The interaction of an O star wind with a Herbig-Haro jet

Abstract

Context. Herbig-Haro jets ejected from young, low mass stars in the proximity of O/B stars will interact with the more or less isotropic winds from the more massive stars. An example of this are the jets from the stars within the proplyds near θ-Orionis. Aims. In this paper, we consider the interaction of an externally photoionized HH jet with an isotropic wind ejected from the ionizing photon source. We study this problem through numerical simulations, allowing us to obtain predictions of the detailed structure of the flow and predictions of Hα intensity maps. This is a natural extension of a previously developed analytic model for the interaction between a jet and an isotropic stellar wind. Methods. We present 3D simulations of a bipolar HH jet interacting with an isotropic wind from a massive star, assuming that the radiation from the star photoionizes all of the flow. We describe different possible flow configurations, exploring a limited set of jet and stellar wind parameters and orientations of the jet/counterjet ejection. We have computed 6 models, two of which also include a time-variability in the jet velocity. Results. We compare the locus of the computed jet/counterjet systems with the analytic model, and find very good agreement except for cases in which the direction of the jet (or the counterjet) approaches the direction to the wind source (i.e., the O star). For the models with variable ejection velocities, we find that the internal working surfaces follow straighter trajectories (and the inter-working surface segments more curved trajectories) than the equivalent steady jet model.