Radial velocities and metallicities from infrared Ca ii triplet spectroscopy of open clusters

II. Berkeley 23, King 1, NGC 559, NGC 6603, and NGC 7245^⋆,⋆⋆

¹ Instituto de Astrofísica de Canarias, La Laguna, 38205 Tenerife Spain
e-mail: rcarrera@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38207 Tenerife, Spain
³ Departament d’Astronomia i Meteorologia, Universitat de Barcelona, ICC/IEEC, 08007 Barcelona, Spain
⁴ Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, 08193 Bellaterra, Spain

Received: 16 December 2014
Accepted: 1 April 2015

Abstract

Context. Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature.

Aims. We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters.

Methods. We acquired medium-resolution spectra (R ~ 8000) in the infrared region Ca ii triplet lines (~8500 Å) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5 m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain). Radial velocities were obtained by cross-correlation fitting techniques. The relationships available in the literature between the strength of infrared Ca ii lines and metallicity were also used to derive the metallicity for each cluster.

Results. We obtain ⟨V_r⟩ = 48.6 ± 3.4, −58.4 ± 6.8, 26.0 ± 4.3, and −65.3 ± 3.2 km s^-1 for Berkeley 23, NGC 559, NGC 6603, and NGC 7245, respectively. We found [ Fe/H ] = −0.25 ± 0.14 and −0.15 ± 0.18 for NGC 559 and NGC 7245, respectively. Berkeley 23 has low metallicity, [ Fe/H ] = −0.42 ± 0.13, which is similar to other open clusters in the outskirts of the Galactic disc. In contrast, we derived high metallicity ([ Fe/H ] = +0.43 ± 0.15) for NGC 6603, which places this system among the most metal-rich known open clusters. To our knowledge, this is the first determination of radial velocities and metallicities from spectroscopy for these clusters, except NGC 6603, for which radial velocities had been previously determined. We have also analysed ten stars in the line of sight to King 1. Because of the large dispersion obtained in both radial velocity and metallicity, we cannot be sure that we have sampled true cluster members.