标题： 聚星团中的CP2恒星：深度Δa测光 显示英文标题

标题： CP2 stars in clusters: deep Delta a-photometry

摘要： 在疏散星团中寻找化学元素奇特（CP）星的研究中，通过光电测光法采样5200埃处的特征通量衰减特征（Maitzen 1976）的方法迄今为止只提供了距离太阳通常不超过1000秒差距的天体的数据。 如果想要研究离太阳更远位置的CP星，就需要用CCD测光法代替传统的测光法。 我们的研究首次展示了CCD测光法在Delta a系统中对于一个明显比之前研究对象更远的富疏散星团的结果，即Melotte 105（2千秒差距，log年龄=8.5）。 与已发表的uvby测光数据比较，我们得出了系统颜色指数g_1-y的校准值，这对于推导出peculiarity指数Delta a是必要的。为此，我们达到了平均精度为0.007星等。 发现了六颗仅有轻微奇特Delta a值的天体，但需要光谱证据和额外的测光数据来证实它们的奇特性。 显示英文摘要

摘要： The search for chemically peculiar (CP) stars in open clusters using photoelectric photometry sampling the presence of the characteristic flux depression feature at 5200A via the Delta a-system (Maitzen 1976) has so far delivered data for objects usually no more distant than 1000 pc from the Sun. If one intends to study the presence of CP stars at larger distances from the Sun, classical photometry has to be replaced by CCD photometry. For the first time, our investigation presents the results of CCD-photometry in the Delta a-system for a rich open cluster which is at a distance clearly beyond hitherto studied objects, Melotte 105 (2 kpc, log age = 8.5). Comparison with published uvby-photometry yields the calibration of the colour index g_1-y of our system, which is necessary for deriving the peculiarity index Delta a. For this we achieve an average accuracy of 0.007 mag. Six objects with only marginally peculiar Delta a-values were found, but spectroscopic and additional photometric evidence is needed to substantiate their peculiarity.