通过硅酸盐、冰和毫米观测表征嵌入的年轻恒星天体的性质
Characterizing the nature of embedded young stellar objects through silicate, ice and millimeter observations
摘要：
（节略）对YSO的分类办法是以评价周围包层的耗散程度为基础的，其主要影响是来自中心YSO的光辐射的消光和远红外线的再发射。由于消光是沿视线方向柱密度的一种性质，当从侧面观察时，原行星盘的存在可能会导致错误的分类。我们使用轴对称三维辐射转移程序RADMC和RADICAL进行了辐射转移计算，显示了不同几何形状对YSO演化阶段主要指标的影响，如2和24 μ m之间的通量斜率、测热温度以及硅酸盐和冰的光学深度。我们表明，从中间角度来看，系统的“经典”指标的演变准确地跟踪信封列密度，他们都同意彼此。另一方面，对于大于~ 65度的倾角，边缘上系统被错误分类。特别是，硅酸盐的发射，典型的前主序星与磁盘，变成吸收时，磁盘柱密度达到1 e22厘米-2，对应的，例如，5e-3 Msun耀斑盘在64度。类似的效果是注意到在所有其他分类指标研究阿尔法，Tbol，和H2O和CO2冰吸收强度。这种错误分类对平坦谱源（α ~0）的性质有很大的影响，其数量可以通过简单的几何参数来解释，而无需调用演化。一个可靠的分类方案，使用最少的观测数的毫米通量与一个单一的盘和干涉仪的观测构成。
英文摘要：
(Abridged) Classification schemes for YSOs are based on evaluating the degree of dissipation of the surrounding envelope, whose main effects are the extinction of the optical radiation from the central YSO and re-emission in the far-infrared. Since extinction is a property of column density along the line of sight, the presence of a protoplanetary disk may lead to a misclassification when the system is viewed edge-on. We performed radiative transfer calculations, using the axysimmetric 3D radiative transfer codes RADMC and RADICAL, to show the effects of different geometries on the main indicators of YSO evolutionary stage, like the slope of the flux between 2 and 24mum, the bolometric temperature and the optical depth of silicates and ices. We show that for systems viewed at intermediate angles the 'classical' indicators of evolution accurately trace the envelope column density, and they all agree with each other. On the other hand, edge-on system are misclassified for inclinations larger than ~65deg. In particular, silicate emission, typical of pre-main sequence stars with disks, turns into absorption when the disk column density reaches 1e22cm-2, corresponding e.g. to a 5e-3 Msun flaring disk viewed at 64deg. A similar effect is noticed in all the other classification indicators studied alpha, Tbol, and the H2O and CO2 ices absorption strengths. This misclassification has a big impact on the nature of the flat-spectrum sources (alpha ~0), whose number can be explained by simple geometrical arguments without invoking evolution. A reliable classification scheme using a minimal number of observations is constituted by observations of the mm-flux with both a single dish and an interferometer.
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