Ionization structure of the Orion nebula: infrared line observations and models

Technical Report · Wed Oct 01 04:00:00 EDT 1986

OSTI ID:6482183

Simpson, J P; Rubin, R H; Erickson, E F; Haas, M R

Observations of the (O III) 52 and 88 micron lines and the (N III) 57 micron line have been made at 6 positions and the (Ne III) 36 micron line at 4 positions in the Orion Nebula to probe its ionization structure. The measurements, made with a -40'' diameter beam, were spaced every 45'' in a line south from and including the Trapezium. The wavelength of the (Ne III) line was measured to be 36.013 + or - 0.004 micron. Electron densities and abundance ratios of N(++)/O(++) have been calculated and compared to other radio and optical observations. Detailed one component and two component (bar plus halo) spherical models were calculated for exciting stars with effective temperatures of 37 to 40,000K and log g = 4.0 and 4.5. Both the new infrared observations and the visible line measurements of oxygen and nitrogen require T sub eff approx less than 37,000K. However, the double ionized neon requires a model with T sub eff more than or equal to 39,000K, which is more consistent with that inferred from the radio flux or spectral type. These differences in T sub eff are not due to effects of dust on the stellar radiation field, but are probably due to inaccuracies in the assumed stellar spectrum. The observed N(++)/O(++) ratio is almost twice the N(+)/O(+) ratio. The best fit models give N/H = 8.4 x 10 to the -5 power, O/H = 4.0 x 10 to the -4 power, and Ne/H = 1.3 x 10 to the -4 power. Thus neon and nitrogen are approximately solar, but oxygen is half solar in abundance. From the infrared O(++) lines it is concluded that the ionization bar results from an increase in column depth rather than from a local density enhancement.

• Research Organization: National Aeronautics and Space Administration, Moffett Field, CA (USA). Ames Research Center
• OSTI ID: 6482183
• Report Number(s): N-87-19313; NASA-TM-88368; A-86421; NAS-1.15:88368
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
DATA
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
ELEMENTS
EMISSION SPECTRA
EXPERIMENTAL DATA
FLUIDS
GASES
INFORMATION
INFRARED RADIATION
MATHEMATICAL MODELS
NEBULAE
NEON
NITROGEN
NONMETALS
NUMERICAL DATA
OXYGEN
RADIATIONS
RARE GASES
SPECTRA
STAR MODELS