Computer Science
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984esasp.218..337c&link_type=abstract
In ESA Fourth European IUE Conf. p 337-340 (SEE N84-35135 24-88)
Computer Science
3
Computerized Simulation, Iue, Photoionization, Planetary Nebulae, Stellar Models, Cosmic Dust, Electron Density Profiles, Stellar Atmospheres, Stellar Composition, Stellar Temperature
Scientific paper
A photoionization model of NGC 3918 was constructed using high and low resolution IUE spectra, images of the nebula in H and OIII lines, together with optical, infrared and radio fluxes. The model has a nucleus with Teff = 117,000 K (the He II Zanstra temperature) and log g = 5.9. Nebular electron density diagnostics include SII, OII, CIII, SiIII, NeIV, and IOV line ratios, and yield projected densities in the range 3000 to 10,000 per cucm. Initial, homogeneous models give low-excitation line fluxes much weaker than observed; either a cylindrical or patchy geometry may explain this discrepancy. The nebula is carbonrich with C/O = 1.6, and IRAS fluxes can be matched with graphite grains of sizes 0.015 to 0.35 microns located inside the ionized region. The gas-to-dust ratio is 440 by mass. The expansion velocity of the nebula for 0+ ions is 25 km/sec.
Barlow Michael J.
Clegg Robin E. S.
Harrington Patrick J.
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