The Time Evolution of the HH 1 Jet Modeled as a Variable Outflow

Abstract

The HH 1 jet is a chain of knots extending out to ∼20″ from the VLA 1 source of the HH 1/2 system. Four epochs of [S II] images obtained with the Hubble Space Telescope over a ∼20 yr period show that these knots have a time-evolving intensity as they travel away from the outflow source. We present an axisymmetric, gas-dynamic simulation of a two-sinusoidal-mode variable ejection velocity jet (including a treatment of the non-equilibrium ionization of the gas) from which we obtain predictions of the time evolution of the chain of knots close to the outflow source. Both the intensity versus position dependence (for the successive knots) and the time evolution of the [S II] intensities of the individual knots obtained from the simulations agree in a very impressive way with the HH 1 jet observations. This is one of the most striking illustrations of the success of variable jet models at reproducing the observed properties of HH jets. Also, this work represents the first attempted comparison between models and observations of astrophysical jets with both time and spatial resolution.