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arXiv 1003.3658astro-ph.GA
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M54(NGC6715)中的变星星族

The population of variable stars in M54 (NGC6715)

A. Sollima, C. Cacciari, M. Bellazzini, S. Colucci

摘要:

本文对位于人马座矮球状星系中心的球状星团M54的13 '× 13'视场内的177颗变星进行了新的B、V和I CCD时间序列测光,其中94颗是新发现的变星。总样本包括2颗造父变星、144颗RR型天琴座星(108颗RR 0和36颗RR 1)、3颗SX型凤凰座星、7颗食双星(5颗W UMA和2颗大陵五双星)、3颗分类不确定变星和18颗长周期变星。大部分的天琴座RR变星可能属于M54。提供了所有观测到的短周期变量的星历。M54 RR型天琴座变星的脉动性质接近奥斯特霍夫I型星团,但也存在大量的长周期ab型RR型天琴座。我们利用观测到的天琴座RR的性质来估计M54的红化和距离模,E(B-V)=0.16 +/- 0.02和(m-M)_0=17.13 +/- 0.11,分别与最近的估计值非常吻合。金属丰度已估计的一个子集的47 RR天琴座恒星,特别是质量好的光变曲线,从傅立叶参数的V光变曲线。得到的金属丰度分布呈对称钟形,平均值<[Fe/H]>=-1.65,标准差σ =0.16 dex。有七颗恒星被认为可能属于人马座星系,基于它们的金属丰度过高或过低。这个证据,如果得到证实,可能表明这个星系中的老恒星跨越了广泛的金属丰度。

英文摘要:

We present new B, V and I CCD time-series photometry for 177 variable stars in a 13'X 13' field centered on the globular cluster M54 (lying at the center of the Sagittarius dwarf spheroidal galaxy), 94 of which are newly identified variables. The total sample is composed of 2 anomalous Cepheids, 144 RR Lyrae stars (108 RR0 and 36 RR1), 3 SX Phoenicis, 7 eclipsing binaries (5 W UMA and 2 Algol binaries), 3 variables of uncertain classification and 18 long-period variables. The large majority of the RR Lyrae variables likely belong to M54. Ephemerides are provided for all the observed short-period variables. The pulsational properties of the M54 RR Lyrae variables are close to those of Oosterhoff I clusters, but a significant number of long-period ab type RR Lyrae are present. We use the observed properties of the RR Lyrae to estimate the reddening and the distance modulus of M54, E(B-V)=0.16 +/- 0.02 and (m-M)_0=17.13 +/- 0.11, respectively, in excellent agreement with the most recent estimates. The metallicity has been estimated for a subset of 47 RR Lyrae stars, with especially good quality light curves, from the Fourier parameters of the V light curve. The derived metallicity distribution has a symmetric bell shape, with a mean of <[Fe/H]>=-1.65 and a standard deviation sigma=0.16 dex. Seven stars have been identified as likely belonging to the Sagittarius galaxy, based on their too high or too low metallicity. This evidence, if confirmed, might suggest that old stars in this galaxy span a wide range of metallicities.

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