A high-precision abundance analysis of the nuclear benchmark star HD 20

• Verfasst von: Hanke, Michael [VerfasserIn]
• Verfasst von: Hansen, Camilla Juul [VerfasserIn]
• Verfasst von: Ludwig, Hans-Günter [VerfasserIn]
• Verfasst von: Cristallo, Sergio [VerfasserIn]
• Verfasst von: McWilliam, Andrew [VerfasserIn]
• Verfasst von: Grebel, Eva K. [VerfasserIn]
• Verfasst von: Piersanti, Luciano [VerfasserIn]
• Titel: A high-precision abundance analysis of the nuclear benchmark star HD 20
• Verf.angabe: Michael Hanke, Camilla Juul Hansen, Hans-Günter Ludwig, Sergio Cristallo, Andrew McWilliam, Eva K. Grebel, and Luciano Piersanti
• E-Jahr: 2020
• Jahr: 16 March 2020
• Umfang: 28 S.
• Fussnoten: Gesehen am 28.04.2020
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2020
• Band/Heft Quelle: 635(2020) Artikel-Nummer A104, 28 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201937189
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1696285402

Abstract

Metal-poor stars with detailed information available about their chemical inventory pose powerful empirical benchmarks for nuclear astrophysics. Here we present our spectroscopic chemical abundance investigation of the metal-poor ([Fe/H] = -1.60 ± 0.03 dex), r-process-enriched ([Eu/Fe] = 0.73 ± 0.10 dex) halo star HD 20, using novel and archival high-resolution data at outstanding signal-to-noise ratios (up to ∼1000 Å-1). By combining one of the first asteroseismic gravity measurements in the metal-poor regime from a TESS light curve with the spectroscopic analysis of iron lines under non-local thermodynamic equilibrium conditions, we derived a set of highly accurate and precise stellar parameters. These allowed us to delineate a reliable chemical pattern that is comprised of solid detections of 48 elements, including 28 neutron-capture elements. Hence, we establish HD 20 among the few benchmark stars that have nearly complete patterns and low systematic dependencies on the stellar parameters. Our light-element (Z ≤ 30) abundances are representative of other, similarly metal-poor stars in the Galactic halo that exhibit contributions from core-collapse supernovae of type II. In the realm of the neutron-capture elements, our comparison to the scaled solar r-pattern shows that the lighter neutron-capture elements (Z ≲ 60) are poorly matched. In particular, we find imprints of the weak r-process acting at low metallicities. Nonetheless, by comparing our detailed abundances to the observed metal-poor star BD +17 3248, we find a persistent residual pattern involving mainly the elements Sr, Y, Zr, Ba, and La. These are indicative of enrichment contributions from the s-process and we show that mixing with material from predicted yields of massive, rotating AGB stars at low metallicity improves the fit considerably. Based on a solar ratio of heavy- to light-s elements - which is at odds with model predictions for the i-process - and a missing clear residual pattern with respect to other stars with claimed contributions from this process, we refute (strong) contributions from such astrophysical sites providing intermediate neutron densities. Finally, nuclear cosmochronology is used to tie our detection of the radioactive element Th to an age estimate for HD 20 of 11.0 ± 3.8 Gyr.