## Searching for interstellar C60+ using a new method for high signal-to-noise HST/STIS spectroscopy

Cordiner, M.A. and Cox, N.L.J. and Lallement, R. and Najarro, F. and Cami, J. and Gull, T.R. and Foing, B.H. and Linnartz, H. and Proffitt, C.R. and Sarre, Peter and Charnley, S.B. (2017) Searching for interstellar C60+ using a new method for high signal-to-noise HST/STIS spectroscopy. Astrophysical Journal Letters, 843 (1). L2/1-L2/6. ISSN 2041-8213

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## Abstract

Due to recent advances in laboratory spectroscopy, the first optical detection of a very large molecule has been claimed in the diffuse interstellar medium (ISM): ${{\rm{C}}}_{60}^{+}$ (ionized Buckminsterfullerene). Confirming the presence of this molecule would have significant implications regarding the carbon budget and chemical complexity of the ISM. Here we present results from a new method for ultra-high signal-to-noise ratio (S/N) spectroscopy of background stars in the near-infrared (at wavelengths of 0.9–1 μm), using the Hubble Space Telescope (HST) Imaging Spectrograph (STIS) in a previously untested "STIS scan" mode. The use of HST provides the crucial benefit of eliminating the need for error-prone telluric-correction methods in the part of the spectrum where the ${{\rm{C}}}_{60}^{+}$ bands lie and where the terrestrial water vapor contamination is severe. Our STIS spectrum of the heavily reddened B0 supergiant star BD+63 1964 reaches an unprecedented S/N for this instrument (~600–800), allowing the detection of the diffuse interstellar band (DIB) at 9577 Å attributed to ${{\rm{C}}}_{60}^{+}$, as well as new DIBs in the near-IR. Unfortunately, the presence of overlapping stellar lines, and the unexpected weakness of the ${{\rm{C}}}_{60}^{+}$ bands in this sightline, prevents conclusive detection of the weaker ${{\rm{C}}}_{60}^{+}$ bands. A probable correlation between the 9577 Å DIB strength and interstellar radiation field is identified, which suggests that more strongly irradiated interstellar sightlines will provide the optimal targets for future ${{\rm{C}}}_{60}^{+}$ searches.

Item Type: Article © Copyright 2017 IOP Publishing Instrumentation: spectrographs, ISM: molecules, Line: identification, Techniques: spectroscopic University of Nottingham, UK > Faculty of Science > School of Chemistry https://doi.org/10.3847/2041-8213/aa78f7 Smith, Ruth 30 Jun 2017 08:47 12 Oct 2017 23:54 http://eprints.nottingham.ac.uk/id/eprint/43860

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