This region is not considered farther in this work because too weak.

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Although no SiO emission was detected towards the cloud position, Ceccarelli et al. (2000b) modeled the observed SiO (from $J_{\rm up} = 1$ to 8) emission towards IRAS 16293, taking into account the envelope physical structure, and found that the SiO abundance is $4.0\times 10^{-12}$ in the outer envelope. In analogy with other molecules for which the abundances found in the outer envelope are equal to the (measured) abundances in the surrounding molecular clouds, we assumed $4.0\times 10^{-12}$ for the SiO abundance in L1689N. In a similar way, although weak formaldehyde emission is detected at the cloud position, we used the abundance found in the IRAS 16293 outer envelope for the cloud too.

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... W2

Since no SiO emission is detected in HE2, the density and temperature cannot be constrained in this position.

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