Go upstream of the Milky Way!

Transcription

1 Go upstream of the Milky Way! A journey to the source of elements Univ.), Yuhri Ishimaru (Ochanomizu Univ.), S. Wanajo (Sophia U.),, N. Prantzos (IAP), W. Aoki (NAO),, S. G. Ryan (Open U.)

2 Chemical Components of Pebbles of MW Big Bang Stellar Evolution α-elements odd-z elements Fe-peak elements n-capture elements IA VIIIA H IIA IIIA IVA VA VIAVIIA He Li Be B C N O F Ne Na Mg IIIB IVB VB VIB VIIB VIII VIII VIII IB IIB Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr NbMoTc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Db Jl Rf Bh Hn Mt Lanthanoids La Ce Pr NdPmSm Eu Gd Tb Dy Ho Er Tm Yb Lu Actinoids Ac Th Pa U Np Pu AmCm Bk Cf Es FmMdNo Lr

3 Inhomogeneous Chemical Evolution Model Star Formation is assumed to be induced by SUPERNOVAE Supernova ejects gas & metal Supernova models; Nomoto et al. '97 (for Z stars) and Woosley & Weaver '95 (for 0~Z stars) R SNR Inter-Stellar Gas evolves as standard 1-zone chemical evoluiton with outflow (halo) or inflow (disc) Supernova Remnant expands and mixed with ISM The expansion radius is given from ISM density+metallicity R SNR ρ ISM -18/49 Z ISM -5/98 E 51 31/98 (Cioffi et al. 1988) New Stars formed from ISM+SNR Chemical compositions are given by their mass average

4 Nomoto et al. 97 Woosley & Weaver 95 SN Yields Nomoto et al. 97 Constant yields vs. metal dependent yields Umeda & Nomoto 02 effects of Pop III stars and hypernovae

5 Stellar Abundance Enriched by First SNe Nomoto et al. 97 Woosley & Weaver Z stars Stars from Supernova remnant + Evolved gas + Zero-metal gas Number = SN progenitor mass Dispersions come from variations of of SN SN yields in in different mass SNe.

6 Statistical Comparison of Dispersions Nomoto et al. 97 Woosley & Weaver 95 N97 WW95 Average of ISM Average of Stars 50% Confidence region 90% Confidence region Observational Data Average 50% Confidence region (Norris et al. 2001)

7 Statistical Comparison of Dispersions Constant R SNR 1.5 Dispersion in R SNR N97 WW95 50% Confidence Average yields mixing length Width of of scatters cannot be be reduced by by gas-mixing efficiency

8 [X/Fe] [X/Fe] [X/Fe] α-elements WW95 N97 UN03 Z<10-3 Z : Pop.III (HN) Z>10-2 Z : Z SN

9 α-elements WW95 N97 UN03

10 [X/Fe] [X/Fe] [X/Fe] Iron-peak elements WW95 N97 UN03

11 Iron-peak elements WW95 N97 UN03

12 Neutron-Capture Elements Dispersions in in [r/fe] of of MPS are are extremely large! These stars are are enriched by by only one or or a few SNe. The origin of of r-process must be be in in specific SNe! However, the origin of of r-process has been an an open question. CS shows almost pure solar-system r-process pattern CS Sneden et al. 2000

13 Possible Sites of R-Process Synthesis of heavier elements from seed nuclei by neutron capture Prompt Shock of SNeII 8~10 M (Hillebrandt et al. 84; Wheeler et al. 98) Neutrino Wind of SNeII >10 M (Woosley et al. 94) heavier stars (Wanajo et al. 2000) Neutron Star Envelope Fall Neutron Star Envelope Neutrino Wind Fall

14 Enrichment of Eu If the r-process site is... Prompt shock by SNII: Neutrino Wind of SNII: Stars of 8~10M Stars of >30M Average 50% Confidence 90% Confidence cf. Ishimaru & Wanajo 99

15 Observational Data Can Distinguish? Prompt It shock was too by difficult SNII: by previous Neutrino observations. Wind of SNII: Observations of stars with [Fe/H]<-3 is required! Stars of 8~10M Stars of >30M A possible telescope is SUBARU!

16 S01A Observation by Subaru HDS Observers: Ishimaru, Wanajo, Ryan, Aoki Observing Date: 07/23/2001~07/24/2001 (S01A) We selected 3 stars having [Ba/Fe]~-1, typical for their metallicities. Target HD4306 CS CS [Fe/H] [Mg/Fe] [Ca/Fe] [Ti/Fe] [Sr/Fe] [Ba/Fe] [Eu/Fe] <-0.2 Sub-solar values of [Eu/Fe] at [Fe/H]<-3 3 are detected for the first time

17 New Data for [Eu/Fe] All of 3 stars show sub-solar [Eu/Fe]!! Ishimaru, Wanajo, Aoki, Ryan, 2004, ApJ 600, L47 m mr =8~10M m mr >30M The data strongly supports 8~10 M as as the r-process site!!

18 Puzzles in Ba & Sr Sr Srenhancements are are seen in in very metal-poor stars If the origin of Sr is identical to that of Ba, [Sr/Ba] should be constant.? There must be be a distinct origin for for Sr Sr

19 Is It Weak S-Process? But But large Sr Srenhancements in in very metal-poor stars cannot be be reproduced by by weak s-process Because weak s-yield is strongly correlated with stellar metallicity

20 We Suggest Weak R-Process! While massive r-elements are produced mainly by `main r-process, lighter nuclei can be produced also by `failed r-process. Eu & Ba: from SNeII of 8~10 M stars Sr: from SNeII of >30 M stars If If 2 distinct sites of of r-process exist, Sr Srenhancements can be be explained

21 Weak R-Process Pattern? While main r-process produces heavier elements (Ba, Eu, etc), lighter elements (Sr, etc) are also produces by weak r-process

22 But Where Is the Boundary? How can we determine the upper mass limit of weak r-products???? Intermediate mass nuclei Pd Pd & Ag Ag must provide clues!

23 Recent Studies Most of elements of these stars agree with solar r-process pattern Sneden et al Hill et al Cowan et al Johnson & Bolte 2002 Pd also agrees with r-process? But Ag is lower than ss r-process? Which is is the origin of of Pd Pd & Ag, main r r or or weak r? r?

24 S02A Observation by Subaru HDS We selected two types of stars; 1) high [Sr/Ba] stars and 2) low [Sr/Ba] stars [Fe/H] [Sr/Fe] [Ba/Fe] [Eu/Fe] [Sr/Ba] Target [Pd/Fe] [Ag/Fe] Johnson 02+Johnson Bolte 02 HD BD-11 o Preliminary Results: HD BD-11 o < Stars

25 Abundance Pattern of HD Abundance pattern seems to to follow `weak r-process But But no no enhancement of of Pd Pd is is seen! Pd Pd is is main-r products? Again, Ag Ag is is significantly lower than r-pattern.

26 Abundance Pattern of BD-11 o 145 Abundance pattern shows contamination by by s-process But But still still Ag Ag is is lower than either r-pattern or or s-pattern Ag-deficient must be be an an interesting problem!

27 Pd Comes from Main r? If Pd is produced i) mainly by main r-process, [Sr/Pd] must correlate with [Sr/Ba]. ii) mainly by weak r-process, [Pd/Ba] must correlate with [Sr/Ba] But BD-11 o 145 may be significantly affected by s-process. [Sr/Pd] seems to correlate with [Sr/Ba]. Pd may be produced by main r-process. But weak correlation of [Pd/Ba] and [Sr/Ba] may suggest that the weak r/main r ratio of Pd is larger than that of Ba.

28 SUMMARY What can we find from pebbles of the Milky Way? Dispersions in abundances of MPS constrain variations in SN yields Especially, Eu + Ba & Sr abundances tell... 1) Subaru observation data suggests SNe II of 8~10M stars as the site of `main r-process 2) Lighter nuclei must be produced by `weak r-process 3) Pd may be beyond the upper mass limit of weak r products 4) The origin of Ag is problematic Neither main r, weak r, nor s-process seems to produce plenty of Ag. Some problems may exist in nuclear data or the solar abundance.

29 In Japanese... People say the Milky Way Galaxy as Silver River We will find the origin of Ag from the Milky Way in the near future...