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

On the basis of our new simultaneous photom-etry and spectroscopy (885 uvby differential measurements in 11 nights and 154 spectrograms of the FeIIλ4508 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 pul-sational models to our data, we estimate the inclination of rotational axis to be about 50 • 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 sec-torial 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.