标题： 作为动力学信标的视向加速度：发现并表征海豚星团中第一颗T矮星伴星HIP 21152 B 显示英文标题

标题： Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades

摘要： 具有精确测定年龄和模型无关质量的基准棕矮星伴星是检验次恒星演化模型并探测巨行星和棕矮星形成的强大工具。 在这里，我们报告了HIP 21152 B（Hyades中第一颗成像的棕矮星伴星）的独立发现，并对该系统的轨道和大气特性进行了全面表征。 HIP 21152 是一项正在进行的高对比度成像巡天计划的目标，该计划针对在Hipparcos和Gaia之间表现出自行变化的恒星，同时Bonavita等人（2022）和Kuzuhara等人（2022）最近也发现了它。 我们的Keck/NIRC2和SCExAO/CHARIS对HIP 21152的成像揭示了一颗分离距离为$0.37^{\prime\prime}$（16天文单位）的共运动伴星。 我们对所有可用的相对自行数据和径向速度以及Hipparcos-Gaia自行数据进行了联合轨道拟合，得到了一个动力学质量为$24^{+6}_{-4}\,\mathrm{M_{Jup}}$的结果，这比演化模型预测值低$1{-}2{\sigma}$。 包括云属性演化的混合网格最能再现动力学质量。 我们还识别出一颗分离距离为$1837^{\prime\prime}$或$7.9 \times 10^4 \, \mathrm{au}$的共运动早期L型矮星，其推断质量接近氢燃烧极限。 最后，我们使用Saumon & Marley（2008）的大气模型和一系列反演方法分析了HIP 21152 B的光谱和测光数据。 最佳拟合的基于网格的模型具有$f_{\mathrm{sed}}=2$，表明存在云， $T_{\mathrm{eff}}=1400 \, \mathrm{K}$，以及$\log{g}=4.5 \, \mathrm{dex}$。 这些结果与该天体的光谱类型为$\mathrm{T0\pm1}$一致。 作为金牛座星团中的首个基准棕矮星伴星，HIP~21152~B 加入了数量虽少但正在增长的具有明确年龄和动力学质量的次恒星伴星行列。 显示英文摘要

摘要： Benchmark brown dwarf companions with well-determined ages and model-independent masses are powerful tools to test substellar evolutionary models and probe the formation of giant planets and brown dwarfs. Here, we report the independent discovery of HIP~21152~B, the first imaged brown dwarf companion in the Hyades, and conduct a comprehensive orbital and atmospheric characterization of the system. HIP~21152 was targeted in an ongoing high-contrast imaging campaign of stars exhibiting proper motion changes between Hipparcos and Gaia, and was also recently identified by Bonavita et al. (2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of HIP~21152 revealed a comoving companion at a separation of $0.37^{\prime\prime}$ (16 au). We perform a joint orbit fit of all available relative astrometry and radial velocities together with the Hipparcos-Gaia proper motions, yielding a dynamical mass of $24^{+6}_{-4}\,\mathrm{M_{Jup}}$, which is $1{-}2{\sigma}$ lower than evolutionary model predictions. Hybrid grids that include the evolution of cloud properties best reproduce the dynamical mass. We also identify a comoving wide-separation ($1837^{\prime\prime}$ or $7.9 \times 10^4 \, \mathrm{au}$) early-L dwarf with an inferred mass near the hydrogen-burning limit. Finally, we analyze the spectra and photometry of HIP~21152~B using the Saumon & Marley (2008) atmospheric models and a suite of retrievals. The best-fit grid-based models have $f_{\mathrm{sed}}=2$, indicating the presence of clouds, $T_{\mathrm{eff}}=1400 \, \mathrm{K}$, and $\log{g}=4.5 \, \mathrm{dex}$. These results are consistent with the object's spectral type of $\mathrm{T0\pm1}$. As the first benchmark brown dwarf companion in the Hyades, HIP~21152~B joins the small but growing number of substellar companions with well-determined ages and dynamical masses.