EDIBLES II. On the detectability of C60+ bands
  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 9577\AA\: bands, (ii) a large redshift of the
9632\AA\: band for the Orion star HD 37022, and (iii) the non-detection of the
weaker 9428\AA~DIB. Here we address these three points. (i) We show that the
model stellar line correction for the 9632\AA~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 9632\AA\ 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
9428\AA\ band cannot be ruled out, even in the same observations that a
previous study claimed it was not present.
