Rotation measurement of 18 B-type binaries

Using the HeI 5857 A line observed with a Reticon at the conde focus of the 2.1-metre reflector of McDonald Observatory, we measured the Vsini value for 18 binaries of spectral type B by fitting the observed profile to that of a standard star convolved with Gray's rotational broadening function.

Our results for the two components of ξ² CrB and the primary of 25 Ser are less than half the catalogue values. The profiles of U CrB and v Sco have a narrow central absorption and very wide wings, and our measured value of 75 km/s for ν Sco, based on the central absorption, is much smaller than the catalogue value of 210 km/s. The profile of AR Cas was found to change with phase.

Our values agree with Slettebak's new system better than with his old system.