Astron. Astrophys. 350, 529-540 (1999)

6. Conclusions

The main conclusions of this work can be summarised as follows:

• We have observed the Class 0 source L1448-mm with ISO-LWS and SWS, detecting a far infrared spectrum which is very rich in emission lines from water vapour and CO with rotational number 14. Several other molecular lines were observed including the pure rotational transitions of H₂ from S(3) to S(5) and the OH fundamental line at 119 µm.

• All of the molecular species present in the LWS spectrum can be modelled as being excited in a warm region with 700-1400 K and 3 10⁴-5 10⁵ cm^{- 3}, extending about 0.01 pc. In the hypothesis that the H₂ and CO rotational lines co-exist, a CO/H₂ ratio equal to 10^-2 is found; such a high value may indicate either that the CO and H₂ emission probe different clumps of gas, or that most of the hydrogen in the region is present in atomic form.

• Applying a LVG model we were able to derive the abundances and the total cooling of all the observed species; the main result from this work is that H₂O is the main coolant of the gas surrounding L1448-mm, with an abundance X(H₂O) of about 5 10^-4.

• A non-dissociative shock travelling at V15-25 km s^-1 seems to be the most likely excitation mechanism for reproducing most of the characteristics of the emission derived from the ISO spectra. Other alternatives, such as the possibility that the emission is associated with high velocity J-type shocks or it is directly originated in the protostellar envelope have been also considered but seem less compelling in explaining our observations. We suggest that such a low velocity shock originates in a region along the molecular jet traced by SiO and EHV CO millimeter line emission.

• We also speculate that the occurrence of multiple shocks over a relatively short interval of time could explain the very high water abundance observed in L1448, in comparison with other similar protostellar sources.

© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999
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