Bands of solid CO₂ in the 2-3 mu m spectrum of S 140:IRS1

Abstract

We investigate the 2-3 μm ISO-SWS spectrum of the luminous protostellar object S 140:IRS1. Two narrow absorption features are detected at 2.70 and 2.77 mu m, which are well fitted with laboratory spectra of the nu₁ + nu₃ and the 2nu₂ + nu₃ combination modes of solid CO₂. The ice in this line of sight must have been subjected to significant heating, in agreement with previously studied CO₂ bands. A combined laboratory fit to all CO₂ bands detected toward S 140:IRS1 shows, among others, the need for particle shape calculations for the CO₂ stretch mode. Finally, we discuss the absence of features of isolated H₂O and dangling OH groups in the spectrum of S 140:IRS1. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.