Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.286..303h&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 2, pp. 303-314.
Astronomy and Astrophysics
Astronomy
53
Techniques: Photometric, Stars: Fundamental Parameters, Stars: Individual: Cd-24 7599, Stars: Oscillations, Delta Scuti
Scientific paper
92h of new Whole Earth Telescope observations have been acquired for the delta Scuti star CD-24 7599. All the seven pulsation modes reported by Handler et al. are confirmed. However, significant amplitude variations which are not caused by beating of closely spaced frequencies occurred within two years. Analysing the combined data of both WET runs, we detect six further pulsation modes, bringing the total number up to 13. We also examine our data for high-frequency pulsations similar to those exhibited by rapidly oscillating Ap stars, but we do not find convincing evidence for variability in this frequency domain. From new colour photometry and spectroscopy we infer that CD-24 7599 is a hot main-sequence delta Scuti star with approximately solar metallicity and vsini=52& plusmn2kms^-1. We 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 simultaneous presence of l=1 and l=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 of CD-24 7599. It is in the first half of its main-sequence evolution, and has a mass of 1.85 +/-0.05 M_solar and a mean density of rho^-=0.246+/-0.020rho^-_solar. This yields a seismological distance of 650 +/- 70 pc, which is as accurate as distance determinations for delta Scuti stars observed in clusters. Most of the pulsation modes are pure p modes of radial order k=4-6, but the g_1 mode of l=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-24 7599 becomes particularly interesting for testing convective overshooting theories.
Ashoka B. N.
Babu Chandra V.
Bard Steven
Bhat B. C.
Bradley Paul Andrew
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