Although the study of X-ray binaries has led to major breakthroughs in high-energy astrophysics, their circumbinary environment at scales of ∼100–10,000 au has not been thoroughly investigated. In this paper, we undertake a novel and exploratory study by employing direct and high-contrast imaging techniques on a sample of X-ray binaries, using adaptive optics and the vortex coronagraph on Keck/NIRC2. High-contrast imaging opens up the possibility to search for exoplanets, brown dwarfs, circumbinary companion stars, and protoplanetary disks in these extreme systems. Here we present the first near-infrared high-contrast images of 13 high-mass X-ray binaries located within ∼2–3 kpc. The key results of this campaign involve the discovery of several candidate circumbinary companions ranging from substellar (brown dwarf) to stellar masses. By conducting an analysis based on Galactic population models, we discriminate sources that are likely background/foreground stars and isolate those that have a high probability (≳60%–99%) of being gravitationally bound to the X-ray binary. This paper seeks to establish a preliminary catalog for future analyses of proper motion and subsequent observations. With our preliminary results, we calculate the first estimate of the companion frequency and the multiplicity frequency for X-ray binaries: ≈0.6 and 1.8 ± 0.9, respectively, considering only the sources that are most likely bound to the X-ray binary. In addition to extending our comprehension of how brown dwarfs and stars can form and survive in such extreme systems, our study opens a new window to our understanding of the formation of X-ray binaries.
The First High-contrast Images of Near High-mass X-Ray Binaries with Keck/NIRC2
Abstract
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© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We also want to thank V. Christiaens for his help with VIP. We thank Lauren M. Weiss, Marie-Eve Naud, and Anjali Rao for their contribution to the Keck/NIRC2 proposal.
M.P.-E. is supported by the Institute for Data Valorisation (IVADO) through the M. Sc. Excellence Scholarship, by the Department of Physics of the Université de Montréal, and by the Institute for Research on Exoplanets (iREx). J.H.L. is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chair programs and wishes to acknowledge the support of an NSERC Discovery Grant and the NSERC accelerator grant.
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Additional details
- ISSN
- 1538-4357
- W. M. Keck Foundation
- Institut de Valorisation des Données
- RN001080
- Université de Montréal
- Natural Sciences and Engineering Research Council
- Canada Research Chairs
- Caltech groups
- Astronomy Department