The bipolar outflow and disk of the brown dwarf ISO 217
The bipolar outflow and disk of the brown dwarf ISO 217
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棕矮星 ISO 217 的双极流出和圆盘
DOI：
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发表时间：
2012
期刊：
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通讯作者：
T. Henning
中科院分区：
文献类型：
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作者：
V. Joergens;A. Pohl;A. Sicilia;T. Henning
基于2009年UVES/VLT光谱观测到的6716A和6731A的禁止（SII）发射线的光谱天文测量，我们发现非常年轻的褐矮星候选天体ISO217 （M6.25）驱动着一个具有更强和稍快红移成分的本质上不对称的双极流出。ISO217只是为数不多的褐矮星和非常低质量的恒星（M5-M8）中的一颗，它们被探测到有流出物，这表明金牛座T阶段继续处于恒星的极限。我们测量到（SII）中流出的空间延伸可达±190mas（约±30AU），速度可达±40-50km " 1。我们发现基本的流出特性（空间扩展、速度和流出位置角度）与2007年5月惠兰及其同事在发现光谱中确定的顺序相似。我们的研究表明，在几年的时间尺度上，两个叶瓣之间的速度不对称性是可变的，而且当使用更现实的恒星静止速度时，2007年发现的两倍的强烈不对称性可能比最初预期的要小。我们还检测到（FeII）的禁线发射！7155A，我们认为外流的内部热区域可能是其潜在的起源。为了全面了解ISO217系统，我们基于SED在0.66 ~ 24µm范围内的辐射传输建模，确定了其吸积盘的性质。该磁盘模型与70 μ m的Herschel/PACS数据非常吻合。我们发现磁盘是喇叭和中间倾斜（i # 45 $）。最佳拟合模型的总盘质量为4% 10 " 6 M&，与文献中ISO217的吸积和流出率（# 10 " 10 M& yr " 1）相比，这是低的。我们提出，这种差异可以解释为，由于强烈的未检测到的颗粒生长，磁盘质量比模型推断的高，或者平均吸积速率和流出速率比测定值低。我们表明，从H”模型和流出叶可见的两个角度来看，圆盘倾角明显超过45美元，这与SED数据不一致。因此，尽管这颗褐矮星的倾斜角度处于中间，但它的圆盘似乎并没有掩盖（SII）中的红色流出成分，这在金牛座T天体中是非常罕见的（只有另一个例子）。
We show that the very young brown dwarf candidate ISO217 (M6.25) is driving an intrinsically asymmetric bipolar outflow with a stronger and slightly faster red-shifted component based on spectro-astrometry of forbidden (SII) emission lines at 6716A and 6731A observed in UVES/VLT spectra taken in 2009. ISO217 is only one of a handful of brown dwarfs and very low-mass stars (M5-M8) for which an outflow has been detected and that show that the T Tauri phase continues at the substellar limit. We measure a spatial extension of the outflow in (SII) of up to ±190mas (about ±30AU) and velocities of up to ±40-50kms " 1 . We find that the basic outflow properties (spatial extension, velocities, and outflow position angle) are of similar order as those determined in the discovery spectra from May 2007 of Whelan and coworkers. We show that the velocity asymmetry between both lobes is variable on timescales of a few years and that the strong asymmetry of a factor of two found in 2007 might be smaller than originally anticipated when using a more realistic stellar rest-velocity. We also detect forbidden line emission of (FeII)! 7155A, for which we propose as a potential origin the hot inner regions of the outflow. To comprehensively understand the ISO217 system, we determine the properties of its accretion disk based on radiative transfer modeling of the SED from 0.66 to 24µm. This disk model agrees very well with Herschel/PACS data at 70µm. We find that the disk is flared and intermediately inclined (i # 45 $ ). The total disk mass of the best-fit model is 4 % 10 " 6 M& , which is low compared to the accretion and outflow rate of ISO217 from the literature (# 10 " 10 M& yr " 1 ). We propose that this discrepancy can be explained by either a higher disk mass than inferred from the model because of strong undetected grain growth and/or by an on average lower accretion rate and outflow rate than the determined values. We show that a disk inclination significantly exceeding 45 $ , as suggested from H" modeling and from both lobes of the outflow being visible, is inconsistent with the SED data. Thus, despite its intermediate inclination angle, the disk of this brown dwarf does not appear to obscure the red outflow component in (SII), which is very rarely seen for T Tauri objects (only one other case).