Abstract:
Rotational velocities for 112 members of the Scorpio-Centaurus association brighter than 8.5 magnitudes are derived from spectra obtained with a dispersion of 47 A/mm. Hydrogen and helium line intensities are determined from the same spectra, and the equivalent width of the H-gamma line is used to obtain a mean distance modulus of 6.0 + or - 0.09 magnitudes. Mean helium abundances are also computed for five bright members of the association as well as for 10 members of the upper Scorpius subgroup and three members of the upper Centaurus-Lupus subgroup. The results show that: (1) the mean rotational velocities in this association follow the Abt-Hunter (1962) field curve very closely except for stars of spectral type B7 or later; (2) the distribution of rotational velocities is the same for objects earlier than B7 in both subgroups; (3) members of spectral type B7 or later rotate very much faster than the field stars; (4) the helium abundance seems to be similar for both subgroups; and (5) the higher hydrogen line intensities for members of the upper Scorpius subgroup are probably an evolutionary effect.
