The distribution of the rotation axes of A-type stars

The distribution of the spin axes of A-type stars was studied using a sample of 166 normal A2–A9 field stars of luminosity classes IV or V. No dependence of the projected rotational velocities υ sin i on galactic latitude was found, and so the spin axes are not aligned perpendicular to the galactic plane. This suggests that angular momentum was efficiently dissipated during the early stages of collapse of the molecular clouds in which the stars were born and that the protostars may have been formed through collisions of turbulent elements in the clouds. A sample of visual binaries with normal A2–A9 components and known orbits was also investigated. No correlation between υ sin i and orbital inclination was found. This excludes a general alignment of the spin axes of the components perpendicular to the orbital planes and gives strong support for the idea that visual binaries were formed by the pairing of stars resulting from independent condensations in the interstellar medium.