Nitrogen oxide in protostellar envelopes and shocks: the ASAI survey
  The high-sensitivity of the IRAM 30-m 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 $^2\Pi_{\rm 1/2}$ $J$ = 3/2 $\to$ 1/2 (at 151 GHz) and the
$^2\Pi_{\rm 1/2}$ $J$ = 5/2 $\to$ 3/2 (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
($\sim$ 5 km s$^{-1}$) blue-shifted emission. For SVS13-A the analysis leads to
$T_{\rm ex}$ $\geq$ 4 K, $N(\rm NO)$ $\leq$ 3 $\times$ 10$^{15}$ cm$^{-2}$, and
indicates the association of NO with the protostellar envelope. In L1157-B1, NO
is tracing the extended outflow cavity: $T_{\rm ex}$ $\simeq$ 4--5 K, and
$N(\rm NO)$ = 5.5$\pm$1.5 $\times$ 10$^{15}$ cm$^{-2}$. Using C$^{18}$O,
$^{13}$C$^{18}$O, C$^{17}$O, and $^{13}$C$^{17}$O ASAI observations we derive
an NO fractional abundance less than $\sim$ 10$^{-7}$ for the SVS13-A envelope,
in agreement with previous measurements towards extended PDRs and prestellar
objects. Conversely, a definite $X(NO)$ enhancement is measured towards
L1157-B1, $\sim$ 6 $\times$ 10$^{-6}$, showing that the NO production increases
in shocks. The public code UCLCHEM was 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 10$^5$ cm$^{-3}$ and a kinetic temperature of 40
K. The NO abundance in L1157-B1 is reproduced with pre-shock densities of
10$^5$ cm$^{-3}$ subjected to a $\sim$ 45 km s$^{-1}$ shock.
