白矮星行星中公共包层演化的大气特征
Atmospheric Signatures of Common Envelope Evolution in White Dwarf Planets
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中文总结 AI 辅助
该研究利用MESA模型模拟公共包层演化过程，发现被白矮星吞没的行星吸积物质后热辐射会显著增强，其大气特征可作为探测白矮星近距行星动力学历史的新手段。
中文摘要 AI 辅助
已确认的系外行星中，多数在距离主序（MS）恒星1天文单位（au）范围内运行。当这些行星的恒星宿主脱离主序阶段时，大量行星会被恒星吞没并摧毁，在恒星演化至白矮星（WD）最终状态时，其周围形成空的“禁区”。不过，已发现若干已确认及候选的白矮星行星位于该禁区内。目前已提出两种形成场景解释这些近距行星的存在：高偏心率迁移和公共包层演化（CEE），但现有观测检验极少能区分这两种路径。本研究探讨公共包层演化是否会留下可探测的大气特征。我们使用恒星天体物理学实验模块（MESA）模型，模拟被吞没的行星向内螺旋进入渐近巨星分支（AGB）恒星的过程，并允许行星通过邦迪-霍伊尔-利特尔顿吸积方式吸积质量。假设行星质量范围为1-13倍木星质量（M$_{\rm Jup}$）、吸积效率范围为0.01-1.0，我们发现行星在最极端的爱丁顿极限场景下可吸积多达初始质量的48%。由于吸积的物质富含氢和氦，我们预计这会降低行星的整体金属丰度。通过模拟发射光谱，我们发现公共包层演化可使类似WD 1856 b的冷行星的热辐射最多增加9.0%；对于较低的吸积效率（0.01-0.5），热辐射增幅为0.1-3.6%。该特征在最有利的情况下可能被观测到，为研究白矮星周围近距行星的动力学历史提供了潜在的新探测手段。
英文摘要
The majority of confirmed exoplanets orbit within 1 au of a main-sequence (MS) star. When their stellar hosts evolve off the MS, many of these planets will be engulfed and destroyed, creating empty "forbidden" zones around the stars as they evolve to their final state as a white dwarf (WD). However, several confirmed and candidate WD planets have been found within this forbidden zone. Two formation scenarios have been proposed to explain the existence of these close-in planets: high-eccentricity migration and common envelope evolution (CEE). There are currently few observational tests to distinguish between these pathways. In this study, we investigate whether CEE could leave a detectable atmospheric signature. Using Modules for Experiments in Stellar Astrophysics (MESA) models, we simulate an engulfed planet inspiraling into an AGB star, and allow the planet to accrete mass via Bondi-Hoyle-Lyttleton accretion. Assuming a range of planet masses (1$-$13 M$_{\mathrm{Jup}}$) and accretion efficiencies (0.01$-$1.0), we find that the planet can accrete up to 48% of its initial mass in the most extreme Eddington-limited scenario. Because this accreted material is enriched in hydrogen and helium, we expect it to decrease the planet's bulk metallicity. Using simulated emission spectra, we find that CEE can increase thermal emission by up to 9.0% for a cool planet such as WD 1856 b. For lower accretion efficiencies (0.01$-$0.5), thermal emission increases between 0.1$-$3.6%. This signature may be observable in the most favorable cases, providing a potential new probe for investigating the dynamical history of close-in planets around WDs.
