EDIBLES II. On the detectability of C60+ bands

Abstract

Gas phase spectroscopic laboratory experiments for the buckminsterfullerene cation C60+ resulted in accurate rest wavelengths for five C60+ transitions that have been compared with diffuse interstellar bands (DIBs) in the near infra-red. Detecting these in astronomical spectra is difficult due to the strong contamination of ground-based spectra by atmospheric water vapor, to the presence of weak and shallow stellar lines and/or blending with other weak DIBs. The detection of the two strong bands has been claimed by several teams, and the three additional and weaker bands have been detected in a few sources. Certain recent papers have argued against the identification of C60+ based on spectral analyses claiming (i) a large variation in the ratio between the equivalent widths of the 9632 and 9577Å\: bands, (ii) a large redshift of the 9632Å\: band for the Orion star HD 37022, and (iii) the non-detection of the weaker 9428Å~DIB. Here we address these three points. (i) We show that the model stellar line correction for the 9632Å~DIB overestimates the difference between the strengths of the lines in giant and dwarf star spectra, casting doubts on the conclusions about the ratio variability. (ii) Using high quality stellar spectra from the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES), recorded with the ESO/Paranal Ultraviolet Echelle Spectrograph (UVES) in about the same atmospheric conditions, we find no wavelength shift in the 9632Å band towards HD 37022. (iii) Using EDIBLES spectra and data from the Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) at CFHT we show that the presence of a weak 9428Å band cannot be ruled out, even in the same observations that a previous study claimed it was not present.

arXiv comment8 pages, 9 figures, accepted in Astronomy and Astrophysics

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Cited by in corpus (20)

• Confirming interstellar C${}_{60}^{+}$ using the Hubble Space Telescope
• Searching for stable fullerenes in space with computational chemistry
• Polyacenes and diffuse interstellar bands
• The EDIBLES survey III. C2-DIBs and their profiles
• CRIRES high-resolution near-infrared spectroscopy of diffuse interstellar band profiles. Detection of 12 new DIBs in the YJ band and the introduction of a combined ISM sight line and stellar analysis approach
• Survey of near-infrared diffuse interstellar bands in $Y$ and $J$ bands. I. Newly identified bands
• Diffuse bands 9577 and 9633 -- relations to other interstellar features
• The diffuse interstellar band around 8620 Å I. Methods and application to the GIBS data set
• The EDIBLES survey V: Line profile variations in the $\lambda \lambda$5797, 6379, and 6614 diffuse interstellar bands as a tool to constrain carrier sizes
• Updated extraction of the APOGEE 1.5273 μm diffuse interstellar band: a Planck view on the carrier depletion in dense cores
• C${}_{60}^{+}$ diffuse interstellar band correlations and environmental variations
• The diffuse interstellar band around 8620 Å II. Kinematics and distance of the DIB carrier
• A high resolution study of near-IR diffuse interstellar bands, search for small scale structure, time variability and stellar features
• C60 Cation as the Carrier of the 9577 and 9632 Angstrom Diffuse Interstellar Bands: Further Support from the VLT/X-Shooter Spectra
• The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds
• Near-Infrared Diffuse Interstellar Bands towards Her 36
• Measuring the Diffuse Interstellar Bands at 5780, 5797, and 6614 Å in Low-Resolution Spectra of Cool Stars from LAMOST
• The EDIBLES survey VI. Searching for time variations of interstellar absorption features
• Mapping the diffuse interstellar bands $\lambda$5780 and $\lambda$6284 in the luminous infrared galaxy merger NGC 6240
• Families and Clusters of Diffuse Interstellar Bands: a Data-Driven Correlation Analysis