标题： CCD 光度学对球状星团 Omega 半人马座的研究。 I. 由 Caby 光度学得到的 RR 大陵变量星的金属丰度 显示英文标题

标题： CCD Photometry of the Globular Cluster Omega Centauri. I. Metallicity of RR Lyrae Stars from Caby Photometry

摘要： 我们利用Caby测光系统的hk指数，给出了球状星团Omega Centauri中131颗造父变星的新金属丰度测量值。 与Delta-S和其他方法相比，hk方法在确定造父变星的金属丰度方面具有明显优势，并使我们获得了迄今为止该星团造父变星中最完整且最一致的金属丰度数据。 对于与Butler等人（1978年）和Gratton等人（1986年）的Delta-S观测共有的造父变星，我们发现我们的金属丰度[Fe/H](hk)系统性地偏离了它们的Delta-S金属丰度，而对于观测良好的场星RRab型造父变星，我们的[Fe/H](hk)与先前的光谱测量结果一致。我们认为这是由于与该星团相关的早期Delta-S观测存在较大的误差所致。 由我们的新数据得出的Mv(RR)-[Fe/H]和周期偏移-[Fe/H]关系与Lee（1991年）提出的演化模型一致，证实了造父变星的亮度不仅取决于金属丰度，还取决于演化状态。 通过使用周期-振幅图，我们还识别出了在-1.9<[Fe/H]<-1.5范围内高度演化的RRab型造父变星，这与合成水平分支模型预测的结果一致。 显示英文摘要

摘要： We present new measurements of the metallicity of 131 RR Lyrae stars in the globular cluster Omega Centauri, using the hk index of the Caby photometric system. The hk method has distinct advantages over Delta-S and other techniques in determining the metallicity of RR Lyrae stars, and has allowed us to obtain the most complete and homogeneous metallicity data to date for the RR Lyrae stars in this cluster. For RR Lyrae stars in common with the Delta-S observations of Butler et al. (1978) and Gratton et al. (1986), we have found that our metallicities, [Fe/H](hk), deviate systematically from their Delta-S metallicity, while our [Fe/H](hk) for well observed field RRab stars are consistent with previous spectroscopic measurements. We conclude that this is due to the larger errors associated with the previous Delta-S observations for this cluster. The Mv(RR) - [Fe/H] and period-shift - [Fe/H] relations obtained from our new data are consistent with the evolutionary models predicted by Lee (1991), confirming that the luminosity of RR Lyrae stars depends on evolutionary status as well as metallicity. Using the period - amplitude diagram, we have also identified highly evolved RRab stars in the range of -1.9 < [Fe/H] < -1.5, as predicted from the synthetic horizontal-branch models.