Open clusters in dense fields: the importance of field‐star decontamination for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37
Open clusters in dense fields: the importance of field‐star decontamination for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37
复制标题
稠密视场中的疏散星团：场星净化对于 NGC 5715、Lyngå 4、Lyngå 9、Trumpler 23、Trumpler 26 和 Czernik 37 的重要性
DOI：
--
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
E. Bica
中科院分区：
文献类型：
--
作者：
C. Bonatto;E. Bica
投射到稠密恒星场上的星团通常需要场星（FS）去污，以确认其性质并导出内在光度和结构基本参数。这项工作的重点是疏散星团 (OC) 或候选 NGC 5715、Lynga4、Lynga 9、Trumpler 23、Trumpler 26 和 Czernik 37，这些星团预计位于 317° � 2.° 2 和 |b| 范围内。 2. ◦ 8，针对拥挤的凸起和/或椎间盘区域。为了解决这些困难的物体，我们开发了一种基于 2MASS J、(J − H) 和 (J − Ks) 数据以及各自的不确定性的颜色星等图 FS 去污算法，以检测背景上的星团恒星过量情况。另一方面，颜色幅度滤波器用于构建恒星径向密度分布和质量函数。结果提供了令人信服的证据，证明 Lynga9 和 Czernik 37 是中龄 OC，并且首次测量了它们的基本参数。 Trumpler 23 是一个特别具有挑战性的物体，因为除了高背景水平之外，它的场在近红外波段呈现出可变的吸收。我们确认这是一个中年OC。 Trumpler 26 的研究比之前的工作更加详细，而 NGC 5715 和 Lynga 4 的基本参数也是首次确定。这些 OC 位于太阳圈内 0.9-1.6 kpc 处，年龄与毕星团相似。从结构上来说，King 的简介对它们进行了很好的描述。在所有情况下，核心半径和极限半径都明显小于太阳圈外附近 OC 的半径。我们通过模拟测试背景水平对簇半径确定的影响。他们表明，对于中心星团，半径可能被低估约 10-20%，这表明当前样本测量的小尺寸也反映了与动态演化效应相关的内在特性。这些天体可能遭受了重要的潮汐效应，这可能加速了动力学演化，特别是在最里面的天体 Czernik 37 中。
Star clusters projected on to dense stellar fields in general require field-star (FS) decontam- ination to confirm their nature and derive intrinsic photometric and structural fundamental parameters. This work focuses on the open clusters (OCs) or candidates NGC 5715, Lynga4 , Lynga 9, Trumpler 23, Trumpler 26 and Czernik 37 which are projected within 317 ◦ � 2. ◦ 2 and |b| 2. ◦ 8, against crowded bulge and/or disc fields. To tackle these difficult objects we develop a colour-magnitude diagram FS-decontamination algorithm based on 2MASS J, (J − H) and (J − Ks) data, and respective uncertainties, to detect cluster star excesses over the background. On the other hand, colour-magnitude filters are used to build stellar radial density profiles and mass functions. The results convey compelling evidence that Lynga9 and Czernik 37 are intermediate-age OCs, and their fundamental parameters are measured for the first time. Trumpler 23 is a particularly challenging object, since besides high back- ground level, its field presents variable absorption in near-infrared bands. We confirm it to be an intermediate-age OC. Trumpler 26 is studied in more detail than in previous works, while NGC 5715 and Lynga 4 have fundamental parameters determined for the first time. These OCs are located 0.9-1.6 kpc within the solar circle, with ages similar to that of the Hyades. Structurally, they are well described by King profiles. In all cases, core and limiting radii are significantly smaller than those of nearby OCs outside the solar circle. We test the effect of background levels on cluster radii determinations by means of simulations. They indicate that for central clusters, radii may be underestimated by about 10-20 per cent, which suggests that the small sizes measured for the present sample reflect as well intrinsic properties related to dynamical evolution effects. The objects probably have been suffering important tidal ef- fects that may have accelerated dynamical evolution, especially in Czernik 37, the innermost object.