On the absolute scale of mass-loss in red giants. II. Circumstellar absorption lines in the spectrum of alpha Sco B and mass-loss of alpha Sco A.

Summary. The rate of mass-loss of the M supergiant cc Sco A is determined by means of high dispersion spectra of cc Sco A, cc Sco B, and of the Antares emission nebula as M=7 10- M0/yr. A model atmosphere analysis of the spectrum of ccScoB yields Teff=18500 K, logg=3.9, and a mass of 7 M0. cc Sco B is a normal main-sequence B star. The comparable strengths of circumstellar Ti II and Ca II absorption lines in the spectrum of cc Sco B require that the lines are formed in a H II region. In case of neutral hydrogen in the line of sight of cc Sco B, Ca II would be completely ionized and the Ca Ii lines - would be invisibly weak while with respect to Ti II ionization there is only small difference between a H II and a H I region. In agreement with this finding, the observed population of fine structure levels within the ground state of Ti II can be explained only through electron collisions in an HIl region at a density Of 10 cm -3. A picture consistent with Ti II and nebular [Fe II] radial velocities and with the orbit of the Antares binary system emerges if the B star is placed somewhat in front of the M star. The B star's H II region, calculated in a spherical M star envelope with densities as deter- mined from both relative and absolute Ti II line strengths, is then unlimited in front of the B star (electron temperature 2500 K, no [Fe II] emission) while the rear edge is found to be slightly behind the plane of the M star (in the line of sight of cc Sco B) with K and [FeII] emission. This agrees with the electron temperature Te 4000 K as found by Swings (1972) from relative [Fe II] emission line intensities and with the slightly positive velocity of the [Fe II] lines. Using the results for cc Sco A, cc1 Her (Paper I), and 2Lyr, which have different masses (18 M0, 1.8 M0, 8 M0), luminosities and evolutionary stages, the semi- empirical mass-loss formula dM/dt [M0/yr] = c L/g. R (solar units) is calibrated with c=(5.5+1) .10-13. Key words: mass-loss in Red Giants - stellar evolution - excitation of fine structure levels - emission nebulae