Sidelight on the Diffuse Interstellar Bands Problem

Abstract

I investigate the conditions upon which atmospheric absorption may participate to the observation of a diffuse interstellar band (DIB), and the implications it would have. A necessary condition is that the spectrum of reddened stars comprises a few percent of starlight forward scattered by the interstellar cloud on the line of sight. Reciprocally, this scattered starlight could, in part, explain the complexity of the DIB spectrum and several observed DIB properties. It will also affect the interstellar extinction curve and the value of the RV parameter. the column density of molecular hydrogen (13), and Meyer's (4) calculations (which indicate that molecules should not be abundant enough to produce DIBs in low column density regions), hamper the hypothesis. The idea that molecules could be synthesized in dense clouds before being released, and eventually transformed, in the diffuse interstellar medium seems to me a bit far fetched (how do the DIB carriers reach the diffuse high latitude interstellar medium?). PAHs (polycyclic aromatic hydrocarbon mole-cules) are often cited as DIB carriers, but no evidence supports the claim (8, 14). There is anyway no published spectrum of PAHs or any other supposed interstellar material that would reproduce even part of the DIB spectrum.