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

<jats:title>Abstract</jats:title>
<jats:p>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 H<jats:sub>2</jats:sub> 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 ([<jats:italic>v’</jats:italic>,<jats:italic>J’</jats:italic>] = [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<jats:sup>−1</jats:sup> for the single and narrow components, and −10 km s<jats:sup>−1</jats:sup> 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 <jats:sc>i</jats:sc>] surveys of T Tauri stars. We estimate H<jats:sub>2</jats:sub> mass-loss rates of 10<jats:sup>−9</jats:sup> to 10<jats:sup>−11</jats:sup>
<jats:italic> M</jats:italic>
<jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>, but incomplete knowledge of wind parameters limits comparisons to global models.</jats:p>