The ACS Survey of Galactic Globular Clusters. VII. Relative Ages
| Autor: | Brian Chaboyer, Ata Sarajedini, I. Neill Reid, Jay Anderson, Aaron Dotter, Alfred Rosenberg, Giampaolo Piotto, Steven R. Majewski, Ivan R. King, Nathaniel Paust, Luigi R. Bedin, Maren Hempel, Michael H. Siegel, Antonino Milone, Antonio Aparicio, Antonio Marín-Franch |
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| Jazyk: | angličtina |
| Rok vydání: | 2008 |
| Předmět: |
Physics
education.field_of_study Milky Way Metallicity Astrophysics (astro-ph) Population FOS: Physical sciences Astronomy and Astrophysics Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Space and Planetary Science Globular cluster Satellite galaxy Halo education Reionization Astrophysics::Galaxy Astrophysics Dwarf galaxy |
| Popis: | The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope (HST) Treasury program designed to provide a new large, deep and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters' main sequence turn offs, using main-sequence fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2-7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can be divided into two groups -- a population of old clusters with an age dispersion of ~5% and no age-metallicity relation, and a group of younger clusters with an age-metallicity relation similar to that of the globular clusters associated with the Sagittarius dwarf galaxy. These results are consistent with the Milky Way halo having formed in two phases or processes. The first one would be compatible with a rapid ( 50 pages, 14 figures. Accepted for publication in ApJ |
| Databáze: | OpenAIRE |
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