows a broad class of realistic scenarios to be addressed. The applied flow variability provides very promising perspectives for the comparison of the models with observations.

Nonradial and nonpolytropic astrophysical outflows

“…Recent simulations (Meliani et al 2006;Romanova et al 2009;Matsakos et al 2009;Fendt 2009) also show the interplay of mixing between the two components. Several authors, e.g.…”

“…Though important to model, those outflows are not necessarily more important on the long-term duration compared to the continuous underlying steady flow, as suggested by Romanova et al (2009). Moreover, Matsakos et al (2009) have shown that the variability of the source does not destroy the continuous steady jet. Indeed, they use the first solution presented in this paper, as initial condition for the inner spine jet of their simulations, but use a polytropic equation of state.…”

“…By investigating various boundary conditions and initial configurations, they confirmed that disk winds could indeed be accelerated and collimated by their own magnetic field. More recently several authors Stute et al 2008;Matsakos et al 2009) have shown that analytical solutions such as the radially self-similar ones are structurally stable. This result indicates that these solutions are good complementary tools to numerical simulations.…”

“…Matsakos et al 2009). As mentioned in the introduction, Matsakos et al (2009) used as initial condition our solution for the inner spine jet but with different thermodynamics.…”

“…Matsakos et al 2009). As mentioned in the introduction, Matsakos et al (2009) used as initial condition our solution for the inner spine jet but with different thermodynamics. Switching to a polytropic equation of state reduces the radius of this inner part of the outflow by a significant factor, as shown in Matsakos et al (2008).…”