The Gaia-ESO Survey: The inner disc, intermediate-Age open cluster Pismis 18

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Context. Pismis 18 is a moderately populated, intermediate-Age open cluster located within the solar circle at a Galactocentric distance of about seven kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. Aims. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Methods. Gaia-ESO Survey data for 142 potential members, lying on the upper main sequence and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia Second Data Release (Gaia DR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. Results. The average radial velocity of 26 high confidence members is-27.5 ± 2.5 (std) km s-1 with an average proper motion of pmra =-5.65 ± 0.08 (std) mas yr-1 and pmdec =-2.29 ± 0.11 (std) mas yr-1. According to the new estimates, based on high confidence members, Pismis 18 has an age of τ = 700+40-50 Myr, interstellar reddening of E(B-V) = 0.562+0.012-0.026 mag and a de-reddened distance modulus of DM0 = 11.96+0.10-0.24 mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = +0.23 ± 0.05 dex, with [α/Fe] = 0.07 ± 0.13 and a slight enhancement of s-and r-neutron-capture elements. Conclusions. With the present work, we fully characterized the open cluster Pismis 18. We confirmed its present location in the inner disc. We estimated a younger age than the previous literature values and we gave, for the first time, its metallicity and its detailed abundances. Its [α/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey.


  • D. Hatzidimitriou
  • E. V. Held
  • E. Tognelli
  • A. Bragaglia
  • L. Magrini
  • L. Bravi
  • K. Gazeas
  • A. Dapergolas
  • A. Drazdauskas
  • E. Delgado-Mena
  • E. D. Friel
  • R. Minkevičiute
  • R. Sordo
  • G. Tautvaišiene
  • G. Gilmore
  • S. Randich
  • A. Vallenari
  • E. J. Alfaro
  • E. Flaccomio
  • A. C. Lanzafame
  • E. Pancino
  • R. Smiljanic
  • A. Bayo
  • M. Bergemann
  • G. Carraro
  • A. R. Casey
  • M. T. Costado
  • F. Damiani
  • E. Franciosini
  • A. Gonneau
  • P. Jofré
  • J. Lewis
  • L. Monaco
  • L. Morbidelli
  • C. C. Worley
  • S. Zaggia
External organisations
  • National and Kapodistrian University of Athens
  • National Observatory of Athens
  • University of Pisa
  • INFN Section of Pisa
  • INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna
  • INAF - Osservatorio Astrofisico di Arcetri
  • Vilnius University
  • Centre for Astrophysics of the University of Porto
  • Indiana University
  • University of Cambridge
  • CSIC Instituto de Astrofísica de Andalucía (IAA)
  • INAF Palermo Astronomical Observatory
  • University of Catania
  • Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
  • University of Valparaíso
  • Max Planck Institute for Astronomy
  • University of Padova
  • Monash University
  • Diego Portales University
  • Andrés Bello National University
  • University of Cádiz
  • INAF - Osservatorio Astronomico di Padova
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology


  • Galaxy: Abundances, Galaxy: disk, Galaxy: formation, Open clusters and associations: individual: Pismis 18, Stars: Abundances
Original languageEnglish
Article numberA90
JournalAstronomy and Astrophysics
Publication statusPublished - 2019 Jun
Publication categoryResearch