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Kinematical Structure of Wolf-Rayet Winds. I. Terminal Wind Velocity

Niedzielski A., Skórzyński W.

Acta Astronomica

2002

Vol. 52, No. 1

81--104

New terminal wind velocities for 164 Wolf-Rayet stars (from the Galaxy and LMC) based on P Cyg profiles of λ1550 CIV resonance line were derived from the archive high and low resolution IUE spectra available form the INES database. The high resolution data on 59 WR stars (39 from the Galaxy and 20 from LMC) were used to calibrate the empirical relation (λminAbs-λpeakEmis) vs. terminal wind velocity, which was then used for determinations of the terminal wind velocities from the low resolution IUE data. We almost doubled the previous most extended sample of such measurements. Our new measurements, based on high resolution data, are precise within 5-7%. Measurements, based on the low resolution spectra have the formal errors of ≈40-60%. A comparison of the present results with other determinations suggests higher precision of ≈20%. We found that the terminal wind velocities for the Galactic WC and WN stars correlate with the WR spectral subtype. We also found that the LMC WN stars have winds slower than their Galactic counterparts, up to two times in the case of the WNE stars. No influence of binarity on terminal wind velocities was found. Our extended set of measurements allowed us to test application of the radiation driven wind theory to the WR stars. We found that, contrary to OB stars, terminal wind velocities of the WR stars correlate only weakly with stellar temperature. We also note that the terminal to escape velocity ratio for the WR stars is relatively low: 2.55±1.14 for the Galactic WN stars and 1.78±0.70 for the Galactic WCs. This ratio decreases with temperature of WR stars, contrary to what is observed in the case of OB stars. The presented results show complex influence of chemical composition on the WR winds driving mechanism efficiency. Our kinematical data on WR winds suggest evolutionary sequence: WNL→WNE→WCE→WCL.