CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited
CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited
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球状星团 NGC 5053 的 CCD 时间序列光度测量：重新审视 RR Lyrae、Blue Stragglers 和 SX Phoenicis 星
DOI：
10.1111/j.1365-2966.2009.15931.x
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发表时间：
2009
影响因子：
4.8
通讯作者：
D. Bramich
中科院分区：
文献类型：
--
作者：
A. Ferro;S. Giridhar;D. Bramich
我们报道了球状星团NGC5053的CCDV、r和I时间序列光度测量结果。已知的8颗天琴座RR天琴座恒星在我们的图像中出现了新的最大光亮时刻，并对它们的周期进行了修正。对它们的V光曲线进行傅立叶分解，估计其物理参数。讨论了基于傅里叶变换的铁丰度、温度、质量和半径的精度。发现了5颗已知的SX Phe恒星的新周期，并对它们的长期周期变化进行了批判性的讨论。天琴座RR恒星的平均铁丰度为[Fe/H]~-1.97±0.16，本分析不支持较低的铁丰度。天琴座RR星的绝对星等定标得到的平均真距离模数为16.12±0.04，或距离为16.7±0.3kpc。观测彩色星等图(CMD)与理论等时线的比较表明，该星系团的年龄为12.5±2.0Gyr。对所有已报道的蓝离散星(BS)及其V、I星等进行了仔细的鉴定，得出结论：BS12、BS22、BS23和BS24不是蓝离散星。另一方面，报道了三个新的BS。在七颗黑洞中发现了可变性，其中五颗很可能是SX Phe类型，还有一颗红巨星。新的SX Phe恒星遵循已建立的周期-光度关系，并指示与天琴座RR恒星的距离一致的距离。
We report the results of CCD V, r and I time-series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images, and their periods are revised. Their V light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier-based iron abundances, temperatures, masses and radii is given. New periods are found for the five known SX Phe stars, and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H] ~ - 1.97 ± 0.16 and lower values are not supported by the present analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an average true distance modulus of 16.12 ± 0.04 or a distance of 16.7 ± 0.3 kpc. Comparison of the observational colour magnitude diagram (CMD) with theoretical isochrones indicates an age of 12.5 ± 2.0 Gyr for the cluster. A careful identification of all reported blue stragglers (BS) and their V, I magnitudes leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other hand, three new BS are reported. Variability was found in seven BS, very likely of the SX Phe type in five of them, and in one red giant star. The new SX Phe stars follow established Period-Luminosity relationships and indicate a distance in agreement with the distance from the RR Lyrae stars.