The Large Flux Variations of 17 Com A as Recorded by FUSE

Inspection of archival FUSE spectra of the Ap star 17 Com A (HD 108662) reveals large flux variations from 905 to 1187 Å over the 5.0808 days rotational period. These variations are of larger amplitude than those observed in the ultraviolet range with IUE from 1200 to 2000 Å. At 1161 Å, where the flux reaches a maximum, the variation of flux with rotational phase shows a double-wave structure similar to that of the Transiting Exoplanet Survey Satellite lightcurve. 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 17 Com A contains mostly blends of low-excitation lines of Mn II, Cr II and Fe II and interesting lines of C I, C III, P II, S II and Cl I.