AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 71. Between the Stars II: The ISM, Galactic and Extragalactic
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[71.15] Chemical Composition and Temperature Fluctuations in M17

M. Peimbert (IAUNAM), C. Esteban (IAC), S. Torres-Peimbert (IAUNAM), J. Garc\'{\i}a-Rojas (IAC)

We present echelle spectroscopy in the 3500 to 10300 Å\ range for two positions of the galactic H\thinspace{\sc ii} region M17. The data have been obtained using the 2.1 m telescope at Observatorio Astronómico Nacional in San Pedro Mártir, Baja California. We measure the intensities of 160 emission lines, in particular 36 permitted lines of C+, N0, N+, N++, O0, O+, Ne0, Si0, and Si+. We determine electron temperatures and densities using different line intensity ratios as well as abundances from collisionally excited lines for a large number of ions and elements. We derive the He+, C++ and O++ ionic abundances from recombination lines, these nebular values are almost independent of the temperature structure of the nebula. We determine accurate t2 values by comparing the O++ ionic abundance obtained from collisionally excited lines and recombination lines. A comparison of the chemical abundances of the Sun, M17, M8, and the Orion nebula is made. We present strong observational constraints based on abundance ratios and compare them with recent models of galactic chemical evolution.

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