In the spectrum of the fifth-magnitude peculiar A star HD 124224 the absorption lines of He 1 vary in strength with a period of only 0-52 day. The lines of Si 11 are always much stronger than in normal stars. They vary out of phase with the helium lines, but in phase with a group of unidentified lines that seem generally to occur in the so-called ' silicon stars

The lines of this spectrum are shallow and wide, and radial velocity determinations are inaccurate on this account. The hydrogen lines indicate no velocity changes, but He I 4026 is displaced to the violet before maximum strength, and to the red after. The silicon lines, on the other hand, are probably displaced in the opposite sense. These displacements, together with the diffuseness of the lines, strongly suggest that we have to do here with a star that rotates in half a day about an axis perpendicular to the line of sight. If this is so, the helium lines are produced preferentially near the approaching limb before maximum strength, and near the receding limb after maximum strength.