The non-monotonic, strong metallicity dependence of the wide-binary fraction

Author:

Hwang Hsiang-Chih1ORCID,Ting Yuan-Sen2345,Schlaufman Kevin C1ORCID,Zakamska Nadia L1ORCID,Wyse Rosemary F G1ORCID

Affiliation:

1. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

2. Institute for Advanced Study, Princeton, NJ 08540, USA

3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

4. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA

5. Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., Weston, ACT 2611, Australia

Abstract

ABSTRACT The metallicity dependence of the wide-binary fraction (WBF) IN stellar populations plays a critical role in resolving the open question of wide-binary formation. In this paper, we investigate the metallicity ([Fe/H]) and age dependence of the WBF (binary separations between 103 and 104 au) for field F and G dwarfs within 500 pc by combining their metallicity and radial velocity measurements from LAMOST Data Release 5 (DR5) with the astrometric information from Gaia DR2. We show that the WBF strongly depends on the metallicity: as metallicity increases, the WBF first increases, peaks at [Fe/H] ≃ 0, and then decreases at the high-metallicity end. The WBF at [Fe/H] = 0 is about two times larger than that at [Fe/H] = −1 and +0.5. This metallicity dependence is dominated by the thin-disc stars. Using stellar kinematics as a proxy of stellar age, we show that younger stars have a higher WBF at fixed metallicity close to solar. We propose that multiple formation channels are responsible for the metallicity and age dependence. In particular, the positive metallicity correlation at [Fe/H] < 0 and the age dependence may be due to the denser formation environments and higher mass clusters at earlier times. The negative metallicity correlation at [Fe/H] > 0 can be inherited from the similar metallicity dependence of close binaries, and radial migration may play a role in enhancing the WBF around the solar metallicity.

Funder

National Aeronautics and Space Administration

Space Telescope Science Institute

Johns Hopkins University

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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