High-resolution abundance analysis of very metal-poor r-I stars

Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly\ud enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a\ud better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak.\ud Aims. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with −3.4 ≤ [Fe/H] ≤ −2.4 classified\ud as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is (are) responsible for\ud the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars.\ud Methods. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph,\ud using spectra in the wavelength ranges 3400–4500 Å, 6800–8200 Å, and 8700–10 000 Å, with resolving power R ∼ 40 000 (blue arm)\ud and R ∼ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code\ud Turbospectrum.\ud Results. We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al,\ud K, and Sc, the iron-peak elements V, Cr,Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr,Mo, Ru, and Pd),\ud the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the\ud actinides (Th) regions. The results are compared with values for these elements for r-II and “normal” very and extremely metal-poor\ud stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions\ud about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for\ud the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the\ud main r-process) are nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak\ud r-process) are more enhanced in r-I stars than in r-II stars, suggesting that differing nucleosynthesis pathways were followed by stars\ud belonging to these two different classifications.CAPESCNPqFAPESPCNRSPhysics Frontiers Center/Joint Institute for Nuclear Astrophysics (JINA) - PHY 08-22648NSF - PHY1102511FONDATION MERACJSPS Grants-in-Aid for Scientific Research - 2322400