C$_{60}^+$ - looking for the bucky-ball in interstellar space

TL;DR

This study critically examines the spectral evidence for C60+ in space, addressing atmospheric and stellar line contamination issues, and questions its presence in interstellar clouds based on high-quality spectral data.

Contribution

It provides a detailed analysis of spectral contamination issues affecting the detection of C60+ in space, challenging previous claims of its interstellar presence.

Findings

Contamination from Earth's water vapor lines complicates spectral analysis.

Blending of C60+ bands with stellar MgII lines affects detection reliability.

High-resolution spectra cast doubt on the interstellar presence of C60+.

Abstract

The laboratory gas phase spectrum recently published by Campbell et al. has reinvigorated attempts to confirm the presence of the C$_{60}^+$ cation in the interstellar medium, thorough an analysis of the spectra of hot, reddened stars. This search is hindered by at least two issues that need to be addressed: (i) the wavelength range of interest is severely polluted by strong water- vapour lines coming from the Earth's atmosphere; (ii) one of the major bands attributed to C$_{60}^+$, at 9633 \AA, is blended with the stellar Mg{\sc ii} line, which is susceptible to non-local-thermodynamic equilibrium effects in hot stellar atmospheres. Both these issues are here carefully considered here for the first time, based on high-resolution and high signal-to-noise ratio echell\'e spectra for 19 lines of sight. The result is that the presence of C$_{60}^+$ in interstellar clouds is brought into question.