The Origins of Fluorescent H2Emission From T Tauri Stars

We survey fluorescent H2 emission in HST/STIS spectra of the classical TTauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DG Tau, and theweak-lined T Tauri star (WTTS) V836 Tau. From each of those sources we detectbetween 41-209 narrow H2 emission lines, most of which are pumped by strongLy-alpha emission. H2 emission is not detected from the WTTS V410 Tau. Thefluorescent H2 emission appears to be common to circumstellar environmentsaround all CTTSs, but high spectral and spatial resolution STIS observationsreveal diverse phenomenon. Blueshifted H2 emission detected from RU Lupi, TTau, and DG Tau is consistent with an origin in an outflow. The H2 emissionfrom TW Hya, DF Tau, and V836 Tau is centered at the radial velocity of thestar and is consistent with an origin in a warm disk surface. The H2 lines fromRU Lupi, DF Tau, and T Tau also have excess blueshifted H2 emission thatextends to as much as -100 km/s. The strength of this blueshifted componentfrom DF Tau and T Tau depends on the upper level of the transition. In allcases, the small aperture and attenuation of H2 emission by stellar windsrestricts the H2 emission to be formed close to the star. The Ly-alpha and theH2 emission blueshifted by 15 km/s relative to RU Lupi are extended to the SWby 0.07 arcsec, although the faster H2 gas that extends to about 100 km/s isnot spatially extended. We also find a small reservoir of H2 emission from TWHya and DF Tau consistent with an excitation temperature of about 2.5x10^4 K.Comment: 38 pages, 18 figures, 14 tables. Accepted by ApJ