Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. III. Mode identifications and physical calibrations in HD 2724

Abstract

On the basis of our new simultaneous photometry and spectroscopy (885 \( uvby \) differential measurements in 11 nights and 154 spectrograms of the FeII\( \lambda \)4508 region in 5 nights), we can detect 12 probable periodicities in the variability pattern of this star, determining the frequencies of 7 without any ambiguity. Through a direct fit of pulsational models to our data, we estimate the inclination of rotational axis to be about 50\( ^{\circ} \) and get a reliable identification of 4 modes as well as useful bits of information about the others: no retrograde mode is visible, whereas the star seems to show a certain preference for purely sectorial prograde oscillations. Finally, the attribution of our lowest frequency to the radial fundamental pulsation allows a new calibration of physical parameters. In particular, the gravity can be determined with unusual accuracy and the luminosity evaluation becomes more consistent with the Hipparcos astrometry. This work is based on observations performed at the European Southern Observatory (ESO), La Silla, Chile.