Energetic processes revealed by spectrally resolved high-J CO lines in low-mass star-forming regions with Herschel-HIFI

Herschel -HIFI observations of high- J lines (up to J u  = 10) of 12 CO, 13 CO and C 18 O are presented toward three deeply embedded low-mass protostars in NGC 1333. The observations show several energetic components including shocked and quiescent gas. Radiative transfer models are used to quantify the C 18 O envelope abundance which require a jump in the abundance at an evaporation temperature, T ev  ~ 25 K, providing new direct evidence of a CO ice evaporation zone around protostars. The abundance in the outermost part of the envelope, X 0 , is within the canonical value of 2 × 10 -4 ; however the inner abundance, X in , is found around a factor of 3–5 lower than X 0 .