Pos(NIC XI)257 3)

PoS(NIC XI)257 http://pos.sissa.it/ 3). The Th abundances . 0 + < rvatory Echelle Spectrograph Th, as well as of other heavy s of very metal-poor stars. The ffected by blending of other ele- ese metal-rich stars include young [Fe/H] al-poor stars is very efficient. The Th/Eu abundance ratios of our sam- oscopy with Subaru Telescope High < ss does not show large dispersion, or ower than the solar-system value. This 5 . an, Yamashina-ku, Kyoto, Mitaka, Tokyo 181-8588, Japan 2 − 1) stars show some scatter, and the average is − > e Commons Attribution-NonCommercial-ShareAlike Licence. ∗ [email protected] [email protected] mixing of interstellar matter before formation of these met are determined mostly using the Thments 5989 than Å the line, 4019 which Å is one lesspreliminary that a results has of our been measurements used are inple presented. previous show no studie The significant scatter, and theresult average is suggests slightly that l the actinide production by the r-proce Th/Eu ratios in relatively metal-rich ([Fe/H] Speaker. We have been determining abundances of the actinide element neutron-capture elements, based onDispersion high resolution Spectrograph spectr (HDS) and(GAOES). Our Gunma sample Astronomical covers wide metallicity Obse range ( higher than found in metal-poor stars. This suggests that th objects where decay of Th is less significant. ∗ Copyright owned by the author(s) under the terms of the Creativ c

Satoshi Honda Kwasan Observatory, Kyoto University, Ohmine-cho Kita Kaz Wako Aoki National Astronomical Observatory of Japan, 2-21-1E-mail: Osawa, 607-847, Japan E-mail: Thorium (Th) Enrichment in the Milky Way Galaxy 11th Symposium on Nuclei in theJuly Cosmos, 19-23, NIC 2010 XI Heidelberg, Germany PoS(NIC XI)257 esolving Wako Aoki or weather r features [4]. wide metallic- ts by r-process viously studied. llicity [3], but the f metal-poor stars s. For this reason, m high resolution panel of Figure 1; ements in neutron- 000 for bright and , in cool giants (with ess of spectral lines . The effective tem- e estimate of effective 70 lso measured from the orption lines in mildly e condition of r-process = elements and molecules, and Gunma Astronomical e measurements. This line In such stars (in particular R ensitive to the adopted stel- m the Th 5989 Å line. The note that efforts to measure ss predict that the production of 10) with low effective temperature < V 2 ) or adopted from literature. We note that the abundance K − V 000. The GAOES spectra were obtained with , 50 > R ). The Subaru spectra were obtained in a service program in 2008 with a r K ) of 90,000, or in observing runs of other programs during twilight or in po R Our targets are bright red giants (most of them have In order to investigate the enrichment of Th in the Milky Way Galaxy covering a The difficulties in observational studies of Th abundances are the weakn Th abundances have been measured from the Th II 4019 Å line for most o The actinide Th is a key element to understand the production of heavy elemen Standard abundance analyses have been made for Fe and other elements 5000 . 2. Measurements of Th abundances ity range, we have been extendingThe the Th measurements to 5989 higher Å metallicity lineeffective than is pre temperatures useful lower for than this 4500This purpose, K), article because and presents the the line the line isspectra preliminary with is detectable results the little Subaru of Telescope blended High our Dispersion withObservatory measurements Spectrograph Eschelle othe (HDS) obtained Spectrograph (GAOES). fro in the optical range, and alsoin contaminations particular of to spectral the features Th of 4019measurements other of Å Th line have been that limited has to been verycapture metal-poor used elements stars in with (see most large enhanc Roederer of previous etTh studie al.[2] abundance and from references the 4019 therein).uncertainty Å We due line to have the been blending made is for inevitable objects in with the solar analysis. meta in previous studies. Thismetal-poor line stars is, studied however, in severely the blendedcool present with red work other giants), (upper abs the panel Th of IIis Figure 5989 Å 1). almost line free is from sufficiently strong contaminationssee for of abundanc also other Aoki species et in al.atomic metal-poor [6]). line stars data (lower We of measured Nilsson Thlines et abundances in al. for the [5] X red are stars region adopted. (e.g. fro Eu The II Eu 6036 abundances Å, are 6645 a Å). power ( conditions with neutron-capture reactions. Indeed, model calculations of ther-process r-proce elements is sensitive to thesite model parameters (e.g. corresponding Wanajo to & th Ishimaru [1]). ( lar parameters, while the metallicity (Fe abundance)temperature. is rather dependent on th ratios between Th and other neutron-capture elements (e.g. Eu) are not s Th enrichment in the Galaxy 1. Introduction peratures are estimated from colors ( less metal-poor stars. PoS(NIC XI)257 2611 ◦ 15 dex), . 0 Wako Aoki = ε oor stars rep- log ∆ ction of metallicity We note that, while en circles). Our study ess statistically agrees ru spectra of BD+30 2 are slightly lower than dance ratio is determined − = 3) stars might be supplied by a single h II 5989 Å line is sufficiently strong for 2) would be integration of the products − ∼− erature of 4250K, [Fe/H]=-1.4), while the Th II > three different Th abundances ( 3 5. The red solid line indicates the average of Th/Eu for . 2 − > Examples of Th II lines at 4019 Å and 5989 Å detected in the Suba Figure 2 shows a preliminary result of the Th/Eu abundance ratios as a fun We here discuss the Th/Eu abundance ratios in metal-poor stars. Eu in metal-p We found that the Th/Eu ratios at the metallicity around [Fe/H] r-process event, those of less metal-poor stars ([Fe/H] resents the yields ofby r-process the by production progenitors. of Hence, thesethese two heavy the elements elements Th/Eu in by abun extremely r-process metal-poor and ([Fe/H] the decay of Th. of many events. (filled circles). The solid lines are calculated spectra for Figure 1: Th enrichment in the Galaxy 3. Enrichment of Th in the Galactic halo while the dotted linemeasurements means in that this for cool no metal-poor4019 Th giant Å (effective contribution. is temp highly contaminated The by T other species. for our sample (filled symbols) andcovers those the determined metallicity by range previous of studies [Fe/H] (op 0.5 dex metallicity bins and the bars mean their standard deviations. the solar value. This suggests that the Th/Eu ratio produced by the r-proc PoS(NIC XI)257 Wako Aoki t, some star- s decayed in 2: objects that maller than that − ]. We note that, iled comparisons = tal-poor stars reflect ld as halo population uired. 1 possibly implies that n the 4019 Å line, more nterestingly, the average e believed to be formed ult of a wide distribution parameters. − 5) stars studied by previous oduction is very sensitive to < . 1) on average, and the scatter 2 wn for our sample (filled circles − − > < [Fe/H] < 2 − esults) and others (open circles: Roederer et 1. Our sample of this metallicity range tions. − ects suggested to be thick disk stars. The solid . The red solid line indicates the average of Th/Eu < 4 [Fe/H] < 2 − A preliminary result of the abundance ratios of Th/Eu are sho The small scatter of Th/Eu in the metallicity range The Th/Eu ratio becomes higher at higher metallicity ([Fe/H] al. [2] and references therein). The filled triangles are obj Figure 2: and triangles: Subaru/HDS results; filled diamonds: GAOES r horizontal line is the Th/Eu ratio of solar-system material for 0.5 dex metallicity bins and bars mean the standard devia with the value estimated for the initial solar composition, but larger amount of Th ha Th enrichment in the Galaxy these stars. This isin an the expected early phase result of becausebetween the these our Milky results metal-poor Way from stars formation. the ar Thcareful It calibration II should of 5989 be the Å noted abundance line that, measurements and from for previous the deta ones two based lines o is req stars. Hence, the Th/Eu ratiosof and ages their of scatter metal-rich can stars be in interpreted our as sample. a res should include some objects of the Galactic disk population, which are not as o becomes slightly larger than found in mixing of interstellar matter into-star the scatter Milky of Way Th/Eu halo is was found already in efficient. extremely metal-poor By ([Fe/H] contras have particularly high Th/Euhowever, are the sometimes scatter of called Th/Eu asexpected found from "actinide-boost” in r-process stars models extremely [1], metal-poor [7 which starsthe predict environment is that and the still can actinides much vary pr by s one order or more by changes of model work. This would indicate that thethe chemical yields abundances of of a these limited extremely number me ofof r-process Th/Eu events (or ratios even in a single such event). extremely I metal-poor stars is higher than that at [Fe/H] PoS(NIC XI)257 The End Wako Aoki laxy, ARAA tribute to the the universality (1963) 2009 uclear Physics A ements because of ve. Measurements , (275) 2005 e analysis of metal- 698 434 uired to make more careful Experimental oscillator (L15) 2007 59 rly Galaxy ApJ rdström, ance ratios, A&A Pfeiffer, J. J. Cowan, & C. Sneden, The age of the Galactic thin disk from Th/Eu First Determination of the Actinide Thorium 5 (368) 2002 (255) 2005 The Discovery and Analysis of Very Metal-Poor Stars in the Ga r-process calculations and Galactic chemical evolution, N 382 430 Thorium-rich halo star HD 221170: Further evidence against (676) 2006 (531) 2005 of the r-process, A&A strengths in Th II, A&A nucleocosmochronology. I. Determination of [Th/Eu] abund of Nucleosynthesis: Production of Lead and Thorium in the Ea 777 Abundance for a Red Giant of the Ursa Minor Dwarf Galaxy, PASJ 43 We are conducting more detailed abundance analyses for our sample. In th [4] A. Yushchenko, et al. [6] W. Aoki, S. Honda, K. Sadakane, & N. Arimoto, [5] H. Nilsson, Z. G. Zhang, H. Lundberg, S. Johansson, & B. No [3] E. F. del Peloso, L. da Silva, G. F. Porto de Mello, [7] T. C. Beers, N. Christlieb, [2] I. U. Roederer, K. -L. Kratz, A. Frebel, N. Christlieb, B. [1] S. Wanajo, Y. Ishimaru, rich stars, measurements of Eu are sometimesblending more of uncertain other than the species Th to measur thecalibration absorption of lines. the Further abundance measurements efforts are fromfor req the two larger lines sample as covering mentioned wide abo understanding metallicity of range enrichment will of improve actinides the in statistics the and Milky Way con Galaxy. References Th enrichment in the Galaxy