Chamaleon I和TW Hydrae协会晚期M型成员的物理参数：尘埃沉降、年龄分散和活动
Physical parameters of late M-type members of Chamaleon I and TW Hydrae Association: Dust settling, age dispersion and activity
摘要：
虽然中晚期M型矮星是我们恒星邻居中最常见的恒星，但我们对这些天体的了解仍然有限。开放的问题包括它们的角动量的演变，内部结构，大气中的尘埃沉降，人口中的年龄分布。此外，在年轻时，晚型M的质量低于氢燃烧极限，因此是关于褐矮星形成机制的争论中的关键对象。在这项工作中，我们确定和详细研究的两个样本的年轻，晚M型源属于Chamaeleon I暗云或TW长蛇座协会的物理参数，并将它们与其他年轻的集群，也为老年人，领域，矮星的文献中获得的结果进行比较。我们使用多波长光度法来构建和分析SED，以确定光球和磁盘存在的一般属性。我们还使用低分辨率光学和近红外光谱来研究活动，吸积，重力和有效的温度敏感指标。我们提出了一个基于VO的光谱指数，是温度和年龄敏感。我们得出的物理参数，使用独立的技术确认已经共同的功能/问题的年龄/光度蔓延。特别是，我们强调两个褐矮星显示非常相似的温度，但明显不同的表面重力（解释调用极端早期吸积）。我们还展示了如何，尽管在理论模型中的尘埃处理有很大的改进，但在同时再现这些冷年轻物体的光学和近红外特征方面仍有进一步进展的空间。
英文摘要：
Although mid-to-late type M dwarfs are the most common stars in our stellar neighborhood, our knowledge of these objects is still limited. Open questions include the evolution of their angular momentum, internal structures, dust settling in their atmospheres, age dispersion within populations. In addition, at young ages, late-type Ms have masses below the hydrogen burning limit and therefore are key objects in the debate on the brown dwarf mechanism of formation. In this work we determine and study in detail the physical parameters of two samples of young, late M-type sources belonging to either the Chamaeleon I Dark Cloud or the TW Hydrae Association and compare them with the results obtained in the literature for other young clusters and also for older, field, dwarfs. We used multi-wavelength photometry to construct and analyze SEDs to determine general properties of the photosphere and disk presence. We also used low resolution optical and near-infrared spectroscopy to study activity, accretion, gravity and effective temperature sensitive indicators. We propose a VO-based spectral index that is both temperature and age sensitive. We derived physical parameters using independent techniques confirming the already common feature/problem of the age/luminosity spread. In particular, we highlight two brown dwarfs showing very similar temperatures but clearly different surface gravity (explained invoking extreme early accretion). We also show how, despite large improvement in the dust treatment in theoretical models, there is still room for further progress in the simultaneous reproduction of the optical and near-infrared features of these cold young objects.
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