Abundance patterns of r-process enhanced metal-poor stars Satoshi Honda 1, Wako Aoki 2, Norbert Christlieb 3, Timothy C. Beers 4, Michael W.Hannawald 2 Toshitaka Kajino 2, Hiroyasu Ando 2, Paul S. Barklem 3 1 Gunma Astronomical Observatory, 2 National Astronomical Observatory of Japan, 4 Michigan State University, 3 Uppsala Astronomical Observatory

Nucleosynthesis H 、 He 、（ Li ） Big Bang Nucleosynthesis α-elements(Mg,Ca,Si…) 、 iron-peak Stellar nucleosynthesis αelements → Type II SNe iron → Type Ia SNe The elements heaver than iron Neutron capture s-process （ Ba, Pb, etc. ） AGB stars r-process （ Eu, Au, Th, etc. ） still unknown! Burbidge, Burbidge, Fowler, Hoyle 1957

Type II SNe neutrino wind cf. Woosley et al prompt explosion cf. Sumiyoshi et al Neutron star mergers cf. Rosswog et al Collapsars cf. Pruet et al NSM Freiburghaus et al SNe Wanajo et al Collapsar Fujimoto et al The possible site for the r-process

Observations of r-process enhanced stars Behavior of Eu abundance as a function of [Fe/H] Large dispersion in [Fe/H] < -2.5 Almost no data in [Fe/H]<-3 Honda et al Subaru/HDS Francois et al VLT/UVES Barklem et al Type II SNeType I SNe

Models of galactic chemical evolution Ishimaru et al [Fe/H] ＜ - ３ is important ! Argast et al M Cescutti et al Tsujimoto et al NSM SNe Donder & Vanbeveren 2003 Mathews et al Argast et al ～ 50M solar

Observations of r-process enhanced stars Behavior of Eu abundance as a function of [Fe/H] Large dispersion in [Fe/H] < -2.5 Almost no data in [Fe/H]<-3 r-II star [Ba/Eu] < 0 r-II ： [Eu/Fe]>+1 r-I ： +1>[Eu/Fe]>+0.3 Beers & Christlieb 2005 Honda et al Subaru/HDS Francois et al VLT/UVES Barklem et al Type IIType I

Detailed analysis of r-II stars Universal pattern 56<Z<72 Th, (and U) line was detected. age determination Sneden et al Hill et al Christlieb et al CS CS CS Frebel et al HE decayed

Multiple r-process sites Some metal-poor stars show a significantly different abundance pattern from that of the solar system r- process abundance pattern. This results support the existence of two process (main and weak r-process). Sneden et al Honda et al CS HD HD88609

r-II stars discovered by HERES ← s-process rich stars are also included. follow-up observations are required. Barklem et al Hamburg/ESO R-process Enhanced Star survey

Subaru/HDS observations （ S05B-152) HE HE CS B (mag) Teff (K) [Fe/H] [Eu/Fe] Obs. date R ～ 50, ～ 5250 Å S/N 100 ～ 150 ＠ 4000 Å Christlieb et al. 2004, Barklem et al Honda et al These targets were obtained from HERES.

The spectra of r-II stars HE CS HE solar Wavelength （Å） Fe Eu Fe S/N 100 S/N 150

Behavior of Eu abundance as a function of metallicity r-II stars exists only in the region of -3.2<[Fe/H]<-2.6.

abundance patterns These objects are in agreement with the solar ｒ -process pattern. No weak r-process. Sr Ba Eu Th La Ir

Abundance patterns of r-II stars CS , CS , CS , CS , HE , HE average Eu

The region of Th II 4019 line HE Th II CS HE The spectra of HE may contain the sky-background. CH It was not completely remove.

Thorium is detected in two objects Th II Nd II 12 CH Fe I 13 CH HE CS Uranium is undetectable.

Th/Eu as a function of [Fe/H] The ratio of Th/Eu show scatter. The width of the scatter is not so large. CS CS CS initial Th/Eu Sneden et al HE HE

Summary and future work We confirmed that those objects are r-II stars. r-II stars exist only in the region of -2.4 < [Fe/H] < These objects are in agreement with the solar ｒ -process pattern. No weak r-process. The ratio of Th/Eu shows scatter. Remove the sky-background in the spectra of HE completely. Determine the upper limit of U 、 Pb abundances. More telescope time in dark night. The number of samples is increased. SEGUE, LAMOST, etc.