Searching for Interstellar {{\rm{C}}}_{60}^{+} Using a New Method for High Signal-to-noise HST/STIS Spectroscopy
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): {{{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 {{{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 {{{C}}}60+, as well as new DIBs in the near-IR. Unfortunately, the presence of overlapping stellar lines, and the unexpected weakness of the {{{C}}}60+ bands in this sightline, prevents conclusive detection of the weaker {{{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 {{{C}}}60+ searches.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2017
- DOI:
- 10.3847/2041-8213/aa78f7
- arXiv:
- arXiv:1704.01501
- Bibcode:
- 2017ApJ...843L...2C
- Keywords:
-
- instrumentation: spectrographs;
- ISM: molecules;
- line: identification;
- techniques: spectroscopic;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in ApJL, June 2017