부산대학교 도서관

Among Neptunian mass planets exoplanets ($20-50$ M$_\oplus$), puffy hot Neptunes are extremely rare, and their unique combination of low mass and extended radii implies very low density ($\rho < 0.3$ 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 ($\rho = 0.269_{-0.024}^{+0.028}$ 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 spectrograph and transit photometry from TESS, we determined a planet mass of $M_{\rm{p}} = 26.1\pm1.9\ M_{\oplus}$ and radius of $R_{\rm{p}} = 8.10\pm0.17\ R_{\oplus}$. TOI-1173 A $b$ is the first puffy Super-Neptune planet detected in a wide binary system (separation $\sim 11,400$ AU). We explored several mechanisms to understand the puffy nature of TOI-1173 A $b$, and showed 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.
Comment: Article submitted and is under revision to the AAS Astrophysical Journal. Welcome any comments and suggestions!