Globular Clusters


r-process elements in globular clusters

Otsuki, Kaori; Honda, Satoshi; Aoki, Wako; Kajino, Toshitaka; Truran, James W.; Dwarkadas, Vikram; Medina, Anibal

From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution, IAU Symposium Proceedings of the international Astronomical Union 228, Held in Paris, France, May 23-27, 2005. edited by Hill, V.; François, P.; Primas, F. Cambridge: Cambridge University Press, 2005., pp.403-404




We have observed seven giants in the metal-poor globular cluster M15 using Subaru/HDS. We confirmed that there are significant star-to-star variations in the neutron-capture elemental abundances. This abundance variation means there were primordial chemical inhomogeneities in the proto-globular cluster cloud of M15. This result implies that there was insufficient time for complete mixing after r-process nucleosynthesis. It suggests that the main r-process occurs probably in supernovae which explode in later stages of globular cluster formation.

On the formation of globular clusters

Medina, A. D.; Dwarkadas, V. V.; Ricker, P. M.; Truran, J. W., Jr.

American Astronomical Society Meeting 207, #128.10; Bulletin of the American Astronomical Society, Vol. 37, p.1373



Although globular clusters have been studied for decades, their formation mechanism still remains unclear. In this poster we focus on one of the assumed scenarios for their formation, that of self-enrichment within the proto-globular cluster cloud. The ejecta from multiple supernova explosions arising from an early generation of stars sweeps up the ambient gas within the cloud as it expands outwards, slowing down in the process until it becomes radiative. The transition to the radiative stage can lead to the onset of hydrodynamic instabilities and mixing of the ejecta products with the surroundings. If the proto-cluster cloud can avoid disruption the gas may condense to form stars, giving rise to a low metallicity globular cluster. We have investigated this model using one and two-dimensional numerical hydrodynamic simulations in spherical geometry. The simulations were carried out using the FLASH code, a modular, adaptive-mesh, parallel, multi-dimensional, multi-species PPM based hydrodynamic code, including radiative cooling via a cooling function.

This work is supported by the National Science Foundation under Grant PHY 02-16783 for the Frotier Center "Joint Institute for Nuclear Astrophysics" (JINA).

Neutron-capture elements in globular cluster M15

Otsuki, Kaori; Honda, S.; Aoki, W.; Kajino, T.; Medina, A.; Truran, J.; Dwarkadas, V.; Mathews, G. J.

Proceedings of the International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX. 25-30 June 2006, CERN., p.36.1




We used high-resolution, high signal-to-noise ratio spectra obtained with the Subaru Telescope to determine neutron-capture elemental abundances in metal-poor globular cluster M15. We con- firmed that there are star-to-star abundance variations in the abundance of heavy neutron-capture elements and there is no significant s-process contribution. We have found that there are anti- correlations between the abundance ratios of light to heavy neutron-capture elements and the abundance of heavy neutron-capture elements. Our observaitonal results indicates that at least two different processes have enriched light neutron-capture elements in the M15 progenitor. It has been pointed out that light neutron-capture elements in field stars should have been enriched by more than one process although astrophysical sites for such processes are still uncertain. Abun- dance distributions of neutron-capture elements in M15 give clues to understand the origin of light and heavy r-process elements.