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RRLYRAE STARS IN NGC 6388 AND NGC 6441: A NEW OOSTERHOFF GROUP?

机译:NGC 6388和NGC 6441中的RRLYRAE明星:新的奥斯特霍夫乐队?

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摘要

NGC 6388 and NGC 6441 are anomalies among Galactic globular clusters in that they cannot be readily placed into either Oosterhoff group I or Oosterhoff group II despite their significant numbers of RR Lyrae variables. The mean pulsation periods, (P_ab), of their RRab variables, at 0.71 and 0.76 days, respectively, are even larger than for Oosterhoff II clusters. Moreover, Oosterhoff II clusters are very metal poof, whereas NGC 6388 and NGC 6441 are the most metal-rich globular clusters known to contain RR Lyrae stars. The location of the NGC 6388 and NGC 6441 RRab variables in the period-amplitude diagram implies that the RR Lyrae stars in those two clusters are brighter than expected for their metallicities. Our results therefore indicate that a universal relationship may not exist between the luminosity and the metallicity of RR Lyrae variables.
机译:NGC 6388和NGC 6441是银河系球状星团中的异常,因为尽管它们具有大量的RR Lyrae变量,但它们不易放置在Oosterhoff I组或Oosterhoff II组中。他们的RRab变量的平均搏动周期(P_ab)分别为0.71和0.76天,甚至比Oosterhoff II集群更大。此外,Oosterhoff II团簇是非常金属的po,而NGC 6388和NGC 6441是已知含RR天琴星的最富金属的球状团簇。 NGC 6388和NGC 6441 RRab变量在周期幅度图中的位置表明,这两个星团中的RR天琴星比它们的金属性要亮。因此,我们的结果表明,RR Lyrae变量的光度和金属度之间可能不存在普遍关系。

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