GEMINI/GeMS观测揭示了严重模糊的球状星团Liller 1的结构
GEMINI/GeMS observations unveil the structure of the heavily obscured globular cluster Liller 1
摘要：
通过利用特殊的高分辨率能力的近红外相机GSAOI结合多共轭自适应光学系统GeMS在GEMINI南望远镜，我们研究了严重模糊的球状星团Liller 1在银河系凸起的结构和物理特性。我们获得了迄今为止该星团最深、最精确的色星等图，达到Ks ~ 19（低于主序关断水平）。我们利用这些数据重新确定了系统的重心，发现它位于文献值东南约2.2”处。我们还为该星团建立了新的恒星密度和表面亮度分布，并重新推导了其主要结构和物理参数（尺度半径，浓度参数，中心质量密度，总质量）。我们发现Liller 1的浓度（浓度参数c=1.74）和伸展（潮汐半径r_t=298”和核心半径r_c=5.39”）比以前认为的要小得多。通过使用这些新确定的结构参数，我们估计了Liller 1的质量M_tot = 2.3 x 10^6 Msun（对于Kroupa IMF，Mtot = 1.5 x 10^6 Msun），这与银河系中质量最大的星团（半人马座ω和泰山5）相当。此外，Liller 1在银河系所有星团中的碰撞率（仅次于Terzan 5）第二高，因此证实它是形成碰撞物体（如毫秒彗星）的理想环境。
英文摘要：
By exploiting the exceptional high-resolution capabilities of the near-IR camera GSAOI combined with the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope, we investigated the structural and physical properties of the heavily obscured globular cluster Liller 1 in the Galactic bulge. We have obtained the deepest and most accurate color-magnitude diagram published so far for this cluster, reaching Ks ~ 19 (below the main sequence turn-off level). We used these data to re-determine the center of gravity of the system, finding that it is located about 2.2" south-east from the literature value. We also built new star density and surface brightness profiles for the cluster, and re-derived its main structural and physical parameters (scale radii, concentration parameter, central mass density, total mass). We find that Liller 1 is significantly less concentrated (concentration parameter c=1.74) and less extended (tidal radius r_t=298" and core radius r_c=5.39") than previously thought. By using these newly determined structural parameters we estimated the mass of Liller 1 M_tot = 2.3 x 10^6 Msun (Mtot = 1.5 x 10^6 Msun for a Kroupa IMF), which is comparable to that of the most massive clusters in the Galaxy (omega Centauri and Terzan 5). Also Liller 1 has the second highest collision rate (after Terzan 5) among all star clusters in the Galaxy, thus confirming that it is an ideal environment for the formation of collisional objects (such as millisecond pulsars).
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