A spectroscopic study of the open cluster NGC 6475 (M 7) - Chemical abundances from stars in the range Teff = 4500–10 000 K
A spectroscopic study of the open cluster NGC 6475 (M 7) - Chemical abundances from stars in the range Teff = 4500–10 000 K
复制标题
对疏散星团 NGC 6475 (M 7) 的光谱研究 - Teff = 4500–10 000 K 范围内恒星的化学丰度
DOI：
10.1051/0004-6361/200811507
复制
发表时间：
2009
影响因子：
6.5
通讯作者：
I. Saviane
中科院分区：
文献类型：
--
作者：
S. Villanova;G. Carraro;I. Saviane
目标。星团是研究银河系及其邻近星系动力学和化学演化的关键天体，也是检验恒星演化理论最重要的实验室。特别是，化学成分是使用不同的方法从不同类型的恒星（热主序星、冷主序星、水平分支星、RGB星）获得的。我们的首要目标是将这些方法应用于疏散星团 NGC 6475 的恒星，通过获得最重要元素的普查，我们将能够测试它们的一致性。我们的第二个目标是研究表面化学丰度的演化作为恒星演化阶段的函数。我们最终希望为这个集群建立更强大的基本参数。方法。我们从 ESO 数据库中选择了疏散星团 NGC 6475 7 颗恒星的高信噪比高分辨率光谱，覆盖 T eff 范围 4500-10 000 K，光度等级为 V（矮星）和 III（巨星）。我们测定了几种元素的化学丰度。对于热恒星（T eff > 9000 K），我们应用巴尔默线拟合方法获得大气参数，而对于冷恒星（T eff < 6500 K），我们应用Fel/II线的丰度平衡。对于两组明星来说，必须使用不同的阵容。对某些元素（C、N、O、Na、Mg）应用 LTE 近似和 NLTE 校正。许多元素的丰度是通过测量谱线的等效宽度来获得的。对于那些仅具有混合线（O、He）的光谱，将真实光谱与合成光谱进行比较。 V 和 Ba 考虑了超精细结构。结果。首先，我们表明我们使用的两种方法给出的丰度在误差范围内一致。这意味着冷恒星和热恒星的衍生化学含量不存在明显的相对系统效应。另一方面，巨星表现出明显的化学特性，而矮星会影响轻元素（直到硅），也许还有Ba。这可以解释为进化效应。然后，一旦我们对星团的金属丰度有了新的估计（[Fe/H] = +0.03 ± 0.02，[α/Fe] = -0.06 ± 0.02），我们就将合适的等时线拟合到星团的 CMD 以获得基本参数（E(B - V) = 0.08 ± 0.02，(m - M) o = 7.65 ± 0.05，年龄 = 200 ±50）。
Aims. Clusters of stars are key objects for studying the dynamical and chemical evolution of the Galaxy and its neighbors, and are the most important laboratories to test the theory of stellar evolution. In particular, chemical composition is obtained from different kinds of stars (hot main-sequence stars, cool main-sequence stars, horizontal-branch stars, RGB stars) using different methodologies. Our first aim is to apply these methodologies to the stars of the open cluster NGC 6475 and, by obtaining a census of the most important elements, we will be able to test their consistency. Our second aim is to study the evolution of the surface chemical abundances as a function of the evolutionary phase of a star. We finally want to establish more robust fundamental parameters for this cluster. Methods. We selected high S/N high resolution spectra of 7 stars of the open cluster NGC 6475 from the ESO database covering the T eff range 4500-10 000 K and of luminosity class V (dwarf) and III (giants). We determined the chemical abundances of several elements. For hot stars (T eff > 9000 K), we applied the Balmer line fitting method to obtain atmospheric parameters, while for cool stars (T eff < 6500 K), the abundance equilibrium of FeI/II lines. For the two groups of stars, the use of different line-lists was mandatory. LTE approximation together with NLTE correction for some elements (C, N, O, Na, Mg) were applied. The abundances of many elements were obtained by measuring of the equivalent width of spectral lines. For those ones having only blended lines (O, He), real spectra were compared to synthetic ones. Hyperfine structure was taken into account for V and Ba. Results. First of all, we showed that the two methodologies we used give abundances that agree within the errors. This implies that no appreciable relative systematic effects are present for the derived chemical content of cool and hot stars. On the other hand, giants stars show clear chemical peculiarities with respect to the dwarfs affecting light elements (up to Si) and maybe Ba. This can be explained as an evolutionary effect. Then, once we had a new estimation of the metallicity for the cluster ([Fe/H] = +0.03 ± 0.02, [α/Fe] = -0.06 ± 0.02), we fitted suitable isochrones to the CMD of the cluster to obtain the basic parameters (E(B - V) = 0.08 ± 0.02, (m - M) o = 7.65 ± 0.05, Age = 200 ± 50).
织女星高分辨率和高信噪比频谱图集
DOI：
--
发表时间：
2007
期刊：
Publ.Astron.Soc.Japan 59
影响因子：
--
作者：
Takeda;Y.
通讯作者：
Y.