SIMBAD references

2011ApJ...731..130S - Astrophys. J., 731, 130 (2011/April-3)

A Spitzer survey of mid-infrared molecular emission from protoplanetary disks. II. Correlations and local thermal equilibrium models.


Abstract (from CDS):

We present an analysis of Spitzer Infrared Spectrograph observations of H2O, OH, HCN, C2H2, and CO2emission, 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, H2 O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L{sstarf}. 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 H2 O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H2 O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near ∼1018/cm2 and 450 K for all sources, suggesting a high abundance of H2 O 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.

Abstract Copyright:

Journal keyword(s): protoplanetary disks

Simbad objects: 75

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