A High-resolution Mid-infrared Survey of Water Emission from Protoplanetary Disks

Abstract

We present the largest survey of spectrally resolved mid-infrared water emission to date, with spectra for 11 disks obtained with the Michelle and TEXES spectrographs on Gemini North. Water emission is detected in six of eight disks around classical T Tauri stars. Water emission is not detected in the transitional disks SR 24 N and SR 24 S, in spite of SR 24 S having pretransitional disk properties like DoAr 44, which does show water emission. With R ~ 100,000, the TEXES water spectra have the highest spectral resolution possible at this time, and allow for detailed line shape analysis. We find that the mid-IR water emission lines are similar to the "narrow component" in CO rovibrational emission, consistent with disk radii of a few astronomical units. The emission lines are either single peaked, or consistent with a double peak. Single-peaked emission lines cannot be produced with a Keplerian disk model, and may suggest that water participates in the disk winds proposed to explain single-peaked CO emission lines. Double-peaked emission lines can be used to determine the radius at which the line emission luminosity drops off. For HL Tau, the lower limit on this measured dropoff radius is consistent with the 13 au dark ring. We also report variable line/continuum ratios from the disks around DR Tau and RW Aur, which we attribute to continuum changes and line flux changes, respectively. The reduction in RW Aur line flux corresponds with an observed dimming at visible wavelengths.