The structure and kinematics of the HH 444 photoionized jet in the σ Orionis region

Abstract

HH 444 is a stellar jet which is immersed in the H II region photoionized by σ Orionis. Spatially resolved, high spectral resolution observations of the H α and [N II] λ λ 6548, 6584 lines have been obtained for this object. These observations reveal for the first time the detailed velocity structure of the stellar jet and its associated bow-shock. The line profiles are modeled with gasdynamic numerical simulations, using a 3D code that also includes the transfer of the ionizing radiation from an external source (i.e., σ Orionis for the case of HH 444). In order to reproduce the observed characteristics of the line profiles, we find that an axially peaked initial velocity profile for the jet and a non-zero initial opening angle for the flow with a time-variable ejection velocity is required. With these three ingredients we can reproduce the observed acceleration of the material along the jet beam, the rapid H α intensity drop for increasing distances from the source, and the knotty structure of the jet, respectively.