TEMPERATURE-VARIATIONS AND N O IN THE ORION NEBULA FROM HST OBSERVATIONS/

Using the Goddard High Resolution Spectrograph (GHRS) and the Faint Ob ject Spectrograph (FOS) on the Hubble Space Telescope, we measured the flux of the N II] (2s2p(3) S-5(2) --> 2s(2)2p(2) P-3(2,1)) lines at l ambda(vac) = 2143.45, 2139.68 Angstrom in the Orion Nebula-the first d etection of these lines in an H II region. In order to assess the N+/O + ratio, we also measured the flux of the [O II] (2p(3) P-2(1/2,3/2)0 --> 2p(3) S-4(3/2)0) lines at lambda(vac) = 2471.05, 2471.12 Angstrom. In addition, with the FOS, other emission lines were measured in the same aperture in order to assess the average electron temperature and mean-square temperature variation (t(2)) in the N+ region, as well as the N+/O+ ratio. When we require that the empirically determined value s be equal for (N+/O+)(uv) (obtained from the N II] 2142 and [O II] 24 71 lines) and (N+/O+)(opt) (obtained from the [N II] 6585 and [O II] 3 728 lines), we obtain the following. For the (N+, O+) zone, the averag e electron density is similar to 7000 cm(-3), the average electron tem perature is 9500 K, t(2) = 0.032, and N+/O+ = 0.14. By comparing our F OS observations to predicted fluxes, utilizing our two previous photoi onization models, we are able to derive the N/O ratio. There is fairly good agreement between (N/O0)(uv) and (N/O)(opt) as derived from the two models with a range between 0.13 and 0.18. This range also encompa sses our model-derived values for (N/O)(ir) (0.17-0.18), which fit the observed far-infrared line ratio [N III] 57 mu m/[O III] 52 mu m. The empirically derived N+/O+ value requires a correction for the possibi lity that the N+ and O+ regions are not identical. Our overall results place the gas-phase Orion N/O ratio in the range 0.13-0.18, which is somewhat higher than solar.