We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157 .
We made use of ( sub- ) mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions ( CHESS ) and Astrochemical Surveys at IRAM ( ASAI ) key science programs .
We detected ^ { 12 } C ^ { 32 } S , ^ { 12 } C ^ { 34 } S , ^ { 13 } C ^ { 32 } S , and ^ { 12 } C ^ { 33 } S emissions , for a total of 18 transitions , with E _ { u } up to \sim 180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles , revealing high-velocity emission , up to 20 km s ^ { -1 } with respect to the systemic .
The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO .
These components have been related to the cavity walls produced by the \sim 2000 yr B1 shock and the older ( \sim 4000 yr ) B2 shock , respectively .
The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region .
Our CS observations show that this molecule is highlighting the dense , n _ { H _ { 2 } } = 1–5 \times 10 ^ { 5 } cm ^ { -3 } , cavity walls produced by the episodic outflow in L1157 .
In addition , the highest excitation ( E _ { u } \geq 130 K ) CS lines provide us with the signature of denser ( 1–5 \times 10 ^ { 6 } cm ^ { -3 } ) gas , associated with a molecular reformation zone of a dissociative J-type shock , which is expected to arise where the precessing jet impacting the molecular cavities .
The CS fractional abundance increases up to \sim 10 ^ { -7 } in all the kinematical components .
This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem .