摘要：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 theGaia-ESO Survey.Aims. New data from theGaia-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 theGaiaSecond Data Release (GaiaDR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry fromGaiaDR2 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−1with an average proper motion of pmra = −5.65 ± 0.08 (std) mas yr−1and pmdec = −2.29 ± 0.11 (std) mas yr−1. According to the new estimates, based on high confidence members, Pismis 18 has an age ofτ= 700+40−50Myr, interstellar reddening ofE(B−V) = 0.562+0.012−0.026mag and a de-reddened distance modulus of DM0= 11.96+0.10−0.24mag. 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 ofs- andr-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 theGaia-ESO survey.
关键词：enstars: abundancesopen clusters and associations: individual: Pismis 18Galaxy: abundancesGalaxy: formationGalaxy: disk
