Letter

Stars caught in the braking stage in young Magellanic Cloud clusters

  • Nature Astronomy 1, Article number: 0186 (2017)
  • doi:10.1038/s41550-017-0186
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Abstract

The colour–magnitude diagrams of many Magellanic Cloud clusters (with ages up to 2 billion years) display extended turnoff regions where the stars leave the main sequence, suggesting the presence of multiple stellar populations with ages that may differ even by hundreds of millions of years 1,2,3 . A strongly debated question is whether such an extended turnoff is instead due to populations with different stellar rotations3,4,5,6 . The recent discovery of a ‘split’ main sequence in some younger clusters (~80–400 Myr) added another piece to this puzzle. The blue side of the main sequence is consistent with slowly rotating stellar models, and the red side consistent with rapidly rotating models7,8,9,10. However, a complete theoretical characterization of the observed colour–magnitude diagram also seemed to require an age spread9. We show here that, in the three clusters so far analysed, if the blue main-sequence stars are interpreted with models in which the stars have always been slowly rotating, they must be ~30% younger than the rest of the cluster. If they are instead interpreted as stars that were initially rapidly rotating but have later slowed down, the age difference disappears, and this ‘braking’ also helps to explain the apparent age differences of the extended turnoff. The age spreads in Magellanic Cloud clusters are thus a manifestation of rotational stellar evolution. Observational tests are suggested.

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References

  1. 1.

    , , & Multiple stellar populations in three rich Large Magellanic Cloud star clusters. Astrophys. J. Lett. 681, L17–L20 (2008).

  2. 2.

    , , & Multiple stellar populations in Magellanic Cloud clusters. I. An ordinary feature for intermediate age globulars in the LMC? Astron. Astrophys. 497, 755–771 (2009).

  3. 3.

    , & Can rotation explain the multiple main-sequence turn-offs of Magellanic Cloud star clusters? Mon. Not. R. Astron. Soc. 412, L103–L107 (2011).

  4. 4.

    , , & Population parameters of intermediate-age star clusters in the Large Magellanic Cloud. III. Dynamical evidence for a range of ages being responsible for extended main-sequence turnoffs. Astrophys. J. 737, 4 (2011).

  5. 5.

    et al. The star formation history of the Large Magellanic Cloud star clusters NGC 1846 and NGC 1783. Mon. Not. R. Astron. Soc. 430, 2774–2788 (2013).

  6. 6.

    , & The exclusion of a significant range of ages in a massive star cluster. Nature 516, 367–369 (2014).

  7. 7.

    et al. The extended main-sequence turn-off cluster NGC 1856: rotational evolution in a coeval stellar ensemble. Mon. Not. R. Astron. Soc. 453, 2637–2643 (2015).

  8. 8.

    et al. Multiple stellar populations in Magellanic Cloud clusters. IV. The double main sequence of the young cluster NGC 1755. Mon. Not. R. Astron. Soc. 458, 4368–4382 (2016).

  9. 9.

    , , , & Dissecting the extended main sequence turn-off of the young star cluster NGC 1850. Mon. Not. R. Astron. Soc. 467, 3628–3641 (2017).

  10. 10.

    et al. Multiple stellar populations in Magellanic Cloud clusters. V. The split main sequence of the young cluster NGC1866. Preprint at (2016).

  11. 11.

    et al. Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC 1856. Mon. Not. R. Astron. Soc. 450, 3750–3764 (2015).

  12. 12.

    et al. Populations of rotating stars. III. SYCLIST, the new Geneva population synthesis code. Astron. Astrophys. 566, A21 (2014).

  13. 13.

    & Stellar evolution with rotation. V. Changes in all the outputs of massive star models. Astron. Astrophys. 361, 101–120 (2000).

  14. 14.

    et al. Grids of stellar models with rotation. I. Models from 0.8 to 120 M at solar metallicity (Z = 0.014). Astron. Astrophys. 537, A146 (2012).

  15. 15.

    et al. Populations of rotating stars. I. Models from 1.7 to 15 M at Z = 0.014, 0.006, and 0.002 with Ω/Ωcrit between 0 and 1. Astron. Astrophys. 553, A24 (2013).

  16. 16.

    , , & No evidence for significant age spreads in young massive LMC clusters. Astron. Astrophys. 575, A62 (2015).

  17. 17.

    et al. The VLT-FLAMES Tarantula Survey. X. Evidence for a bimodal distribution of rotational velocities for the single early B-type stars. Astron. Astrophys. 550, A109 (2013).

  18. 18.

    , & A stellar rotation census of B stars: From ZAMS to TAMS. Astrophys. J 722, 605–619 (2010).

  19. 19.

    et al. A high fraction of Be stars in young massive clusters: evidence for a large population of near-critically rotating stars. Mon. Not. R. Astron. Soc. 465, 4795–4799 (2017).

  20. 20.

    , , & The Böhm–Vitense gap: the role of turbulent convection. Astrophys. J. Lett. 564, L93–L96 (2002).

  21. 21.

    et al. Two distinct sequences of blue straggler stars in the globular cluster M 30. Nature 462, 1028–1031 (2009).

  22. 22.

    , , , & Discovery of rotational braking in the magnetic helium-strong star Sigma Orionis E. Astrophys. J. Lett. 714, L318–L322 (2010).

  23. 23.

    Dynamical tides in close binary systems, I. Astrophys. Space Sci. 1, 179–215 (1968).

  24. 24.

    Tidal friction in close binary stars. Astron. Astrophys. 57, 383–394 (1977).

  25. 25.

    in Tidal Effects in Stars, Planets and Disks. EAS Publ. Series Vol. 29 (eds Goupil, M.-J. & Zahn, J.-P.) 67–90 (2008).

  26. 26.

    , , & The radial distributions of the two main-sequence components in the young massive star cluster NGC 1856. Preprint at (2016).

  27. 27.

    et al. Deep Advanced Camera for Surveys imaging in the globular cluster NGC 6397: reduction methods. Astron. J 135, 2114–2128 (2008).

  28. 28.

    et al. The ACS survey of Galactic globular clusters. XII. Photometric binaries along the main sequence. Astron. Astrophys. 540, A16 (2012).

  29. 29.

    et al. Transforming observational data and theoretical isochrones into the ACS/WFC Vega-mag system. Mon. Not. R. Astron. Soc. 357, 1038–1048 (2005).

  30. 30.

    & Effect of horizontal turbulent diffusion on transport by meridional circulation. Astron. Astrophys. 253, 173–177 (1992).

  31. 31.

    & Rotational velocities of A-type stars. IV. Evolution of rotational velocities. Astron. Astrophys. 537, A120 (2012).

  32. 32.

    , & Classical Be stars. Rapidly rotating B stars with viscous Keplerian decretion disks. Astron. Astrophys. Rev. 21, 69 (2013).

  33. 33.

    & Tidal effects in binaries of various periods. Astrophys. J. 616, 562–566 (2004).

  34. 34.

    & Gravity darkening in rotating stars. Astron. Astrophys. 533, A43 (2011).

  35. 35.

    A new non-linear limb-darkening law for LTE stellar atmosphere models. Astron. Astrophys. 363, 1081–1190 (2000).

  36. 36.

    The luminosity function and stellar evolution. Astrophys. J. 121, 161 (1955).

  37. 37.

    & New grids of ATLAS9 model atmospheres. Preprint at (2004).

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Acknowledgements

We thank C. Georgy and S. Ekström for creating and maintaining the interactive Web page for the Geneva stellar models at https://obswww.unige.ch/Recherche/evoldb/index/. A.M. acknowledges support by the Australian Research Council through Discovery Early Career Researcher Award DE150101816.

Author information

Affiliations

  1. INAF—Osservatorio Astronomico di Roma, I-00040 Monte Porzio, Rome, Italy.

    • Francesca D’Antona
    • , Paolo Ventura
    •  & Marcella Di Criscienzo
  2. Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory 2611, Australia.

    • Antonino P. Milone
  3. Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, 09042 Monserrato, Italy.

    • Marco Tailo
  4. Department of Astronomy, Indiana University, Bloomington, Indiana 47405, USA.

    • Enrico Vesperini

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Contributions

F.D. and A.M. jointly designed and coordinated this study. F.D. proposed and designed the rotational evolution model. F.D., E.V., A.M. and P.V. worked on the theoretical interpretation and implications of the observations. M.T. and M.D.C. carried out the simulations and the analysis. All authors read, commented on and approved submission of this article.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Francesca D’Antona.

Supplementary information

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    Supplementary Information

    Supplementary Figures 1–7 and Supplementary Tables 1–2.