A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions

Aaron M. Geller; Robert D. Mathieu

doi:10.1038/nature10512

A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions

Aaron M. Geller^*, Robert D. Mathieu

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

91 Scopus citations

Abstract

In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7×10 ⁹-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.

Original language	English (US)
Pages (from-to)	356-359
Number of pages	4
Journal	Nature
Volume	478
Issue number	7369
DOIs	https://doi.org/10.1038/nature10512
State	Published - Oct 20 2011

Funding

Acknowledgements We thank the staff of the WIYN Observatory and the many graduate and undergraduate students who have assisted in observing NGC 188. Thanks to J. Hurley, A. Sills, N. Leigh, R. Taam and H. Perets for their comments and suggestions. Both A.M.G. and R.D.M. were visiting astronomers at Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy under cooperative agreement with the National Science Foundation. The WIYN Observatory is a joint facility of the University of Wisconsin–Madison, Indiana University, Yale University and the US National Optical Astronomy Observatories. This work was funded by the US National Science Foundation grant AST-0908082 to the University of Wisconsin–Madison, the Wisconsin Space Grant Consortium and the Lindheimer Fellowship at Northwestern University.

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10.1038/nature10512

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title = "A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions",

abstract = "In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7×10 9-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.",

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note = "Funding Information: Acknowledgements We thank the staff of the WIYN Observatory and the many graduate and undergraduate students who have assisted in observing NGC 188. Thanks to J. Hurley, A. Sills, N. Leigh, R. Taam and H. Perets for their comments and suggestions. Both A.M.G. and R.D.M. were visiting astronomers at Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy under cooperative agreement with the National Science Foundation. The WIYN Observatory is a joint facility of the University of Wisconsin–Madison, Indiana University, Yale University and the US National Optical Astronomy Observatories. This work was funded by the US National Science Foundation grant AST-0908082 to the University of Wisconsin–Madison, the Wisconsin Space Grant Consortium and the Lindheimer Fellowship at Northwestern University.",

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N2 - In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7×10 9-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.

AB - In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7×10 9-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.

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A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions

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