Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star

• Verfasst von: Koch-Hansen, Andreas [VerfasserIn]
• Verfasst von: Hansen, Camilla Juul [VerfasserIn]
• Titel: Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star
• Verf.angabe: Andreas Koch, Moritz Reichert, Camilla Juul Hansen, Melanie Hampel, Richard J. Stancliffe, Amanda Karakas, and Almudena Arcones
• E-Jahr: 2019
• Jahr: 13 February 2019
• Umfang: 10 S.
• Fussnoten: Gesehen am 22.02.2019
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2019
• Band/Heft Quelle: 622(2019) Artikel-Nummer A159, 10 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201834241
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1587918757

Abstract

Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements. However, the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor (CEMP) and/or CH-stars, with only two such objects known to date. This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo. Recently, two contenders of these classes of stars were discovered in the bulge, at [Fe/H] = −1.5 and −2.5 dex, both of which show enhancements in [C/Fe] of 0.4 and 1.4 dex (respectively), [Ba/Fe] in excess of 1.3 dex, and also elevated nitrogen. The more metal-poor of the stars can be well matched by standard <i>s<i/>-process nucleosynthesis in low-mass asymptotic giant branch (AGB) polluters. The other star shows an abnormally high [Rb/Fe] ratio. Here, we further investigate the origin of the abundance peculiarities in the Rb-rich star by new, detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis. The <i>i<i/>-process with intermediate neutron densities between those of the slow (<i>s<i/>-) and rapid (<i>r<i/>)-neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both <i>r<i/>- and <i>s<i/>-process elements (class CEMP-<i>r<i/>/<i>s<i/>), rather than invoking a superposition of yields from the respective individual processes. However, the peculiar bulge star is incompatible with a pure <i>i<i/>-process from a single ingestion event. Instead, it can, statistically, be better reproduced by more convoluted models accounting for two proton ingestion events, or by an <i>i<i/>-process component in combination with <i>s<i/>-process nucleosynthesis in low-to-intermediate mass (2-3 <i>M<i/><sub>⊙<sub/>) AGB stars, indicating multiple polluters. Finally, we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities.