2020RNAAS...4..160M

Inspection of archival IUE spectra of the bright rapidly oscillating Ap star α Cir A reveal large flux variations from 1600 to 2000 Å over the 4.4790 day rotational period. At 1965 Å, where the flux reaches a maximum, the flux more than doubles between phases of maximum and minimum flux. These large flux variations are most likely caused by the passage of spots or belts of overabundant elements in the line of sight as the star rotates. The FUSE spectrum of α Cir B, the K5V dwarf close to α Cir A, contains several emission lines of O VI, C III and C II which are probably formed in the transition region and the chromosphere of this star. The O VI lines completely disappear over a timescale of a few days which probably reflects rotationaly modulated magnetic activity.