SIMBAD references

We present observations of the NH₃(J, K) = (1, 1) and (2, 2) inversion transitions toward the infrared dark cloud G28.34+0.06, using the Very Large Array. Strong NH₃ emission is found to coincide well with the infrared absorption feature in this cloud. The northern region of G28.34+0.06 is dominated by a compact clump (P2) with a high rotation temperature (29 K) and large line width (4.3 km/s), and is associated with a strong water maser (240 Jy) and a 24 µm point source with far-IR luminosity of 10³ L_☉. We infer that P2 has embedded massive protostars although it lies in the 8 µm absorption region. The southern region has filamentary structures. The rotation temperature in the southern region decreases with the increase of the integrated NH₃intensity, which indicates an absence of strong internal heating in these clumps. In addition, the compact core P1 in the south has small line width (1.2 km/s) surrounded by extended emission with larger line width (1.8 km/s), which suggests a dissipation of turbulence in the dense part of the cloud. Thus, we suggest that P1 is at a much earlier evolutionary stage than P2, possibly at a stage that begins to form a cluster with massive stars.