Intense Diffuse Far-Ultraviolet Emission from the Orion Nebula

Abstract

We present spectra of the diffuse far-UV (900-1200 A) emission from a region near the Orion Nebula: the first high-resolution spectra of the diffuse background radiation. These observations were made using serendipitous Far Ultraviolet Spectroscopic Explorer (FUSE) observations and were only possible because of the strength of the diffuse emission (≈3 × 105 photons cm-2 sr-1 s-1 A-1) and the sensitivity of the FUSE instrument. Preliminary modeling suggests that the light is scattered starlight from the Trapezium stars, primarily θ1 Ori C. However, a comparison of the spectra with nearby stars shows significant differences in the presence and strength of the absorption lines, particularly in the Lyβ line where there is much less interstellar absorption in our diffuse spectrum. We believe that we are indeed observing scattered light from the Trapezium stars but through a line of sight with much less matter than the direct line to the stars.