A Luminous Blue Variable Star Interacting with a Nearby Infrared Dark
  Cloud
  G79.29+0.46 is a nebula created by a Luminous Blue Variable (LBV) star
candidate characterized by two almost circular concentric shells. In order to
investigate whether the shells are interacting with the infrared dark cloud
(IRDC) G79.3+0.3 located at the southwestern border of the inner shell, we
conducted Jansky Very Large Array observations of NH3(1,1), (2,2) and c-C3H2,
and combined them with previous Effelsberg data. The overall NH3 emission
consists of one main clump, named G79A, elongated following the shape of the
IRDC, plus two fainter and smaller cores to the north, which spatially match
the inner infrared shell. We analysed the NH3 spectra at each position with
detected emission and inferred linewidth, rotational temperature, column
density and abundance maps, and find that: i) the linewidth of NH3(1,1) in the
northern cores is 0.5 km/s, slightly larger than in their surroundings; ii) the
NH3 abundance is enhanced by almost one order of magnitude towards the
northwestern side of G79A; iii) there is one `hot slab' at the interface
between the inner infrared shell and the NH3 peak of G79A; iv) the western and
southern edges of G79A present chemical differentiation, with c-C3H2 tracing
more external layers than NH3, similar to what is found in PDRs. Overall, the
kinematics and physical conditions of G79A are consistent with both
shock-induced and UV radiation-induced chemistry driven by the LBV star.
Therefore, the IRDC is not likely associated with the star-forming region DR15,
but located farther away, near G79.29+0.46 at 1.4 kpc.
