Observations of selected Perseus Arm H II regions
Talent, David Leroy
Dufour, Reginald J.
Master of Science
The results of an investigation of the optical spectra of four galactic H II regions: NGC 7635, NGC 7538, NGC 2359, and NGC 1624 are presented. The nebulae, located in the Perseus Arm of the Galaxy at distances ranging from 11 to 14 kpc from the galactic center (3.5 to 5. kpc from the sun), were examined using the Intensified Image Dissector Scanner (IIDS) on the 2.1-meter telescope at Kitt Peak National Observatory (KPNO). From the measurement of selected emission-line strengths in the XX37-41 and XA46-74 spectral ranges, the relative abundances of He, N, O, Ne, S, and Ar are calculated with respect to H (log(H) = 12.) for each nebula. Electron densities are derived for the H II regions from the ratio of the [S II] line intensities, I (6716)/I (6731) , while their temperatures are obtained from the ratio of the [N II] line intensities, 1(5759/1(6583). The effects of temperature fluctuations on the abundance calculations are also discussed. The derived chemical abundances are examined in the context of possible chemical abundance gradients in the Galaxy. Significant radial gradients are found for oxygen and nitrogen: dlog(/H)/dR = -.12+.3 kpc-1 and dlog(N/H)/dR = -.16+.3 kpc-1. In each nebula several positions were observed. In this paper particular attention is given to an examination of the condensations in NGC 7635, while an overabundance of nitrogen in NGC 2359 is discussed in the context of its association with the Wolf-Rayet star HD 56925 (WN5).