INFRARED [FE II] EMISSION LINES FROM RADIATIVE ATOMIC SHOCKS

Abstract

[Fe II] emission lines are prominent in the infrared (IR) and important as diagnostic tools for radiative atomic shocks. We investigate the emission characteristics of [Fe II] lines using a shock code developed by Raymond (1979) with updated atomic parameters. We rst review general characteristics of the IR [Fe II] emission lines from shocked gas, and derive their uxes as a function of shock speed and ambient density. We have compiled available IR [Fe II] line observations of interstellar shocks and compare them to the ratios predicted from our model. The sample includes both young and old supernova remnants in the Galaxy and the Large Magellanic Cloud and several Herbig-Haro objects. We nd that the observed ratios of the IR [Fe II] lines generally fall on our grid of shock models, but the ratios of some mid-IR lines, e.g., [Fe II] 35.35 μm=[Fe II] 25.99 m, [Fe II] 5.340 μm=[Fe II] 25.99 μm, and [Fe II] 5.340 μm=[Fe II] 17.94 m, are signicantly oset from our model grid. We discuss possible explanations and conclude that while uncertainties in the shock modeling and the observations certainly exist, the uncertainty in atomic rates appears to be the major source of discrepancy.