A Search for Mid-Infrared Molecular Hydrogen Emission from Protoplanetary Disks
A. Carmona, M. E van den Ancker, Th. Henning, Ya. Pavlyuchenkov, C. P. Dullemond, M. Goto, W. F-. Thi, J. Bouwman, L. B. F. M. Waters
备注：
16 pages, 9 figures, accepted by A&A. v2: typo in footnote ** corrected, v3: corrections of the A&A language editor included, typo in title of Fig. 1. corrected
We observed the Herbig Ae/Be stars UX Ori, HD 34282, HD 100453, HD 101412, HD 104237 and HD 142666, and the T Tauri star HD 319139 and searched for H2 0-0 S(2) emission at 12.278 micron and H2 0-0 S(1) emission at 17.035 micron with VISIR, ESO-VLT's high-resolution MIR spectrograph. None of the sources present evidence for H2 emission. Stringent 3sigma upper limits to the integrated line fluxes and the mass of optically thin warm gas in the disks are derived. The disks contain less than a few tenths of Jupiter mass of optically thin H2 gas at 150 K at most, and less than a few Earth masses of optically thin H2 gas at 300 K and higher temperatures. We compare our results to a Chiang and Goldreich (1997, CG97) two-layer disk model. The upper limits to the disk's optically thin warm gas mass are smaller than the amount of warm gas in the interior layer of the disk, but they are much larger than the amount of molecular gas in the surface layer. We present a calculation of the expected thermal H2 emission from optically thick disks, assuming a CG97 disk structure, a gas-to-dust ratio of 100 and Tgas = Tdust. The expected H2 thermal emission fluxes from typical disks around Herbig Ae/Be stars (10^-16 to 10^-17 erg/s/cm2 at 140 pc) are much lower than the detection limits of our observations (5*10^-15 erg/s/cm2). H2 emission levels are very sensitive to departures from the thermal coupling between the molecular gas and dust. Additional sources of heating of gas in the disk's surface layer could have a major impact on the expected H2 disk emission. In the observed sources the molecular gas and dust in the surface layer have not significantly departed from thermal coupling (Tgas/Tdust< 2) and that the gas-to-dust ratio in the surface layer is very likely lower than 1000.
The First Detection of Spatially Resolved Mid-Infrared Scattered Light from a Protoplanetary Disk
我们报告空间分辨11.8微米的图像，在W。M.凯克10米望远镜，围绕前主序星HK Tau B的原行星盘。HK Tau B相对于HK Tau A的中红外形态和天体测量表明，在HK Tau B的中红外观测到的通量已经从其近边缘的盘的上表面散射。这是第一个在中红外波长的散射光中观察到的原行星盘的例子。蒙特卡罗模拟表明，该盘的范围（半高宽=0。“5，或70天文单位）的散射光星云在中红外线是非常敏感的尘埃大小分布。11.8微米的测量值可以通过包含尺寸在1.5-3微米量级的颗粒的尘埃颗粒群来最好地建模;仅具有亚微米颗粒尺寸或延伸超过5微米的幂律尺寸分布的颗粒群不能再现所观察到的形态。这些颗粒明显大于ISM中的预期，这意味着颗粒生长已经发生;这种生长是尘埃盘本身演化的结果，还是最初发生在暗云中仍然是一个悬而未决的问题。
Stabilization of the Shear Instability in a Dust Layer of a Protoplanetary Disk and Possible Formation of Planetesimals due to Gravitational Fragmentation of the Dust Layer
Gas phase water in the surface layer of protoplanetary disks
最近对HDO在464 GHz向DM Tau的原行星盘的基态跃迁的观测发现，在外盘中平面上方的区域存在水蒸气（Ceccarelli et al 2005）。在没有非热解吸过程的情况下，水应该几乎完全冻结在谷物地幔上，HDO无法检测到。在这封信中，我们提出了一个化学模型，探讨了冰地幔被FUV（6 eV < h nu < 13.6eV）光子光解吸的可能性。我们表明，平均星际FUV场足以在整个磁盘的磁盘中平面上方创建一层水蒸气。假设光解吸率为10^{-3}，则该层中的水丰度预计为~ 3 x 10^{-7}，平均H2O柱密度为~ 1.6 x 10^{15} cm^{-2}。预测是非常弱的依赖于模型的细节，如入射FUV辐射场，在磁盘中的气体密度。基于该模型，我们预测DM Tau中的气态HDO/H2O比率为~ 1%。此外，我们预测的基态过渡的水在557 GHz是不可检测的ODIN和/或HSO-HIFI。
