Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid

TL;DR

This study analyzes the chemical abundances of 58 metal-poor stars in the Galactic bulge, revealing typical alpha-element enhancements and suggesting these stars are not accreted debris or second-generation globular cluster stars, with evidence of s-process enrichment.

Contribution

It provides detailed abundance measurements for bulge stars, re-examines certain element abundances, and offers insights into their origins and evolutionary history.

Findings

Alpha-element enhancements consistent with bulge stars

Stars are not N-rich, indicating they are not second-generation globular cluster stars

Ce enrichment suggests s-process contribution from early massive stars

Abstract

The central part of the Galaxy host a multitude of stellar populations, including the spheroidal bulge stars, stars moved to the bulge through secular evolution of the bar, inner halo, inner thick disk, inner thin disk, as well as debris from past accretion events. We identified a sample of 58 candidate stars belonging to the stellar population of the spheroidal bulge, and analyse their abundances. The present calculations of Mg, Ca, and Si lines are in agreement with the APOGEE-ASPCAP abundances, whereas abundances of C, N, O, and Ce are re-examined. We find normal $\alpha$-element enhancements in oxygen, similar to magnesium, Si, and Ca abundances, which are typical of other bulge stars surveyed in the optical in Baade's Window. The enhancement of [O/Fe] in these stars suggests that they do not belong to accreted debris. No spread in N abundances is found, and none of the sample stars is N-rich, indicating that these stars are not second generation stars originated in globular clusters. Ce instead is enhanced in the sample stars, which points to an s-process origin such as due to enrichment from early generations of massive fast rotating stars, the so-called spinstars