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

TodayPast

Chemical inhomogeneity of early galaxy

Ba & Fe are formed in SNe II

Two events:Forms Ba & FeForms 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. 2004

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

• ~104-6 stars, ~106M

• 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 modelsConstraints on GC formation models & the origin of r-process elements

ObservationsSeven red giants in M15 using Subaru/HDS

– Three high Ba stars and four low Ba stars from Sneden et al.(1997)

– July 25,26 2004– 3550-5250 A, R=50,000– One star(K479) is excluded for

this discussionwide spectral linessignificant contribution from other stars?(but no signature of contamination

in slit viewer nor HST image.)

Heavy r-process elements La, Eu in M15formed only by main r-process

star-to-star abundance variation in heavy neutron-capture elements

No significant s-process contribution

Burris et al.2000Arlandini et al.1999

Light r-process elements Y, Zr in M15formed 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 formationWeak r-process event complete mixing of gas main r-process events

Pre-enrichment modelsEx. clouds collisions

face-on collision of cloudsshock induce star formation Globular clusterChemically enriched cloud

Main r-processes

Weak r-processes

Self-enrichment models

1st generation stars from metal-free PGCC

Globular cluster1st generation SNe induce2nd generation star formation

Main r-processesWeak r-processes

light SNe II ormassive SNe II of 2nd 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. 1995 (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. 2001 (closed circles), Ramirez & Cohen 2003 (open circles), M4: Ivans et al. 1999.

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