Origin of the Iron Bands in Supernovae Spectra

Abstract

THE visible-region crystal-field spectra of Fe2+ and Fe3+ ions located in silicate minerals show several similar features, in particular a number of relatively sharp bands marking field-independent transitions, which are difficult to assign unless attendant chemical analyses are available. Three absorption bands at 6200 A, 4430 A and 3800 A in optical spectra of Type I supernova were recently assigned1,2 to transitions within octahedral Fe3+ ions in andradite garnet, while two other bands at 5100 A (19,600 cm−1) and 5700 A (17,500 cm−1) were attributed to Fe2+ ions in almandine garnet. Runciman3 also feels that the supernova bands are due mainly to Fe, but he suggests that they may mark transitions in Fe2+ ions in pyroxene minerals. Many stars have appreciable excess emission at 10 and 20 µm, the origin of which has been attributed to circumstellar silicates4–7, possibly orthopyroxenes and olivines.