Synthetic images and long-slit spectra of protostellar jets

We construct synthetic images and long-slit spectra of protostellar jets modeled as steady state X-winds. Assuming uniform ionization fractions and electron temperatures, we calculate non-LTE level populations for five-level atoms. Synthetic images in the [S II] λ6716/λ6731 and [O I] λ6300/λ6364 lines have roughly the same surface brightness as observed jets if we ignore their knotty structure. Long-slit spectra taken with the slit placed along the central axis of the jet, or slightly displaced laterally from it, provide strong evidence in support of the X-wind theory. In both the models and the actual objects, wide line profiles, containing both large positive and negative velocities, are often seen at the base of the flow, indicative of a wide-angle wind. As one progresses up the length of the slit, the line profiles narrow to straddle the projected velocity of a highly collimated jet.