Long-term photometric monitoring of RR Lyrae stars in Messier 3
Long-term photometric monitoring of RR Lyrae stars in Messier 3
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Messier 3 中天琴座 RR 星的长期光度监测
DOI：
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发表时间：
2011
期刊：
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通讯作者：
J. Claver
中科院分区：
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作者：
J. Jurcsik;G. Hajdu;B. Szeidl;K. Ol'ah;J. Kelemen;'A. s'odor;A. Saha;P. Mallick;J. Claver
在测光观测的120年时基上，研究了球状星团M3（M3）中134颗天琴座RR型星的周期变化行为。表现出最规则行为的子样本变量的平均周期变化率（β = 0.01 d Myr−1）与基于水平分支恒星演化模型的理论预期非常一致。然而，很大一部分变量显示的周期变化与进化的预期相矛盾。在所研究的134颗恒星中，只有54颗变星的周期变化行为是规则的（恒定或线性变化），在23种情况下，轻微的不规则性叠加在规则变化上，其余57颗恒星显示不规则的周期变化。50%的RRab星的光变曲线是不稳定的，也就是说，这些变星表现出Blazhko调制。大部分变星具有特殊的行为（表现出光变曲线调制和/或不规则的O−C变化），这表明，可能有规律的周期变化与其演化阶段不一致的变星也可能表现出脉动光变曲线和/或周期的某种不稳定性，但现有的观测还没有揭示这一点。在某些恒星中，Blazhko效应的时间外观，以及在某些情况下脉动周期的不规则快速变化之前或之后的70-90年的规则变化，支持了这一假设。
精确的傅立叶参数的光变曲线的RRab变量来自所有可用的CCD数据。在奥斯特霍夫I序列上的大的、均匀的恒星样本使我们能够研究显示增加和减少的周期变化的变量的光变曲线的特性。结果表明，在给定的相位差下，增周期变星的振幅比减周期变星的振幅平均小0.002-0.014等。此外，在一个给定的周期，他们的相位差往往是小0.03-0.07拉德比变量的相位差与减少周期。通过蒙特卡罗模拟证明了检测到的差异的真实性。
The period-change behaviour of 134 RR Lyrae stars in the globular cluster Messier 3 (M3) is investigated on the ∼120 yr time-base of the photometric observations. The mean period-change rates (β≈ 0.01 d Myr−1) of the subsamples of variables exhibiting the most regular behaviour are in good agreement with theoretical expectations based on horizontal branch stellar evolution models. However, a large fraction of variables show period changes that contradict the evolutionary expectations. Among the 134 stars studied, the period-change behaviour of only 54 variables is regular (constant or linearly changing), slight irregularities are superimposed on the regular variations in 23 cases and the remaining 57 stars display irregular period variations. The light curve of ∼50 per cent of the RRab stars is not stable, that is, these variables exhibit Blazhko modulation. The large fraction of variables with peculiar behaviour (showing light-curve modulation and/or irregular O−C variation) indicates that, probably, variables with regular period changes incompatible with their evolutionary stages also could display some kind of instability of the pulsation light curve and/or period, but the available observations have not disclosed it yet. The temporal appearance of the Blazhko effect in some stars, and the 70–90 yr long regular changes preceded or followed by irregular, rapid changes of the pulsation period in some cases, supports this hypothesis.
Accurate Fourier parameters of the light curves of the RRab variables are derived from all the available CCD data. The large, homogeneous sample of stars on the Oosterhoff I sequence enable us to investigate the characteristics of the light curves of the variables showing increasing and decreasing period changes. It is found that, at a given phase-difference value, period-increasing variables have 0.002–0.014 mag smaller amplitudes on average than period-decreasing variables have. Also, at a given period, their phase differences tend to be smaller by 0.03–0.07 rad than the phase differences of variables with decreasing periods. The realness of the detected differences is proven by Monte Carlo simulations.