GG Tau A系统中的轨道动力学：探究其神秘的盘
Orbital dynamics in the GG Tau A system: investigating its enigmatic disc
AI总结：
本研究针对GG Tau A系统盘结构几何不明的问题，通过新天体测量数据、流体动力学模拟及多波段观测对比，发现非共面轨道在短时间尺度下与观测匹配最佳，提出系统年龄或偏心率增长机制的相关疑问。
摘要：
GG Tau是研究最多的多星年轻恒星系统之一：GG Tau A是一个被大质量盘环绕的等级式三合星系统，其伴星GG Tau B本身也是一个双星系统。尽管已有大量观测尝试，人们对GG Tau A系统的几何结构仍不清楚。我们提供了该系统的新天体测量数据，并针对两条代表性轨道开展了一系列流体动力学模拟，以测试它们对由尘埃和气体组成的盘的影响。我们在短时间尺度和长时间尺度上测试了两种情景的动力学演化。我们从模拟中得到了合成通量发射，并将其与1300μm的ALMA尘埃连续谱发射以及1.67μm的SPHERE尘埃散射图像进行对比，以推断最可能的轨道排布。我们利用档案数据中的6个新历元扩展了双星轨道参数的分析，结果表明仅靠当前的测量无法打破共面轨道族与非共面轨道族之间的参数简并。我们发现，盘偏心率增长的起始时间尺度τ_ecc是决定系统形态的一个基本时间尺度。数值模拟结果显示，在短于τ_ecc的时间尺度下，非共位构型（Δθ=30°）得到的模拟结果与观测匹配度最佳，呈现出近乎圆形的空腔和尘埃环。然而，对于两种情景而言，当时间尺度长于τ_ecc时，空腔大小及其偏心率都会迅速增大，模型将无法再复现观测到的形态。这意味着要么该系统的年龄短于τ_ecc，要么盘偏心率的增长未被触发或已被耗散。这一发现引发了关于GG Tau A系统未来演化的疑问，更广泛地说，也引发了关于偏心双星及其环双星盘时间演化的疑问。
英文摘要：
GG Tau is one of the most studied multiple young stellar systems: GG Tau A is a hierarchical triple surrounded by a massive disc and its companion, GG Tau B, is also a binary. Despite numerous observational attempts, an understanding of the geometry of the GG Tau A system is still elusive. We provide new astrometric measures of the system and we run a set of hydrodynamical simulations with two representative orbits to test how they impact a disc composed of dust and gas. We test the dynamical evolution of the two scenarios on short and long timescales. We obtain synthetic flux emission from our simulations and we compare them with 1300 $μ$m ALMA dust continuum emission and 1.67 $μ$m SPHERE dust scattering images to infer the most likely orbital arrangement. We extend the analysis of the binary orbital parameters using six new epochs from archival data, showing that the current measurements alone are not capable of breaking the degeneracy between families of coplanar and misaligned orbits. We found that the time-scale for the onset of the disc eccentricity growth, $τ_{ecc}$, is a fundamental time-scale for the morphology of the system. Results from numerical simulations show that the best match between is obtained with the misaligned configuration ($Δθ= 30^\circ$) on timescales shorter than $τ_{ecc}$. The results exhibit an almost circular cavity and dust ring. However, for both scenarios, the cavity size and its eccentricity quickly grow for timescales longer than $τ_{ecc}$ and the models do not reproduce the observed morphology anymore. This implies that either the age of the system is shorter than $τ_{ecc}$ or that the disc eccentricity growth is not triggered or dissipated. This finding raises questions on the future evolution of the GG Tau A system and, more in general, on the time evolution of eccentric binaries and their circumbinary discs.
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