The chemically peculiar double-lined spectroscopic binary HD 90264

The helium-weak stars are usually identified as magnetic, chemically peculiar (CP) stars, while the HgMn subclass is not. This binary, a member of the Sco-Cen association, is the first CP binary to show both. The helium lines are variable in the more massive component, suggesting a magnetic field (which is not available directly but suggested by the polarimetry). With a mass ratio of 1.2 and probably a synchronized rotation (along with a possible small orbital eccentricity), this is a unique system for testing ideas on the formation of chemical anomalies in main sequence stars.