银河系第四象限有十六个被忽视的疏散星团。UBVI光度法和Gaia DR2与ASteCA的联合分析
Sixteen overlooked open clusters in the fourth Galactic quadrant. A combined analysis of UBVI photometry and Gaia DR2 with ASteCA
摘要：
目的：本论文有两个主要目的：（1）测定银河系中已知度为270 $^\circ-$ 300 $^\circ$的16个微弱的、大多数未被研究的疏散星团的内禀性质，为今后的研究提供探测银河系结构的依据。(2)通过比较来自测光的星团距离与来自盖亚DR 2星团的星团距离，解决先前报道的盖亚DR 2星团的系统学问题。方法：对16个疏散星团进行深UBVI光度测量。使用ASeCA软件包以自动方式对观测结果进行简化和分析，以获得个体距离、红化、质量、年龄和金属丰度。测光距离进行了比较，从贝叶斯分析盖亚DR 2松弛。结果：16个星团中有10个是真实的或高可能的疏散星团。其中两个相当年轻，并遵循隆突臂的痕迹和已经检测到的翘曲。其余的星团被放置在英仙座臂和船底座臂之间的臂间区域，正如对较老天体的预期。我们发现范登伯格-哈根85星团的年龄为7.5 $\times$ 10 $^9$岁，成为迄今为止在银河系中发现的最古老的疏散星团之一。讨论了这10个星团与太阳附近星系结构的关系。从测光和测量数据的距离的比较，反过来，揭示了不同程度的分歧。结论：最近报道的盖亚DR 2视差数据的各种零点校正被认为是光度和视差距离之间的比较。结果往往会改善与这些修正。光度距离分析表明平均校正值为$\sim$ +0.026 mas（将添加到视差中）。校正可能具有更复杂的距离依赖性，但解决该细节水平将需要更大的聚类样本。
英文摘要：
Aims: This paper has two main objectives: (1) To determine the intrinsic properties of 16 faint and mostly unstudied open clusters in the poorly known sector of the Galaxy at 270$^\circ-$300$^\circ$, to probe the Milky Way structure in future investigations. (2) To address previously reported systematics in Gaia DR2 parallaxes by comparing the cluster distances derived from photometry with those derived from parallaxes. Methods: Deep UBVI photometry of 16 open clusters was carried out. Observations were reduced and analyzed in an automaticway using the ASteCA package to get individual distances, reddening, masses, ages and metallicities. Photometric distances were compared to those obtained from a Bayesian analysis of Gaia DR2 parallaxes. Results: Ten out of the 16 clusters are true or highly probable open clusters. Two of them are quite young and follow the trace of the Carina Arm and the already detected warp. The rest of the clusters are placed in the interarm zone between the Perseus and Carina Arms as expected for older objects. We found that the cluster van den Berg-Hagen 85 is 7.5$\times$10$^9$ yrs old becoming then one of the oldest open cluster detected in our Galaxy so far. The relationship of these ten clusters with the Galaxy structure in the solar neighborhood is discussed. The comparison of distances from photometry and parallaxes data, in turn, reveals a variable level of disagreement. Conclusions: Various zero point corrections for Gaia DR2 parallax data recently reported were considered for a comparison between photometric and parallax based distances. The results tend to improve with some of these corrections. Photometric distance analysis suggest an average correction of $\sim$+0.026 mas (to be added to the parallaxes). The correction may have a more intricate distance dependency, but addressing that level of detail will require a larger cluster sample.
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