Probing the Hot, Dense Gas near Massive Protostars via Water Absorption

The regions surrounding massive protostars are complex in terms of structure, dynamics, and chemistry. Warm conditions drive a significant fraction of the oxygen into water, increasing H2O abundances such that water is ubiquitous in these environments. As a result, water is a sensitive tracer of the various physical components (e.g., envelope, outflow, jet, disk) associated with massive protostars. While Herschel/HIFI has revealed abundant emission from warm water around massive protostars, those observations predominantly probe the large scale structures of the envelope and outflows. To probe the hot, dense gas in the innermost regions surrounding massive protostars requires complementary observations of ro-vibrational H2O transitions in the near- to mid-infrared. We have observed select spectral windows in the 5-7 micron range at about 4 km/s resolution with SOFIA/EXES toward a small sample of massive protostars, targeting ro-vibrational transitions of water arising from states with energies ranging from 0 to 4000 K above the ground state. I will present findings from our analysis of these data, and include comparisons to previous observations of water in these objects made at THz frequencies with Herschel/HIFI, at far-IR wavelengths with Herschel/PACS, and in the mid-IR at low spectral resolution with ISO-SWS.