No 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.

We present an analytic model of a collimated ejection with a “single pulse” Gaussian ejection velocity. This flow produces a dense “head” (the leading working surface) joined to the outflow source by a “tail” of lower velocity material. For times greater than the duration of the ejection pulse, this tail develops a linear radial velocity vs. position structure. This “head/tail plasmon” structure is interesting for modelling astrophysical “bullets” joined to their outflow sources by structures with “Hubble law” radial velocity dependencies. We study the case of a Gaussian ejection velocity law with a constant and a Gaussian ejection density history, We compare these two cases, and find that the main effect of the different ejection density histories is to change the mass and the density stratification of the plasmon tail.

Massive young star clusters contain dozens or hundreds of massive stars that inject mechanical energy in the form of winds and supernova explosions, producing an outflow which expands into their surrounding medium, shocking it and forming structures called superbubbles. The regions of shocked material can have temperatures in excess of 10 6 K, and emit mainly in thermal X-rays (soft and hard). This X-ray emission is strongly affected by the action of thermal conduction, as well as by the metallicity of the material injected by the massive stars. We present three-dimensional numerical simulations exploring these two effects, metallicity of the stellar winds and supernova explosions, as well as thermal conduction.

We present two axisymmetric simulations of a high velocity clump in a photoionized region: one for the case of a uniform, low density environment and a second one for the case of a clump first traveling within a high density medium and then emerging into a low density environment. We show that the second scenario results in the production of an axial tail of dense material with a linear velocity vs. position ramp (with zero velocity at the high/low density environment transition). This material comes from a confined bow shock (produced by the clump when it was within the dense cloud) that emerges into the low environmental density region.