HD 143811 AB b: A Directly Imaged Planet Orbiting a Spectroscopic Binary in Sco-Cen

We present confirmation of HD 143811 AB b, a substellar companion to spectroscopic binary HD 143811 AB through direct imaging with the Gemini Planet Imager (GPI) and Keck NIRC2.

HD 143811 AB was observed as a part of the Gemini Planet Imager Exoplanet Survey (GPIES) in 2016 and 2019 and is a member of the Sco-Cen star formation region. The companion object is detected ∼430 mas from the host star by GPI. With two GPI epochs and one from Keck/NIRC2 in 2022, we confirm through common proper motion analysis that the object is bound to its host star.

We derive an orbit with a semi-major axis of 64+32−14 au and eccentricity ∼0.23. Spectral analysis of the GPI H-band spectrum and NIRC2L photometry provides additional proof that this object is a substellar companion. We compare the spectrum of HD 143811 AB b to PHOENIX stellar models and Exo-REM exoplanet atmosphere models and find that Exo-REM models provide the best fits to the data.

From the Exo-REM models, we derive an effective temperature of 1042+178−132 K for the planet and translate the derived luminosity of the planet to a mass of 5.6±1.1 M_Jup assuming hot-start evolutionary models. HD 143811 AB b is one of only a few planets to be directly imaged around a binary, and future characterization of this object will shed light on the formation of planets around binary star systems.

Comments: 16 pages, 7 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2509.06729 [astro-ph.EP] (or arXiv:2509.06729v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.06729
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Submission history
From: Nathalie Jones
[v1] Mon, 8 Sep 2025 14:24:21 UTC (2,379 KB)
https://arxiv.org/abs/2509.06729

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