Infrared Emission Lines of [Fe II] as Diagnostics of Shocked Gas in Stellar Jets

We predict fluxes for the brightest lines of [Fe II] at wavelengths longer than 8000 Å for several radiative shocks whose parameters resemble those typically present in stellar jets. The models show that the brightest lines are those at 1.257, 1.643, 5.340, 17.94, and 25.99 μm. Depending on the model, these lines typically have comparable fluxes and are usually brighter than the [O I] 63.3 μm and [Si II] 34.8 μm lines. We call attention to the 5.34 μm line of Fe II, which cannot be seen from the ground but should be easily observable with the Spitzer satellite and SOFIA for many sources. This line should be an excellent probe of outflows from the youngest stars; at mid-IR wavelengths, it penetrates through most dusty regions of star formation, yet has a short enough wavelength to retain good spatial resolution in diffraction-limited images obtainable from space.