Detection of H[TINF]2[/TINF] Pure Rotational Line Emission from the GG Tauri Binary System

We present the first detection of the low-lying pure rotational emissionlines of H2 from circumstellar disks around T~Tauri stars, using the ShortWavelength Spectrometer on the Infrared Space Observatory. These lines providea direct measure of the total amount of warm molecular gas in disks. The J=2->0S(0) line at 28.218 mum and the J=3->1 S(1) line at 17.035 mum have beenobserved toward the double binary system GG Tau. Together with limits on theJ=5->3 S(3) and J=7->5 S(5) lines, the data suggest the presence of gas atT_kin=110+-10 K with a mass of (3.6+-2.0)x10^-3 M_sol (3sigma). This amounts to~3% of the total gas + dust mass of the circumbinary disk as imaged bymillimeter interferometry, but is larger than the estimated mass of thecircumstellar disk(s). Possible origins for the warm gas seen in H2 arediscussed in terms of photon and wind-shock heating mechanisms of thecircumbinary material, and comparisons with model calculations are made.Comment: 14 pages including 1 figure. To appear in Astrophysical Journal Letter