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The excitation of solar-like oscillations in a δ Sct star by efficient envelope convection

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Abstract

Delta Scuti (δ Sct)1 stars are opacity-driven pulsators with masses of 1.5–2.5M, their pulsations resulting from the varying ionization of helium. In less massive stars2 such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in δ Sct stars extends only about 1 per cent of the radius3, but with sufficient energy to excite solar-like oscillations4,5. This was not observed before the Kepler mission6, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δ Sct star HD 187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.

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Figure 1: Fourier amplitude spectra of the Kepler light curve of HD 187547.
Figure 2: Time-Fourier spectrum.
Figure 3: Échelle diagram of HD 187547.

Change history

  • 29 September 2011

    The labelling of the Fig. 1c y-axis was corrected.

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Acknowledgements

We thank the entire Kepler team, without whom these results would not be possible. V.A., G.Ha. and G.Ho. were supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung. V.A. also thanks L. Fossati for his help. A.M. acknowledges the funding of AstroMadrid, who was also supported by Spanish grants. T.R.B. and D.S. acknowledge support from the Australian Reseach Council. T.L was supported by the Austrian Agency for International Cooperation in Education and Research. K.U. acknowledges financial support from the Deutsche Forschungsgemeinschaft. Funding for this Discovery mission is provided by NASA’s Science Mission Directorate.

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Contributions

V.A. discovered the star among the Kepler targets, analysed it and found the solar-like oscillations (as a part of her PhD thesis), did spectroscopic analyses, frequency analyses, the test on the stochastic nature of the signal, and interpretations, and wrote the paper. G.Ha. had the idea for this project and supervised V.A., helped with analyses, interpretations and writing the paper. T.L.C. contributed to the analyses of the stochastic modes and also to the test on the stochastic nature of the signal. A.O.T. observed the target spectroscopically at Nordic Optical Telescope, identified the star as an Am star and did spectroscopic analyses. A.M. contributed to the statistical test on the nature of the stochastic signal. T.K. helped interpretations, data analyses and writing the paper, and delivered the mode lifetimes. D.S. helped with data analyses, writing the paper and made Fig. 2. A.G. helped with theoretical interpretations and the time-Fourier analyses. T.R.B. helped with interpretations and writing the paper. H.K. contributed to the analyses, also by supervising V.A., and is a member of the Kepler Asteroseismic Investigation Steering Committee. J.C-D. helped with the theoretical support, writing the paper and is a member of the Kepler Asteroseismic Investigation Steering Committee. T.L. confirmed the Am identification, excluding the Ap character of the star. G.C., A.F. and A.K. did spectroscopic analyses. P.D.C. was Principal Investigator and observer for the spectroscopic data from McDonald observatory. K.U. was Co-Investigator of the McDonald data and coordinated the ground-based observations. H.B. was Principal Investigator for the observations with the NARVAL spectrograph and did spectroscopic analyses. G.Ho. and P.L. helped with theoretical interpretations and writing the paper. D.W.K. helped with the Am classification and writing the paper and is leader of the delta Scuti working group of the Kepler Asteroseismic Science Consortium. J.V.C., C.A. and B.D.C. are part of the Kepler team and were involved in designing and operating the satellite. All co-authors contributed to discussions and commented on the manuscript.

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Correspondence to V. Antoci.

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The authors declare no competing financial interests.

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Antoci, V., Handler, G., Campante, T. et al. The excitation of solar-like oscillations in a δ Sct star by efficient envelope convection. Nature 477, 570–573 (2011). https://doi.org/10.1038/nature10389

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