标题： vbyCaHbeta 星团的CCD photometry。 VIII. 超金属富集的老年疏散星团NGC 6791 显示英文标题

标题： vbyCaHbeta CCD Photometry of Clusters. VIII. The Super-Metal Rich, Old Open Cluster NGC 6791

摘要： 使用中间带vbyCaHbeta系统的CCD光度法对富金属的老年疏散星团NGC 6791进行了研究。 初步分析得出[Fe/H]高于+0.4，且有异常高的消光，并且年龄低于5 Gyr。 (b-y)_0与给定温度下[Fe/H]之间的重新校准表明，传统的颜色-金属丰度关系低估了高金属丰度时转折点恒星的颜色。 通过修正的关系，NGC 6791的hk得到的金属丰度和消光分别为[Fe/H] = +0.45 ± 0.04 和 E(b-y) = 0.113 ± 0.012 或 E(B-V) = 0.155 ± 0.016。 使用相同的技术，对NGC 6253的光度重新分析得到了[Fe/H] = +0.58 ± 0.04 和 E(b-y) = 0.120 ± 0.018 或 E(B-V) = 0.160 ± 0.025。 所引用的误差包括内部误差和外部误差。 对于NGC 6791，从m_1得到的金属丰度比从hk得到的低一个因子二，这一结果可能与该星团DDO测光中始终偏低的金属丰度以及高色散光谱中发现的碳缺乏有关。 E(B-V)与银河系消光图预测的值相同。 当E(B-V) = 0.15且[Fe/H] = +0.45时，可用的等年龄线预测年龄为7.0 ± 1.0 Gyr，视向距离模数为(m-M) = 13.60 ± 0.15，不确定性主要来源于等年龄线之间的一致性问题。 使用修订后的较低消光重新分析NGC 6253确认，在hk和m_1金属丰度标度上，尽管NGC 6253的年龄不到NGC 6791的一半，但它的金属丰度至少与NGC 6791一样高，甚至可能更丰富。 显示英文摘要

摘要： CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-rich, old open cluster, NGC 6791. Preliminary analysis led to [Fe/H] above +0.4 with an anomalously high reddening and an age below 5 Gyr. A revised calibration between (b-y)_0 and [Fe/H] at a given temperature shows that the traditional color-metallicity relations underestimate the color of the turnoff stars at high metallicity. With the revised relation, the metallicity from hk and the reddening for NGC 6791 become [Fe/H] = +0.45 +/- 0.04 and E(b-y) = 0.113 +/- 0.012 or E(B-V) = 0.155 +/- 0.016. Using the same technique, reanalysis of the photometry for NGC 6253 produces [Fe/H] = +0.58 +/-0.04 and E(b-y) = 0.120 +/- 0.018 or E(B-V) = 0.160 +/- 0.025. The errors quoted include both the internal and external errors. For NGC 6791, the metallicity from m_1 is a factor of two below that from hk, a result that may be coupled to the consistently low metal abundance from DDO photometry of the cluster and the C-deficiency found from high dispersion spectroscopy. E(B-V) is the same value predicted from Galactic reddening maps. With E(B-V) = 0.15 and [Fe/H] = +0.45, the available isochrones predict an age of 7.0 +/- 1.0 Gyr and an apparent modulus of (m-M) = 13.60 +/- 0.15, with the dominant source of the uncertainty arising from inconsistencies among the isochrones. The reanalysis of NGC 6253 with the revised lower reddening confirms that on both the hk and m_1 metallicity scales, NGC 6253, while less than half the age of NGC 6791, remains at least as metal-rich as NGC 6791, if not richer.