Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

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Abstract

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell1,2. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion3. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes4. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies5. Here we report observations of gravity-mode period spacings in red giants6 that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly 50 seconds) and those that are also burning helium (period spacing 100 to 300 seconds).

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Figure 1: Mixed modes and avoided crossings in red giant stars.
Figure 2: Oscillation power spectra and échelle diagrams of two red giant stars observed with Kepler.
Figure 3: Asteroseismic diagrams for red giants observed with Kepler.

References

  1. 1

    Schwarzschild, M. & Härm, R. Red giants of population II. II. Astrophys. J. 136, 158–165 (1962)

  2. 2

    Iben, I., Jr Low-mass red giants. Astrophys. J. 154, 581–595 (1968)

  3. 3

    Sweigart, A. V. & Gross, P. G. Evolutionary sequences for red giant stars. Astrophys. J. Suppl. Ser. 36, 405–437 (1978)

  4. 4

    Charbonnel, C. in Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis (eds Barnes, T. G. & Bash, F. N. ) 119–130 (Vol. 336, Astronomical Society of the Pacific Conference Series, 2005)

  5. 5

    Aerts, C., Christensen-Dalsgaard, J. & Kurtz, D. W. Asteroseismology (Springer, 2010)

  6. 6

    Beck, P. G. et al. Detection of gravity-mode period spacings in red giant stars by the Kepler Mission. Science (in the press)

  7. 7

    De Ridder, J. et al. Non-radial oscillation modes with long lifetimes in giant stars. Nature 459, 398–400 (2009)

  8. 8

    Kallinger, T. et al. Oscillating red giants in the CoRoT exo-field: asteroseismic radius and mass determination. Astron. Astrophys. 509, A77 (2010)

  9. 9

    Bedding, T. R. et al. Solar-like oscillations in low-luminosity red giants: first results from Kepler. Astrophys. J. 713, L176–L181 (2010)

  10. 10

    Huber, D. et al. Asteroseismology of red giants from the first four months of Kepler data: global oscillation parameters for 800 stars. Astrophys. J. 723, 1607–1617 (2010)

  11. 11

    Mosser, B. et al. The universal red-giant oscillation pattern. An automated determination with CoRoT data. Astron. Astrophys. 525, L9 (2011)

  12. 12

    Dziembowski, W. A., Gough, D. O., Houdek, G. & Sienkiewicz, R. Oscillations of α UMa and other red giants. Mon. Not. R. Astron. Soc. 328, 601–610 (2001)

  13. 13

    Christensen-Dalsgaard, J. Physics of solar-like oscillations. Sol. Phys. 220, 137–168 (2004)

  14. 14

    Dupret, M. et al. Theoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giants. Astron. Astrophys. 506, 57–67 (2009)

  15. 15

    Montalbán, J., Miglio, A., Noels, A., Scuflaire, R. & Ventura, P. Seismic diagnostics of red giants: first comparison with stellar models. Astrophys. J. 721, L182–L188 (2010)

  16. 16

    Di Mauro, M. P. et al. Solar-like oscillations from the depths of the red-giant star KIC 4351319 observed with Kepler. Mon. Not. R. Astron. Soc. (submitted)

  17. 17

    Tassoul, M. Asymptotic approximations for stellar nonradial pulsations. Astrophys. J. Suppl. Ser. 43, 469–490 (1980)

  18. 18

    Miglio, A., Montalbán, J., Eggenberger, P. & Noels, A. Gravity modes and mixed modes as probes of stellar cores in main-sequence stars: from solar-like to β Cep stars. Astron. Nachr. 329, 529–534 (2008)

  19. 19

    Aizenman, M., Smeyers, P. & Weigert, A. Avoided crossing of modes of non-radial stellar oscillations. Astron. Astrophys. 58, 41–46 (1977)

  20. 20

    Deheuvels, S. & Michel, E. New insights on the interior of solar-like pulsators thanks to CoRoT: the case of HD 49385. Astrophys. Space Sci. 328, 259–263 (2010)

  21. 21

    Jenkins, J. M. et al. Initial characteristics of Kepler long cadence data for detecting transiting planets. Astrophys. J. 713, L120–L125 (2010)

  22. 22

    Mosser, B. & Appourchaux, T. On detecting the large separation in the autocorrelation of stellar oscillation times series. Astron. Astrophys. 508, 877–887 (2009)

  23. 23

    Gough, D. O. in Hydrodynamic and Magnetodynamic Problems in the Sun and Stars (ed. Osaki, Y. ) 117–143 (Univ. Tokyo Press, 1986)

  24. 24

    Girardi, L. A secondary clump of red giant stars: why and where. Mon. Not. R. Astron. Soc. 308, 818–832 (1999)

  25. 25

    Miglio, A. et al. Probing populations of red giants in the galactic disk with CoRoT. Astron. Astrophys. 503, L21–L24 (2009)

  26. 26

    Kjeldsen, H. & Bedding, T. R. Amplitudes of stellar oscillations: the implications for astero-seismology. Astron. Astrophys. 293, 87–106 (1995)

  27. 27

    Christensen-Dalsgaard, J. ASTEC – the Aarhus STellar Evolution Code. Astrophys. Space Sci. 316, 13–24 (2008)

  28. 28

    Kjeldsen, H., Bedding, T. R. & Christensen-Dalsgaard, J. Correcting stellar oscillation frequencies for near-surface effects. Astrophys. J. 683, L175–L178 (2008)

  29. 29

    Ventura, P., D'Antona, F. & Mazzitelli, I. The ATON 3.1 stellar evolutionary code. A version for asteroseismology. Astrophys. Space Sci. 316, 93–98 (2008)

  30. 30

    Pietrinferni, A., Cassisi, S., Salaris, M. & Castelli, F. A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones. Astrophys. J. 612, 168–190 (2004)

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Acknowledgements

We acknowledge the entire Kepler team, whose efforts made these results possible. We thank M. Biercuk for comments. Funding for this Discovery mission was provided by NASA's Science Mission Directorate. T.R.B and D.S. were supported by the Australian Research Council; P.B. and C.A. were supported by European Community's 7th Framework Programme (PROSPERITY); S.H. was supported by the Netherlands Organisation for Scientific Research (NWO). The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Author information

T.R.B, B.M., P.B., Y.P.E, R.A.G., S.H., C.A., A.-M.B. and F.C. measured and interpreted period spacings; B.M., D.H., R.A.G., S.H., T.K., W.J.C., C.B., D.L.B. and S.M. calculated power spectra and measured large frequency separations; J.M., J.C.-D., A.M., D.S., T.R.W., K.B., M.P.D.M., M.-A.D., M.-J.G., S.K., A.N., V.S.A. and P.V. calculated and interpreted theoretical models; J.D.R., S.H., S.F., Y.P.E., D.S., T.M.B., H.K., J.C.-D. and R.L.G contributed to the coordination of the project, including the acquisition and distribution of the data; and J.M.J. constructed the photometric time series from the original Kepler pixel data. All authors discussed the results and commented on the manuscript.

Correspondence to Timothy R. Bedding.

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The authors declare no competing financial interests.

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Supplementary Table

This file contains a Supplementary Table listing the Red Giants that are shown in Figure 3 of the main paper. (PDF 106 kb)

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Bedding, T., Mosser, B., Huber, D. et al. Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars. Nature 471, 608–611 (2011) doi:10.1038/nature09935

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