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Neutron-Capture Element Abundances in the Globular Cluster M15.
The Astrophysical Journal
|June 20, 2000
Summary
This study analyzed red giant stars in M15, finding their neutron-capture element abundances match the solar system r-process distribution. This implies the age of neutron-capture material in M15 stars is 14+/-3 billion years.
Area of Science:
- Astronomy
- Astrophysics
- Stellar Evolution
Background:
- Globular clusters like M15 provide insights into early galactic chemical evolution.
- Neutron-capture elements are crucial for understanding nucleosynthesis and stellar ages.
Purpose of the Study:
- To determine the abundances of neutron-capture elements in red giant stars within the M15 globular cluster.
- To use the radioactive element thorium as a chronometer to estimate the age of the neutron-capture material.
Main Methods:
- Obtained high-resolution, blue-violet spectra of three red giant branch tip stars in M15 using the Keck I High-Resolution Echelle Spectrograph.
- Analyzed spectral data to determine abundances of heavy elements (Z>=56), including thorium (Th) and europium (Eu).
Main Results:
- The observed abundances of heavy elements in the studied stars align with a scaled solar system r-process (rapid neutron-capture process) distribution.
- A weighted mean Th/Eu ratio suggests an age of 14+/-3 billion years for the neutron-capture material in M15 stars.
Conclusions:
- The findings support the hypothesis of a common r-process source for heavy elements in M15.
- The derived age is consistent with other recent age estimates for Galactic globular clusters, aiding in understanding the Milky Way's formation timeline.