arXiv 0905.45752009-05-28astro-ph.GAastro-ph.SR

一颗真正的0级原恒星--NGC1333-IRAS2A的运动学

The kinematics of NGC1333-IRAS2A - a true Class 0 protostar

C. Brinch, J. K. Jørgensen, M. R. Hogerheijde

备注：: 8 pages, 8 figures, accepted for publication in A&A
DOI：: 10.1051/0004-6361/200810831

摘要：

低质量恒星的形成是通过气体和尘埃的致密核心的引力坍缩来描述的。在坍缩过程中的某个时刻，原恒星周围会形成一个圆盘，由于角动量守恒，圆盘会随着核心的收缩而旋转并变大。问题是磁盘形成过程发生的早。在本文中，我们的目标是描述一个深嵌入，0类年轻恒星对象，NGC 1333-IRAS 2A，基于高角分辨率（< 1 $''$ $\approx$ 200 AU）的干涉测量HCN和H $^{13}$ CN J = 4-3的亚毫米阵列，并测试是否可以检测到拱星盘的气体运动学特征的基础上。我们采用了一个物理模型，已被证明可以很好地描述的对象，并获得一个适合的参数化模型的速度场，使用二维轴对称辐射传输代码。通过对高角分辨率数据的参数化和拟合，表征了中心动力质量和下落速度与旋转速度之比。我们发现在所有尺度上都有大量的下沉和非常少的旋转。中心物体的质量相对较低，为0.25 M $_\odot$。作为一个低恒星质量的对象相比，信封质量，我们得出结论，NGC 1333-IRAS 2A是一致的建议，作为一个0级对象，它代表了恒星形成的最早阶段。相对于自转的大量下沉也表明这是一个年轻的物体。然而，我们发现需要一个中心的紧凑组件的规模为几百AU的连续数据的基础上，这表明，磁盘形成后不久发生的初始引力坍缩。数据没有显示出一个独特的速度场为0.1 M $_\odot$组件。

英文摘要：

Low-mass star formation is described by gravitational collapse of dense cores of gas and dust. At some point during the collapse, a disk is formed around the protostar and the disk will spin up and grow in size as the core contracts because of angular momentum conservation. The question is how early the disk formation process occurs. In this paper we aim to characterize the kinematical state of a deeply embedded, Class 0 young stellar object, NGC1333-IRAS2A, based on high angular resolution (< 1$''$ $\approx$ 200 AU) interferometric observations of HCN and H$^{13}$CN J = 4-3 from the Submillimeter Array, and test whether a circumstellar disk can be detected based on gas kinematic features. We adopt a physical model which has been shown to describe the object well and obtain a fit of a parameterized model of the velocity field, using a two-dimensional axis-symmetric radiation transfer code. The parameterization and fit to the high angular resolution data characterize the central dynamical mass and the ratio of infall velocity to rotation velocity. We find a large amount of infall and very little rotation on all scales. The central object has a relatively low mass of 0.25 M$_\odot$ . As an object with a low stellar mass compared to the envelope mass, we conclude that NGC1333-IRAS2A is consistent with the suggestion that, as a Class 0 object, it represents the earliest stages of star formation. The large amount of infall relative to rotation also suggests that this is a young object. We do however find the need of a central compact component on scales of a few hundred AU based on the continuum data, which suggests that disk formation happens shortly after the initial gravitational collapse. The data do not reveal a distinct velocity field for this 0.1 M$_\odot$ component.

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