Abstract:

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 64−14+32 au and eccentricity ∼0.23. Spectral analysis of the GPI H-band spectrum and NIRC2 L’ 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 1042−132+178 K for the planet and translate the derived luminosity of the planet to a mass of 5.6±1.1​MJup 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.

Figure 1 caption:

Figure 1: Reduced flux maps of HD 143811 AB obtained by Gemini/GPI in 2016 and 2019 (left and center) and Keck/NIRC2 in 2022 (right). These images are 2​”×2​”. North is up and East is left. The star is at the center of the image behind the coronagraph. Arrows indicates the location of the companion. Intensity scales are linear and vary for each image in order to highlight the companion.