年轻木星类星体AF Lep b的富硫大气揭示其发生了显著的固体吸积
A Sulfur-Rich Atmosphere for the Young Jupiter Analog AF Lep b Reveals Significant Solid Accretion
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中文总结 AI 辅助
本研究通过多台望远镜观测年轻木星类星体AF Lep b的大气，发现其富硫特性及56±7倍地球质量的固体吸积量，表明气态巨行星金属吸积过程与轨道距离、行星质量关联较弱。
中文摘要 AI 辅助
AF Lep b是质量（3-4倍木星质量）和半长轴（9天文单位）方面最接近木星的类星体之一，适合进行光谱表征。我们利用詹姆斯·韦伯空间望远镜（JWST）的近红外光谱仪（NIRSpec）对该行星进行了2.85-5.3微米、分辨率约3000的高对比度光谱观测，检测到了二氧化碳（CO₂）、硫化氢（H₂S）、甲烷（CH₄）、碳-12一氧化碳（¹²CO）（以及碳-13一氧化碳（¹³CO））和水（H₂O）；同时，利用JWST的近红外相机（NIRCam）成像获取了该行星4.0-4.7微米的连续谱流量。将JWST观测结果与甚大望远镜干涉仪（VLTI）的重力仪（GRAVITY）、甚大望远镜（VLT）的偏振高对比度系外行星研究光谱仪（SPHERE）获取的1.0-2.5微米光谱相结合，我们开展了包含云层和非平衡化学效应、且允许碳（C）、氧（O）、硫（S）丰度独立变化的大气反演研究。AF Lep b表现出C、O、S的金属富集，其C/H为太阳值的2.9±0.5倍，O/H为太阳值的3.7±0.6倍，S/H为太阳值的4.7±0.7倍。该行星略低于太阳的C/O和C/S比值与其观测位置附近的形成过程相符，不支持其在一氧化碳雪线之外形成。AF Lep b的硫富集意味着其形成过程中发生了显著的原行星盘固体吸积，我们估算该行星包含56±7倍地球质量的固体。AF Lep b的C、O、S富集水平与木星及HR 8799 bcde等其他超级木星相似。我们还发现，这些已成像行星的大气金属富集程度，与质量大于约1倍木星质量的凌日气态巨行星的整体金属富集程度相近，表明气态巨行星的金属吸积过程及效率可能并不强烈依赖于轨道距离或行星质量。
英文摘要
AF Lep b is one of the closest analogs to Jupiter in terms of mass ($3-4~M_{\rm{Jup}}$) and semi-major axis ($9$ AU) amenable to spectroscopic characterization. We present JWST/NIRSpec high-contrast spectroscopy of the planet from $2.85-5.3~μ$m at $R\sim3000$, which provide detections of CO$_2$, H$_2$S, CH$_4$, $^{12}$CO (and $^{13}$CO), and H$_2$O, as well as complementary JWST/NIRCam imaging that captures the planet's continuum flux from $4.0-4.7~μ$m. Combining the JWST observations with spectra from VLTI/GRAVITY and VLT/SPHERE ($1.0-2.5~μ$m), we carry out atmospheric retrievals that include the effects of clouds and disequilibrium chemistry while allowing the C, O, and S abundances to vary independently. AF Lep b exhibits metal enrichment across C, O, and S with $\rm C/H=2.9\pm0.5$, $\rm O/H=3.7\pm0.6$, and $\rm S/H=4.7\pm0.7~\times$ solar (and stellar). The planet's slightly sub-solar C/O and C/S are consistent with formation near its observed location, and disfavor formation beyond the CO snowline. The sulfur enrichment in AF Lep b implies significant accretion of disk solids during formation, and we estimate the planet contains $56\pm7~M_{\oplus}$ of solids. The C, O, and S enrichment levels of AF Lep b are similar to those of Jupiter, and other super-Jupiters like HR 8799 bcde. We also show that the degree of atmospheric metal enrichment of these imaged planets is similar to the bulk metal enrichment of transiting gas giants with masses greater than $\sim1~M_{\rm{Jup}}$, suggesting that the process and efficiency of metal accretion for gas giants may not be strongly dependent on orbital distance or planet mass.
