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The Australia Telescope National Facility Colloquium
11:00-12:00 Tue 04 Nov 2008

ATNF Marsfield Lecture Theatre

César Esteban

(Instituto de Astrofísica de Canarias)

CII and OII recombination lines in the optical spectra of HII regions - César Esteban Colloquium

The detection of faint recombination lines (RLs) of heavy-element ions in the spectra of ionized nebulae opens the possibility to test whether the standard methods to derive abundances - based on bright collisionally excited lines (CELs) - are confident or not. This is a necessary test, because most of our current knowledge about the chemical composition of the extragalactic Universe comes from the analysis of CELs in HII region spectra. In this talk I will review the main results of our research based on deep échelle spectra of Galactic and extragalactic HII regions taken with the 4.2m WHT, 8m VLT and 10m Keck telescopes. Our results indicate that ionic abundances determined from RLs are always a factor of about two times higher than those determined from CELs. The reasons and consequences of that "abundance discrepancy" will be discussed. Finally, I will briefly report on the current status of the new 10m GTC (Gran Telescopio de Canarias) telescope at Roque de los Muchachos Observatory (La Palma, Spain) that will be put in operation before the end of this year.

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