microns
Normalised SWS spectra of NGC 7538 IRS9, GL4176, GL2136 and GL 2591, shifted by 0.0, -0.2, -0.4 and -0.6 respectively. A model H2O spectrum is shown for comparison (click here for full size image).
This spectrum was presented in letter "Infrared absorption of H2O toward massive young stars", van Dishoeck, E.F. et al., that was published in the
ISO dedicated issue of Astronomy and Astrophysics
Letters.