We report the discovery of quiescent emission from molecular hydrogen gas located in the circumstellar disks of six pre-main sequence stars, including two weak-line T Tauri stars (TTS), and one Herbig AeBe star, in the Chamaeleon I star forming region. For two of these stars, we also place upper limits on the 2->1 S(1)/1->0 S(1) line ratios of 0.4 and 0.5. Of the 11 pre-main sequence sources now known to be sources of quiescent near-infrared hydrogen emission, four possess transitional disks, which suggests that detectable levels of H2 emission and the presence of inner disk holes are correlated. These H2 detections demonstrate that these inner holes are not completely devoid of gas, in agreement with the presence of observable accretion signatures for all four of these stars and the recent detections of [Ne II] emission from three of them. The overlap in [Ne II] and H2 detections hints at a possible correlation between these two features and suggests a shared excitation mechanism of high energy photons. Our models, combined with the kinematic information from the H2 lines, locate the bulk of the emitting gas at a few tens of AU from the stars. We also find a correlation between H2 detections and those targets which possess the largest H\alpha equivalent widths, suggesting a link between accretion activity and quiescent H2 emission. We conclude that quiescent H2 emission from relatively hot gas within the disks of TTS is most likely related to on-going accretion activity, the production of UV photons and/or X-rays, and the evolutionary status of the dust grain populations in the inner disks.
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
The Astrophysical Journal, Volume 678, Issue 2, pp. 1088-1098.
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