Abstract
We model gas and dust emission from intermediate-aged ( ∼ 107 years) disks extending 1-20 AU around a solar mass central star. The models self-consistently treat thermal balance and chemistry, and calculate the vertical density and temperature structure of the gas in a disk. The models cover gas masses 10-3 - 1 M[J] and dust masses 10-7 - 10-4 M[J], so that the dust is fairly optically thin to stellar radiation. We focus on infrared emission lines from various gas species such as the rotational lines of H[2], OH, H[2]O and CO molecules and the fine structure lines of carbon, oxygen, sulfur, iron, and silicon atoms and ions, many of which are observable by the Spitzer Space Telescope. We find that the [SI] 25.23 μ m line is the strongest emission line for a wide range of disk and stellar parameters, followed by emission from [SiII] 34.8 μ m and [FeII] 26 μ m. [FeI] 24 μ m is strong when gas masses are high ( ≳ 0.1 M[J]). Emission from the rotational lines of H[2] is more difficult to detect, unless disk gas masses are substantial ( ≳ 0.1 M[J]). The models presented here will be useful in future infrared studies of the timescale for the dispersion of gas in a planet-forming disk, and testing core accretion models of giant planet formation.
