Evidence of a Disk Wind Origin for Fluorescent H₂ in Classical T Tauri Stars₂ in Classical T Tauri Stars

We use far-ultraviolet spectra of 36 T Tauri stars, predominately from the Hubble Space Telescope (HST) ULLYSES program, to examine the kinematic properties of fluorescent H2 emission lines for evidence of disk outflows. Leveraging improvements to the HST Cosmic Origins Spectrograph wavelength solution, we coadd isolated lines within four fluorescent progressions ([v’,J’] = [1,4], [1,7], [0,2], and [3,16]) to improve signal-to-noise ratio (S/N), and we fit each coadded line profile with one or two Gaussian components. Of the high-S/N line profiles (S/N ≥ 12 at the peak of the profile), over half are best fit with a combination of a broad and a narrow Gaussian component. For profiles of the [1,4] and [1,7] progressions, we find a systematic blueshift of a few kilometers per second between the broad and narrow centroid velocities and stellar radial velocities. For the [0,2] progression, we find centroid velocities consistently blueshifted with respect to stellar radial velocities on the order of −5 km s−1 for the single and narrow components, and −10 km s−1 for the broad components. Overall, the blueshifts observed in our sample suggest that the molecular gas traces an outflow from a disk wind in some sources, and not solely disk gas in Keplerian rotation. The low-velocity systematic blueshifts, as well as emitting radii as inferred from line FWHMs, observed in our sample are similar to those observed with optical [O i] surveys of T Tauri stars. We estimate H2 mass-loss rates of 10−9 to 10−11 M ⊙ yr−1, but incomplete knowledge of wind parameters limits comparisons to global models.