Diffuse Interstellar Bands, molecular and atomic line measurements with APO and FUSE.

In a new attempt to discover the origin of the long unidentified diffuse interstellar bands, a new atlas of lines between 3900A and 8700A has been constructed. Spectra with S/N > 1000 for four stars: HD 183143, HD 166739, Cygnus OB2-5 and HD 204827, recorded with the echelle spectrograph on the 3.5-meter telescope at Apache Point Observatory were compared with unreddened stars of the same or similar spectral types. The spectra have a resolution of 8 km/sec. Some 500 bands are listed, about 150 of them not previously noticed. Cygnus OB2-5 and HD 204827 have 50 bands of the type that are well correlated with C2 and prominent in dense diffuse clouds. While those bands are relatively weaker in the other two stars, those two stars have stronger bands of the classical DIBs such as lambda 5780, 6284 and 6613. Several of the bands show markedly different profiles between the four stars surveyed. Complementarily, over 20 stars in our APO atlas were observed with the FUSE satellite in order to measure the molecular hydrogen content and determine the physical conditions of the gas along their sightlines. We will show how the combined FUSE and APO data gave us the unprecedented opportunity to search for -- and constrain-- new links between the species producing the DIBs and the known atomic and molecular indicators of the physical and chemical conditions of the interstellar gas.