ON MODE-IDENTIFICATION IN DELTA-SCUTI

UV light amplitudes and phase shifts obtained from the IUE observation s are discussed for pulsating star delta Scuti. The published ground-b ased photometric and radial velocity data are also included in the ana lysis. The observations are compared with model calculations which tak e into account temperature and pressure changes during pulsation cycle . A promising approach for determination of oscillation parameters is based on the analysis of observed phase shifts between radial velocity data and light curves obtained at a sufficiently wide wavelength regi on. Usefulness of the IUE and infrared data for the pulsation mode dis crimination in delta Scuti stars is pointed out. The best fit solution for delta Sct yields 1H radial mode of oscillation for the main perio d P0 = 0.d1937697. We obtain the phase shift between temperature and r adius variations, psi(T) equal to 2.0 radians. Pulsations are non-adia batic, with the ratio of fractional temperature amplitude to fractiona l radius amplitude, B, equal to 2.96, whereas adiabatic value is B(ad) = 10.2. For the P1 = 0.d1867756 component we obtain P2 overtone of l = 2 With psi(T) = 1.708 radian and B = 2.224 as a preliminary mode ide ntification. Both components predict the stellar radius of about 4.1 R ..