Astronomy and Astrophysics, volume 315, 510-520 (1996/11-3)
Spectroscopic study of the outflowing disk winds of B[e] supergiants in the Magellanic Clouds.
ZICKGRAF F.-J., HUMPHREYS R.M., LAMERS H.J.G.L.M., SMOLINSKI J., WOLF B. and STAHL O.
Abstract (from CDS):
We report on UV high resolution spectroscopic observations of R50 in the Small Magellanic Cloud, and R82 and HenS22 in the Large Magellanic Cloud obtained with the International Ultraviolet Explorer. The observed stars are supposed to represent edge-on cases of B[e] supergiants for which a two-component stellar wind model has previously been suggested. The spectra are characterized by P Cygni-type lines of FeII. The observations show that the three stars have very slowly expanding winds with terminal velocities derived from the blue absorption edges of 75, 100, and 120km/s, respectively. Fits of the FeII lines of Hen S22 and R82 using the SEI method lead to even slower velocities of about 60 to 80km/s, respectively. This is about a factor of ten slower than the terminal velocity of normal B-type supergiants. The results are consistent with the assumption that the observed stars are viewed edge-on. We derived optical depths of the absorption components of the FeII resonance lines of Hen S22 and R82 of larger than about 5, yielding lower limits for the disk mass-loss rates of the order of 6x10–7 and 5x10–7M☉/yr, respectively. The very low terminal velocity of the disk can be explained by the fact that the disks of the B[e] supergiants are on the low-velocity side of the bi-stability jump of radiation driven winds (which reduces v∞/vesc) and a rotational velocity of about 0.75 of the critical rotation velocity (which reduces the effective vesc). The effective gravity derived from v∞ and v∞/vesc=1.3 is very low. It is on the order of loggeff=0.2 to 0.7.