Astrophys. J., 558, 771-779 (2001/September-2)
Terminal speeds and ion fractions from [Ca IV] 3.207 µm in three single WN stars.
IGNACE R., CASSINELLI J.P., QUIGLEY M. and BABLER B.
Abstract (from CDS):
We report on the forbidden emission lines of [Ca IV] at 3.207 µm and [Ne III] at 15.56 µm based on Infrared Space Observatory observations. The data set consists of three single Wolf-Rayet stars (WR 1, WR 134, and WR 136) and three binary systems (WR 11, WR 146, and WR 147). For the single stars, only the [Ca IV] line was observed. Our primary objectives are to determine the wind terminal speed from the emission-line widths, derive ion number fractions, and discuss the relation between emission profile shapes and wind flow geometry. Compared to previous determinations of the terminal speed, we find values that are similar or somewhat smaller. Interestingly, the line width at the continuum level is typically 10%-30% broader than at the half-maximum level. The extra broadness suggests the effect of turbulence in the wind. For the ion fraction, we assume that calcium is not enriched in any of the W-R winds. Ion fractions of Ca+3 and Ne+2 are derived for the binary systems and found to be consistent with previously published values. For the new observations of the single WN stars, all of the ion fractions for Ca+3 have similar values, which are close to the maximum expected value, thus suggesting that Ca+3 is the dominant ion at large radii in the wind. Finally, the line profile shapes in the binaries WR 11, WR 146, and WR 147 appear asymmetric, as might be expected from such systems. For WR 136, the [Ca IV] profile is flat-topped, consistent with a spherical flow. For WR 1 and WR 134, the [Ca IV] profiles are too weak to draw conclusions about the wind flow geometry.
Infrared: Stars - Stars: Abundances - Stars: Winds, Outflows - Stars: Wolf-Rayet
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