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arXiv 0912.2869astro-ph.SR
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大质量年轻恒星天体中红外辐射的起源:W33A的多基线VLTI观测

The origin of mid-infrared emission in massive young stellar objects: multi-baseline VLTI observations of W33A

W. J. de Wit, M. G. Hoare, R. D. Oudmaijer, S. L. Lumsden

摘要:

利用VLTI和VLBI仪器对大质量年轻天体W33 A的星周结构进行了100 AU尺度的观测。提出了4个基线上的N波段振动,这与球对称几何不一致。的可见度光谱和SED的同时相比,二维轴对称的灰尘辐射转移模型的几何形状,包括一个旋转扁平的信封和外流腔。我们假设一个O7.5 ZAMS星作为中心源,与观测到的热光度一致。的意见也进行了比较,模型与(尘埃和气体)吸积盘。一个令人满意的模型,它再现了每个(u,v)点的可见度光谱。它拟合了硅酸盐吸收、中红外斜率、远红外峰和SED的(亚)mm。其产生与观察一致的350微米形态。在100 AU尺度上的10微米发射主要是由流出物雕刻的腔体的辐照壁决定的。的vibrillation排除存在的尘埃盘总(气体和尘埃)的质量超过0.01 Msun。然而,在尘埃升华半径内部的光学厚度的吸积盘,可以以与包层质量下降速率相等的速率(高达10^(-3)Msun/yr)吸积,而不会因为W33 A的极大质量包层的消光而对维日数产生实质性影响。

英文摘要:

The circumstellar structure on 100 AU scales of the massive young stellar object W33A is probed using the VLTI and the MIDI instrument. N-band visibilities on 4 baselines are presented which are inconsistent with a spherically symmetric geometry. The visibility spectra and SED are simultaneously compared to 2D axi-symmetric dust radiative transfer models with a geometry including a rotationally flattened envelope and outflow cavities. We assume an O7.5 ZAMS star as the central source, consistent with the observed bolometric luminosity. The observations are also compared to models with and without (dusty and gaseous) accretion disks. A satisfactory model is constructed which reproduces the visibility spectra for each (u,v) point. It fits the silicate absorption, the mid-IR slope, the far-infrared peak, and the (sub)mm of the SED. It produces a 350 micron morphology consistent with observations. The 10 micron emission on 100 AU scales is dominated by the irradiated walls of the cavity sculpted by the outflow. The visibilities rule out the presence of dust disks with total (gas and dust) masses more than 0.01 Msun. However, optically thick accretion disks, interior to the dust sublimation radius, are allowed to accrete at rates equalling the envelope's mass infall rate (up to 10^(-3) Msun/yr) without substantially affecting the visibilities due to the extinction by the extremely massive envelope of W33A.

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