Erratum: Precise reddening and metallicity of NGC 6752 from FLAMES spectra
Erratum: Precise reddening and metallicity of NGC 6752 from FLAMES spectra
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DOI：
10.1051/0004-6361:20053019
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发表时间：
2005-05
影响因子：
6.5
通讯作者：
R. Gratton;A. Bragaglia;E. Carretta;F. Angeli;S. Lucatello;Y. Momany;G. Piotto;A. U. D. Padova;I. A. Bologna;Astron. Dept. Bologna Univ.;Observatoire de la Côte d'Azur;Nice
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文献类型：
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作者：
R. Gratton;A. Bragaglia;E. Carretta;F. Angeli;S. Lucatello;Y. Momany;G. Piotto;A. U. D. Padova;I. A. Bologna;Astron. Dept. Bologna Univ.;Observatoire de la Côte d'Azur;Nice
球状星团的准确红度可以通过比较使用无红指示剂（Hα）的温度获得的色温关系与标准色温校准给出的色温关系来获得。这种推导的主要困难是，由于对每个单独的星星去除仪器特征的不确定性，单个恒星的温度误差很大。FLAMES在VLT 2上提供的大量多路复用机会使我们能够从一次1300秒的曝光中获得以Hα为中心的光谱，分辨率为R = 6000和5 < S/N < 50。这组光谱被用来获得有效的温度从拟合的Her配置文件与典型的误差约为±200 K和红化估计与个人的误差为0.05马格。平均所有个人的红化，高精度的红化估计得到的集群：E（B - V）= 0.046 ± 0.005。同样的曝光提供了红巨星分支隆起附近7颗恒星的UVES光谱，分辨率为40000和20 < S/N < 40。这些光谱，结合来自颜色的温度（根据我们的高精度红化值进行了校正），提供了Fe丰度，内部误差为0.026 dex，平均金属丰度[Fe/H] = -1.48 ± 0.01 ± 0.06 dex（随机+系统）。获得了其他几种元素的丰度，例如，可以精确估计α元素和Fe之间的比值（[α/Fe| = +0.27 ± 0.01）。从UVES数据中可以明显看出O-Na的相互关系，这与过去的结果一致。这一分析显示了FLAMES在球状星团分析中的作用：通过这里描述的程序获得的精确的红化和金属丰度，结合星团动力学或主序拟合的距离测定，以及高质量的颜色-星等图，可以推导出单个球状星团的年龄，误差低于1 Gyr。
Accurate reddenings for Globular Clusters could be obtained by comparing the colour-temperature relation obtained using temperatures from a reddening-free indicator (Hα) with that given by standard colour-temperature calibrations. The main difficulty in such derivations is the large errors in temperatures for individual stars due to uncertainties on the removal of instrumental signature for each individual star. The large multiplexing opportunity offered by FLAMES at VLT2 allowed us to obtain spectra centred on Hα at a resolution of R = 6000 and 5 < S/N < 50 for 120 stars near the turn-off of NGC 6752 with GIRAFFE from a single 1300 seconds exposure. This set of spectra was used to derive effective temperatures from fittings of Her profiles with typical errors of about ±200 K and reddening estimates with individual errors of 0.05 mag. Averaging all individual reddenings, a high precision reddening estimate was obtained for the cluster: E(B - V) = 0.046 ± 0.005. The same exposure provided UVES spectra of seven stars near the red giant branch bump at a resolution of 40000 and 20 < S/N < 40. These spectra, combined with temperatures from colours (corrected for our high precision reddening value), provided Fe abundances with internal errors of 0.026 dex and with average metallicity [Fe/H] = -1.48 ± 0.01 ± 0.06 dex (random + systematic). Abundances were obtained for several other elements, allowing e.g. an accurate estimate of the ratio between the α-elements and Fe ([α/Fe| = +0.27 ± 0.01). The O-Na anticorrelation is evident from our UVES data, in agreement with past results. This analysis shows the power of FLAMES for analysis of globular clusters: the accurate reddenings and metal abundances obtained by a procedure like that described here, combined with distance determinations from cluster dynamics or main sequence fitting, and high quality colour-magnitude diagrams, could allow derivation of ages with errors below 1 Gyr for individual globular clusters.