Evidence for Nonlinear Generation of VUV Light in H2-Containing Clouds Near B-Type Supergiants. Connection with H2 Theory of Diffuse Interstellar Bands (DIBS)

It is shown by several examples that the few dozens of relatively narrow emission bands which are observed in the 900-1200A spectral range of the VUV light that is seen toward B-type stars can be assigned as fourth-leg components of H2 four-wave parametric oscillation (FWPO) processes. The data analyzed are archived spectra obtained during the first ORFEUS VUV space probe. Our model clearly implies that the tenuous - essentially collisonless - H2-containing clouds in which the emission bands are generated are interstellar, but are located sufficiently close to the stars themselves to enable them to be driven by the stars' VUV blackbody continua into a highly excited state in which coherent FWPO processes continually occur on many H2 transitions. Some known properties of broadband stimulated Raman scattering (SRS) and FWPO are reviewed in the context of this model. Connections are made with the H2 DIBs theory of Sorokin & Glownia 1996, which is strongly supported by the results obtained in the presented work.