The δ Scuti star θ Tucanae ? II . uvby colour variations and pulsational / orbital properties

On the basis of almost 1500 uvby photometric observations of θ Tucanae collected in 1993, we discuss the colour variation of this multi-periodic δ Scuti star and debate some of its binary and pulsational properties. The frequencies f1 = 0.281 and f2 = 0.142 cd−1 embody orbital motion in a 7. d04 day ellipsoidal configuration characterised by a light curve with unequal maxima and minima and a colour index 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 order of 0.10–0.15. We present dependable numerical values for colour phase differences and amplitude ratios Ab−y/Ay, φb−y − φy, Av−y/Ay, φv−y − φy and Au−y/Ay, φu−y−φy which canbe used for pulsation-mode identification. The principal pulsation frequency f7 = 20.28 cd−1 is reconcilable with a radial mode.