HR 8799行星的组成反映了固态和金属富集气体的吸积
The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
AI总结：
研究HR 8799行星的组成，通过光谱分析揭示其大气成分和元素丰度，发现外行星吸积了富含氮的气体，支持了行星形成过程中固态和气体吸积的模型。
摘要：
拥有四颗巨行星（质量约为5-10倍木星质量，温度约900-1200 K）围绕在15-70天文单位之间，HR 8799为研究巨行星形成提供了独特的测试平台。我们利用JWST/NIRSpec IFU观测（2.85-5.3μm，R≈2700）获取了HR 8799 b的光谱，并对c、d、e行星的高信噪比光谱进行了分析。我们检测到CO、CH4、H2O、H2S、CO2以及b行星的NH3。结合NIRSpec光谱与1-5μm光度计数据，我们进行了大气检索，考虑了非平衡化学和云层，并允许C/H、O/H、N/H和S/H独立变化。虽然四颗行星在碳和氧的富集程度上相似，但随着轨道距离增加，S/H（固态指示器）呈现上升趋势。从b行星的NH3丰度估计出N/H约为21.2±16.2倍恒星值，表明外行星吸积了大量富含氮的气体。整体元素丰度模式与行星b在CO雪线和更远的N2雪线之间形成，而内行星吸积了3倍恒星质量的CO富集盘气体。多余的挥发性质量来自碎石迁移和蒸发，暗示了750±200倍地球质量的碎石流量。随着轨道距离增加，S/H上升表明更远的固态吸积，这与碎石和行星esimal吸积模型（2倍最小质量太阳星云）的预期一致。
英文摘要：
With four giant planets ($m\sim5-10~M_{\rm Jup}$, $T_\rm{eff}\sim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formation and probing compositional trends across the protoplanetary disk. We present new JWST/NIRSpec IFU observations ($2.85-5.3~μ$m, $R\approx2700$) that now include the spectrum of HR 8799 b, and higher S/N spectra for HR 8799 c, d, and e compared to that in Ruffio & Xuan et al. We detect CO, CH$_4$, H$_2$O, H$_2$S, CO$_2$, and for planet b, NH$_3$. We combine the NIRSpec spectra with $1-5 μ$m photometry to perform atmospheric retrievals that account for disequilibrium chemistry and clouds, and allow C/H, O/H, N/H, and S/H to scale independently. While the four planets are similarly enriched in carbon and oxygen, with C/H and O/H between $3-5\times$ stellar, we observe a tentative trend of increasing S/H - a tracer of refractory solids - from $2-5 \times$ stellar with increasing orbital distance. From HR 8799 b's NH$_3$ abundance, we estimate $\rm N/H=21.2^{+16.2}_{-8.8}\times$ stellar, suggesting the outer planet accreted significant amounts of N-rich gas. Overall, the elemental abundance patterns we observe are consistent with a picture where planet b formed between the CO snowline and the more-distant N$_2$ snowline, while the inner planets accreted $3 \times$ stellar CO-enriched disk gas within the CO snowline. The excess volatile mass from pebble drift and evaporation implies an integrated pebble flux of $750 \pm 200~M_{\oplus}$. The increase in the planets' S/H with orbital distance implies more solid accretion further out, which is quantitatively compatible with expectations from both pebble and planetesimal accretion ($2 \times$ Minimum Mass Solar Nebula) paradigms.
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