The Absolute Age of the Globular Cluster M15 Using Near-infrared Adaptive Optics Images from PISCES/LBT

Journal
THE ASTROPHYSICAL JOURNAL
Date Issued
2015
Author(s)
Monelli, M.
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Bono, G.
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Ferraro, I.
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Iannicola, G.
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Massari, D.
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Boutsia, K.
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Close, L.
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Fini, L.
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Guerra, J. C.
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Hill, J.
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Kulesa, C.
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McCarthy, D.
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Quiros-Pacheco, F.
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Skemer, A.
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DOI
10.1088/0004-637X/812/1/25
Description
The authors warmly thank Don VandenBerg for sharing the new set of isochrones prior to publication. Support for this work has been provided by the Education and Science Ministry of Spain (grant AYA2010-16717). G.F. has been supported by the Futuro in Ricerca 2013 (grant RBFR13J716). This work was partially supported by PRIN–INAF 2011 “Tracing the formation and evolution of the Galactic halo with VST” (P.I.: M. Marconi) and by PRIN–MIUR (2010LY5N2T) “Chemical and dynamical evolution of the Milky Way and Local Group galaxies” (P.I.: F. Matteucci).
Abstract
We present deep near-infrared J, {K}{{s}} photometry of the old, metal-poor Galactic globular cluster M15 obtained with images collected with the LUCI1 and PISCES cameras available at the Large Binocular Telescope (LBT). We show how the use of First Light Adaptive Optics (FLAO) system coupled with the PISCES camera allows us to improve the limiting magnitude by ̃2 mag in {K}{{s}}. By analyzing archival Hubble Space Telescope data, we demonstrate that the quality of the LBT/PISCES color-magnitude diagram is fully comparable with analogous space-based data. The smaller field of view is balanced by the shorter exposure time required to reach a similar photometric limit. We investigated the absolute age of M15 by means of two methods: (i) by determining the age from the position of the main-sequence turnoff (MSTO), and (ii) by the magnitude difference between the MSTO and the well-defined knee detected along the faint portion of the MS. We derive consistent values of the absolute age of M15, that is, 12.9 ± 2.6 Gyr and 13.3 ± 1.1 Gyr, respectively.

Observations were carried out using the Large Binocular Telescope at Mount Graham, AZ. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; the Ohio State University; and the Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.

Volume
812
Issue
1
Start page
25
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