2022RNAAS...6...21M

Forty-one spectra of 78 Vir (A2p ScrCrEu) obtained through the large apertures of the SWP and LWP/LWR cameras on board International Ultraviolet Explorer (IUE) are compared to look for variations of the absolute flux of 78 Vir over the spectral range 1200-3000 Å. Large variations of the spectral energy distribution occur in the far ultraviolet shortwards of 2000 Å. In contrast, the flux at wavelengths larger than 2000 Å does not vary but several lines are variable between phases of far-UV (FUV) maximum and FUV minimum. The large FUV variability is probably caused by changes in the continuous and line opacity driven by modest horizontal gradients of the abundances of chemical elements over the surface of 78 Vir as the star is probably seen at a low inclination angle. The FUV flux at 1500 Å varies in anticorrelation with the FES counts (optical brightness) recorded before each exposure by the Fine Error Sensor on board IUE.