The Shock Dynamics of Heterogeneous YSO Jets:3D Simulations Meet Multi-epoch Observations

Abstract

High-resolution observations of young stellar object (YSO) jets show them to be composed of many small-scale knots or clumps. In this paper, we report results of 3D numerical simulations designed to study how such clumps interact and create morphologies and kinematic patterns seen in emission line observations. Our simulations focus on clump scale dynamics by imposing velocity differences between spherical, over-dense regions, which then lead to the formation of bow shocks as faster clumps overtake slower material. We show that much of the spatial structure apparent in emission line images of jets arises from the dynamics and interactions of these bow shocks. Our simulations show a variety of time-dependent features, including bright knots associated with Mach stems where the shocks intersect, a "frothy" emission structure that arises from the presence of the Nonlinear Thin Shell Instability along the surfaces of the bow shocks, and the merging and fragmentation of clumps. Our simulations use a new non-equilibrium cooling method to produce synthetic emission maps in Hα and [S II]. These are directly compared to multi-epoch Hubble Space Telescope observations of Herbig-Haro jets. We find excellent agreement between features seen in the simulations and the observations in terms of both proper motion and morphologies. Thus we conclude that YSO jets may be dominated by heterogeneous structures and that interactions between these structures and the shocks they produce can account for many details of YSO jet evolution.

Exploring astrophysics-relevant magnetohydrodynamics with pulsed-power laboratory facilities

“…The bow shock driven by the fast plasma flow develops a number of regular, larger scale structures with the size comparable to the bow shock radius. It is interesting to note that very similar structures were recently observed in numerical simulations of the astrophysical bow shocks (Hansen et al, 2017) where they were interpreted as due to development of thin-shell instability advected along the bow-shock. Similar structures of bow shock were also seen in computational studies of radiatively cooled astrophysical jets (see e.g.…”

Erratum: Simulating radiative magnetohydrodynamical flows with astrobear: implementation and applications of non-equilibrium cooling

“…An important application of the new non-equilibrium cooling routines in AstroBEAR is simulations of HH objects. In previous studies, we have run simulations of pulsed jets (Hansen et al 2015b) and interacting bow shocks (Hansen et al 2017). The example outflow and synthetic emission map we show here is similar to the simulations from the latter work.…”

“…There are other similarities between Figure 8 and Figure 7 such as the heterogeneous nature of the emission. These structures and other details of such outflows will are discussed in (Hansen et al 2017).…”

First radiative shock experiments on the SG-II laser

“…We can estimate characteristic time scales for the growth of hydrodynamic instabilities from a shocked-clump model presented in Ref. [21]. For a strong shock, the Rayleigh-Taylor instability is expected to grow in a time scale given by t RT ∼ √ η r spot v shock with η the ratio of post-shock to pre-shock density, r spot the radius of the laser focal spot and v shock the tip shock velocity.…”