Departamento de Astronomìa, Universidad de Concepción, Casilla 160-C, Concepciòn, Chile.
Nature. 2012 Apr 4;484(7392):75-7. doi: 10.1038/nature10966.
RR Lyrae pulsating stars have been extensively used as tracers of old stellar populations for the purpose of determining the ages of galaxies, and as tools to measure distances to nearby galaxies. There was accordingly considerable interest when the RR Lyrae star OGLE-BLG-RRLYR-02792 (referred to here as RRLYR-02792) was found to be a member of an eclipsing binary system, because the mass of the pulsator (hitherto constrained only by models) could be unambiguously determined. Here we report that RRLYR-02792 has a mass of 0.26 solar masses M[symbol see text] and therefore cannot be a classical RR Lyrae star. Using models, we find that its properties are best explained by the evolution of a close binary system that started with M[symbol see text] and 0.8M[symbol see text]stars orbiting each other with an initial period of 2.9 days. Mass exchange over 5.4 billion years produced the observed system, which is now in a very short-lived phase where the physical properties of the pulsator happen to place it in the same instability strip of the Hertzsprung-Russell diagram as that occupied by RR Lyrae stars. We estimate that only 0.2 per cent of RR Lyrae stars may be contaminated by systems similar to this one, which implies that distances measured with RR Lyrae stars should not be significantly affected by these binary interlopers.
天琴座 RR 变星被广泛用作示踪年老恒星群体的指标，以确定星系的年龄，并作为测量附近星系距离的工具。当天琴座 RR 变星OGLE-BLG-RRLYR-02792（这里称为 RRLYR-02792）被发现是一个食双星系统的成员时，人们对此产生了浓厚的兴趣，因为脉动器的质量（迄今为止仅受模型限制）可以明确确定。在这里，我们报告说 RRLYR-02792 的质量为 0.26 个太阳质量 M[符号见正文]，因此不可能是经典的 RR 变星。使用模型，我们发现它的性质最好通过一个紧密双星系统的演化来解释，该系统由 M[符号见正文]和 0.8M[符号见正文]恒星组成，它们以 2.9 天的初始周期相互绕转。在 54 亿年的时间里进行了质量交换，产生了我们现在观察到的系统，该系统目前处于非常短暂的阶段，脉动器的物理性质恰好使其处于与 RR 变星相同的赫罗图不稳定带中。我们估计，只有 0.2%的 RR 变星可能会受到类似的系统污染，这意味着使用 RR 变星测量的距离不应该受到这些双星闯入者的显著影响。
