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Oxygen and Magnesium Abundance in the Ultra-Metal-Poor Giants CS22949-037 and CS29498-043: Challenges in Models of Atmospheres

G. Israelian·N. Shchukina·R. Rebolo·G. Basri·J. I. Gonzalez-Hernandez·T. Kajino
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Abstract

We report the results of a non-LTE Fe, O and Mg abundance analysis of the carbon-nitrogen-rich ultra-metal-poor giants CS29498--043 and CS22949--037. The abundance of oxygen has been derived from measurements of the oxygen triplet at 7771-5 A in high resolution spectra obtained with KeckI/HIRES and the forbidden line [OI] 6300 A detected in the TNG/SARG spectra of CS29498-043. Detailed non-LTE analysis of Fe lines has provided reliable stellar parameters which, however, do not resolve the oxygen abundance conflict as derived from the OI 7771-5 A triplet and the [OI] 6300 A forbidden lines. We obtained the following oxygen abundance: for CS22949-037 [O/Fe] =3.13, 1.95; and for CS29498-043; [O/Fe]=3.02, 2.49, based on the OI 7771-5 A triplet and the [OI] 6300 A forbidden line, respectively. A similar conflict appears to exist between the forbidden resonance line MgI 4571 A and several subordinate lines, such as MgI 5172 and 5183 A. Our analysis demonstrates the failure of standard plane--parallel atmosphere models to describe the physical conditions in the line-forming regions of these ultra-metal-poor giants.

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G. Israelian, N. Shchukina, R. Rebolo, G. Basri, J. I. Gonzalez-Hernandez, T. Kajino. 2004-03-01. Oxygen and Magnesium Abundance in the Ultra-Metal-Poor Giants CS22949-037 and CS29498-043: Challenges in Models of Atmospheres. https://doi.org/10.1051/0004-6361%3A20035785

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