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Published October 10, 2009 | Published
Journal Article Open

The Coevality of Young Binary Systems


Multiple star systems are commonly assumed to form coevally; they thus provide the anchor for most calibrations of stellar evolutionary models. In this paper, we study the binary population of the Taurus-Auriga association, using the component positions in an HR diagram in order to quantify the frequency and degree of coevality in young binary systems. After identifying and rejecting the systems that are known to be affected by systematic errors (due to further multiplicity or obscuration by circumstellar material), we find that the relative binary ages, |Δlog τ|, have an overall dispersion σ_(|Δlog τ|) ~0.40 dex. Random pairs of Taurus members are coeval only to within σ_(|Δlog τ|) ~0.58 dex, indicating that Taurus binaries are indeed more coeval than the association as a whole. However, the distribution of |Δlog τ| suggests two populations, with ~2/3 of the sample appearing coeval to within the errors (σ_(|Δlog τ|) ~0.16 dex) and the other ~1/3 distributed in an extended tail reaching |Δlog τ| ~0.4-0.9 dex. To explain the finding of a multipeaked distribution, we suggest that the tail of the differential age distribution includes unrecognized hierarchical multiples, stars seen in scattered light, or stars with disk contamination; additional follow-up is required to rule out or correct for these explanations. The relative coevality of binary systems does not depend significantly on the system mass, mass ratio, or separation. Indeed, any pair of Taurus members wider than ~10' (~0.7 pc) shows the full age spread of the association.

Additional Information

© 2009 American Astronomical Society. Received 2009 February 11; accepted 2009 August 28; published 2009 September 23. The authors thank R. White and G. Herczeg for helpful feedback on several of the ideas presented here, as well as E. Mamajek for a helpful discussion of Taurus membership issues. We also thank the referee for a prompt and helpful review. A. L. K. was supported by a NASA Origins grant to L. A. H. and by a SIM Science Study. This work makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and the IPAC/Caltech, funded by NASA and the NSF. This work also made extensive use of the SIMBAD database, operated at CDS, Strasbourg, France.

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