Peculiarities of {\alpha}-element abundances in Galactic open clusters

TL;DR

This study analyzes the chemical abundances of alpha-elements in 90 Galactic open clusters, revealing differences from field stars that suggest diverse formation histories involving high-velocity clouds and Galactic fountains.

Contribution

It provides a comprehensive catalog of open cluster parameters and detailed spectroscopic abundance data, highlighting the impact of different formation scenarios on chemical compositions.

Findings

Clusters with high, elongated orbits have lower [O,Mg/Fe] than field stars.

Metal-rich clusters with high, elongated orbits show higher alpha-element ratios than field stars.

Evidence supports formation of some clusters via interactions with high-velocity clouds and Galactic fountains.

Abstract

A catalog compiling the parameters of 346 open clusters, including their metallicities, positions, ages, and velocities has been composed. The elements of the Galactic orbits for 272 of the clusters have been calculated. Spectroscopic determinations of the relative abundances, [el/Fe], for 14 elements synthesized in various nuclear processes averaged over data from 109 publications are presented for 90 clusters. Since no systematic effects distorting the relative abundances of the studied elements in these clusters have been found, these difference suggest real differences between clusters with high, elongated orbits and field stars. In particular, this supports the earlier conclusion, based on an analysis of the elements of the Galactic orbits, that some clusters formed as a result of interactions between high-velocity, metal-poor clouds and the interstellar medium of the Galactic thin disk. On average, clusterswith high, elongated orbits and metallicities ${\rm [Fe/H]} < - 0.1$ display lower relative abundances of the primary \'a elements than do field stars. The low [O,Mg/Fe] ratios of these clusters can be understood if the high-velocity clouds that gave rise to them were formed of interstellar material from regions where the star-formation rate and/or the masses of Type II supernovae were lower than near the Galactic plane. It is also shown that, on average, the relative abundances of the primary $\alpha$-elements are higher in relatively metal-rich clusters with high, elongated orbits than in field stars. This can be understood if clusters with ${\rm [Fe/H]} > - 0.1$ formed as a result of interactions between metal-rich clouds with intermediate velocities and the interstellar medium of the Galactic disk; such clouds could form from returning gas in a so-called "Galactic fountain".