A binary star fraction of 76 per cent and unusual orbit parameters for the blue stragglers of NGC 188

Abstract

Blue straggler stars lie on or near the main sequences of star clusters (all members of which formed around the same time), but typically are more luminous than the turn-off stars and therefore long ago should have evolved off the main sequence to become giants and white dwarfs. They are thought to derive from normal main-sequence stars that have undergone a recent increase in mass. Statistical evidence indicates that in globular star clusters the blue stragglers probably form from binary stars1. The specific formation processes, such as mass transfer, mergers or stellar collisions during dynamical encounters of binary stars, remain unresolved. Here we report that 16 of the 21 blue stragglers (76 per cent) in the old (7-Gyr; ref. 2) open cluster NGC 188 are currently in binary systems, a frequency three times that found among normal solar-type main-sequence stars. These blue straggler binaries have a remarkable period–eccentricity distribution, with all but three having orbital periods of 1,000 days. Moreover, these stars are rotating faster than normal main-sequence stars of the same surface temperatures. These data show that most, and possibly all, blue stragglers derive from multiple-star systems, and indicate that the several formation processes operate simultaneously. We suggest that rapid rotation of blue stragglers may place upper limits on their ages.

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Figure 1: Colour–brightness diagram for members of NGC 188.
Figure 2: NGC 188 orbital eccentricity/log period ( e –log  P ) distributions.
Figure 3: Distribution of projected rotation velocity in the colour–brightness diagrams of NGC 188 and NGC 6819.

References

  1. 1

    Knigge, A., Leigh, N. & Sills, A. A binary origin for ‘blue stragglers’ in globular clusters. Nature 457, 288–290 (2009)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Sarajedini, A., von Hippel, T., Kozhurina-Platais, V. & Demarque, P. WIYN Open Cluster Study. II. UBVRI CCD photometry of the open cluster NGC 188. Astron. J. 118, 2894–2907 (1999)

    ADS  Article  Google Scholar 

  3. 3

    Geller, A. M., Mathieu, R. D., Harris, H. C. & McClure, R. D. WIYN Open Cluster Study. XXXII. Stellar radial velocities in the old open cluster NGC 188. Astron. J. 135, 2264–2278 (2008)

    ADS  Article  Google Scholar 

  4. 4

    Platais, I., Kozhurina-Platais, V., Mathieu, R. D., Girard, T. M. & van Altena, W. F. WIYN Open Cluster Study. XVII. Astrometry and membership to V = 21 in NGC 188. Astron. J. 126, 2922–2935 (2003)

    ADS  Article  Google Scholar 

  5. 5

    Mathieu, R. D. in Stellar Clusters and Associations: Convection, Rotation and Dynamos (eds Pallavicini, R., Micela, G. & Sciortino, S.) 517–531 (Astron. Soc. Pacif. Conf. Ser. 198, Astronomical Society of the Pacific, 2000)

    Google Scholar 

  6. 6

    Geller, A. M., Mathieu, R. D., Harris, H. C. & McClure, R. D. WIYN Open Cluster Study. XXXVI. Spectroscopic binary orbits in NGC 188. Astron. J. 137, 3743–3760 (2009)

    ADS  Article  Google Scholar 

  7. 7

    Duquennoy, A. & Mayor, M. Multiplicity among solar-type stars in the solar neighbourhood. II. Distribution of the orbital elements in an unbiased sample. Astron. Astrophys. 248, 485–524 (1991)

    ADS  Google Scholar 

  8. 8

    Meibom, S. & Mathieu, R. D. A robust measure of tidal circularization in coeval binary populations: the solar-type spectroscopic binary population in the open cluster M35. Astrophys. J. 620, 970–983 (2005)

    ADS  Article  Google Scholar 

  9. 9

    Girardi, L. et al. Theoretical isochrones in several photometric systems. I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets. Astron. Astrophys. 391, 195–212 (2002)

    ADS  Article  Google Scholar 

  10. 10

    Latham, D. W. Spectroscopic binaries in M67. Highlights Astron. 14, 444–445 (2007)

    ADS  Google Scholar 

  11. 11

    Milone, A. A. E. & Latham, D. W. in Evolutionary Processes in Interaction Binary Stars (eds Kondo, Y., Sisteró, R. F. & Polidan, R. S.) 475–478 (Proc. IAU Symp. 151, Springer, 1992)

    Google Scholar 

  12. 12

    Sills, A., Adams, T. & Davies, M. B. Blue stragglers as stellar collision products: the angular momentum question. Mon. Not. R. Astron. Soc. 358, 716–725 (2005)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Portegies Zwart, S., Hut, P., McMillan, S. L. W. & Verbunt, F. Star cluster ecology II. Binary evolution with single-star encounters. Astron. Astrophys. 328, 143–157 (1997)

    ADS  Google Scholar 

  14. 14

    Mermilliod, J.-C. & Mayor, M. in Binaries as Tracers of Stellar Formation (eds Duquennoy, A. & Mayor, M.) 183–201 (Cambridge Univ. Press, 1992)

    Google Scholar 

  15. 15

    Mathieu, R. D., Latham, D. W. & Griffin, D. W. Orbits of 22 spectroscopic binaries in the open cluster M67. Astron. J. 100, 1859–1881 (1990)

    ADS  Article  Google Scholar 

  16. 16

    Perets, H. B. &. Fabrycky, D. C. On the triple origin of blue stragglers. Astrophys. J. 697, 1048–1056 (2009)

    ADS  Article  Google Scholar 

  17. 17

    Sandquist, E. L., Latham, D. W., Shetrone, M. D. & Milone, A. A. E. The blue straggler RS Canum Venaticorum star S1082 in M67: a detailed light curve and the possibility of a triple. Astron. J. 125, 810–824 (2003)

    ADS  Article  Google Scholar 

  18. 18

    van den Berg, M., Orosz, J., Verbunt, F. & Stassun, K. The blue straggler S1082: a triple system in the old open cluster M 67. Astron. Astrophys. 375, 375–386 (2001)

    ADS  CAS  Article  Google Scholar 

  19. 19

    Carney, B. W., Latham, D. W., Laird, J. B., Grant, C. E. & Morse, J. A. A survey of proper-motion stars. XIV. Spectroscopic binaries among metal-poor field blue stragglers. Astron. J. 122, 3419–3435 (2001)

    ADS  Article  Google Scholar 

  20. 20

    Hurley, J. R., Tout, C. A. & Pols, O. R. Evolution of binary stars and the effect of tides on binary populations. Mon. Not. R. Astron. Soc. 329, 897–928 (2002)

    ADS  Article  Google Scholar 

  21. 21

    Hurley, J. R., Pols, O. R., Aarseth, S. J. & Tout, C. A. A complete N-body model of the old open cluster M67. Mon. Not. R. Astron. Soc. 363, 293–314 (2005)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Kraft, R. P. Studies of stellar rotation. V. The dependence of rotation on age among solar-type stars. Astrophys. J. 150, 551–570 (1967)

    ADS  Article  Google Scholar 

  23. 23

    Skumanich, A. Time scales for Ca II emission decay, rotational braking, and lithium depletion. Astrophys. J. 171, 565–567 (1972)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Meibom, S. in The Ages of Stars (eds Mamajek, E. E., Soderblom, D. R. & Wyse, R. F. G.) 357–362 (Proc. IAU Symp. 258, Cambridge Univ. Press, 2009)

    Google Scholar 

  25. 25

    Mathieu, R. D., Meibom, S. & Dolan, C. J. WIYN Open Cluster Study. XVIII. The tidal circularization cutoff period of NGC 188. Astrophys. J. 602, L121–L123 (2004)

    ADS  Article  Google Scholar 

  26. 26

    Mazeh, T. Eccentric orbits in samples of circularized binary systems: the fingerprint of a third star. Astron. J. 99, 675–677 (1990)

    ADS  Article  Google Scholar 

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Acknowledgements

We thank the staff of the WIYN Observatory and the many graduate and undergraduate students who have assisted in observing NGC 188. The WIYN Observatory is a joint facility of the University of Wisconsin–Madison, Indiana University, Yale University and the US National Optical Astronomy Observatories. We thank D. Fabrycky, J. Hurley, N. Leigh, H. Perets and A. Sills for their comments. This work was funded by the US National Science Foundation grant AST-0406615 and the Wisconsin Space Grant Consortium.

Author Contributions R.D.M. and A.M.G. contributed equally to this work.

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Correspondence to Robert D. Mathieu.

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Mathieu, R., Geller, A. A binary star fraction of 76 per cent and unusual orbit parameters for the blue stragglers of NGC 188. Nature 462, 1032–1035 (2009). https://doi.org/10.1038/nature08568

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