Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) with the participation of ISAS and NASA.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

SiO emission is usually associated with the outflow strong shocks (e.g. Bachiller & Perez Gutierrez 1997), and it is believed to be a product of grain mantle desorption (Caselli et al. 1997; Schilke et al. 1997).

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... $J_{\rm up} \geq 21$

CO 21-20 is definitively undetected, CO 22-21 is blended with OH at 119 $\mu$ m, while CO 23-22 and CO 24-23 are blended with water lines at 113.5 and 108.8 $\mu$ m line respectively. One can note that the 108 $\mu$ m is wider than expected, which could be due to the presence of the CO 24-23 line. Nonetheless, this detection would be inconsistent with the non detection of lower and higher J CO lines. Higher spectral resolution observations are needed to settle the question.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.