Infrared spectroscopy of the supernova remnant IC 443

Abstract

Infrared spectroscopy of IC 443 is presented. The following lines were detected at various positions: forbidden Fe II 1.664 micron, Br gamma, and H2 1-0 S(1). The most striking feature of the spectra is the forbidden Fe II 1.644 micron/Br gamma ratio, which is typically about 30. In an H II region, a forbidden Fe II 1.644 micron/Br gamma ratio of about 0.06 is expected. It is shown that the high forbidden Fe II 1.644 micron/Br gamma ratio in IC 443 is due to shock excitation, and it is argued that measurement of IR forbidden Fe II lines is a sensitive new probe for shocked gas, especially where the extinction to the emitting region is high or where the shocks are too slow to excite optical lines.