L(alpha)-induced two-photon absorption of visible light emitted from an O-type star by H2(+) ions located near the surface of the Stromgren sphere surrounding the star: A possible explanation for the diffuse interstellar absorption bands (DIDs)
Abstract
In this paper, a new model is proposed to account for the DIB's (Diffuse Interstellar Bands). In this model, the DIB's result from a non-linear effect: resonantly-enhanced two-photon absorption of H(2+) ions located near the surface of the Stromgren sphere that surrounds an O- or B- type star. The strong light that is required to 'drive' the two-photon transition is provided by L(alpha) light emerging from the Stromgren sphere that bounds the H II region surrounding the star. A value of approximately 100 micro W/sq cm is estimated for the L(alpha) flux at the Stromgren radius, R(s), of a strong (O5) star. It is shown that a c.w. L(alpha) flux of this intensity should be sufficient to induce a few percent absorption for visible light radiated by the same star at a frequency (omega2) that completes an allowed two-photon transition, provided (1) the L(alpha) radiation happens to be nearly resonant with the frequency of a fully-allowed absorber transition that effectively represents the first step in the two-photon transition, and (2) an effective column density approximately 10(sup18)/sq cm of the absorber is present near the Stromgren sphere radius, Rs.
- Publication:
-
The Diffuse Interstellar Bands
- Pub Date:
- May 1994
- Bibcode:
- 1994dib..nasa...99G
- Keywords:
-
- Absorption Spectra;
- Carrier Frequencies;
- Hydrogen Ions;
- Light (Visible Radiation);
- Lyman Alpha Radiation;
- O Stars;
- Photons;
- Quantum Chemistry;
- Spectral Emission;
- H Ii Regions;
- Nonlinearity;
- Photon Absorptiometry;
- Photon-Electron Interaction;
- Astronomy