The Chemical Composition of Praesepe (M44)

TL;DR

This study analyzes the chemical composition of 11 stars in the Praesepe cluster, revealing elemental abundances and patterns that inform stellar and Galactic evolution, with new detailed abundance measurements for multiple elements.

Contribution

First high-resolution spectral analysis of Praesepe stars providing detailed abundances of 16 elements, including comparisons with field stars and giants.

Findings

Fe/H = +0.12, slightly above solar

Li decreases with temperature, matching Hyades pattern

Ba is enhanced relative to solar and field stars

Abstract

Star clusters have long been used to illuminate both stellar evolution and Galactic evolution. They also hold clues to the chemical and nucleosynthetic processes throughout the history of the Galaxy. We have taken high signal-to-noise, high-resolution spectra of 11 solar-type stars in the Praesepe open cluster to determine the chemical abundances of 16 elements: Li, C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni, Y, and Ba. We have determined Fe from Fe I and Fe II lines and find [Fe/H] = +0.12 $\pm$0.04. We find that Li decreases with temperature due to increasing Li depletion in cooler stars; it matches the Li-temperature pattern found in the Hyades. The [C/Fe] and [O/Fe] abundances are below solar and lower than the field star samples due to the younger age of Praesepe (0.7 Gyr) than the field stars. The alpha-elements, Mg, Si, Ca, and Ti, have solar ratios with respect to Fe, and are also lower than the field star samples. The Fe-peak elements, Cr and Ni, track Fe and have solar values. The neutron capture element [Y/Fe] is found to be solar, but [Ba/Fe] is enhanced relative to solar and to the field stars. Three Praesepe giants were studied by Carrera and Pancino; they are apparently enhanced in Na, Mg, and Ba relative to the Praesepe dwarfs. The Na enhancement may indicate proton-capture nucleosynthesis in the Ne -> Na cycling with dredge-up into the atmospheres of the red giants.