Letter

A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf

  • Nature volume 554, pages 7376 (01 February 2018)
  • doi:10.1038/nature25136
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Abstract

White-dwarf stars are the end product of stellar evolution for most stars in the Universe1. Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution2,3. Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles4. However, the internal structure of white-dwarf stars—in particular their oxygen content and the stratification of their cores—is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes5,6. Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogen-deficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data7,8 coupled with asteroseismic sounding techniques9,10 to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology11.

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Acknowledgements

S.C., N.G. and W.Z. acknowledge financial support from Programme National de Physique Stellaire (PNPS) of CNRS/INSU, France, and from the Centre National d'Études Spatiales (CNES, France). We also acknowledge support from the Agence Nationale de la Recherche (ANR, France) under grant ANR-17-CE31-0018, funding the INSIDE project. This work was granted access to the high-performance-computing resources of the CALMIP computing centre under allocation number 2017-p0205. This work was supported by the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT, Canada) through a postdoctoral fellowship awarded to N.G. G.F. also acknowledges the contribution of the Canada Research Chair Program, and W.Z. the LAMOST fellowship as a young researcher, supported by the Special Funding for Advanced Users, budgeted and administrated by the Center for Astronomical Mega-Science, Chinese Academy of Sciences. V.V.G. is an F.R.S.-FNRS Research Associate. The authors acknowledge the Kepler team and everyone who has contributed to making this mission possible. Funding for the Kepler mission is provided by NASA’s Science Mission Directorate.

Author information

Affiliations

  1. Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, Centre National de la Recherche Scientifique (CNRS), UPS, Centre National d’Études Spatiales (CNES), 14 Avenue Edouard Belin, F-31400 Toulouse, France

    • N. Giammichele
    • , S. Charpinet
    •  & W. Zong
  2. Département de Physique, Université de Montréal, Montréal, Québec H3C 3J7, Canada

    • N. Giammichele
    • , G. Fontaine
    • , P. Brassard
    •  & P. Bergeron
  3. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, Arizona 85721, USA

    • E. M. Green
  4. Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, 19C Allée du six-août, B-4000 Liège, Belgium

    • V. Van Grootel
    •  & M.-A. Dupret
  5. Department of Astronomy, Beijing Normal University, Beijing 100875, China

    • W. Zong

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Contributions

N.G. wrote the manuscript and performed the seismic analysis of KIC08626021. S.C. and G.F. contributed to the writing of the manuscript. S.C., P.Br. and N.G. contributed to the development of the numerical codes used in this analysis. E.M.G. obtained the spectroscopic data for KIC08626021. P.Be. and G.F. performed the model atmospheric analysis. W.Z. provided Fig. 1. V.V.G., G.F. and M.A.D. performed non-adiabatic complementary analysis. All authors discussed the results and contributed to their interpretation.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to N. Giammichele.

Reviewer Information Nature thanks M. Salaris, O. Straniero and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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