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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20140703T103000
DTEND;TZID=Atlantic/Canary:20140703T113000
UID:iactalks-653
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/653
CREATED:2014-07-03T10:30:00+01:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Deriving model-based chemical abundances in ionized gaseos nebulae 
DESCRIPTION:Deriving model-based chemical abundances in ionized gaseos nebu
 lae \nDr. Enrique Pérez Montero\n\nThere is an increasing multiplicity of
  proposed methodologies to derive chemical abundances in HII regions from 
 the measurement of the relative fluxes of their optical emission lines. Pa
 rticularly there is a known discrepancy between the prediction of some wid
 ely used grids of photoionization models and the results of the direct ana
 lysis of the spectra from their integrated physical properties (i.e. densi
 ty, temperature). In this seminar, I will introduce HII-CHI-mistry, a Chi 
 square approximation to compare observations with results of a large grid 
 of models calculated using CLOUDY and varying the oxygen abundance, the ni
 trogen-to-oxygen ratio and the ionization parameter, covereing all possibl
 e conditions observed so far in massive complexes of star-formation. Inclu
 ding N/O as an additional variable allows the correct interpretation of th
 e [NII] 6584 emission lines, widely used to derive abundances both in the 
 Local and the Early Universe in the infra-red part of the spectrum.\nThe u
 se of this method leads to a derivation of both Z and N/O totally consiste
 nt with the results from the direct method when emission line ratios sensi
 tive to the temperature are available (e.g. [OIII] 50007/4363). On the con
 trary, when these ratios are not available, what is the most common situat
 ion in metal-rich/distant objects, it is necessary to assume empirical con
 straints to the space of parameters covered by the model-grid to arrive to
  solutions in the whole range of metallicity. Among the applications of th
 is methods it is a consistent study of the metallicity in a wide range of 
 potential variations (e.g. gradients of Z in disc galaxies, mass-metallici
 ty relation, etc ...)
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