Kinematical Structure of Wolf-Rayet Winds. II. Internal Velocity Scatter in WN Stars

The shortward edge of the absorption core velocities - vblack as determined from low resolution archived IUE spectra from the INES database are presented for three P Cyg profiles of NV 1240, HeII 1640 and NIV 1720 for 51 Galactic and 64 LMC Wolf-Rayet stars of the WN subtype. These data, together with vblack of CIV 1550 line presented in Niedzielski and Skórzyński (2002) are discussed. Evidences are presented that vblack of CIV 1550 rarely displays the largest wind velocity among the four lines studied in detail and therefore its application as an estimator of the terminal wind velocity in WN stars is questioned. An average vblack of several lines is suggested instead but it is pointed out that vblack of HeII 1640 usually reveals the highest observable wind velocity in Galactic and LMC WN stars. It is shown that the stratification strength decreases from WNL to WNE stars and that for WNL stars there exists a positive relation between vblack and the Ionization Potential. The velocity scatter between vblack obtained from different UV lines is found to correlate well with the X-ray luminosity of single WN stars (correlation coefficient R=0.82 for the data obtained from the high resolution IUE spectra) and therefore two clumpy wind models of single WN stars are presented that allow the velocity scatter to persist up to very large distances from the stellar surface (r≈500-1000R*). These models are used to explain the specific features of single WN stars like broad absorption troughs of strong lines having different vblack, X-ray fluxes, IR/radio continua and stratification relations.