EDP Sciences
Free access
Volume 491, Number 1, November III 2008
Page(s) 229 - 238
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:200809983
Published online 01 October 2008

A&A 491, 229-238 (2008)
DOI: 10.1051/0004-6361:200809983

The Antares emission nebula and mass loss of $\sf\alpha$ Scorpii A

D. Reimers, H.-J. Hagen, R. Baade, and K. Braun

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: dreimers@hs.uni-hamburg.de

Received 16 April 2008 / Accepted 25 August 2008

Aims. The Antares nebula is a peculiar emission nebula seen in numerous [ $\ion{Fe}{ii}$] lines and in radio free-free emission, probably associated with the H II region caused by $\alpha$ Sco B in the wind of $\alpha$ Sco A. High-resolution spectra with spatial resolution were used to study the emission line spectrum, the physical nature of the nebula and to determine the mass-loss rate of the M supergiant $\alpha$ Sco A.
Methods. The Antares nebula was mapped with long-slit (10$\arcsec$) and high-resolution (R = 80 000) spectra using UVES at the VLT. The resulting 2-D images were used to reconstruct a 3-D picture of the H II region and its absolute location in space relative to $\alpha$ Sco A.
Results. We found that the Antares nebula shows, in addition to numerous [Fe II] lines, the Balmer line recombination spectrum H$_{\alpha}$, H$_{\beta}$ up to H10, and [N II] 6583/6548 Å, H$_{\alpha}$ and [N II] with the same extent as seen in cm radio free-free emission. Combining velocity information from optical and GHRS/HST spectra with H$_{\alpha}$ velocities, the H II region is found to be located ~215 AU behind the plane of the sky of $\alpha$ Sco A. From the H$_{\alpha}$/[N II] intensity ratio and the non-visibility of the [O II] 3726/3729 Å lines we estimate a low mean electron temperature of $\overline{T}_{\rm e}$ = 4900 K and an N abundance enhanced by a factor of ~3 due to the CNO cycle in $\alpha$ Sco A. The shape and size of the H II region yield a mean mass-loss rate of (1.05 $\pm$ 0.3) $\times$ 10-6 $M_{\odot}$ yr-1. The [Fe II] lines originate predominantly at the edges (rear and front) of the H II region. UV continuum pumping as well as collisional excitation seem to be responsible for the observed iron lines.

Key words: binaries: visual -- circumstellar matter -- stars: mass-loss -- stars: late-type

© ESO 2008