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arXiv 0706.2102astro-ph
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年轻疏散星团Blanco 1的低质量函数：从30 Mj到3 Mo

The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo

Estelle Moraux, Jerome Bouvier, John Stauffer, David Barrado Y Navascues, Jean-Charles Cuillandre

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18 pages, 15 figures and 5 tables accepted in A&A
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摘要：

我们用CFH 12 K相机对年轻的疏散星团Blanco 1进行了深宽视场光学巡天，观测范围从I带和z带到Iz ~ 24，观测范围为2.3平方度。考虑到两个不同的集群年龄（1亿和1.5亿年），我们选择集群成员候选人的基础上，他们在（I，I-z）CMD相对于等时线的位置，并估计污染的前景晚型场矮星使用统计参数，红外测光和低分辨率光谱。我们发现，我们的调查应包含约57%的集群成员在0.03-0.6钼质量范围内，包括30-40褐矮星。候选者的径向分布提供了证据，表明质量偏析已经发生在集群中。我们考虑到它来估计整个恒星/亚恒星边界的集群质量函数。我们发现，在0.03Mo和0.6Mo之间，团簇的质量分布并不依赖于它的确切年龄，并很好地代表了一个单一的幂律，与指数α =0.69 +/- 0.15。在从0.03Mo到3 Mo的整个质量域上，质量函数通过对数正态函数更好地拟合，其中m0=0.36 +/-0.07Mo和sigma=0.58 +/-0.06。Blanco 1质量函数、其他年轻疏散星团的MF和银盘MF之间的比较表明，IMF，从亚恒星域到更高质量的部分，并不依赖于初始条件。我们讨论了这一结果的影响，到目前为止发展的理论来解释起源的质量分布。

英文摘要：

We performed a deep wide field optical survey of the young (~100-150 Myr) open cluster Blanco1 to study its low mass population well down into the brown dwarf regime and estimate its mass function over the whole cluster mass range.The survey covers 2.3 square degrees in the I and z-bands down to I ~ z ~ 24 with the CFH12K camera. Considering two different cluster ages (100 and 150 Myr), we selected cluster member candidates on the basis of their location in the (I,I-z) CMD relative to the isochrones, and estimated the contamination by foreground late-type field dwarfs using statistical arguments, infrared photometry and low-resolution optical spectroscopy. We find that our survey should contain about 57% of the cluster members in the 0.03-0.6 Mo mass range, including 30-40 brown dwarfs. The candidate's radial distribution presents evidence that mass segregation has already occured in the cluster. We took it into account to estimate the cluster mass function across the stellar/substellar boundary. We find that, between 0.03Mo and 0.6Mo, the cluster mass distribution does not depend much on its exact age, and is well represented by a single power-law, with an index alpha=0.69 +/- 0.15. Over the whole mass domain, from 0.03Mo to 3Mo, the mass function is better fitted by a log-normal function with m0=0.36 +/- 0.07Mo and sigma=0.58 +/- 0.06. Comparison between the Blanco1 mass function, other young open clusters' MF, and the galactic disc MF suggests that the IMF, from the substellar domain to the higher mass part, does not depend much on initial conditions. We discuss the implications of this result on theories developed to date to explain the origin of the mass distribution.

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