Unresolved Binaries in the Intermediate Mass Range in the Pleiades Star Cluster

Abstract

The identification of binary stars of different mass ratios in resolved stellar populations is a challenging task. We show how the photometric diagram constructed with the pseudo-colors (H-W2)-W1 vs W2-(BP-K) can be employed to estimate the binary and multiple star ratios and the distribution of their component mass ratio $q$ effectively. As an application, we investigate the Pleiades star cluster in the range of primary component mass between 0.5 and 1.8 $M_{\odot }$. The binary star ratio is found to be between 0.54$\pm$0.11 and 0.70$\pm$0.14. On the other hand, the ratio of systems with multiplicity more than 2 is between 0.10$\pm$0.00 and 0.14$\pm$0.01. The distribution of the component mass ratio $q$ has been approximated by a power law with the exponent between -0.53$\pm$0.10 and -0.63$\pm$0.22. Below 0.5 $M_{\odot }$, we expect a large number of brown dwarfs among secondary components.

9 pages, 6 eps figure, in press in the Astronomical Journal

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• Photometric Determination of Unresolved Main-sequence Binaries in the Pleiades: Binary Fraction and Mass Ratio Distribution
• Signature of a chemical spread in the open cluster M37
• Resolving Pleiades binary stars with Gaia and speckle interferometric observations
• Stellar masses and mass ratios for Gaia open cluster members
• The broadening of the main sequence in the open cluster M38
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