Confirming Interstellar C 60 + Using the Hubble Space Telescope

Abstract

Recent advances in laboratory spectroscopy lead to the claim of ionized Buckminsterfullerene (C ) as the carrier of two diffuse interstellar bands (DIBs) in the near-infrared. However, irrefutable identification of interstellar C requires a match between the wavelengths and the expected strengths of all absorption features detectable in the laboratory and in space. Here we present Hubble Space Telescope ( HST ) spectra of the region covering the C 9348, 9365, 9428, and 9577 Å absorption bands toward seven heavily reddened stars. We focus in particular on searching for the weaker laboratory C bands, the very presence of which has been a matter for recent debate. Using the novel STIS-scanning technique to obtain ultra-high signal-to-noise spectra without contamination from telluric absorption that afflicted previous ground-based observations, we obtained reliable detections of the (weak) 9365, 9428 Å and (strong) 9577 Å C bands. The band wavelengths and strength ratios are sufficiently similar to those determined in the latest laboratory experiments that we consider this the first robust identification of the 9428 Å band, and a conclusive confirmation of interstellar .