Line Emission from Gas in Optically Thick Dust Disks around Young Stars

Abstract

We present self-consistent models of gas in optically-thick dusty disks and calculate its thermal, density and chemical structure. The models focus on an accurate treatment of the upper layers where line emission originates, and at radii $\gtrsim 0.7$ AU. We present results of disks around $\sim 1{\mathrm{M}}_{\odot }$ stars where we have varied dust properties, X-ray luminosities and UV luminosities. We separately treat gas and dust thermal balance, and calculate line luminosities at infrared and sub-millimeter wavelengths from all transitions originating in the predominantly neutral gas that lies below the ionized surface of the disk. We find that the [ArII] 7$\mu$m, [NeII] 12.8$\mu$m, [FeI] 24$\mu$m, [SI] 25$\mu$m, [FeII] 26$\mu$m, [SiII] 35 $\mu$m, [OI] 63$\mu$m and pure rotational lines of H${}_2$, H${}_2$O and CO can be quite strong and are good indicators of the presence and distribution of gas in disks. We apply our models to the disk around the nearby young star, TW Hya, and find good agreement between our model calculations and observations. We also predict strong emission lines from the TW Hya disk that are likely to be detected by future facilities. A comparison of CO observations with our models suggests that the gas disk around TW Hya may be truncated to $\sim 120$ AU, compared to its dust disk of 174 AU. We speculate that photoevaporation due to the strong stellar FUV field from TW Hya is responsible for the gas disk truncation.

Accepted to Astrophysical Journal

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Cited by in corpus (16)

• X-ray irradiated protoplanetary disk atmospheres I: Predicted emission line spectrum and photoevaporation
• Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA
• The Impact of Dust Evolution and Photoevaporation on Disk Dispersal
• Formation of Water in the Warm Atmospheres of Protoplanetary Disks
• Measuring tiny mass accretion rates onto young brown dwarfs
• [NeII] emission line profiles from photoevaporative disc winds
• Analytical Formulas of Molecular Ion Abundances and N2H+ Ring in Protoplanetary Disks
• Constraining the Sub-AU-Scale Distribution of Hydrogen and Carbon Monoxide Gas around Young Stars with the Keck Interferometer
• The TEXES Survey For H2 Emission From Protoplanetary Disks
• Unbiased mm-wave Line Surveys of TW Hya and V4046 Sgr: The Enhanced C2H and CN Abundances of Evolved Protoplanetary Disks
• An outflow origin of the [NeII] emission in the T Tau triplet
• Shielding by Water and OH in FUV and X-ray Irradiated Protoplanetary Disks
• Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
• Dispersal of protoplanetary disks by central wind stripping
• Velocity-Resolved [Ne III] from X-Ray Irradiated Sz 102 Microjets
• The gas disk: Evolution and chemistry