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

Cordiner, M.A.; Cox, N.L.J.; Lallement, R.; Najarro, F.; Cami, J.; Gull, T.R.; Foing, B.H.; Linnartz, H.; Proffitt, C.R.; Sarre, Peter; Charnley, S.B.

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.

• Journal Article Type: Article
• Acceptance Date: Jun 6, 2017
• Publication Date: Jun 23, 2017
• Deposit Date: Jun 30, 2017
• Publicly Available Date: Jun 30, 2017
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 843
• Issue: 1
• Article Number: L2
• DOI: https://doi.org/10.3847/2041-8213/aa78f7
• Keywords: Instrumentation: spectrographs, ISM: molecules, Line: identification, Techniques: spectroscopic
• Public URL: https://nottingham-repository.worktribe.com/output/867491
• Publisher URL: http://iopscience.iop.org/article/10.3847/2041-8213/aa78f7/meta;jsessionid=1BA9F62A98399C1E536259D74BD073F0.c1.iopscience.cld.iop.org
• Additional Information: © Copyright 2017 IOP Publishing