了解在初期恆星體中的環星盤內的氣體是如何消散、塵埃是如何成長、並且恆星盤是如何演進成碎屑盤，能提供關鍵的資訊以增進我們對行星形成的認識。近年來的觀測發現，恆星盤可能有一種以上的演化路徑。為了能夠由實際物理參數辨別恆星盤演化的路徑，我們提出一套基於光譜型態的統計分析方法。在這方法中我們採用了兩個主要參數λturn-off和αexcess.λturn-off定義為光譜中能夠測量到excess的最短波長；αexcess定義為excess部分的斜率。我們比較由Robitaille et al. (2006)初期恆星體模型所預測的λturn-off和αexcess以及由Spitzer c2d計畫所實際觀測到的λturn-off和αexcess，並且分析恆星盤在恆星盤質量-恆星盤內徑的分布。這樣的分布顯示了恆星盤有兩種獨立的演化路徑，分別符合典型的恆星盤演化模型與同步消散的恆星盤演化模型。另外我們發現在Chamaeleon II和Lupus區域內缺少按照典型方式演化的恆星盤，而不像在Ophiuchus、Perseus、Serpens中存在著兩種不同的恆星盤。這樣的差異可能是肇因於典型恆星盤擁有較快的演化速度。

Understanding how circumstellar disks of young stellar objects dissipate gas and small dust grains and evolve into debris disks is crucial for advancing our knowledge in planet formation. Recent observations suggest that multiple pathways may exist for the disk evolution. In order to clearly identify the evolutionary paths by variation of physical parameters, here we perform a statistical analysis on two morphological parameters of the spectral energy distributions (SEDs), λturn-off and αexcess, where λturn-off is the wavelength where the disk flux equal to the stellar flux, and αexcess is the spectral slope at wavelengths longer than λturn-off. We compare λturn-off and αexcess from the theoretical SEDs by Robitaille et al. (2006) with those of the observational results from the Spitzer's c2d Legacy project, and found the distribution of transition disks in disk mass and disk inner radius space. The distribution suggests there are at least two independent evolutionary paths, consistent with, respectively, the typical transition disk scenario and homologously depleted disk scenario. In addition, we find that the Chamaeleon II and Lupus clouds lack of typical transition disks, unlike Ophiuchus, Perseus or Serpens clouds. The difference may be explained by a shorter evolutionary timescale for typical transition disks than that for homologously depleted disks.

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