On Mode Identification in delta Scuti

Abstract

UV light amplitudes and phase shifts obtained from the IUE observations are discussed for pulsating star delta Scuti. The published ground-based photometric and radial velocity data are also included in the analysis. The observations are compared with model calculations which take 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 region. Usefulness of the IUE and infrared data for the pulsation mode discrimination in delta Scuti stars is pointed out. The best fit solution for delta Sct yields 1H radial mode of oscillation for the main period P_0=0.1937697 d. We obtain the phase shift between temperature and radius variations, psi_T equal to 2.0 radians. Pulsations are non-adiabatic, with the ratio of fractional temperature amplitude to fractional radius amplitude, B, equal to 2.96, whereas adiabatic value is B_ad=10.2. For the P_1=0.1867756 d component we obtain p_2 overtone of l =2 with psi_T=1.708 radian and B=2.224 as a preliminary mode identification. Both components predict the stellar radius of about 4.1 R_odot.