Title: Quantifying the scale of star formation across the Perseus spiral arm using young clusters around Cas OB5 Show Chinese title

Title: 利用御夫座OB5周围的年轻星团量化英仙臂的恒星形成规模

Abstract: Cas OB5 is an OB association located at a distance of 2.5-3 kpc that intercepts the Perseus spiral arm. It carries a moderate amount of reddening ($A_V \sim$ 2-3 mag) and contains several well-known open clusters within its boundaries, such as King 12, NGC 7788, and NGC 7790. The availability of modern clustering algorithms, together with \textit{Gaia} DR3 kinematics and complementary spectroscopic data, makes it a suitable site for studies of Galactic structure. We seek to quantify the spatial scale of star formation in the spiral arms, using Cas OB5 as a pilot target before extending our study to more distant and extinguished regions of the Galaxy. We selected 129,695 candidate OBA stars in a 6x8 deg$^2$ region around Cas OB5. We applied a spectral energy distribution (SED) fitting process to this sample to derive the physical parameters. Through this process, we found 56 379 OBA stars, which we then clustered using HDBSCAN. We identified 17 open clusters inside this area, four of which appear to form a coherent structure that we identify as Cas OB5. Nevertheless, our findings suggest that these clusters belong to two different age groups despite sharing a similar position and kinematics. Spectroscopic observations confirm the youth of NGC 7788 (10-15 Myr) compared to NGC 7790 ($110\pm15\:$Myr). We have determined a spatial scale for star formation of a few tens of pc to a few hundreds of pc, comparing the clustered to the diffuse population of Cas~OB5 across this part of the Perseus arm. A spectroscopic analysis was required to complement the clustering algorithm, so that we could separate younger OCs (tracers of the spiral arm) from older ones. These results highlight the need to combine these techniques to fully disentangle the Milky Way structure. Show Chinese abstract

Abstract: Cas OB5是一个位于2.5-3千秒差距距离处的OB星协，横跨英仙座旋臂。它具有适度的消光（$A_V \sim$2-3 mag），并且在其边界内包含几个已知的疏散星团，例如King 12、NGC 7788和NGC 7790。现代聚类算法以及\textit{盖亚}数据释放3（DR3）的运动学和互补光谱数据的可用性，使其成为研究银河系结构的理想场所。 我们希望量化旋臂中恒星形成的尺度大小，以Cas OB5作为试点目标，之后再扩展到更遥远且被遮蔽的银河系区域。我们在Cas OB5周围一个6×8度的$^2$区域内选定了129,695颗候选OBA型恒星。我们对该样本进行了光谱能量分布（SED）拟合过程，以推导出物理参数。通过这一过程，我们发现了56,379颗OBA型恒星，并使用HDBSCAN对其进行聚类。我们在该区域内识别出了17个疏散星团，其中四个似乎形成了一个连贯的结构，我们将其识别为Cas OB5。 然而，我们的发现表明，尽管这些星团共享相似的位置和运动学特性，但它们属于两个不同的年龄组。光谱观测确认了NGC 7788（10-15百万年）比NGC 7790（$110\pm15\:$百万年）年轻。我们通过比较Cas OB5在这个英仙座旋臂部分的聚集体与弥散群体，确定了恒星形成的空间尺度为几十到几百秒差距。为了补充聚类算法，需要进行光谱分析，以便我们可以区分较年轻的疏散星团（旋臂的示踪者）和较老的星团。这些结果强调了结合这些技术以完全解开银河系结构的重要性。