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Issue A&A Volume 419, Number 1, May III 2004 Page(s) 191 - 201 Section Interstellar and circumstellar matter DOI 10.1051/0004-6361:20034054

A&A 419, 191-201 (2004)
DOI: 10.1051/0004-6361:20034054

The connection between W31, SGR 1806-20, and LBV 1806-20: Distance, extinction, and structure

S. Corbel¹ and S. S. Eikenberry<sup>2

1</sup>  Université Paris VII and Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
²  Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611, USA
    e-mail: eiken@astro.ufl.edu

(Received 4 July 2003 / Accepted 3 October 2003)

Abstract
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 H II complex W31. Based on observations of CO emission lines and NH ₃ 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_-1.3 kpc in agreement with Corbel et al. (1997). 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 -30 km s ^-1 spiral arm at a distance from the Sun of   kpc 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_-1.3 kpc, implying that W31 could be decomposed into two components along the line of sight.

Key words: stars: neutron -- stars: individual:  SGR 1806-20 -- stars: individual: LBV 1806-20 -- ISM: individual: W31 -- Galaxy: structure -- Galaxy: kinematics and dynamics

Offprint request: S. Corbel, corbel@discovery.saclay.cea.fr

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