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arXiv 1101.0165astro-ph.EP
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原行星盘系统中的远紫外“连续谱”I:电子碰撞H2和吸积激波

The Far-Ultraviolet "Continuum" in Protoplanetary Disk Systems I: Electron-Impact H2 and Accretion Shocks

Kevin France, Hao Yang, Jeffrey L. Linsky

摘要:

为了更好地描述原行星盘中两个重要的远紫外连续辐射源,我们对经典金牛座T星DF Tau和V4046 Sgr进行了深光谱观测。这些新的哈勃太空望远镜-宇宙起源光谱仪观测揭示了碰撞激发的H2和吸积冲击发射的线和连续发射的组合。在V4046 Sgr的1400-1650 A波段光谱中,H2是主要的发射,而在DF Tau的远紫外光谱中,吸积连续谱的贡献很大。我们比较了V4046 Sgr的光谱,电子碰撞引起的H2发射模型,以约束发射区域的物理性质,在磁盘内的衰减进行校正后。我们发现与H2模型的宽谱特征相当吻合,这意味着N(H2)~ 10^{18} cm^{-2},T(H2)= 3000^{+1000}-500} K,特征电子能量在~ 50 - 100 eV范围内。我们建议,自吸收和碳氢化合物提供的主要衰减H2线内的磁盘起源的光子。对于DF Tau和V4046 Sgr,我们发现远紫外数据的线性拟合可以再现近紫外/光学吸积谱。我们讨论了悬而未决的问题,这些过程如何在原恒星/原行星盘,包括有效的温度和绝对强度的辐射场在低质量的原行星环境。我们发现,在低质量系统中,912- 2000 A连续谱的有效温度约为10^{4} K,通量为1 AU时星际水平的10^{5-7}倍。

英文摘要:

We present deep spectroscopic observations of the classical T Tauri stars DF Tau and V4046 Sgr in order to better characterize two important sources of far-ultraviolet continuum emission in protoplanetary disks. These new Hubble Space Telescope-Cosmic Origins Spectrograph observations reveal a combination of line and continuum emission from collisionally excited H2 and emission from accretion shocks. H2 is the dominant emission in the 1400-1650 A band spectrum of V4046 Sgr, while an accretion continuum contributes strongly across the far-ultraviolet spectrum of DF Tau. We compare the spectrum of V4046 Sgr to models of electron-impact induced H2 emission to constrain the physical properties of the emitting region, after making corrections for attenuation within the disk. We find reasonable agreement with the broad spectral characteristics of the H2 model, implying N(H2) ~ 10^{18} cm^{-2}, T(H2) = 3000^{+1000}_{-500} K, and a characteristic electron energy in the range of ~ 50 - 100 eV. We propose that self-absorption and hydrocarbons provide the dominant attenuation for H2 line photons originating within the disk. For both DF Tau and V4046 Sgr, we find that a linear fit to the far-UV data can reproduce near-UV/optical accretion spectra. We discuss outstanding issues concerning how these processes operate in protostellar/protoplanetary disks, including the effective temperature and absolute strength of the radiation field in low-mass protoplanetary environments. We find that the 912-2000A continuum in low-mass systems has an effective temperature of ~10^{4} K with fluxes 10^{5-7} times the interstellar level at 1 AU.

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