Numerical Models of Externally Irradiated Herbig–Haro Objects

Abstract

Abstract We use 3D radiation–hydrodynamic simulations to study the effects of an external photoionization source on the structure of a Herbig–Haro (HH) jet launched from a young stellar object. Different ionizing photon rates are considered as well as a time-dependent ejection velocity and density. From our numerical results, synthetic Hα emission maps are computed in order to study how the external ionizing source affects the observed morphology of the jet and counterjet. We find that, as expected, the outflow has jet/counterjet and side-to-side asymmetries (with brighter Hα emission toward the external photoionizing source). We find that, for a variable ejection velocity, jet morphologies similar to different observed externally irradiated jets can be straightforwardly obtained. Models of jets with a variable ejection density (and constant outflow velocity) produce morphologies that are not seen in observed HH jets and are, therefore, not justified by the presently available observations.