Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....118.2394g&link_type=abstract
The Astronomical Journal, Volume 118, Issue 5, pp. 2394-2408.
Astronomy and Astrophysics
Astronomy
24
Ism: Bubbles, Ism: Individual (Anonymous Mr 100), Stars: Circumstellar Matter, Stars: Wolf-Rayet, Stars: Individual (Wr 134 Hd=191765)
Scientific paper
We have surveyed a 2.6dx2.6d field centered on the Wolf-Rayet (W-R) star HD 191765 (=WR 134) in the H I 21 cm line and in the 1420 and 408 MHz radio continuum, using the Synthesis Telescope of the Dominion Radio Astrophysical Observatory, to search for direct evidence of the interaction between the W-R star wind and the interstellar medium. An arc-shaped structure is present in the 1420 MHz continuum image, which perfectly matches the optical nebula Anon (MR 100). That this gas is not visible on our 408 MHz map hints at the thermal nature of the source. This ionized gas could be associated with luminous blue variable or red supergiant ejecta swept up by the W-R wind and photoionized by the strong ultraviolet flux from the star. However, this suggestion needs to be confirmed by clear CNO enrichment measurements in the northwest region of the nebula. 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, MHI~1830 Msolar), 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 (~1.3x106 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 deg). 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.
Gervais Simon
St-Louis Nicole
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