2-MU-M CO OVERTONE ABSORPTION IN YOUNG STELLAR OBJECTS

(CO)-C-12 overtone absorption bands have been detected in five of 10 low-luminosity YSOs studied in the Ophiuchus cloud core. The majority of those showing absorption have class II spectral energy distributions. The majority of the class I objects show no spectral features at all. If the bands are assumed to be photospheric in origin, then the results can be understood as a decrease in veiling by an IR continuum excess as the sources evolve from class I to class II.