Neutron-Capture Elements in the Metal-Poor Globular Cluster M15

Neutron-Capture Elements in the Metal-Poor Globular Cluster M15 Globular cluster M15 (NOAO/AURA/NSF) Subaru Telescope Atomic Number log ε 60 70 80 90 -2 -1.5 -1 -.5 0 .5 1 N-Capture Abundances in Globular Cluster M15 Ba La Ce Nd Sm Eu Gd Dy Th solar r-process solar total M15 weighted <K462+K341+K583> From Sneden et al. ApJL536,85,(2000) The abundances of heavy elements (e.g. iron peak and r-process elements) in globular clusters have generally been believed to be quite uniform. The dispersion in [Fe/H] for cluster stars is generally found (with a few notable exceptions) to be less than ∼ 10 percent. This is in contrast to some lighter elements, whose abundances in cluster stars can have been complicated by the effects of stellar evolution. Recently, however, observational studies have reported a significant spread in the r-process abundances of stars in M15, even though their [Fe/H] are almost identical. In order further to explore this behavior, we have observed six giants in M15 using Subaru/HDS. Our abundance analysis, based on high- quality blue spectra, confirms the existence of significant scatter in heavy r-process element abundances for stars in M15. Furthermore, we have found, for the first time, that there exist trends in abundance ratios of neutron-capture products with the total heavy element enrichment: specifically, the [Y/Eu] ratio decreases with increasing heavy (r-process) element enrichment, as reflected in [Eu/Fe]. Our results indicate that the light neutron-capture elements in these stars cannot be explained by a single r-process event which also enriched the heavy neutron-capture elements: a second r-process contribu- tion is clearly required. Similarly, it has been pointed out that two distinct r-processes contributions are also required to explain the observed neutron-capture elemental abundance patterns in metal-poor field stars. To date, heavy r-process element patterns have been observed for stars in several metal-poor globular clusters, but their exists little data concerning lighter r-process elements (in the region A ≤ 130). Further observations of r-process elements in globular clusters can provide important information concerning both the sites and processes of r-process synthesis and the formation and early evolution of globular clusters. This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This work has been supported by NFS Grant PHY 02-16783 (Joint Institute for Nuclear Astrophysics). 4127 4128 4129 4130 4131 4132 4133 0 0.5 1 Eu II K462 K634 Fe I Ce II Gd II Fe I Dy II Ti II Fe II Mn II Ce II Fe I Examples of spectra of M15 stars. Observed [Eu/H] vs. [Fe/H] of M15 stars. There are high Eu stars and low Eu stars though [Fe/H] are nearly identical within ∼ 10%. [Y/Eu] vs. [Eu/H]. High Eu stars show low [Y/Eu] ratios. Researchers: K. Otsuki 1 , S. Honda 2 , W. Aoki 2 , J. W. Truran 1,4 V. Dwarkadas 1 , A. Medina 1 , G.J. Mathews 3 , T. Kajino 2 1 U. of Chicago 2 NAOJ 3 NDU 4 Argonne National Laboratory

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Transcript of Neutron-Capture Elements in the Metal-Poor Globular Cluster M15

Neutron-Capture Elements in theMetal-Poor Globular Cluster M15

Globular cluster M15(NOAO/AURA/NSF)

Subaru Telescope

Atomic Number

log

60 70 80 90-2

-1.5

-1

-.5

N-Capture Abundances in Globular Cluster M15

SmEu

solar r-process

solar total

M15 weighted <K462+K341+K583>

From Sneden et al.ApJL536,85,(2000)

The abundances of heavy elements (e.g. iron peak and r-processelements) in globular clusters have generally been believed to be quiteuniform. The dispersion in [Fe/H] for cluster stars is generally found(with a few notable exceptions) to be less than ∼ 10 percent. Thisis in contrast to some lighter elements, whose abundances in clusterstars can have been complicated by the effects of stellar evolution.Recently, however, observational studies have reported a significantspread in the r-process abundances of stars in M15, even though their[Fe/H] are almost identical.In order further to explore this behavior, we have observed six giantsin M15 using Subaru/HDS. Our abundance analysis, based on high-quality blue spectra, confirms the existence of significant scatter inheavy r-process element abundances for stars in M15. Furthermore,we have found, for the first time, that there exist trends in abundanceratios of neutron-capture products with the total heavy element en-richment: specifically, the [Y/Eu] ratio decreases with increasingheavy (r-process) element enrichment, as reflected in [Eu/Fe]. Ourresults indicate that the light neutron-capture elements in these starscannot be explained by a single r-process event which also enrichedthe heavy neutron-capture elements: a second r-process contribu-tion is clearly required. Similarly, it has been pointed out that twodistinct r-processes contributions are also required to explain the ob-served neutron-capture elemental abundance patterns in metal-poorfield stars.To date, heavy r-process element patterns have been observed forstars in several metal-poor globular clusters, but their exists littledata concerning lighter r-process elements (in the region A ≤ 130).Further observations of r-process elements in globular clusters canprovide important information concerning both the sites and pro-cesses of r-process synthesis and the formation and early evolutionof globular clusters.This work is based on data collected at the Subaru Telescope, whichis operated by the National Astronomical Observatory of Japan.This work has been supported by NFS Grant PHY 02-16783 (JointInstitute for Nuclear Astrophysics).

4127 4128 4129 4130 4131 4132 41330

0.5

Eu II

K462 K634

Fe I

Ce IIGd IIFe IDy IITi II

Fe II

Mn II

Ce II

Fe I

Examples of spectra of M15 stars.

Observed [Eu/H] vs. [Fe/H] of M15stars. There are high Eu starsand low Eu stars though [Fe/H] arenearly identical within ∼ 10%.