The oxygen abundance of the ultra-metal-poor star HE 0557-4840
2012 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 753, no 2, 150- p.Article in journal (Refereed) Published
We present a high-resolution ultraviolet (UV) spectrum of the ultra-metal-poor (UMP) carbon-enhanced red giant HE 0557-4840 (T-eff/log g/[Fe/H] = 4900/2.2/-4.8). Combining these data with earlier observations, the radial velocity is 212.0 +/- 0.4 km s(-1), with no evidence of variability during 2006 February to 2007 December. One-dimensional (1D) LTE model-atmosphere analysis of UV Fe and CH lines confirms the iron and carbon abundances obtained previously ([Fe/H] = -4.8 and [C/Fe](1D) = +1.7), and places a more stringent limit on nitrogen abundance of [N/Fe](1D) < +1.0. Analysis of the UV OH lines yields [O/Fe](1D) = +2.3 +/- 0.4. When corrections are made for three-dimensional (3D) effects we obtain [C/Fe](3D) = +1.1, [N/Fe](3D) < +0.1, and [O/Fe](3D) = +1.4. Comparison of the abundances of HE 0557-4840 with those of supernova models of Nomoto et al. and Joggerst et al. suggests that none is able to explain fully the observed abundance pattern. For HE 0557-4840, the Frebel et al. transition discriminant D-trans(= log(10([C/H]) + 0.3 x 10([O/H])) = -3.4 +/- 0.2, consistent with fine-structure transitions of C II and O I being a major cooling mechanism of star-forming regions at the earliest times. Of the four stars known to have [Fe/H] less than or similar to -4.3, three are strongly carbon and oxygen enhanced. If the suggestion by Caffau et al. that SDSS J102915+172927 ([Fe/H] = -4.7) does not belong to the class of C-rich, O-rich, UMP stars is supported by future similar discoveries, one will need to consider multiple channels for the production of stars having [Fe/H] less than or similar to -4.3.
Place, publisher, year, edition, pages
Institute of Physics (IOP), 2012. Vol. 753, no 2, 150- p.
early universe, Galaxy: formation, Galaxy: halo, nuclear reactions, nucleosynthesis, abundances, stars: abundances, stars: individual (HE 0557-4840)
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:uu:diva-178082DOI: 10.1088/0004-637X/753/2/150ISI: 000305912700057OAI: oai:DiVA.org:uu-178082DiVA: diva2:542137