High resolution study of the abundance pattern of the heavy elements in very metal-poor field stars

Abstract

The abundances of heavy elements in EMP stars are not well explained by the simple view of an initial basic "rapid" process. In a careful and homogeneous analysis of the "First stars" sample (eighty per cent of the stars have a metallicity [Fe/H]=-3.1$\pm$0.4), it has been shown that at this metallicity [Eu/Ba] is constant, and therefore the Eu-rich stars (generally called "r-rich") are also Ba-rich. The very large variation of [Ba/Fe] (existence of "r-poor" and "r-rich" stars) induces that the early matter was not perfectly mixed. On the other hand, the distribution of the values of [Sr/Ba] vs. [Ba/Fe] appears with well defined upper and lower envelopes. No star was found with [Sr/Ba]<-0.5 and the scatter of [Sr/Ba] increases regularly when [Ba/Fe] decreases. To explain this behavior, we suggest that an early "additional" process forming mainly first peak elements would affect the initial composition of the matter. For a same quantity of accreted matter, this additional Sr production would barely affect the r-rich matter (which already contains an important quantity of Sr) but would change significantly the composition of the r-poor matter. The abundances found in the CEMP-rs stars reflect the transfer of heavy elements from a defunct AGB companion. But the abundances of the heavy elements in CEMP-no stars present the same characteristics as the the abundances in the EMP stars.

9 pages

References in corpus (14)

• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• Discovery of HE 1523-0901, a Strongly r-Process Enhanced Metal-Poor Star with Detected Uranium
• Neutron-capture elements in the very metal-poor star HD122563
• First stars VII. Lithium in extremely metal poor dwarfs
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars
• The r-process in proto-neutron-star wind revisited
• First stars IX -Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios
• Silver and palladium help unveil the nature of a second r-process
• Neutron-capture elements in the very metal-poor star HD88609: another st ar with excesses of light neutron-capture elements
• CS 30322-023: an ultra metal-poor TP-AGB star?
• Cold r-Process in Neutrino-Driven Winds

Cited by in corpus (7)

• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• Abundance patterns of the light neutron-capture elements in very and extremely metal-poor stars
• On the neutron-capture elements across the Galactic thin disk using Cepheids
• The low Sr/Ba ratio on some extremely metal-poor stars
• Homogeneity in the early chemical evolution of the Sextans dwarf Spheroidal galaxy
• Detailed analysis of a sample of field metal-poor N-rich dwarfs
• A comparative study on three modes of s-process nucleosynthesis in extremely metal-poor AGB stars