A New Spectrum Variable of Short Period, HD 124224.

Abstract

The "silicon star" HD 124224 shows absorption lines of He I that vary in strength with a period of 0.5 day. The lines of Si U and a group of unidentified lines vary in opposite phase. Within the large errors of measurement, the radial velocity is constant except for the lines of He I, which before maximum strength are displaced about 5 A to the violet of their position after maximum. The contour of Mg II 4481 is compatible with the hypothesis that the star rotates with a period of 0.5 day, with its axis perpendicular to the line of sight. Suppression of convection by a magnetic field may be responsible for the simultaneous strengthening of He I and weakening of Si U.