Trivalent Transition-Metal Ions in Interstellar Dust

Abstract

BRANCH and Patchett¹ have criticized suggestions that most of the optical bands in spectra of Type I supernovae are caused by d-d transitions in Fe³⁺ ions in oxides² or silicates³ on the grounds that bands of common origin would show similar wavelength shifts with time. They contend that the 6180 Å band, unlike the 4430 Å (these bands and another at 3800 Å I assigned³ to octahedral-Fe³⁺), disappears 1 month after maximum. Also the 4100 Å and 4430 Å bands show an initial (0–20 day) rapid shift in wavelength with time. I feel the disappearance of the 6180 Å band is illusory. In the spectrum⁴ of SN-IC-4182, a new band appears at 6000 Å fourteen days after maximum, and after twenty-four days the 6180 Å band is “reduced” to a shoulder. Another band appears at 6300 Å after sixty-seven days making resolution of the 6000–6300 Å region difficult. However, shoulders at ∼6180 Å are evident by eye in spectra of sixty-seven, 117 and 184 days. Curve-resolution (using a ‘Dupont 310 Analyser’) of the 214- and 224-day spectra indicates the presence of three bands, rather than two, in this region.