Astronomy & Astrophysics

Free access article

A&A 408, 257-285 (2003)
DOI: 10.1051/0004-6361:20030999

Kinematical structure of the circumstellar environments of galactic B[e]-type stars

F.-J. Zickgraf

Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
(Received 27 September 2002 / Accepted 19 June 2003)

Abstract
High resolution line profiles are presented for selected forbidden and permitted emission lines of a sample of galactic B[e]-type stars. The spectral resolution corresponds to 5-7 km s ^-1 with the exception of some line profiles which were observed with a resolution of 9-13 km s ^-1. All H $\alpha$ profiles are characterized by a narrow split or single emission component with a width of ~ 150-250 km s ^-1 (FWHM) and broad wings with a full width of ~ 1000-2000 km s ^-1. The H $\alpha$ profiles can be classified into three groups: double-peaked profiles representing the majority, single-peaked emission-line profiles, and normal P Cygni-type profiles. Likewise, the forbidden lines exhibit in most cases double-peaked profiles. In particular, the majority of stars shows split [O I] $\lambda$ 6300 Å. Double-peaked profiles are also found in several stars for [N II] $\lambda$ 6583 Å and [Fe II] $\lambda$ 7155 Å although these lines in many stars exhibit single-peaked emission profiles. The split forbidden line profiles have peak separations of as little as ~10 km s ^-1, and were therefore only discernible for the first time in the high-resolution spectra. The ratio of violet to red emission peak intensities, V/R, is predominantly smaller or equal to 1. Theoretical profiles were calculated for the optically thin case. A latitude-dependent stellar wind with a radial expansion and a velocity decreasing from the pole to the equator was adopted. This configuration can produce split line profiles if viewed under some angle with respect to the line of sight. In addition an equatorial dust ring with various optical depths was assumed. It can explain line asymmetries observed in some stars. Moreover, the V/R ratios can be understood in terms of this model. The comparison of the observed line profiles with the models thus confirms the assumption of disk-like line-formation regions as commonly adopted for B[e]-type stars.

Key words: stars: circumstellar matter -- stars: early-type -- stars: emission-line, Be -- stars: mass-loss

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