THE ULTRAVIOLET VARIATIONS OF THE DELTA-SCUTI STARS 44-TAURI AND 71-TAURI

We report on low resolution phase resolved ultraviolet spectrophotomet ry of the delta Scuti stars, 44 Tau (F2 IV-V) and 71 Tau (F0V) at diff erent phases of their pulsation cycles performed with the Internationa l Ultraviolet Explorer. For 44 Tau, the amplitude of the flux variatio ns increases towards shorter wavelengths from about 13% around 3000ang strom to 40% around 1800angstrom and the ultraviolet flux varies in ph ase with the optical brightness as recorded with the Fine Error Sensor (FES). During our observations, 71 Tau exhibited only marginal variat ions in the ultraviolet. A comparison of the far ultraviolet spectra o f 44 Tau at maximum and minimum ultraviolet light with low resolution spectra of constant stars indicates that the effective temperature doe s not vary by more than 250K over a cycle. The amplitude of the ultrav iolet variations seem to scale those in the V band and the behaviour o f 44 Tau in the ultraviolet is similar to that of delta Scuti describe d in Monier (1991).