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G79.29+0.46 is a nebula created by a Luminous Blue Variable (LBV) starcandidate characterized by two almost circular concentric shells. In order toinvestigate whether the shells are interacting with the infrared dark cloud(IRDC) G79.3+0.3 located at the southwestern border of the inner shell, weconducted Jansky Very Large Array observations of NH3(1,1), (2,2) and c-C3H2,and combined them with previous Effelsberg data. The overall NH3 emissionconsists of one main clump, named G79A, elongated following the shape of theIRDC, plus two fainter and smaller cores to the north, which spatially matchthe inner infrared shell. We analysed the NH3 spectra at each position withdetected emission and inferred linewidth, rotational temperature, columndensity and abundance maps, and find that: i) the linewidth of NH3(1,1) in thenorthern cores is 0.5 km/s, slightly larger than in their surroundings; ii) theNH3 abundance is enhanced by almost one order of magnitude towards thenorthwestern side of G79A; iii) there is one `hot slab' at the interfacebetween the inner infrared shell and the NH3 peak of G79A; iv) the western andsouthern edges of G79A present chemical differentiation, with c-C3H2 tracingmore external layers than NH3, similar to what is found in PDRs. Overall, thekinematics and physical conditions of G79A are consistent with bothshock-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.

A Luminous Blue Variable Star Interacting with a Nearby Infrared Dark Cloud