RSGC4（Alicante 8）星团是一个真实的星团吗？：红超巨星的特殊视向速度
Is the RSGC4 (Alicante 8) cluster a real star cluster?: Peculiar radial velocities of red supergiant stars
AI总结：
本研究通过分析Scutum复合体中RSG候选星的近红外光谱和动力学特性，发现RSGC4存在异常视向速度散射且可能由视线方向上的RSG与AGB星叠加而成，并非真实星团，揭示了星团长期演化的复杂性。
摘要：
年轻大质量星团，如Scutum复合体中的六个红超巨星团，为恒星形成和星系结构提供了有价值的见解。我们使用浸没光栅红外光谱仪研究了这些星团中60个RSG候选星的高分辨率近红外光谱。在RSGC4的候选星中，我们发现了视向速度的显著散射（$-64$ km/s到$115$ km/s），这与其他具有约$\sim$100 km/s速度的星团不同。RSGC4中的大多数候选星的$Q_{GK_s}$值大于1.7，表明它们可能是早期AGB星。RSGC4中的四个候选星表现出红外过剩和其他候选星中不存在的明显吸收特征。其中两颗星表现出类似于D型共生星的吸收线，在多历元观测中显示出视向速度变化。对相对自行运动的分析表明，RSGC4中没有失控/走离星。RSGC4和RSGC1的动力学特性不同于其他星团的盘状运动：RSGC4具有较低的归一化水平作用量$J_\mathrm{hor}=J_\mathrmϕ/J_\mathrm{tot}$和垂直作用量$J_\mathrm{ver}=(J_\mathrm{z}-J_\mathrm{R})/J_\mathrm{tot}$值以及高偏心率，而RSGC1具有高$J_\mathrm{ver}$值和倾角的垂直运动。我们提出RSGC4可能不是一个真正的星团，而是由沿视线分布在不同环境但距离相似的RSG和AGB组成的复合体。我们的结果表明，Scutum复合体中星团经历了复杂且分层级的长期演化，强调了在核球区域识别星团时考虑密度拥挤之外因素的重要性。
英文摘要：
Young massive star clusters, like the six red supergiant clusters in the Scutum complex, provide valuable insights into star-formation and galaxy structures. We investigated the high-resolution near-infrared spectra of 60 RSG candidates in these clusters using the Immersion Grating Infrared Spectrograph. Among the candidates in RSGC4, we found significant scattering in radial velocity ($-64$ km/s to $115$ km/s), unlike other clusters with velocities of $\sim$100 km/s. Most candidates in RSGC4 have $Q_{GK_s}$ values larger than 1.7, suggesting that they could be early AGB stars. Four candidates in RSGC4 exhibit infrared excess and distinct absorption features absent in other candidates. Two of these stars exhibit absorption lines resembling those of D-type symbiotic stars, showing radial velocity changes in multi-epoch observations. Analysis of relative proper motions revealed no runaway/walkaway stars in RSGC4. The dynamic properties of RSGC4 and RSGC1 differ from the disk-like motions of other clusters: RSGC4 has low normalized horizontal action $J_\mathrm{hor}=J_\mathrmϕ/J_\mathrm{tot}$ and vertical action $J_\mathrm{ver}=(J_\mathrm{z}-J_\mathrm{R})/J_\mathrm{tot}$ values and high eccentricities, while RSGC1 has vertical motions with high $J_\mathrm{ver}$ values and inclinations. We propose that RSGC4 may not be a genuine star cluster but rather a composite of RSGs and AGBs distributed along the line of sight at similar distances, possibly originating from various environments. Our results suggest a complex and hierarchical secular evolution of star clusters in the Scutum complex, emphasizing the importance of considering factors beyond density crowding when identifying star clusters in the bulge regions.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
