Intrinsic iron spread and a new metallicity scale for globular clusters

Elisa Carretta, Angela Bragaglia, Ruth Gratton, V. D'Orazi, Sara Lucatello

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399 Citations (Scopus)

Abstract

We have collected spectra of about 2000 red giant branch (RGB) stars in 19 Galactic globular clusters (GC) using FLAMES@VLT (about 100 stars with GIRAFFE and about 10 with UVES, respectively, in each GC). These observations provide an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We use it to study the cosmic scatter of iron and find that, as far as Fe is concerned, most GCs can still be considered mono-metallic, since the upper limit to the scatter of iron is less than 0.05 dex, meaning that the degree of homogeneity is better than 12%. The scatter in Fe we find seems to have a dependence on luminosity, possibly due to the well-known inadequacies of stellar atmospheres for upper-RGB stars and/or to intrinsic variability. It also seems to be correlated with cluster properties, like the mass, indicating a larger scatter in more massive GCs which is likely a (small) true intrinsic scatter. The 19 GCs, covering the metallicity range of the bulk of Galactic GCs, define an accurate and updated metallicity scale. We provide transformation equations for a few existing scales. We also provide new values of [Fe/H], on our scale, for all GCs in the Harris catalogue.

Original languageEnglish
Pages (from-to)695-706
Number of pages12
JournalAstronomy & Astrophysics
Volume508
Issue number2
DOIs
Publication statusPublished - 2009
Externally publishedYes

Keywords

  • Globular clusters: general
  • Stars: abundances
  • Stars: atmospheres
  • Stars: population II

Cite this

Carretta, E., Bragaglia, A., Gratton, R., D'Orazi, V., & Lucatello, S. (2009). Intrinsic iron spread and a new metallicity scale for globular clusters. Astronomy & Astrophysics, 508(2), 695-706. https://doi.org/10.1051/0004-6361/200913003