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 to 115 km s−1), unlike other clusters with velocities of ∼100 km s−1. Most candidates in RSGC4 have QGKs 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 multiepoch observations. Analysis of relative proper motions revealed no runaway/walkaway stars in RSGC4. The dynamic properties of RSGC4 and RSGC1 differ from the disklike motions of other clusters: RSGC4 has low normalized horizontal action Jhor = Jϕ/Jtot and vertical action Jver = (Jz − JR)/Jtot values and high eccentricities, while RSGC1 has vertical motions with high Jver values and inclinations. We propose that RSGC4 may not be a genuine star cluster but rather a composite of RSGs and AGB stars 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.

中文翻译：

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RSGC4（阿利坎特 8）星团是真正的星团吗？红超巨星的特殊径向速度

年轻的大质量星团，如盾牌座复合体中的六个红色超巨星团，为恒星形成和星系结构提供了宝贵的见解。我们使用浸没式光栅红外光谱仪研究了这些簇中 60 个 RSG 候选者的高分辨率近红外光谱。在 RSGC4 的候选星团中，我们发现径向速度有显着的散射（−64 至 115 km s−1），这与速度为 ∼100 km s−1 的其他星团不同。 RSGC4 中的大多数候选者的 QGK 值大于 1.7，表明它们可能是早期 AGB 恒星。 RSGC4 中的四个候选物表现出其他候选物所没有的红外过量和明显的吸收特征。其中两颗恒星表现出类似于 D 型共生恒星的吸收线，在多历元观测中显示出径向速度的变化。相对自行运动分析表明，RSGC4 中没有失控/失控恒星。 RSGC4 和 RSGC1 的动态特性与其他团簇的盘状运动不同：RSGC4 具有低标准化水平运动 Jhor = Jphi/Jtot 和垂直运动 Jver = (Jz − JR)/Jtot 值和高偏心率，而 RSGC1 具有垂直运动高 Jver 值和倾向。我们认为RSGC4可能不是一个真正的星团，而是RSG和AGB恒星的复合体，这些恒星沿着视线以相似的距离分布，可能源自不同的环境。我们的结果表明盾牌复合体中星团的复杂且分层的长期演化，强调了在识别核球区域中的星团时考虑密度拥挤之外的因素的重要性。