SPECTROPHOTOMETRIC STUDIES OF THE OMEGA NEBULA (M17) - ELECTRON-DENSITY AND IONIZATION

Spectral observations of the diffuse nebula M17 obtained on the 70-cm telescope of the Fesenkov Astrophysical Institute and the 6-m telescop e of the Special Astrophysical Observatory are presented. Maps of the electron density N-e([SII]) and ionization are obtained, characterizin g the physical conditions in 400 regions in the nebula. M17 has the hi ghest degree of ionization of all known Galactic star-forming regions. This ionization could be caused by the radiation from stars of spectr al type O3-O4. Analysis of the electron densities, degrees of ionizati on, and exciting stars indicates that most of the nebular emission is due to six O stars that are located in the dark ''bay'' of the nebula Only one compact HII region with an independent ionization source was identified, in the southwest of the M17 complex. The weakly-emitting H -alpha clumps and filaments in the western part of the nebula have the highest M17 ionization and electron density, and are optical features associated with the powerful radio source M17S, which is screened by a dark cloud with absorption A(v) = 6-18(m). The values of N-e([SII]) and N-e([CIIII]) for four cross sections of the nebula (angular resolu tion 3.6 '' are compared; these characterize the emission of the nebul a in the Hell, [SIII], [NIII], and tin part) [OIII] zones. Areas in wh ich the differences between these two densities are substantial are re vealed.