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The WAGGS project - II. The reliability of the calcium triplet as a metallicity indicator in integrated stellar light.

Usher, CG, Beckwith, T, Bellstedt, S, Alabi, A, Chevalier, L, Pastorello, N, Cerulo, P, Dalgleish, HS, Fraser-McKelvie, A, Kamann, S, Penny, S, Foster, C, McDermid, R, Schiavon, RP and Villaume, A (2018) The WAGGS project - II. The reliability of the calcium triplet as a metallicity indicator in integrated stellar light. Monthly Notices of the Royal Astronomical Society, 482 (1). pp. 1275-1303. ISSN 0035-8711

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Abstract

Using data from the WiFeS Atlas of Galactic Globular cluster Spectra, we study the behaviour of the calcium triplet (CaT), a popular metallicity indicator in extragalactic stellar population studies. A major caveat of these studies is that the potential sensitivity to other stellar population parameters such as age, calcium abundance, and the initial mass function has not yet been empirically evaluated. Here, we present measurements of the strength of the CaT feature for 113 globular clusters in the Milky Way and its satellite galaxies. We derive empirical calibrations between the CaT index and both the iron abundance ([Fe/H]) and calcium abundance ([Ca/H]), finding a tighter relationship for [Ca/H] than for [Fe/H]. For stellar populations, 3 Gyr and older the CaT can be used to reliably measure [Ca/H] at the 0.1 dex level but becomes less reliable for ages of ∼2 Gyr and younger. We find that the CaT is relatively insensitive to the horizontal branch morphology. The stellar mass function however affects the CaT strengths significantly only at low metallicities. Using our newly derived empirical calibration, we convert our measured CaT indices into [Ca/H] values for the globular clusters in our sample.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018: The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 10 Oct 2019 09:28
Last Modified: 10 Oct 2019 09:28
DOI or Identification number: 10.1093/mnras/sty2611
URI: http://researchonline.ljmu.ac.uk/id/eprint/11519

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