Citation:
Rivière-Marichalar P, Fuente A, Goicoechea J R, Pety J, Le Gal R, Gratier P, Guzmán V, Roueff E, Loison J C, Wakelam V, et al. Abundances of sulphur molecules in the Horsehead nebula. First NS$^+$ detection in a photodissociation region. \aap. 2019;628 :A16.