Thanks to recent advances in laboratory gas-phase spectroscopy at low temperatures, the fullerene cation C60+ has emerged as the likely carrier of two of the elusive diffuse interstellar bands (DIBs). The DIBs are a family of absorption features that arise in the spectra of stars as their light passes through the diffuse interstellar medium (ISM). Their identification has been one of the greatest problems in astronomy for the last century, but the likely assignment of C60+ represents a significant breakthrough in the field, and provides new insight into the true extent of chemical complexity in the ISM. Here I will present results from our latest efforts to confirm the identification of interstellar C60+ using the VLT UVES instrument and a new method we have developed for high-signal-to-noise HST STIS spectroscopy, specifically for this task.<br/><br/>The ESO diffuse interstellar band large exploration survey (EDIBLES) employs the powerful VLT UVES spectrograph to study the atomic and molecular content of the diffuse ISM, probing the lines-of-sight towards ~120 bright OB stars in our Galaxy at high signal-to-noise. The goal of EDIBLES is to 'reverse-engineer' the physical properties of the DIB carriers to assist in their identification. Early results from this survey will be presented, relating primarily the question of interstellar C60+.<br/><br/>I will also present new spectra of C60+ DIBs obtained using the 'STIS-scan' technique pioneered by our team using the Hubble Space Telescope, which allows a factor of ten improvement in sensitivity to weak near-infrared absorption features compared to conventional STIS observing methods. The focus is on confirming the presence of the weaker C60+ bands, which reside in a part of the spectrum that is impossible to reliably observe from the ground due to severe contamination by telluric water vapor. The 9577 and 9365 A band strengths appear as expected, but a relatively small 9428/9577 ratio is found in all three of our observed sightlines, in disagreement with the latest laboratory C60+ measurments at 6 K.

Validating the recent identification of interstellar C60+ using VLT UVES and a new method for high-signal-to-noise HST STIS spectroscopy

256th National Meeting (2018)

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