TOI-1173 A b: The First Inflated Super-Neptune in a Wide Binary System

August 2024 • 2024AJ....168...91G

Authors • Galarza, Jhon Yana • Ferreira, Thiago • Lorenzo-Oliveira, Diego • Simon, Joshua D. • Reggiani, Henrique • Piro, Anthony L. • Butler, R. Paul • Netto, Yuri • Valio, Adriana • Ciardi, David R. • Safonov, Boris

Abstract • Among Neptunian mass exoplanets (20‑50 M _⊕), puffy hot Neptunes are extremely rare, and their unique combination of low mass and extended radii implies very low density (ρ < 0.3 g cm^‑3). Over the last decade, only a few puffy planets have been detected and precisely characterized with both transit and radial velocity observations, most notably including WASP-107 b, TOI-1420 b, and WASP-193 b. In this paper, we report the discovery of TOI-1173 A b, a low-density ( g cm^‑3) super-Neptune with P = 7.06 days in a nearly circular orbit around the primary G-dwarf star in the wide binary system TOI-1173 A/B. Using radial velocity observations with the MAROON-X and HIRES spectrographs and transit photometry from TESS, we determine a planet mass of M _p = 27.4 ± 1.7 M _⊕ and radius of R _p = 9.19 ± 0.18 R _⊕. TOI-1173 A b is the first puffy super-Neptune planet detected in a wide binary system (projected separation ∼11,400 au). We explore several mechanisms to understand the puffy nature of TOI-1173 A b and show that tidal heating is the most promising explanation. Furthermore, we demonstrate that TOI-1173 A b likely has maintained its orbital stability over time and may have undergone von-Zeipel–Lidov–Kozai migration followed by tidal circularization, given its present-day architecture, with important implications for planet migration theory and induced engulfment into the host star. Further investigation of the atmosphere of TOI-1173 A b will shed light on the origin of close-in low-density Neptunian planets in field and binary systems, while spin–orbit analyses may elucidate the dynamical evolution of the system.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2024AJ....168...91Y
• PREPRINT http://arxiv.org/abs/2403.06240
• DATA https://archive.gemini.edu/searchform/publication=2024AJ....168...91G
• ELECTR https://doi.org/10.3847%2F1538-3881%2Fad53bf