Herschel -HIFI observations of high- J lines ( up to J _ { \mathrm { u } } =10 ) of ^ { 12 } CO , ^ { 13 } CO and C ^ { 18 } O are presented toward three deeply embedded low-mass protostars in NGC1333 .
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 } \sim 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 \times 10 ^ { -4 } ; however the inner abundance , X _ { in } , is found around a factor of 3-5 lower than X _ { 0 } .