TY - JOUR
T1 - The oxygen abundance of the ultra-metal-poor star HE 0557-4840
AU - Norris, John E.
AU - Christlieb, N.
AU - Bessell, M. S.
AU - Asplund, M.
AU - Eriksson, K.
AU - Korn, A. J.
PY - 2012/7/10
Y1 - 2012/7/10
N2 - 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 ± 0.4kms-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 HE0557-4840, the Frebel et al. transition discriminant D trans(= log(10 [C/H] + 0.3 × 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] ≲ -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] ≲ -4.3.
AB - 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 ± 0.4kms-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 HE0557-4840, the Frebel et al. transition discriminant D trans(= log(10 [C/H] + 0.3 × 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] ≲ -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] ≲ -4.3.
KW - Galaxy: formation
KW - Galaxy: halo
KW - early universe
KW - nuclear reactions, nucleosynthesis, abundances
KW - stars: abundances
KW - stars: individual (HE 0557-4840)
UR - http://www.scopus.com/inward/record.url?scp=84862870629&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/753/2/150
DO - 10.1088/0004-637X/753/2/150
M3 - Article
SN - 0004-637X
VL - 753
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 150
ER -