Solid carbon dioxide in regions of low-mass star formation

We present high-resolution (R similar to 1500-2000) spectra of the 4.27 mum asymmetric stretching feature of solid CO2 in eight lines of sight observed with the Short Wavelength Spectrometer of the Infrared Space Observatory. Two of the sources are field stars located behind the Taurus molecular cloud; the others are young stellar objects (YSOs) of predominantly low-to-intermediate mass. We find a significant source-to-source variation in the solid CO2/H2O abundance ratio in our sample: two lines of sight, Elias 18 and RAFGL 989, have CO2 abundances of similar to 34%-37%, considerably higher than in other lines of sight studied to date. In agreement with a previous study of Elias 16, we confirm a substantial (similar to 20%) abundance of solid CO2 relative to H2O in the quiescent intracloud medium. We compare the CO2 profiles with laboratory spectra of interstellar ice analogs from the Leiden Observatory Laboratory database. Results show that the 4.27 um profiles toward field stars and embedded low-mass objects are remarkably similar to each other and seem to originate mostly in cold H2O-rich ice. In two higher mass YSOs (RAFGL 989 and S255 IRS1), the profiles are clearly different, and at least the latter source shows signs of thermal processing.