Molecules in the Sun and Stars

Molecular constants, derived mainly from band spectra, have been collected for about thirty diatomic molecules likely to occur in the sun and stars, and the dissociation constants calculated. From these and the writer's determinations of the abundance of elements in the sun and the pressures prevailing above the disk and the spots, the amounts of various compounds have been calculated. The results are in good agreement with observations. The prominence of hydrides results from the great abundance of hydrogen and affords an independent proof of this abundance. The moderate weakening of the bands of non-metallic compounds in passing from the spot to the disk arises from dissociation; the great weakening for metaffic compounds, from the combined effect of dissociation of compounds and ionization of metallic atoms. The abundance of F, estimated from SiF, is comparable with that of N or Na; that of B is much smaller. Some of the most abundant molecules-H2, N2, CO-have strong bands only beyond X 3000. The bands of H2 in the visible region come from states of excitation potential exceeding i 1.7 volts and must be too faint to observe. They would be weakened in the spots. For stars similar ~n composition to the sun (with oxygen in excess of carbon), the amounts of H, C, N, 0, T~, and their compounds have been calculated, with the aid of the writer's recent determinations of atmospheric extent and pressure in giants and dwarfs, and are illustrated by diagrams. The observed behavior of the bands is closely represented. The maxima of CH and CN near class K arise from a shift of equilibrium at low temperatures toward the more tightly bound compound GO, and are quantita- tively explained, as is the sensitiveness of the CN bands to absolute magnitude. The predicted maximum intensity of TiO is considerably higher in giants than in dwarfs (agreeing with observations). The S stars belong to the oxygen group and prob- ably contain more Zr than normal. A possible mechanism is suggested for the excitation of metaffic emission lines in long-period variables by the dissociation of compounds, and it is shown that the weak- ening of the sodium lines at minimum cannot be explained by the conversion of the metal to oxide or fluoride. The predicted properties of stars with an excess of carbon over oxygen closely resemble those of classes R and N (as suggested by R. H. Curtiss). The disappearance of the violet cyanogen bands in the later N's is attributed to the absence of continuous background, since the red CN system and the band near X 4600 do not weaken. Dwarf stars with excess of carbon should show spectra of classes R or N. Carbon stars are so rare among giants that it is not remarkable that no carbon dwarf has yet been found. Stars of intermediate composition should exhibit spectra likely to be classed as peculiar examples of class M, R, or N