Knots in stellar jets: crossing shocks or internal working surfaces?

The authors discuss the observational implications of theoretical models for the formation of knots in stellar jets. In particular, they present predictions of the spatial offsets between the Hα and the [S II] emission from two possible models: a "crossing shock" model (in which the knots correspond to incident/reflected shock pairs), and an "internal working surface" model (in which the knots correspond to shock pairs that result from a time-variability of the outflow source). A comparison of the theoretical predictions with observations of the jet-like Herbig-Haro object HH 34 appears to favour the second of these scenarios.