THE DELTA-SCUTI STAR THETA-TUCANAE .2. UVBY COLOR VARIATIONS AND PULSATIONAL ORBITAL PROPERTIES/

On the basis of almost 1500 uvby photometric observations of theta Tuc anae collected in 1993, we discuss the colour variation of this multi- periodic delta Scuti star and debate some of its binary and pulsationa l properties. The frequencies f(1) = 0.281 and f(2) = 0.142 cd(-1) emb ody orbital motion in a 7(d).04 day ellipsoidal configuration characte rised by a light curve with unequal maxima and minima and a colour ind ex that becomes bluer during the minimum phases. The first results of an analysis of the light curve points towards a mass ratio q of the or der of 0.10-0.15. We present dependable numerical values for colour ph ase differences and amplitude ratios A(b-y)/A(y), phi(b-y) - phi(y), A (v-y)/A(y), phi(v-y) - phi(y) and A(u-y)/A(y), phi(u-y)-phi(y) which c an be used for pulsation-mode identification. The principal pulsation frequency f(7) = 20.28 cd(-1) is reconcilable with a radial mode.