New Whole Earth Telescope observations of CD-24 7599: Steps towards δ Scuti star seismology

92 h of new Whole Earth Telescope observations have been acquired for the 0 Scuti star CD-24 7599. All the seven pulsation modes reported by Handler et al. are From new colour photometry and spectroscopy we infer that CD-24 7599 is a hot main sequence 0 Scuti star with approximately solar metallicity and v sin i = 52 ± 2 km s -I. yve cannot yet propose a definite pulsation mode identification, but we report the detection of a characteristic frequency spacing between the different modes. We ascribe it to the simulta neous presence of .e = 1 and .e = 2 modes of consecutive radial order. A comparison of this frequency spacing with frequencies of solar-metallicity models, as well as stability analysis, allows us to constrain tightly the evolutionary state ofCD~24 7599. It is in the first half of its main-sequence evolution, and has a mass of 1.85 ± 0.05 M0 and a mean density of p = 0.246 ± 0.020 P0' This yields a seismological distance of 650 ± 70 pc, which i~ as accurate as distance determinations for 0 Scuti stars observed in clusters. Most of the pulsation modes are pure p modes of radial order k = 4-6, but the gl mode of .e = 2 is likely to be excited and observed as well. Since a significant contribution to this mode's kinetic energy comes from the outer part of the convective core, CD-247599 becomes particularly interesti1)g for testing convective overshooting theories.