通过刻画环绕HD 77946的亚海王星来直面成分混淆问题
Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946
AI总结：
本文通过TESS、HARPS-N和CHEOPS数据刻画了绕F5恒星HD 77946运行的亚海王星HD 77946 b，测定其质量、半径和轨道参数，发现其可能具有约1% H/He大气，并指出该行星是透射光谱研究成分混淆问题的关键目标。
摘要：
我们报告了对HD 77946行星系统的详细刻画。HD 77946是一颗F5型恒星（$M_*$ = 1.17 M$_{\odot}$，$R_*$ = 1.31 R$_{\odot}$），它拥有一颗最近由NASA的凌星系外行星巡天卫星（TESS）发现的凌星行星，该行星被归类为TOI-1778 b。利用TESS测光数据、来自HARPS-N的高分辨率光谱数据以及CHEOPS的测光数据，我们从凌星和视向速度观测中测量了半径和质量，并发现这颗行星HD 77946 b的轨道周期为$P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$天，质量为$M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$，半径为$R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$。结合质量和半径测量结果以及恒星化学组成，该行星的性质表明HD 77946 b是一颗具有约1% H/He大气的亚海王星。然而，水世界模型与硅酸盐/铁-氢模型之间仍然存在简并性，尽管对该行星的内部结构建模更倾向于一颗具有H/He层且该层占其半径相当大比例的亚海王星，但水世界的组成仍不能被排除，因为在$T_{\rm eq} = 1248^{+40}_{-38}~$K的条件下，水可能处于超临界状态。对HD 77946 b的刻画，补充了已被良好刻画的亚海王星这一小样本，是我们在理解行星形成和演化路径道路上的重要一步。此外，HD 77946 b在绕热恒星运行的小型行星中拥有最高的透射光谱指标之一，因此对这颗关键行星进行透射光谱观测可能对约束当前围绕小型系外行星的成分混淆问题至关重要。
英文摘要：
We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
