Issue |
A&A
Volume 645, January 2021
|
|
---|---|---|
Article Number | L10 | |
Number of page(s) | 7 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202039673 | |
Published online | 20 January 2021 |
Letter to the Editor
A relation between the radial velocity dispersion of young clusters and their age
Evidence for hardening as the formation scenario of massive close binaries
1
Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: ramirez@mpia.de
2
Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
3
Institute of Astronomy, KU Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
4
Department of Astronomy, Stockholm University, Oskar Klein Center, 106 91 Stockholm, Sweden
Received:
14
October
2020
Accepted:
18
December
2020
The majority of massive stars (> 8 M⊙) in OB associations are found in close binary systems. Nonetheless, the formation mechanism of these close massive binaries is not understood yet. Using literature data, we measured the radial-velocity dispersion (σ1D) as a proxy for the close binary fraction in ten OB associations in the Galaxy and the Large Magellanic Cloud, spanning an age range from 1 to 6 Myr. We find a positive trend of this dispersion with the cluster’s age, which is consistent with binary hardening. Assuming a universal binary fraction of fbin = 0.7, we converted the σ1D behavior to an evolution of the minimum orbital period Pcutoff from ∼9.5 years at 1 Myr to ∼1.4 days for the oldest clusters in our sample at ∼6 Myr. Our results suggest that binaries are formed at larger separations, and they harden in around 1 to 2 Myr to produce the period distribution observed in few million year-old OB binaries. Such an inward migration may either be driven by an interaction with a remnant accretion disk or with other young stellar objects present in the system. Our findings constitute the first empirical evidence in favor of migration as a scenario for the formation of massive close binaries.
Key words: binaries: close / stars: formation / stars: early-type / open clusters and associations: general / binaries: general
© M. C. Ramírez-Tannus et al. 2021
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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