NGC 3603星团中的大质量逃逸双星

非团环境中的大质量恒星以及大质量双星的起源是理解大质量恒星形成和演化的关键问题之一. 年轻大质量星团内的动力学交会过程是产生大质量逃逸星的重要途径之一. 选取了银河系内年轻大质量星团NGC 3603外围的两个碰撞星风系统候选体MTT68A和MTT71作为研究对象, 通过分析\emphChandra X射线观测以及\emphGaia第2批数据发布(DR2)中的天体测量结果, 研究它们作为相互作用的大质量双星系统的起源. X射线数据的分析表明, 它们的X射线能谱中存在Fe XXV发射线成分; 相较于普通O型星, 以双温等离子体模型拟合得到偏高的高温成分温度($\gtrsim$2.0keV), 并且X射线光度与热光度的比值也较高($\gtrsim10^{-5.8

The Massive Runaway Binaries in NGC 3603 Cluster

Massive stars tend to form in clustered environments. The origin of the massive stars and binaries outside clusters is one key to understand the formation and evolution of massive stars. The authors selected two colliding wind candidates, MTT68 and MTT71, and probed their origin by analyzing the \emphChandra X--ray observation and the proper motions queried from the \emphGaia Data Release 2 (\emphGaia DR2) catalog. Those two targets are located on the margin of NGC 3603, the galactic massive cluster 7.6kpc away. MTT68 has been resolved as a visual binary of MTT68A/B, and MTT68A itself was proposed as a close massive binary. The authors compared the centroid of the X--ray emission and the coordinate queried from \emphGaia DR2 catalog, to those of MTT68A/B on the \emphHST image, and found that both of them are close to MTT68A but far away from MTT68B, which suggests the X--ray characteristic and the astrometry measurement both mainly describe MTT68A instead of MTT68B. They also carried out the X-ray spectral analysis of MTT68A and MTT71, and found (1) the existence of the Fe XXV line in their spectra, (2) a second component of temperature $kT\gtrsim2.0$keV is required when fitting their spectra with hot plasma models, and (3) their ratio of X-ray to bolometric luminosity, lg($L_X/L_bol)\gtrsim-5.8$, is at least one order of magnitude higher than the value of isolated O-type stars. All above features further prove their colliding wind scenario. Besides that, they analyzed the astrometry measurements of MTT68A and MTT71 queried from the \emphGaia DR2 database. MTT71 has an absolute proper motion similar to the overall value of NGC 3603, which suggests it formed associated with NGC 3603 without ejection process. In contrast, MTT68A has a significant proper motion relative to NGC 3603: the relative proper motion in the right ascension direction $\Delta\mu_\alpha=(-2.5\pm1.1)$mascdotyr^-1 and declination direction $\Delta\mu_\delta=(3.3\pm0.9)$mascdotyr^-1, resulting a direction that opposites to the core region of NGC 3603. Hence the authors propose that MTT68A is a massive binary ejected 20kyr ago, and single-binary and binary--binary interactions are possible mechanisms. A search for the massive star with reverse relative proper motion at the opposite side of the cluster will be helpful to verify this hypothesis.