CaltechAUTHORS
Published August 20, 2025 | Version Published
Journal Article Open

Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Centauri A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon NASA Exoplanet Science Institute
  • 3. ROR icon Jet Propulsion Lab
  • 4. ROR icon Johns Hopkins University
  • 5. ROR icon Space Telescope Science Institute
  • 6. ROR icon French National Centre for Scientific Research
  • 7. LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 Place Jules Janssen, 92195 Meudon, France
  • 8. ROR icon University of Cambridge
  • 9. ROR icon University of Chile
  • 10. ROR icon University of Paris
  • 11. ROR icon University of Arizona

Abstract

The James Webb Space Telescope (JWST) observed our closest solar twin, α Centauri A (α Cen A), with the Mid-Infrared Instrument in the F1550C (15.5 μm) coronagraphic imaging mode at three distinct epochs between 2024 August and 2025 April. For the first time with JWST, we demonstrate the application of reference star differential imaging to simultaneously subtract the coronagraphic image of a primary star (α Cen A) and the point-spread function (PSF) of its binary companion (α Cen B) to conduct a deep search for exoplanets and exozodiacal dust emission. We achieve a typical 5σ point-source contrast sensitivity between ∼10−5 and 10−4 at separations ≳ 1″ and an exozodiacal disk (coplanar with α Cen AB) sensitivity of ∼5–8× the solar system’s zodiacal cloud around α Cen A. The latter is an extraordinary limit, representing the deepest sensitivity to exozodiacal disks achieved for any stellar system to date. Additionally, postprocessing with the principal-component-analysis-based Karhunen–Loéve image processing algorithm reveals a point source, called S1, in 2024 August, detected at signal-to-noise ratio of 4–6 (3.3–4.3σ), a projected separation of ≈1."5 (2 au), and with an F1550C flux density (contrast) of ≈3.5 mJy (≈5.5 × 10−5). Various tests conducted with the available data show that S1 is unlikely to be a detector artifact or PSF-subtraction artifact and confirm that it is neither a background nor a foreground object. S1 is not redetected in two follow-up observations (2025 February and April). If S1 is astrophysical in nature, the only explanation is that it has moved to a region of poor sensitivity due to orbital motion. We perform PSF injection–recovery tests and provide 2D sensitivity maps for each epoch to enable orbital completeness calculations. Additional observations, with JWST or upcoming facilities, are necessary to redetect candidate S1 and confirm its nature as a planet orbiting our nearest solar-type neighbor, α Cen A. More broadly, this program highlights the complexity of analyzing a dynamic binary astrophysical scene and the challenges associated with confirming short-period (∼few years) planet candidates identified without prior orbital constraints in direct imaging searches. This Letter is second in a series of two papers: Paper I discusses the observation strategy and presents the astrophysical case (physical and orbital properties) for S1 as a planet candidate.

Copyright and License

© 2025. 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 STScI support staff provided invaluable assistance in the planning and execution of this program. In particular, we thank George Chapman and the Fine Guidance Sensor (FGS) team for their dedicated work in finding and vetting guide stars for this program and Wilson Joy Skipper and the short- and long-range planning teams for their contributions to this challenging observational program. The STScI’s Director’s office provided strong support for this program, from its initial selection as a high-risk, high-reward project, granting time to conduct test observations needed to validate the target acquisition strategy, to the execution of the follow-up DDT programs. We thank the referee for a prompt report and helpful comments that improved this manuscript.

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 2139433. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Programs PID#1618, #6797, and #9252 are supported through contracts JWST-GO-01618.001, JWST-GO-06797.001, and JWST-GO-09252.001. N.G. and E.C. acknowledge funding by the European Union (ERC, ESCAPE, project No. 101044152). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. All of the data presented in this Letter were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi: 10.17909/v8nv-vx17 for the 2024 August observations, doi: 10.17909/cb0x-rn85 for the 2025 February observations, and doi: 10.17909/3z9q-9f65 for the 2025 April observations. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. This research has made use of NASA’s Astrophysics Data System. Software citation information were aggregated using The Software Citation Station 30 (T. Wagg & F. S. Broekgaarden 2024; T. Wagg et al. 2024).

Contributions

A.S. led the writing and submission of this manuscript under the guidance of C.B. and D.M. W.B. conducted the JWST pipeline processing of the MIRI observations. A.S. led the postprocessing analysis of the MIRI observations for point sources and extended emission. N.G., M.S., M.W., and E.C. performed the S/N calculations for extended emission. L.P., A.B., and J.L.-S. conducted independent postprocessing of the MIRI observations to validate the results. K.W., A.B., and P.O.L. provided advice on data reduction. Dust emission models for the exozodiacal disk were developed by M.S. and M.W. P.K. provided the ephemeris for α Cen A. All authors discussed the results and commented on the manuscript.

Facilities

JWST - James Webb Space Telescope (MIRI).

Software References

astropy (Astropy Collaboration et al. 2013, 2018, 2022), matplotlib (J. D. Hunter 2007), numpy (C. R. Harris et al. 2020), pandas (W. McKinney 2010; The pandas development team 2025), Python (G. Van Rossum & F. L. Drake 2009), scipy (P. Virtanen et al. 2020; R. Gommers et al. 2023), astroquery (A. Ginsburg et al. 2019, 2024), scikit-image (S. van der Walt et al. 2014), STPSF (M. D. Perrin et al. 2012; M. D. Perrin et al. 2014), jwst (H. Bushouse et al. 2025), pyKLIP (J. J. Wang et al. 2015), vip (C. A. Gomez Gonzalez et al. 2017; V. Christiaens et al. 2023), spaceKLIP (J. Kammerer et al. 2022; A. L. Carter et al. 2023; A. Carter et al. 2025), and webbpsf_ext (J. Leisenring 2025).

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2508.03812 (arXiv)
Is supplemented by
Dataset: 10.17909/v8nv-vx17 (DOI)
Dataset: 10.17909/cb0x-rn85 (DOI)
Dataset: 10.17909/3z9q-9f65 (DOI)

Funding

National Science Foundation
2139433
National Aeronautics and Space Administration
80NM0018D0004
Space Telescope Science Institute
JWST-GO-01618.001
Space Telescope Science Institute
JWST-GO-06797.001
Space Telescope Science Institute
JWST-GO-09252.001
European Research Council
101044152

Dates

Submitted
2025-06-26
Accepted
2025-07-28
Available
2025-08-11
Published

Caltech Custom Metadata

Caltech groups
Astronomy Department , Infrared Processing and Analysis Center (IPAC) , Division of Physics, Mathematics and Astronomy (PMA) , Physics Department
Publication Status
Published