The Antares emission nebula and mass loss of α Scorpii A

Aims: The Antares nebula is a peculiar emission nebula seen in numerous [Fe II] lines and in radio free-free emission, probably associated with the H ii region caused by α Sco B in the wind of α 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 α 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 α Sco A.
Results: We found that the Antares nebula shows, in addition to numerous [Fe ii] lines, the Balmer line recombination spectrum Hα, Hβ up to H{10}, and [N ii] 6583/6548 Å, Hα 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 Hα velocities, the H ii region is found to be located 215 AU behind the plane of the sky of α Sco A. From the Hα/[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}_e = 4900 K and an N abundance enhanced by a factor of 3 due to the CNO cycle in α Sco A. The shape and size of the H ii region yield a mean mass-loss rate of (1.05 ± 0.3) × 10^-6 M_⊙ 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.

Based on observations under program ID 076.D-0690(A) with the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) Unit 2 (Kueyen) at Paranal, Chile, operated by ESO.