A 3-mode variable ejection velocity, precessing jet model for HH 30

Abstract

Context. HH 30 is a Herbig-Haro (HH) jet showing a chain of aligned knots (with knots covering a range of sizes and knot separations), pointing towards what appears to be a highly fragmented “head”. The chain of knots is detected out to ∼140 �� , and the head is an elongated group of knots centred at a distance of ∼290 �� from the source. Aims. In the paper of Anglada et al. (2006, A&A, submitted), it is suggested that this jet is the result of a multi-period variable velocity ejection, and also having a precession of the outflow axis. The question that we address in our paper is whether or not this ejection variability results in a leading working surface with the high fragmentation of the “head” of the HH 30 jet. Methods. In order to do this, we take at face value the parameters calculated by Anglada et al. (2006) for the ejection variability and the precession and use them to compute a 3D, radiative jet simulation. Our simulation includes a treatment of the non-equilibrium ionization state of the gas, and allows us to compute synthetic emission line maps, which can be compared directly with previously published images of HH 30. Results. We find that our simulation does produce a leading working surface with a striking resemblance to the head of HH 30. We obtain a fragmented emission structure with an extent both along and across the outflow axis that agrees well with the observed jet head. Conclusions. It then appears to be clear that the variable ejection implied by the chain of knots close to the HH 30 source has a direct effect on the head of the jet, producing a highly fragmented structure that is comparable with observations. This is the first time that such a connection has been proven for an HH outflow.