AI 中文总结
本研究确认了围绕富金属亚巨星TOI-5646运行的超热超级海王星TOI-5646b，其为海王星沙漠中最大的宿主恒星，质量损失显著，或有特殊形成历史。
AI 中文摘要
我们报告了对TESS凌星行星候选体的确认，该候选体围绕富金属F8 IV-V型亚巨星TOI-5646（V星等=11.38等；有效温度T=6136 K）运行。通过HARPS-N后续径向速度测量，确认了TOI-5646b的行星属性。我们确定该行星的轨道周期为2.4277天，轨道偏心率与零值兼容。该行星质量为45.9地球质量，半径为6.6地球半径，平衡温度为1935 K，是迄今在海王星沙漠中发现的最热的超级海王星之一。其密度为0.87 g cm^-3，低于大多数其他沙漠居民，但仍遵循以下趋势：海王星沙漠中的行星比海王星脊和稀树草原中的行星密度更高。母星的金属丰度[Fe/H]=0.32，遵循以下趋势：海王星沙漠和脊中的海王星大小系外行星的宿主恒星通常比稀树草原中的宿主恒星金属更丰富。母星的log{g}=4.09，表明该宿主是一颗演化恒星，使该系统成为特殊系统：TOI-5646是迄今发现的拥有海王星大小沙漠行星的最大恒星（1.8太阳半径）。内部结构建模显示，TOI-5646b富含金属，推断的整体金属丰度在0.7至0.95之间。大气演化模拟表明，该行星因宿主恒星强烈的XUV辐射而经历了显著的质量损失（6-16%）。这些结果表明，该行星具有特殊的形成历史（可能涉及原行星盘早期消散）、行星碰撞或晚期潮汐破坏事件，以解释其当前作为海王星沙漠中低密度幸存者的状态。
英文摘要
We report the confirmation of the TESS transiting-planet candidate orbiting the metal-rich F8\,IV-V subgiant star TOI-5646 (V=11.38 mag; T=6136 K). The planetary nature of TOI-5646b was confirmed by means of HARPS-N follow-up radial velocity measurements. We determined that the planet has an orbital period of 2.4277 days and an orbital eccentricity compatible with zero. With a mass of 45.9 Earth masses, a radius of 6.6 Earth radii, and an equilibrium temperature of 1935 K, it is one of the hottest super-Neptune exoplanets ever discovered in the Neptune desert. Its density, 0.87 g cm^-3, is lower than that of most other desert dwellers, but still appears to follow the trend that the desert is populated by dense planets than those in the ridge and savanna. The metallicity of the parent star ([Fe/H]=0.32) follows the trend whereby the host stars of Neptune-sized exoplanets in the desert and the ridge are generally richer in metal than those in the savanna. The log{g} of the parent star (4.09) suggests that the host is an evolved star, making this a peculiar system: TOI-5646 is the largest star (1.8 Solar radii) ever discovered to host a Neptune-sized planet in the desert. Internal structure modelling revealed that TOI-5646b is highly enriched in metals, with an inferred bulk metallicity between 0.7 and 0.95. Atmospheric evolution simulations indicate that the planet has undergone significant mass loss (6-16%) through intense XUV irradiation from its host star. These results indicate a peculiar formation history (potentially involving early protoplanetary disk dispersal), a planetary collision, or a late tidal destruction event, to explain its current state as a low-density survivor in the Neptune desert.
Comments18 pages, 16 figures. Accepted for publication in Astronomy & Astrophysics
