A SPITZER SURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. II. CORRELATIONS AND LOCAL THERMAL EQUILIBRIUM MODELS
A SPITZER SURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. II. CORRELATIONS AND LOCAL THERMAL EQUILIBRIUM MODELS
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DOI：
10.1088/0004-637x/731/2/130
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发表时间：
2011-04
期刊：
影响因子：
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通讯作者：
C. Salyk;K. Pontoppidan;G. Blake;J. Najita;J. Carr
中科院分区：
文献类型：
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作者：
C. Salyk;K. Pontoppidan;G. Blake;J. Najita;J. Carr
我们提出了一个分析的斯皮策红外光谱仪观测H2O，OH，HCN，C2 H2，和CO2的排放量，和CO2的排放量，和CO2-NIRSPEC观测CO的排放量，从不同的样品的金牛座T和赫比格Ae/Be拱星盘。我们发现，大多数中红外分子发射特征的检测和强度是相互关联的，这表明一个共同的起源和类似的激发条件，这中红外线森林。除了金牛座T、赫比格Ae/Be和Pontoppidan等人讨论的过渡盘之间分子线强度的显著差异外，我们注意到，谱线探测效率与13/30 μm光谱斜率反相关，该斜率是颗粒在圆盘大气中沉降程度的量度。我们还注意到探测效率与Hα等效宽度以及吸积率之间的相关性，表明吸积加热对线激发有贡献。如果检测到，H2O线通量与中红外连续通量和其他共变系统参数，如L ε相关。然而，显着的样品变化，特别是在分子线比，仍然存在，其起源尚未得到解释。H2O排放的局部热平衡（LTE）模型表明，线强度主要与最佳拟合的发射面积，这占大多数源到源的H2O排放通量的变化。最佳拟合温度和柱密度只涵盖了一个很小的参数空间范围，所有来源都接近1018 cm−2和450 K，这表明在许多行星形成区域都有高丰度的H2O。其他分子的激发温度范围从1500到1500 K，也与行星形成区的起源一致。我们发现所有分子相对于水的分子比都是10−3，只有CO例外，它的n（CO）/n（H2O）是10 − 1。然而，LTE拟合的警告和差异的方式热化学建模结果的报告，使比较与这些模型困难，并强调需要额外的观察加上使用线生成辐射传输代码。
We present an analysis of Spitzer Infrared Spectrograph observations of H2O, OH, HCN, C2H2, and CO2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions for this mid-infrared line forest. Aside from the remarkable differences in molecular line strengths between T Tauri, Herbig Ae/Be, and transitional disks discussed in Pontoppidan et al., we note that the line detection efficiency is anti-correlated with the 13/30 μm spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and Hα equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H2O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L⋆. However, significant sample variation, especially in molecular line ratios, remains, and its origin has yet to be explained. Local thermal equilibrium (LTE) models of the H2O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H2O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near ∼1018 cm−2 and 450 K for all sources, suggesting a high abundance of H2O in many planet-forming regions. Other molecules have a range of excitation temperatures from ∼500to1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ∼10−3 for all molecules, with the exception of CO, for which n(CO)/n(H2O) ∼ 1. However, LTE fitting caveats and differences in the way thermo-chemical modeling results are reported make comparisons with such models difficult, and highlight the need for additional observations coupled with the use of line-generating radiative transfer codes.