1999ApJ...521L..63T

We present the first detection of the low-lying pure rotational emission lines of H₂ from circumstellar disks around T Tauri stars, using the Short Wavelength Spectrometer on the Infrared Space Observatory. These lines provide a direct measure of the total amount of warm molecular gas in disks. The J=2⟶0 S(0) line at 28.218 µm and the J=3⟶1 S(1) line at 17.035 µm have been observed toward the double binary system GG Tau. Together with limits on the J=5⟶3 S(3) and J=7⟶5 S(5) lines, the data suggest the presence of gas at T_kin~110±10 K with a mass of (3.6±2.0)x10^–3 M_☉ (±3σ). This amounts to ∼3% of the total gas + dust mass of the circumbinary disk as imaged by millimeter interferometry, but it is larger than the estimated mass of the circumstellar disk(s). Possible origins for the warm gas seen in H₂ are discussed in terms of photon and wind-shock heating mechanisms of the circumbinary material, and comparisons with model calculations are made.