Abstract
Ara OB1 is a southern and rather compact stellar association, being its nucleus the open cluster NGC 6193. Herbst and Havlen (1977) suggested that the overall dimensions and structure of the reqion could be a consequence of a supernova event. In order to look further into this problem, a neutral hydrogen study in the 21-cm line was undertaken using the 30m dish of the Instituto Argentino de Radioastronmia. In this paper we would like to report on the main findings, namely: i) a HI structure expanding at a speed of 10 kms-1 and almost 80 parsecs in diameter has been found in the region; ii) the expanding structure, having a total HI mass of 3.5 x 10^3 M⊙, has a systemic radial velocity of -12 kms-1 (LSR), is younger than 4 x 10^6 yr and its geometric centroid with the old open cluster NCC 6167; iii) the distances of NGC 6193, 1.3 ± 0.12 kpc (Herbst and Havlen, 1977); NGC 6167, 1.4 ± 0.2 kpc (Bruck and Smyth, 1967); and the kinematic distance of the HI-expanding feature, 1.2 ± O.2 kpc (this paper), do agree to within the uncertainties; iv) regarding the expanding neutral hydrogen distribution, NGC 6193 is localized at the eastermost edge of the shell. Such region is heavily obscured optically. Based on the above mentioned evidence the following evolutive scenario for this region is proposed:birth of NCC 6167; energetic phenomena (SN events, strong stellar winds) in its most massive stars;formation of the observed HI expanding structure;interaction of this expanding HI feature with interestellar molecular clouds; formation of NC 6193 (or Ara OB1 ).
