发表机构
Observatoire Astronomique de l’Université de Genève; University of Warwick; University of Oxford; Centre for Exoplanets and Habitability, University of Warwick; University of California, Santa Cruz; Universidad Nacional Autónoma de México; European Space Agency (ESA); Universidade do Porto; Keele University; NASA Ames Research Center; NASA Exoplanet Science Institute, Caltech/IPAC; Stephen F. Austin State University; Princeton University（日内瓦大学天文台; 华威大学; 牛津大学; 华威系外行星与宜居性中心; 加州大学圣克鲁兹分校; 墨西哥国立自治大学; 欧洲空间局; 波尔图大学; 基尔大学; 美国宇航局艾姆斯研究中心; NASA系外行星科学研究所/加州理工学院IPAC; 斯蒂芬·F·奥斯汀州立大学; 普林斯顿大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过TESS和HARPS数据确认两颗极端辐射的富挥发分亚海王星及其伴星，发现海王星沙漠边缘低质量亚海王星的巨伴星显著过剩，支持高偏心率潮汐迁移塑造该边缘的作用。
AI 中文摘要
我们利用TESS测光数据和147次HARPS视向速度测量，确认了两颗位于海王星沙漠下边缘附近、受极端辐射的富挥发分亚海王星：TOI-426 b和TOI-1839 b，它们分别围绕类太阳恒星HD 34390和TYC 304-865-1运行。我们采用共享时标和多维高斯过程对恒星活动进行建模。这两颗行星的轨道周期分别约为1.32天和1.42天，半径分别为$2.19\pm0.09$地球半径和$2.27\pm0.10$地球半径，质量分别为$6.7\pm1.8$地球质量和$7.10\pm0.78$地球质量。它们接收到的辐射强度约为地球的1700倍和1050倍，但它们的密度表明含有大量挥发分。我们还探测到一颗凌日亚海王星TOI-1839 c，轨道周期约为4.02天，以及一颗巨伴星TOI-426 c，假设轨道为圆形，其周期为$235.8^{+9.2}_{-8.5}$天，最小质量为$444^{+18}_{-17}$地球质量。内部结构和大气逃逸模型显示，氢/氦包层的质量损失时标为1-100 Myr，而以水为主的包层的质量损失时标为100-1000 Gyr，这支持所有三颗凌日行星为蒸汽世界的解释。种群分析显示，在沙漠边缘附近的低质量亚海王星中，探测到的外部巨伴星数量显著过剩，而该区域预计会发生高偏心率潮汐迁移，使存活的行星轨道圆化：在潮汐存活带内的比例为36%（9/25），带外为6%（9/148）（Fisher精确检验$p=1.4\times10^{-4}$）。这种过剩对样本选择和伴星定义的变化具有稳健性。这些富挥发分行星的存活挑战了仅由原始氢/氦包层蒸发设定的边界，而伴星过剩则支持高偏心率潮汐迁移在塑造海王星沙漠下边缘方面发挥重要作用。
英文摘要
Using TESS photometry and 147 HARPS radial velocities, we confirm two extremely irradiated, volatile-rich sub-Neptunes near the lower edge of the Neptunian desert: TOI-426 b and TOI-1839 b, orbiting the solar-type stars HD 34390 and TYC 304-865-1. We modelled stellar activity with shared-timescale and multidimensional Gaussian processes. The planets have orbital periods of approximately 1.32 and 1.42 days, radii of $2.19\pm0.09$ and $2.27\pm0.10$ Earth radii, and masses of $6.7\pm1.8$ and $7.10\pm0.78$ Earth masses, respectively. They receive approximately 1700 and 1050 times Earth's irradiation, yet their densities require substantial volatile content. We also detect a transiting sub-Neptune, TOI-1839 c, at approximately 4.02 days and a giant companion, TOI-426 c, with a period of $235.8^{+9.2}_{-8.5}$ days and a minimum mass of $444^{+18}_{-17}$ Earth masses, assuming a circular orbit. Interior-structure and atmospheric-escape models yield mass-loss timescales of 1-100 Myr for hydrogen/helium envelopes, compared with 100-1000 Gyr for water-dominated envelopes, favouring a steam-world interpretation for all three transiting planets. A population analysis reveals a striking excess of detected outer giant companions to low-mass sub-Neptunes near the desert edge, where high-eccentricity tidal migration is expected to circularize surviving planets: 36% (9/25) within the tidal survival band versus 6% (9/148) outside it (Fisher exact test $p=1.4\times10^{-4}$). This excess is robust to changes in sample selection and companion definitions. The survival of these volatile-rich planets challenges a boundary set solely by evaporation of primordial hydrogen/helium envelopes, while the companion excess supports an important role for high-eccentricity tidal migration in shaping the lower desert edge.
CommentsAccepted for publication in A&A. 24 pages, 16 figures (including appendices)
