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

Berkeley 26, Berkeley 70, NGC 1798, and NGC 2266^⋆

R. Carrera

Instituto de Astrofísica de Canarias, 38203 La Laguna, Tenerife, Spain Departamento de Astrofísica, Universidad de La Laguna, 38207 La Laguna, Tenerife, Spain
e-mail: rcarrera@iac.es

Received: 18 May 2012
Accepted: 8 July 2012

Abstract

Context. Open clusters are ideal test particles for studying the formation and evolution of the Galactic disk. However, the number of clusters with information about their radial velocities and chemical compositions remains largely insufficient.

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

Methods. We acquired medium-resolution spectra (R ~ 8000) in the region of the infrared Ca II triplet lines (~8500 Å) for several stars in four open clusters with the long-slit spectrograph IDS at the 2.5 m Isaac Newton Telescope, Roque de los Muchachos Observatory, Spain. Radial velocities were obtained by cross-correlating the observed spectra with those of two template stars. We used the relationships available in the literature between the strength of infrared Ca II lines and metallicities to derive the metal content of each cluster.

Results. We provide the first spectroscopic determinations of radial velocities and metallicities for the open clusters Berkeley 26, Berkeley 70, NGC 1798, and NGC 2266. We obtain  ⟨ V_r ⟩  = 68 ± 12,  −15 ± 7, 2 ± 10, and  −16 ± 15 km s^-1 for Berkeley 26, Berkeley 70, NGC 1798, and NGC 2266, respectively. For Berkeley 26 we derive a metallicity of [Fe/H] =  −0.35 ± 0.17 dex. Berkeley 70 has a solar metallicity of [Fe/H] =  −0.01 ± 0.14 dex, while NGC 1798 has a slightly lower metal content of [Fe/H] =  −0.12 ± 0.07 dex. Finally, we derive a metallicity of [Fe/H] =  −0.38 ± 0.06 dex for NGC 2266.