A stellar census in globular clusters with MUSE

Astronomy and Astrophysics, vol. 635, pp. A114

Abstract

Aims. We use the spectra of more than 30 000 red giant branch (RGB) stars in 25 globular clusters (GC), obtained within the MUSE survey of Galactic globular clusters, to calibrate the Ca II triplet metallicity relation and derive metallicities for all individual stars. We investigate the overall metallicity distributions as well as those of the different populations within each cluster. Methods. The Ca II triplet in the near-infrared at 8498, 8542, and 8662 Å is visible in stars with spectral types between F and M and can be used to determine their metallicities. In this work, we calibrate the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch – a cutoff that has traditionally been made to avoid a non-linear relation – using a quadratic function. In addition to the classic relation based on V − VHB, we also present calibrations based on absolute magnitude and luminosity. The obtained relations were used to calculate metallicities for all the stars in the sample and to derive metallicity distributions for different populations within a cluster, which have been separated using so-called “chromosome maps” based on HST photometry. Results. We show that despite the relatively low spectral resolution of MUSE (R = 1900 − 3700) we can derive single star metallicities with a mean statistical intra-cluster uncertainty of ∼0.12 dex. We present metallicity distributions for the RGB stars in 25 GCs and investigate the different metallicities of the populations P3 (and higher) in so-called metal-complex or Type II clusters, finding metallicity variations in all of them. We also detected unexpected metallicity variations in the Type I cluster NGC 2808 and confirm the Type II status of NGC 7078 .

Authors 10

1. Tim-Oliver Husser

   University of Göttingen

   Affiliation as printed

   Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

2. M. Latour

   University of Göttingen

   Affiliation as printed

   Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

3. J. Brinchmann Aachen Leiden Observatory

   Leiden University · Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto · Leiden Observatory

   Affiliation as printed

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

4. S. Dreizler

   University of Göttingen

   Affiliation as printed

   Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

5. Benjamin Giesers

   University of Göttingen

   Affiliation as printed

   Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

6. Fabian Göttgens

   University of Göttingen

   Affiliation as printed

   Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

7. Sebastian Kamann

   Liverpool John Moores University

   Affiliation as printed

   Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK

8. Martin M. Roth

   Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

9. Peter M. Weilbacher

   Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

10. Martin Wendt

    University of Potsdam

    Affiliation as printed

    Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Golm, Germany