A Large H [CSC]i[/CSC] Shell surrounding the Wolf-Rayet Star HD 191765

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Abstract
Our H I maps reveal the existence of a nearly complete shell at a velocity of vsys = -11.44 km s-1 (Rs ≈ 20.9 pc, vexp ≈ 9.9 km s-1, MH I ≈ 1830 M⊙), which, mainly for morphological reasons, we associate with HD 191765 (although a contribution from the nearby W-R star HD 192103 cannot be totally excluded). The dynamical age of this bubble (~1.3 × 106 yr) suggests that it was mainly blown during the main-sequence progenitor O-star phase. The kinematic distance corresponding to a local standard of rest velocity of -11 km s-1 is approximately 5 kpc, which is incompatible with the association distance of HD 191765 of 2.1 kpc. Therefore, we conclude that the H I bubble we have detected was blown in gas already in movement with respect to normal Galactic rotation for this region. There is independent evidence that gas at this velocity is present in this line of sight. Recent Hipparcos data analyzed by Moffat et al. give a supersonic proper motion for HD 191765 (projected velocity ~52 km s-1 at a position angle on the sky of P.A. = -38°). This velocity vector points away from a position very close to the center of the H I bubble, which strengthens the hypothesis of a physical link with the W-R star. The supersonic velocity of the star with respect to the interstellar medium might have generated some compression of the interstellar medium in the southwest region, rendering the Hα gas brighter in that direction with respect to the surroundings.

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