CCD Photometry of RR Lyrae Stars

天琴座RR星是一组脉动恒星，它们出现在银河系的古老区域，如球状星团和一般的银河晕中。由于已知这些变星的光度几乎相同，哈洛·沙普利在本世纪初首次使用它们作为“标准蜡烛”来确定太阳到银河系中心的距离。此外，由于这些恒星中的许多被认为是在大爆炸后不久的银河系崩塌的早期阶段形成的，它们的年龄对确定宇宙的年龄很重要。最近的研究表明，天琴座RR恒星的亮度毕竟与它们的金属含量和年龄有剩余的依赖关系。此外，关于球状星团是在大爆炸后不久形成的，还是在较长一段时间内形成的，还有一个重要的长期争议。要解决这些问题，需要仔细确定这些恒星在不同球状星团中的发生率，它们的周期分布，以及它们的发光体对其表面温度的依赖。过去提高我们对天琴座RR恒星性质的认识的努力，由于它们的模糊和聚集在天空中致密的星团中而受到阻碍。首席调查者建议监测大量天琴座RR恒星在贫金属和富金属球状星团中的光度变化，以分离出这些物理特征的剩余依赖关系。调查人员将在一个小型望远镜上使用现代电荷耦合装置来执行这项工作。这类设备即使对光输出的微小变化也很敏感。此外，由于许多恒星图像可以独立地聚焦在探测器表面上，所以可以在同一图像上使用不变的恒星来减去仪器和地球大气中的不稳定引起的灵敏度变化。

RR Lyrae variables are a group of pulsating stars that occur in old regions of the Galaxy, such as in globular clusters and the general galactic halo. Because these variable stars are all known to have nearly the same luminosity, they were first used as "standard candles" by Harlow Shapley earlier this century to determine the distance from the Sun to the Galaxy's center. Moreover, since many of these stars are thought to have been formed during the early stages of the Galaxy's collapse soon after the Big Bang, their age is important in determining the age of the Universe. Recent work has shown that the luminosities of RR Lyrae stars have a residual dependence after all on their metal content and age. Additionally, there is an important standing controversy over whether globular clusters were all formed soon after the Big Bang or over an extended period of time. To resolve these issues requires a careful determination of the incidence of these stars among various globular clusters, the distribution of their periods, and the dependence of their luminosiites on their surface temperatures. Past efforts to improve our knowledge of the properties of RR Lyrae stars have been hampered by their faintness and their crowding together in dense star conglomerates in the sky. The Principle Investigator proposes to monitor the luminosity variations of a large number of RR Lyrae stars in metal-poor and metal-rich globular clusters to separate out the residual dependences of these physical characteristics. The Investigator will use a modern Charge Coupled Device on a small telescope to perform this work. Such devices are sensitive even to small variations in light output. Additionally, because many star images may be focussed independently on the detector surface, one may use non-variable stars on the same image to subtract out changes in sensitivity caused by instabilities in the instrument and the Earth's atmosphere.