Sulfur abundances in three Galactic clusters: Ruprecht 106, Trumpler 5, and Trumpler 20

F. Lucertini, L. Monaco, E. Caffau, A. Mucciarelli, S. Villanova, P. Bonifacio, L. Sbordone

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Context. Sulfur (S) is one of the lesser-studied α-elements. Published investigations of its behavior have so far focused on local stars, and only a few clusters of the Milky Way have been considered to study this topic. We aim to study the S content of the globular cluster Ruprecht 106 which has never before been studied for this purpose, but is known to present low levels of the [α/Fe] abundance ratio and the open cluster Trumpler 5. The only star studied so far in Trumpler 5 shows an unexpectedly low abundance of S. Aims. With this work, we aim to provide the first S abundance in Ruprecht 106 and to investigate the S content of Trumpler 5 with a larger sample of stars. The open cluster Trumpler 20 is considered as a reference object. Methods. We performed a standard abundance analysis based on 1D model atmospheres in local thermodynamical equilibrium (LTE) and on high-resolution and high-signal-to-noise-ratio UVES-slit and UVES/FLAMES spectra. We also applied corrections for nonLTE. The metallicities of the targets were obtained by studying equivalent widths. Sulfur abundances were derived from multiplets 1, 6, and 8 by spectrosynthesis. Results. We find that the metallicities of Ruprecht 106 and Trumpler 5 are [Fe/H] = 1.37±0.11 and [Fe/H] = 0.49±0.14, respectively. Ruprecht 106 is less S-rich than the other Galactic clusters at similar metallicity. The low S content of Ruprecht 106, [S/Fe]NLTE = 0.52±0.13, is consistent with its shortage of α-elements. This supports an extra-galactic origin of this cluster. We obtained a new and more robust S content value of Trumpler 5 of about [S/Fe]NLTE = 0.05±0.20. According to our results, Trumpler 5 follows the trend of the Galactic disk in the [S/Fe]LTE versus [Fe/H] diagram. Our results for Trumpler 20, of namely [Fe/H]= 0.06±0.15 and [S/Fe]NLTE = 0.28±0.21, are in agreement with those in the literature.

Original languageEnglish
Article numberA137
JournalAstronomy and Astrophysics
Publication statusPublished - 1 Mar 2023


  • Globular clusters: individual: Rup106
  • Open clusters and associations: individual: Tr20
  • Open clusters and associations: individual: Tr5
  • Stars: abundances

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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