James Webb Space Telescope Feed Post

Harvard ADS: Water in protoplanetary disks with JWST-MIRI: spectral excitation atlas, diagnostic diagrams for temperature and column density, and detection of disk-rotation line broadening

Paper abstract: This work aims at providing some general tools for the analysis of water spectra as observed in protoplanetary disks with JWST-MIRI. We use 25 high-quality spectra from the JDISC Survey reduced with asteroid calibrators as presented in Pontoppidan et al. (2024). First, we present a spectral atlas to illustrate the clustering of water transitions from different upper level energies (E_u) and identify single (un-blended) lines that provide the most reliable measurements. With the atlas, we demonstrate two important excitation effects: one related to the opacity saturation of ortho-para line pairs that overlap, and the other to the sub-thermal excitation of v=1-1 lines scattered across the v=0-0 rotational band. Second, from this larger line selection we define a list of fundamental lines spanning E_u from 1500 to 6000 K to develop simple line-ratio diagrams as diagnostics of temperature components and column density. Third, we report the detection of disk-rotation Doppler broadening of molecular lines, which demonstrates the radial distribution of water emission at different E_u and confirms from gas kinematics a radially-extended ~ 170-190 K reservoir recently suggested from the analysis of line fluxes. We also report the detection of narrow blue-shifted absorption from an inner disk wind in ro-vibrational H_2O and CO lines, which may be observed in disks at inclinations > 50 deg. We summarize these findings and tools into a general recipe that should be beneficial to community efforts to study water in planet-forming regions.