The Oldest Open Star Clusters Revisited: Their Distances, Reddenings and Ages

AST 97-31656 Kenneth Janes Janes 博士正在观测附近的五个疏散星团，其年龄大约超过 2,000,000,000 年。该项目的目标是确定这五个疏散星团中恒星的基本属性，特别是年龄。也许星团年龄最大的不确定性是距离尺度的不确定性和确定星际红化的难度。距离尺度（从最近的恒星到宇宙边缘）取决于并建立在恒星视差的基本确定之上。新的依巴谷星表及其精确的视差的出现使得解决其中一些不确定性成为可能——特别是对于疏散星团。因为附近有大量的 I 族主序星，其中许多比亚矮星具有更好的确定视差，并且因为标准恒星颜色系统是由许多相同的视差恒星定义的，所以可以比球状星团更好地将旧的疏散星团距离尺度与依巴谷联系起来。 PI 正在对这五个星团进行新的高精度光度测量，并开发改进的分析工具以减少数据。这五个星团跨越了银河系盘的年龄，因此它们与该问题非常匹配。该项目依赖于中等孔径望远镜的大量观测以及仔细和广泛的校准。对疏散星团恒星进行定期光度监测将能够识别许多（如果不是大多数）非成员恒星以及变星和双星。可能会发现并表征其他有趣的恒星现象：盾牌座δ星、近距离（但非食）系统中的反射效应，以及次要成分可能与木星一样小的食系统。 ***

AST 97-31656 Kenneth Janes Dr. Janes is observing five nearby open star clusters with approximate ages greater than 2,000,000,000 years. The goal of the project is to determine the fundamental properties, particularly the ages, of stars in these five open clusters. Perhaps the greatest uncertainties in the ages of star clusters are the uncertainty in the distance scale and the difficulty in determining interstellar reddening. The distance scale (from the nearest stars to the edge of the Universe) depends and builds upon the fundamental determination of stellar parallax. The availability of the new Hipparcos Catalog with its precise parallaxes makes it possible to resolve some of these uncertainties - especially for open clusters. Because there are large numbers of nearby Population I main-sequence stars, many of which have better determined parallaxes than the subdwarfs, and because the standard star color systems are defined by many of those same parallax stars, it is possible to do a better job of tying the old open cluster distance scale to the Hipparcos than can be done with globular clusters. The PI is obtaining new high precision photometry of these five clusters, and also developing improved analysis tools to reduce the data. The five clusters span the age of the Milky Way disk, so they are well matched to the problem. The project depends upon large numbers of observations on moderate aperture telescopes combined with careful and extensive calibrations. Regular photometric monitoring of open cluster stars will make it possible to identify many, if not most, of the non-member stars, as well as variable stars and binaries. Other interesting stellar phenomena might be found and characterized: delta Scuti stars, reflection effects in close (but non-eclipsing) systems, and eclipsing systems with secondary components perhaps as small as Jupiter. ***