A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

• Published in: The Astrophysical journal Vol. 965; no. 2; pp. 119 - 135
• Main Authors: Sales-Silva, J. V., Cunha, K., Smith, V. V., Daflon, S., Souto, D., Guerço, R., Queiroz, A., Chiappini, C., Hayes, C. R., Masseron, T., Hasselquist, Sten, Horta, D., Prantzos, N., Zoccali, M., Allende Prieto, C., Barbuy, B., Beaton, R., Bizyaev, D., Fernández-Trincado, J. G., Frinchaboy, P. M., Holtzman, J. A., Johnson, J. A., Jönsson, Henrik, Majewski, S. R., Minniti, D., Nidever, D. L., Schiavon, R. P., Schultheis, M., Sobeck, J., Stringfellow, G. S., Zasowski, G.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.04.2024; IOP Publishing
• Subjects: Abundance; Apogees; Cerium; Galactic bulge; Galaxy abundances; Galaxy bulges; Galaxy evolution; Iron; Magnesium; Metallicity; Metals; Milky Way; Milky Way evolution; Neodymium; Nuclear capture; Populations; Stars; Supernovae
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/ad28c2

Abstract This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of ∼2000 stars in the Galactic bulge bar spatially contained within ∣ X Gal ∣ < 5 kpc, ∣ Y Gal ∣ < 3.5 kpc, and ∣ Z Gal ∣ < 1 kpc, and spanning metallicities between −2.0 ≲ [Fe/H] ≲ +0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r -process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd] < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r -process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r -process astrophysical sites, such as magnetorotational supernovae.