Delta Scuti stars in stellar systems: on the variability of HD 220392 and HD 220391

HD 220392 (HR 8895), the brightest member of the visual double star CCDM 23239-5349, is a new short-period variable bright star, probably of the delta Scuti type. The period analysis performed on the complete set of definitive Geneva photometry as well as on the data obtained at the ESO 0.5m telescope shows two periodicities of about 4.7 and 5.5 cycles per day (cpd) with amplitudes of 0.014 and 0.011 mag respectively. A similar period search on the (smaller) dataset obtained for the 1 mag fainter B-component, HD 220391, however shows no periodicity with an amplitude significantly above the noise level of the data (about 0.006 mag). This difference in variability behaviour is discussed from the consideration that both stars form a common origin pair and are located in the delta Scuti instability strip.