2004A&A...419..191C

We present new millimeter and infrared spectroscopic observations towards the radio nebula G10.0-0.3, which is powered by the wind of the Luminous Blue Variable star LBV 1806-20 also closely associated with the soft gamma-ray repeater SGR 1806-20, and believed to be located in the giant Galactic HII complex W31. Based on observations of CO emission lines and NH₃ absorption features from molecular clouds along the line of sight to G10.0-0.3, as well as the radial velocity and optical extinction of the star powering the nebula, we determine its distance to be 15.1^+1.8_–1.3kpc in agreement with Corbel et al. (1997ApJ...478..624C). In addition, this strengthens the association of SGR 1806-20 with a massive molecular cloud at the same distance. All soft gamma-ray repeaters with precise location are now found to be associated with a site of massive star formation or molecular cloud. We also show that W31 consists of at least two distinct components along the line of sight. We suggest that G10.2-0.3 and G10.6-0.4 are located on the -30km/s spiral arm at a distance from the Sun of 4.5±0.6kpc and that G10.3-0.1 may be associated with a massive molecular cloud at the same distance as the LBV star, i.e. 15.1^+1.8_–1.3kpc, implying that W31 could be decomposed into two components along the line of sight.