Neutron-capture Elements in M15 Kaori Otsuki (U Chicago), S. Honda, W. Aoki, T. Kajino (NAOJ) J. W. Truran, V. Dwarkadas, A. Medina (U Chicago) G. J. Mathews (UND) JINA Frontiers 2005 (8/22/2005)

r-process elements in field stars(1) Universal abundance pattern Universal abundance pattern for Z>56  same event  primary process (Sneden et al.2000)

r-process elements in field stars(2) [Ba/Fe] scatter Today Past Chemical inhomogeneity of early galaxy Ba & Fe are formed in SNe II Two events: Forms Ba & Fe Forms Fe without Ba ex. All SNe eject Fe but only particular progenitor mass SNe eject r-process elements (e.g., Ishimaru & Wanajo 1999, Tsujimoto et al. 1999) not all SNe II generate r-process elements Honda et al. 2004

r-process elements in field stars(3) [Sr/Ba] scatter Honda et al There are (at least) two r-process sites: main r-process: Forms all r-process elements weak r-process: Forms Sr (Y, Zr) but not Ba Totally different events? Different progenitor mass SNe? Different phase of same event?

Globular cluster M15 ~ stars, ~10 6 M  same [Fe/H] within 10% *few exceptions not affected by explosive event after their formation Globular clusters Sneden et al. (1997, 2000) star-to-star variation of Ba in M15 Sneden et al. (2000) no s-process enrichment in M15 Difficult to explain with current theoretical models Constraints on GC formation models & the origin of r-process elements

Observations Seven red giants in M15 using Subaru/HDS –Three high Ba stars and four low Ba stars from Sneden et al.(1997) –July 25, – A, R=50,000 –One star(K479) is excluded for this discussion wide spectral lines significant contribution from other stars? (but no signature of contamination in slit viewer nor HST image.)

Heavy r-process elements La, Eu in M15 formed only by main r-process star-to-star abundance variation in heavy neutron-capture elements No significant s-process contribution Burris et al.2000 Arlandini et al.1999

Light r-process elements Y, Zr in M15 formed by main r & weak r-process Uniform weak r-process enrichment inhomogeneities of main r-process enrichment consistent with Galactic chemical evolution models Tumlinson(2005), Travaglio et al.(2001), Ishimaru et al.(2005) Otsuki et al. (2005)  main r-process at the later stage

Globular cluster formation Weak r-process event  complete mixing of gas  main r-process events Pre-enrichment models Ex. clouds collisions face-on collision of clouds shock induce star formation Globular cluster Chemically enriched cloud Main r-processes Weak r-processes Self-enrichment models 1 st generation stars from metal-free PGCC Globular cluster 1 st generation SNe induce 2 nd generation star formation Main r-processesWeak r-processes light SNe II or massive SNe II of 2 nd generation

Neutron-capture elements in other globular clusters ? ? Is there s-process enrichment from cluster stars? Field stars: Simmerer et al. 2004(black closed triangles), Wolf et al (black open triangle), Honda et al. 2004(crosses) GCs: M15: Sneden et al. 2000b(circles), Our new data (squares), M68: Lee et al. 2005, M92: Our new data, M13 & M3: Sneden et al.2004 (closed circles), Cohen & Melendes 2005 (open circles), M5: Ivans et al (closed circles), Ramirez & Cohen 2003 (open circles), M4: Ivans et al

Summary We observed seven giants in globular cluster M15 using Subaru/HDS. There is scatter of heavy neutron-capture elements in M15. There is no significant s-process enrichment in M15. Light r-process elements in M15 also show abundance variations.  uniform weak r-process + uneven main r-process main r-process in the later stage of globular cluster formation