AI 中文总结
研究利用 S301 及参考恒星 S2、S55、S38，通过比较牛顿扭矩与 LT 信号，分离 S301 的 LT 自旋信号与牛顿节点进动，校准牛顿背景以测量人马座 A*自旋参数，为相关研究提供方法与思路。
AI 中文摘要
S301（引力合作团队等，2026 年）的发现，其近日点距离 rp = 280rg，偏心率 e = 0.9825，开启了通过兰斯-蒂林（LT）节点进动测量人马座 A*自旋参数的前景。一个主要障碍是牛顿混淆：任何非球形扩展质量分布也会引起节点进动。我们旨在将 S301 的 LT 自旋信号与牛顿节点进动分离。通过经数值轨道平均扭矩计算验证的解析估计，比较圆盘或扁平质量分布对 S301 以及远心点匹配的参考恒星 S2、S55 和 S38 轨道施加的长期牛顿扭矩。对于延伸到恒星近日点之外的圆盘或扁平分布，高偏心率轨道上的长期牛顿扭矩主要由远心点控制，而 LT 信号主要由近日点控制。因此，远心点与 S301 相当但近日点大得多的恒星，特别是 S2，还有 S55 和 S38，经历相当的牛顿扭矩，而 LT 信号（对于 S2）小约 30 倍。它们测量的进动或其上限可校准牛顿背景的质量和方向，以便从 S301 的进动中减去。S301 的史瓦西拱线进动使轨道近日点相对于任何圆盘进一步旋转，在牛顿贡献中产生系统的时间依赖性，而 LT 信号由自旋矢量固定。扰动天体群体的粒度为这种减法设置了一个随机下限，轨道和恒星平均可抑制此下限。随着引力+天体测量和极大望远镜（ELT）光谱学的持续进行，面内自旋投影可能在近期实现；完整的自旋矢量需要 LT 拱线信号的更长期积累。
英文摘要
The discovery of S301 (GRAVITY Collaboration et al., 2026) with pericenter distance rp= 280rg and eccentricity e=0.9825, opens the prospect of measuring the spin parameter of Sgr A* through Lense--Thirring (LT) nodal precession. A major obstacle is Newtonian confusion: any non-spherical extended mass distribution can also induce nodal precession. We aim to separate the LT spin signal of S301 from the Newtonian nodal precession. We compare the secular Newtonian torque exerted by a disk or flattened mass distribution on the orbits of S301 and of the apocenter-matched reference stars S2, S55, and S38, using analytic estimates validated by numerical orbit-averaged torque calculations. For a disk or flattened distribution extending beyond the stellar pericenters, the secular Newtonian torque on a highly eccentric orbit is controlled mainly by the apocenter, whereas the LT signal is controlled mainly by the pericenter. Thus stars with apocenters comparable to S301's but much larger pericenters, in particular S2, but also S55, and S38, experience comparable Newtonian torques while having ~ 30 times smaller LT signals (for S2). Their measured precessions, or upper limits on them, can therefore calibrate the mass and orientation of the Newtonian background for subtraction from S301's precession. The Schwarzschild apsidal advance of S301 further rotates the orbit's pericenter relative to any disk, producing a systematic time dependence in the Newtonian contribution, while the LT signal remains fixed by the spin vector. Granularity of the perturber population sets a stochastic floor on this subtraction, which orbit- and star-averaging suppress. With continued GRAVITY+ astrometry and Extremely Large Telescope (ELT) spectroscopy, the in-plane spin projection may be within near-term reach; the full spin vector requires a much longer-term accumulation of the LT apsidal signal.
