Upper limit on C₆₀ and C₆₀(+) features in the ISO-SWS spectrum of the reflection nebula NGC 7023

Abstract

We present here the 7.0-8.7 mu m spectrum of the bright reflection nebula NGC 7023. Our observations are made with the Short Wavelength Spectrometer (SWS) on the European satellite Infrared Space Observatory (ISO). The vibrational bands of the ionized fullerene C₆₀(+) are expected at 7.11 and 7.51 mu m, while those of the neutral fullerene C₆₀ are expected at 7.0 and 8.45 mu m. We estimate an upper limit in NGC 7023 for the C₆₀(+) abundance of <0.26% of the interstellar abundance of carbon, while C₆₀ contains <0.27% of interstellar carbon. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: the United Kingdom, France, the Netherlands, Germany), and with the participation of ISAS and NASA.