Herbig Stars' Near-Infrared Excess: An Origin in the Protostellar Disk's Magnetically-Supported Atmosphere
Herbig Stars' Near-Infrared Excess: An Origin in the Protostellar Disk's Magnetically-Supported Atmosphere
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赫比星的近红外过量：原恒星盘磁力支持大气层的起源
DOI：
10.1088/0004-637x/780/1/42
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
S. Hirose
中科院分区：
文献类型：
--
作者：
N. J. Turner;M. Benisty;C. P. Dullemond;S. Hirose
质量为太阳2-8倍的年轻恒星，如赫比格Ae和Be星，经常表现出近红外辐射过剩，太大了，无法用流体静力学支持的星周气体和尘埃盘来解释。同时，携带星周气体到恒星的吸积流被认为是由磁旋湍流驱动的，根据数值MHD模型，磁旋湍流产生了一个由磁场支持的扩展的低密度大气。我们证明，大气层的底部对星光来说是光学厚度的，而位于1天文单位附近的部分足够高，可以将恒星的光度再加工成近红外的部分加倍。我们使用蒙特卡罗辐射传输计算生成了亚微米硅酸盐和碳质颗粒的合成光谱能量分布（SEDs）。合成SED与最近由Mulders & Dominik构建的中位数Herbig SED密切相关，特别是，如果颗粒的质量分数接近圆盘内缘附近的星际，则与大的近红外通量相匹配。
Young stars with masses 2–8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders & Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.