标题： 使用JWST NIRSpec G395H光谱对一颗Y矮星进行高精度大气特征研究：同位素、C/O比值、金属丰度以及六种分子物种的丰度 显示英文标题

标题： High-precision atmospheric characterization of a Y dwarf with JWST NIRSpec G395H spectroscopy: isotopologue, C/O ratio, metallicity, and the abundances of six molecular species

摘要： 詹姆斯韦布空间望远镜（JWST）的发射标志着精确表征Y矮星（目前已知最冷的褐矮星光谱类型）大气特性的关键时刻。 在这项研究中，我们利用JWST搭载的近红外光谱仪（NIRSpec）G395H光栅的中等光谱分辨率观测数据（R $\sim$ 2700），来表征附近的Y矮星WISEPA J182831.08+265037.8（WISE 1828）。 通过NIRSpec G395H的2.88-5.12 $\mathrm{\mu}$微米光谱，我们测量了CO、CO$_2$、CH$_4$、H$_2$S、NH$_3$和H$_2$O的丰度，这些是大气中主要的碳、氮、氧和硫携带物种。 基于通过CHIMERA大气 retrieval 框架检索到的体积混合比，我们报告了C/O比率是$0.45 \pm 0.01$，接近太阳的C/O值0.55，金属丰度为+0.30 $\pm$ 0.02 dex。 与前向建模结果的比较表明，C/O和金属丰度的模型偏差可能分别高达0.03和0.97 dex。 我们还报告了最低限度的$^{12}$CO/$^{13}$CO比率是$>40 $，这与太阳的标称值90一致。 我们的结果突显了JWST在测量C/O比率至百分比级精度以及表征类似于WISE 1828的寒冷行星大气同位素方面的潜力。 显示英文摘要

摘要： The launch of the James Webb Space Telescope (JWST) marks a pivotal moment for precise atmospheric characterization of Y dwarfs, the coldest brown dwarf spectral type. In this study, we leverage moderate spectral resolution observations (R $\sim$ 2700) with the G395H grating of the Near-Infrared Spectrograph (NIRSpec) onboard of JWST to characterize the nearby (9.9 pc) Y dwarf WISEPA J182831.08+265037.8 (WISE 1828). With the NIRSpec G395H 2.88-5.12 $\mathrm{\mu}$m spectrum, we measure the abundances of CO, CO$_2$, CH$_4$, H$_2$S, NH$_3$, and H$_2$O, which are the major carbon, nitrogen, oxygen, and sulfur bearing species in the atmosphere. Based on the retrieved volume mixing ratios with the atmospheric retrieval framework CHIMERA, we report that the C/O ratio is $0.45 \pm 0.01$, close to the solar C/O value of 0.55, and the metallicity to be +0.30 $\pm$ 0.02 dex. Comparison between the retrieval results with the forward modeling results suggests that the model bias for C/O and metallicity could be as high as 0.03 and 0.97 dex respectively. We also report a lower limit of the $^{12}$CO/$^{13}$CO ratio of $>40 $, being consistent with the nominal solar value of 90. Our results highlight the potential of JWST in measuring the C/O ratios down to percent-level precision and characterizing isotopologues of cold planetary atmospheres similar to WISE 1828.