heliocentric distance and velocity at the time of observation was 2.62$\times$10$^{-4}$ s$^{-1}$ (or 1.71$\times$10$^{-15}$ erg s$^{-1}$ molecule$^{-1}$ if scaled to 1 au; see details on the fluorescence model in [@Rousselot2019]). From these values and a Monte-Carlo simulation of the water molecules creating OH radicals in the inner coma (model based on equations given by [@Combi1980]) it is possible to compute the corresponding water production rate for the number of OH radicals observed in the slit (0.44$\times$9.5 arcsec) centered on the nucleus. Using the parameters of H$_2$O radial velocity, OH and H$_2$O lifetimes given in [@Cochran1993] and assuming that 91.8% of water molecules dissociate to OH [@crovisier1989], we found Q(H$_2$O)=1.7$\times$10$^{28}$ molec/s. This result is in excellent agreement with the water production rates computed from TRAPPIST observations in the same period (see Figure \[fig:rate\_H2O\]). It must, nevertheless, be pointed out that it depends of the different parameters and can change a bit with them, especially with the water lifetime.

The $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N isotopic ratios
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The study of the isotopic ratios in comets has attracted considerable attention as it contains information about the conditions which prevailed at the time of formation of these objects in the early Solar System [@Jehin2009; @Hyodo2013]. 