2018MNRAS.474.5694C

The high sensitivity of the IRAM 30-m Astrochemical Surveys At IRAM (ASAI) unbiased spectral survey in the mm window allows us to detect NO emission towards both the Class I object SVS13-A and the protostellar outflow shock L1157-B1. We detect the hyperfine components of the ²Π_1/2J = 3/2 - 1/2 (at 151 GHz) and the ²Π_1/2J = 5/2 - 3/2 (at 250 GHz) spectral pattern. The two objects show different NO profiles: (i) SVS13-A emits through narrow (1.5 km s^–1) lines at the systemic velocity, while (ii) L1157-B1 shows broad (∼5 km s^–1) blueshifted emission. For SVS13-A, the analysis leads to T_ex >= 4 K, N(NO) <= 3 x 10¹⁵ cm^–2, and indicates the association of NO with the protostellar envelope. In L1157-B1, NO is tracing the extended outflow cavity: T_ex ≃ 4-5 K, and N(NO) = 5.5 ± 1.5 x 10¹⁵ cm^–2. Using C¹⁸O, ¹³C¹⁸O, C¹⁷O, and ¹³C¹⁷O ASAI observations, we derive an NO fractional abundance less than ∼10^–7 for the SVS13-A envelope, in agreement with previous measurements towards extended photodissociation regions (PDRs) and prestellar objects. Conversely, a definite X(NO) enhancement is measured towards L1157-B1, ∼6 x 10^–6, showing that the NO production increases in shocks. The public code UCLCHEMwas used to interpret the NO observations, confirming that the abundance observed in SVS13-A can be attained in an envelope with a gas density of 10⁵ cm^–3 and a kinetic temperature of 40 K. The NO abundance in L1157-B1 is reproduced with pre-shock densities of 10⁵ cm^–3 subjected to a ∼45 km s^–1 shock.