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arXiv 1106.4560astro-ph.GA
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河外年轻大质量星团的分辨测光

Resolved photometry of extragalactic young massive star clusters

S. S. Larsen, S. E. de Mink, J. J. Eldridge, N. Langer, N. Bastian, A. Seth, L. J. Smith, J. Brodie, Y. N. Efremov

备注：
15 pages, 12 figures, accepted for publication in A&A
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摘要：

本文给出了星系NGC 1313、NGC 1569、NGC 1705、NGC 5236和NGC 7793中7个年轻大质量星系团的色星等图。星团的年龄在500万年到5000万年之间，质量为10^5 - 10^6 Msun。虽然拥挤使我们无法在星团的中心区域进行测光，但我们仍然能够在每个最富有的星团中测量多达30-100颗超巨星，以及更明亮的主序星。由此产生的CMD和光度功能与人工生成的集群，旨在再现光度误差和完整性尽可能现实的测光比较。与以前的研究一致，我们的CMD显示没有明显的差距之间的H-燃烧的主序星和He-燃烧的超巨星，相反，常见的恒星等时线的预测。一般来说，等时线也无法与观测到的红蓝超巨星的数量比相匹配，尽管将蓝超巨星与主序星分离的困难使这种比较变得复杂。在某些情况下，我们观察到超巨星的光度有很大的差异（1-2等），这是观测误差所不能解释的。通过在模型中加入1000万至3000万年的年龄差，可以重现这种年龄差。然而，年龄差异不能完全解释观测到的CMD形态，其他过程，如相互作用的双星演化，也可能发挥作用。

英文摘要：

We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793. The clusters have ages in the range 5-50 million years and masses of 10^5 -10^6 Msun. Although crowding prevents us from obtaining photometry in the central regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. This spread can be reproduced by including an age spread of 10-30 million years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role.

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