Radial Velocity and Chemical Composition of Evolved Stars in the Open Clusters NGC 6940 and Tombaugh 5

Abstract

Abstract We present and discuss medium resolution (R ∼ 13000), high signal-to-noise ( ), spectroscopic observations in the field of the open clusters NGC 6940 and Tombaugh 5. Spectra were recorded for seven candidate red giant stars in both clusters. For the latter, we present the very first chemical abundance analysis. We derive radial velocities for all the stars in NGC 6940, confirming membership to the cluster for all of them, while on the same ground, we exclude two stars in To 5. We perform a chemical abundance analysis of different atomic species, in particular Fe i, Si i, Ca i, Ti i, and Ni i. The mean metallicity of NGC 6940 is [Fe/H] = +0.09 ± 0.06 dex, in good agreement with previous works, while for To 5 is [Fe/H] = +0.06 ± 0.11 dex. Therefore, both clusters exhibit a chemical composition close to the solar value and do not deviate from the [Fe/H] Galactic radial abundance gradient. With these new values, we estimate the fundamental cluster parameters, after having derived clusters’ distances from the Gaia DR2 database. By adopting these distances, we derive updated estimated for the clusters ages: 1.0 ± 0.1 Gyr of NGC 6940 and 0.25 ± 0.05 Gyr for Tombaugh 5.