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

April 2024 • 2024ApJ...965..119S

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.

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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2024ApJ...965..119S
• PREPRINT http://arxiv.org/abs/2402.14898
• ELECTR https://doi.org/10.3847%2F1538-4357%2Fad28c2