Detailed spectroscopic and photometric analysis of the remarkable planet-hosting wide binary system HD 202772A/B

TL;DR

This study provides a detailed spectroscopic and photometric analysis of the wide binary system HD 202772A/B, revealing the properties of the planet-hosting star, the planetary system, and chemical abundance differences likely due to atomic diffusion.

Contribution

It offers the first detailed characterization of the HD 202772A/B system, including refined planetary parameters and high-precision stellar abundances, highlighting chemical anomalies and their possible origins.

Findings

HD 202772A hosts a highly irradiated hot Jupiter.

HD 202772A shows a refractory element enhancement.

Chemical differences are likely due to atomic diffusion.

Abstract

We conducted a detailed spectroscopic and photometric characterization of the planet-hosting wide binary HD 202772A/B. No planet has been detected around HD 202772B, whereas HD 202772A, more evolved than its companion and near the end of its main-sequence (MS) phase, hosts a transiting hot Jupiter. The system has one of the hottest components ($T_{\mathrm{eff}; A} \sim 6440$ K) and one of the largest surface gravity differences between components ($\Delta\log g_{A-B} \sim 0.4$ dex) among MS planet-hosting wide binaries. Using a global fit including our stellar parameters, radial velocities, and new TESS data, we derive refined properties of the planet orbiting HD 202772A, finding it to be the most irradiated hot Jupiter known in a wide binary. We also constrain the presence of additional transiting planets around HD 202772A and new transiting planets around HD 202772B using TESS photometry. We derive high-precision, strictly differential abundances for 27 species based on Gemini-GRACES spectra. HD 202772A shows lower lithium abundance (by 0.45 dex) relative to B, consistent with their stellar parameter differences. We also detect a small but significant enhancement in refractory elements in HD 202772A, particularly those with condensation temperatures above 1400 K (+0.018 $\pm$ 0.004 dex). We explored several scenarios to explain the observed chemical anomalies. Our analysis suggests that rocky planet engulfment, primordial inhomogeneities, and $\delta$ Scuti-related effects are unlikely to fully account for the chemical pattern. Instead, the differences observed in certain refractory elements might support atomic diffusion as the most plausible explanation.