Observations of Interstellar H and k, Molecular Lines, and Radial Velocities in the Spectra of 300 O and B Stars.

Spectrograms of 300 stars of types 0 and B, observed with the coudé spectrograph and the 100-md telescope in the region XX 3600-4700, have been used in a study of the structure of the interstellar I and K lines, of the presence o~ interstellar molecular and additional atomic lines, and in the measuremen of interstellar radial velocities. A dispersion of 2.9 A/mm was used for 231 stars and of 10 A/mm for 6 fainter stars. About one star in two is found to have complex interstellar H and K lines, and about one star in fou shows one or more interstellar lines of CN, CH i, CH ii, Cai, or Fe i. As many as four cçmponents of H an I K are found in a few stars; 17 stars show triple lines. The radial velocity from individual components i 7 stars exceeds 50 km/sec and reaches nearly 100 km/sec in one case, but the strongest componen nearly always give's a low ve'ocity. Double stars and stars close together in position usually show th same structure for the H and K lines, and nearly the same radial velocities. The radial velocities derive from the molecular lines, withfew exceptions, agree with those from the strongest component of H and K The stars in the Pleiades are remarkable in showing interstellar molecular lines that are exceptionall, strong relative to H and K. The results for this group and other stars showing the molecular lines hay been utilized for a discussion of a possible difference in the place of origin of the absorption of H and I and of the molecular lines, but the evidence is not altogether adequate to afford a decision. The radial velocities, corrected for the solar motion, are used for a determination of the galactic rote tion, although most of the stars are too near to be favorable for the purpose. A calculation based upo 171 near-by stars gives a value of 16.8 km/sec for the rolational constant, in good agreement with othc determinations. More distant stars are too few in number to provide satisfactory results