Intermediate scale structure of the interstellar medium towards NGC 6231 in Sco OB1 with FUSE ^*

Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Corresponding author: O. Marggraf, marggraf@astro.uni-bonn.de

Received: 16 June 2003
Accepted: 2 December 2003

Abstract

The FUSE far-ultraviolet interstellar spectra toward seven targets in NGC 6231 show that the molecules H₂, HD, and CO as well as various atomic species are distributed in several clouds. The main absorption component found on the sight lines lies in the Lupus cloud region at a distance of about 150 pc, and there is a weaker second one, presumably in the Sco OB1 shell surrounding NGC 6231 ( kpc). H₂ excitation modelling is used to constrain the radiation field and the density in the gas; HD is used to estimate the abundance of H⁺. The small angular separation of the target stars allows column density variations to be probed over the field of view, on scales of 0.05 pc in the case of the Lupus cloud distance. They are for H₂ and for . A rather strong radiation field inside the molecular clouds suggests a separation of the gas into smaller cloudlets also along the line of sight.