A luminous blue variable star interacting with a nearby infrared dark cloud

Abstract

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 NH 3(1, 1), (2, 2) and c-C 3H 2, 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 analyzed the NH 3 spectra at each position with detected emission and inferred linewidth, rotational temperature, column density, and abundance maps, and find that: (1) the linewidth of NH3(1, 1) in the northern cores is 0.5 km s-1, slightly larger than in their surroundings; (2) the NH3 abundance is enhanced by almost one order of magnitude toward the northwestern side of G79A; (3) there is one "hot slab" at the interface between the inner infrared shell and the NH 3 peak of G79A; and (4) the western and southern edges of G79A present chemical differentiation, with c-C 3H 2 tracing more external layers than NH3, similar to what is found in photon-dominated regions. 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. © 2014. The American Astronomical Society. All rights reserved.