On the neutron-capture elements across the Galactic thin disk using Cepheids

TL;DR

This study analyzes neutron-capture element abundances in 435 Galactic Cepheids to understand chemical gradients and nucleosynthesis processes across the thin disk, revealing differences between light and heavy s-process elements and their ratios.

Contribution

It provides the first homogeneous, high-resolution abundance analysis of multiple neutron-capture elements in a large Cepheid sample across the Galactic thin disk, highlighting new abundance gradient behaviors.

Findings

Steeper gradient for light s-process element Y compared to heavy s- and r-process elements.

Clear anticorrelation between [La/Eu] ratio and Eu/Fe, indicating nucleosynthesis trends.

Good agreement between observed [La/Y] ratios and AGB star models, despite larger observed spreads.

Abstract

We present new accurate abundances for five neutron-capture (Y, La, Ce, Nd, Eu) elements in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high spectral resolution (R ~ 38,000) and high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking account for similar Cepheid abundances provided either by our group (111 stars) or available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (-1.6 < [Fe/H] < 0.6). We found, using homogeneous individual distances and abundance scales, well defined gradients for the above elements. However, the slope of the light s-process element (Y) is at least a factor of two steeper than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s to r abundance ratio ([La/Eu]) of Cepheids shows a well defined anticorrelation with of both Eu and Fe. On the other hand, Galactic field stars attain an almost constant value and only when they approach solar iron abundance display a mild enhancement in La. The [Y/Eu] ratio shows a mild evidence of a correlation with Eu and, in particular, with iron abundance for field Galactic stars. We also investigated the s-process index - [hs/ls] - and we found a well defined anticorrelation, as expected, between [La/Y] and iron abundance. Moreover, we found a strong correlation between [La/Y] and [La/Fe] and, in particular, a clear separation between Galactic and Sagittarius red giants. Finally, the comparison between predictions for low-mass asymptotic giant branch stars and the observed [La/Y] ratio indicate a very good agreement over the entire metallicity range covered by Cepheids. However, the observed spread, at fixed iron content, is larger than predicted by current models.