原恒星包层的高能辐射和硫化学：AFGL 2591的亚毫米干涉测量
Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591
摘要：
背景：年轻恒星周围的吸积包层内部几千个天文单位的化学物质预计会随着中心恒星的远紫外线和X射线照射而发生很大变化。目的在炽热的内壳层中寻找原恒星高能辐射的分子示踪物。方法：亚毫米波天线阵（SMA）以0.6”的分辨率，在350 GHz的频率下，以CS、SO、HCN、HCN（v2=1）和HC 15 N的谱线观测到了大质量恒星形成区AFGL 2591，探测径向尺度为600-3500 AU，假设距离为1 kpc。SMA的观测结果进行了比较与预测的化学模型拟合到以前的单碟观测。结果：CS和SO主峰在FWHM水平上在空间上扩展，与原恒星X射线模型预测的一致。然而，发现主峰尺寸比模型小近2倍。另一方面，CS、HCN和HC 15 N的谱线，而不是SO和HCN（v2=1）的谱线，显示出在约3500 AU的半径处的基座发射，这是没有预测到的。除SO外，所有的线都显示出在接近的流出锥内的第二个峰。在CS中没有观察到随着半径的增加丰度急剧下降而引起的vitrifos的下降或零，而在SO中只是暂时的。结论：原恒星X射线的发射是支持的建模SO和CS振幅vibrations，包括扩展的主峰CS的良好拟合。广泛的辐射可以解释为远紫外线照射在一个球形非对称的几何形状，可能包括流出壁的规模为3500 - 7000 AU。扩展的CS和SO主峰表明硫在100 K温度半径附近蒸发。
英文摘要：
CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes around young stellar objects is predicted to vary greatly with far-UV and X-ray irradiation by the central star. Aim We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope. METHODS: The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at 350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc. The SMA observations are compared with the predictions of a chemical model fitted to previous single-dish observations. RESULTS: The CS and SO main peaks are extended in space at the FWHM level, as predicted in the model assuming protostellar X-rays. However, the main peak sizes are found smaller than modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500 AU that are not predicted. All lines except SO show a secondary peak within the approaching outflow cone. A dip or null in the visibilities caused by a sharp decrease in abundance with increasing radius is not observed in CS and only tentatively in SO. CONCLUSIONS: The emission of protostellar X-rays is supported by the good fit of the modeled SO and CS amplitude visibilities including an extended main peak in CS. The broad pedestals can be interpreted by far-UV irradiation in a spherically non-symmetric geometry, possibly comprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SO main peaks suggest sulfur evaporation near the 100 K temperature radius.
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