s-Processing in the Galactic Disk. I. Super-Solar Abundances of Y, Zr, La, Ce in Young Open Clusters

TL;DR

This study confirms that young open clusters in the Galactic disk show enhanced abundances of s-process elements like Y, Zr, La, and Ce, indicating a need to revise models of stellar nucleosynthesis and Galactic chemical evolution.

Contribution

It provides new abundance measurements for multiple s-process elements in open clusters, demonstrating a general increase with decreasing age, challenging existing nucleosynthesis models.

Findings

Confirmed increasing [Ba/Fe] with decreasing cluster age

Found similar growth for Y, Zr, La, Ce, indicating a common trend

Suggests low-mass AGB stars produce more s-process elements than previously thought

Abstract

In a recent study, based on homogeneous barium abundance measurements in open clusters, a trend of increasing [Ba/Fe] ratios for decreasing cluster age was reported. We present here further abundance determinations, relative to four other elements hav- ing important s-process contributions, with the aim of investigating whether the growth found for [Ba/Fe] is or not indicative of a general property, shared also by the other heavy elements formed by slow neutron captures. In particular, we derived abundances for yttrium, zirconium, lanthanum and cerium, using equivalent widths measurements and the MOOG code. Our sample includes 19 open clusters of different ages, for which the spectra were obtained at the ESO VLT telescope, using the UVES spectrometer. The growth previously suggested for Ba is confirmed for all the elements analyzed in our study. This fact implies significant changes in our views of the Galactic chemical evolution for elements beyond iron. Our results necessarily require that very low-mass AGB stars (M < 1.5M\odot) produce larger amounts of s-process elements (hence acti- vate the 13 C-neutron source more effectively) than previously expected. Their role in producing neutron-rich elements in the Galactic disk has been so far underestimated and their evolution and neutron-capture nucleosynthesis should now be reconsidered.