标题： ugriz系统的红水平分支星的绝对星等 显示英文标题

标题： The Absolute Magnitudes of Red Horizontal Branch Stars in the ugriz System

摘要： 根据An及其合作者提供的八个球状星团和一个疏散星团中心区域的测光数据，我们在(g-r)0-g0图上选择红水平分支（RHB）星，并对它们在SDSS ugriz系统中的颜色和绝对星等分布进行统计研究。 同时，通过文献中gri与VRI之间的转换公式计算出Johnson VRI系统的绝对星等。 通过数据的线性回归建立了绝对星等作为金属丰度和年龄函数的刻度。 结果发现，这些刻度中的金属丰度系数从蓝色$u$滤光片到红色$z$滤光片逐渐减小，而年龄系数则增大。 Mi = 0.06[Fe/H] + 0.040t + 0.03的刻度具有最小的0.04mag离散，因此当使用RHB星作为距离指示器时，i是在$ugriz$系统中最佳的滤光片。 我们数据的MI刻度与红团簇星的MI刻度比较表明，由于其对年龄有显著依赖性，先前提出的$I$滤光片在距离测定中可能并不比V滤光片更好。 显示英文摘要

摘要： Based on photometric data of the central parts of eight globular clusters and one open cluster presented by An and his collaborators, we select red horizontal branch (RHB) stars in the (g-r)0-g0 diagram and make a statistical study of the distributions of their colors and absolute magnitudes in the SDSS ugriz system. Meanwhile, absolute magnitudes in the Johnson VRI system are calculated through the translation formulae between gri and VRI in the literature. The calibrations of absolute magnitude as functions of metallicity and age are established by linear regressions of the data. It is found that metallicity coefficients in these calibrations decrease, while age coefficients increase, from the blue $u$ filter to the red $z$ filter. The calibration of Mi= 0.06[Fe/H]+0.040t+0.03 has the smallest scatter of 0.04 mag, and thus i is the best filter in the $ugriz$ system when RHB stars are used for distance indicators. The comparison of the MI calibration from our data with that from red clump stars indicates that the previous suggestion that the $I$ filter is better than the V filter in distance determination may not be true because of its significant dependence on age.