Analysis of two SMC H II Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances

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Analysis of two SMC H II Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances

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Analysis of two SMC H II Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances

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Título: Analysis of two SMC H II Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances
Autor: Peña Guerrero, María A.; Peimbert, Antonio; Peimbert, Manuel; Ruiz González, María Teresa
Resumen: We present long-slit spectrophotometry considering the presence of thermal inhomogeneities (t(2)) of two H II regions in the Small Magellanic Cloud (SMC): NGC 456 and NGC 460. Physical conditions and chemical abundances were determined for three positions in NGC 456 and one position in NGC 460, first under the assumption of uniform temperature and then allowing for the possibility of thermal inhomogeneities. We determined t(2) values based on three different methods: (1) by comparing the temperature derived using oxygen forbidden lines with the temperature derived using helium recombination lines (RLs), (2) by comparing the abundances derived from oxygen forbidden lines with those derived from oxygen RLs, and (3) by comparing the abundances derived from ultraviolet carbon forbidden lines with those derived from optical carbon RLs. The first two methods averaged t(2) = 0.067+/-0.013 for NGC 456 and t(2) = 0.036+/-0.027 for NGC 460. These values of t(2) imply that when gaseous abundances are determined with collisionally excited lines they are underestimated by a factor of nearly two. From these objects and others in the literature, we find that in order to account for thermal inhomogeneities and dust depletion, the O/H ratio in low-metallicity H II regions should be corrected by 0.25-0.45 dex depending on the thermal structure of the nebula or by 0.35 dex if such information is not available.
Descripción: Artículo de publicación ISI
URI: http://www.captura.uchile.cl/handle/2250/16741
Fecha: 2012-02-20
Cita del item: ASTROPHYSICAL JOURNAL Volume: 746 Issue: 2 Article Number: 115 Published: FEB 20 2012


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