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Session 46 - Supernova Remnants.
Display session, Tuesday, January 14
We present echelle spectroscopy in the 3550 to 7010 A range for two positions of the Orion Nebula. The data were obtained with the 2.1-m telescope at Observatorio Astronómico Nacional in San Pedro Mártir, Baja California. We have measured the intensities of several permitted lines of C^+, N^+, N^++, O^0, O^+, Ne^0, Si^+, Si^++ which are excited by recombination and fluorescence. We have determined the electron temperature, the electron density and the ionic abundances using different intensity ratios. In particular the O^++/H^+ abundance obtained by recombination lines is 40% higher than that obtained using forbidden [O III] lines. Moreover the C^++/H^+ value derived from the recombination C II 4267 line is a factor of two higher than that derived in previous work for the same zone using C III] 1906+1909 collisionally excited lines. We estimate that a moderate value of t^2 = 0.025 \pm 0.015 can account for these discrepancies.
Program listing for Tuesday