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Direct Imaging Constraints on Binary Planets and Exomoons around Epsilon Indi A b

Matson Garza (Department of Physics, Massachusetts Institute of Technology), Mary Anne Limbach (Department of Astronomy, University of Michigan), Rachel Bowens-Rubin (Department of Astronomy, University of Michigan), Matthew De Furio (Department of Astronomy, The University of Texas at Austin), Elisabeth C. Matthews (Max Planck Institute for Astronomy), Kyle Franson (Department of Astronomy and Astrophysics, The University of California, Santa Cruz), Sarah C. Millholland (Department of Physics, Massachusetts Institute of Technology), Logan A. Pearce (Department of Astronomy, University of Michigan), Andrew Vanderburg (Center for Astrophysics, Harvard & Smithsonian)

arXiv: 2604.23448v1 (astro-ph.EP)
Accepted to AJ, 14 pages with 5 figures
License: CC BY 4.0

Abstract: Epsilon Indi A b is a directly imaged $\sim6 M_{\rm Jup}$ exoplanet orbiting a nearby (3.6 pc) K-dwarf at $\sim 30$ AU. We analyze archival JWST/MIRI 15 $μ$m coronagraphic imaging of this planet to search for directly imaged satellites orbiting Eps Ind A b. Within the planet's Hill sphere (radius $R_H \approx 2.3$ AU or $1.3 λ/D$), we compare single- and double-PSF models using Bayesian evidence. We find that a double-PSF (binary planet) fit is preferred. This apparent preference can most plausibly be explained by systematics, although follow-up observations would be required to fully rule out a binary planet interpretation. We construct a contrast curve of the exoplanet after removing this feature, demonstrating sensitivity to companions as faint as $0.03\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 130$ K, $1.3 M_{\rm Jup}$) at large separations (>2 AU). We also demonstrate sensitivity to brighter companions $0.2\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 180$ K, $2.5 M_{\rm Jup}$) down to separations of 0.52 AU (1.3 pixels; $0.29 λ/D$; 144 mas). This study demonstrates that JWST/MIRI can directly detect exomoons or binary planets inside the Hill sphere of directly imaged exoplanets orbiting neighboring stars.

Submitted to arXiv on 25 Apr. 2026