Detection of diffuse interstellar bands in the infrared

Abstract

THE diffuse interstellar bands (DIBs) are spectral absorption features caused by interstellar matter but not identified with any known atomic or molecular lines. Since 1975, when 39 such bands were known¹, many more have been detected, and in 1988, about 80 were listed². They range in frequency from visible (4,430 Å) to very near infrared wavelengths (8,650 Å) (ref. 3), but their carriers—the atoms or molecules that cause them—remain unknown. We have found two new DIBS in the near infrared, near 11,800 Å and 13,200 Å, in the spectra of reddened O, B and A stars. Their full widths at half maximum are 2.7 ± 0.3 Å and 4.0 ± 0.5 Å respectively, and their equivalent widths are 60 and 135 mÅ per magnitude of extinction. The wavelength of the second DIB is a factor of 1.5 longer than that of the longest wavelength band previously identified, which may be an important constraint on the nature of the carriers of these two bands.