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 observe d with the Short Wavelength Spectrometer of the Infrared Space Observatory. Two of the sources are field stars located behind the Taurus molecular clo ud; the others are young stellar objects (YSOs) of predominantly low-to-int ermediate mass. We find a significant source-to-source variation in the sol id 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 t han in other lines of sight studied to date. In agreement with a previous s tudy of Elias 16, we confirm a substantial (similar to 20%) abundance of so lid CO2 relative to H2O in the quiescent intracloud medium. We compare the CO2 profiles with laboratory spectra of interstellar ice analogs from the L eiden Observatory Laboratory database. Results show that the 4.27 um profil es 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 hig her mass YSOs (RAFGL 989 and S255 IRS1), the profiles are clearly different , and at least the latter source shows signs of thermal processing.