RUBIDIUM-STRONTIUM DATING OF CLAYEY SEDIMENTS
In: International Geology Review, Band 28, Heft 5, S. 569-583
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In: International Geology Review, Band 28, Heft 5, S. 569-583
In: Proceedings of the Academy of Sciences of the Estonian SSR. Physics. Mathematics, Band 31, Heft 3, S. 356
In: International Geology Review, Band 22, Heft 6, S. 718-730
In: Revue roumaine de chimie: Romanian journal of chemistry, Band 64, Heft 3, S. 265-270
In: International Geology Review, Band 28, Heft 7, S. 850-857
In: Alexandria science exchange journal: an international quarterly journal of science and agricultural environments, Band 36, Heft January-March, S. 32-39
ISSN: 2536-9784
In: Forschungsberichte des Landes Nordrhein-Westfalen 1605
A. Einleitung -- B. Die verwendeten Tone und ihre mineralogische Untersuchung -- C. Bestimmung von allgemeinen Oberflächeneigenschaften -- D. Messung der Kationenadsorption -- E. Ableitung eines Selektivitätskoeffizienten -- F. Darstellung der Meßergebnisse -- G. Allgemeine Betrachtungen über die spezifische Adsorption -- H. Ursachen eines selektiven Verhaltens bei den Tonmineralen -- I. Zusammenfassung -- K. Literaturverzeichnis.
Due to their ubiquity and very long main-sequence lifetimes, abundance determinations in M dwarfs provide a powerful and alternative tool to GK dwarfs to study the formation and chemical enrichment history of our Galaxy. In this study, abundances of the neutron-capture elements Rb, Sr, and Zr are derived, for the first time, in a sample of nearby M dwarfs. We focus on stars in the metallicity range-0.5 ≲ [Fe/H] ≲ +0.3, an interval poorly explored for Rb abundances in previous analyses. To do this we use high-resolution, high-signal-to-noise-ratio, optical and near-infrared spectra of 57 M dwarfs observed with CARMENES. The resulting [Sr/Fe] and [Zr/Fe] ratios for most M dwarfs are almost constant at about the solar value, and are identical to those found in GK dwarfs of the same metallicity. However, for Rb we find systematic underabundances ([Rb/Fe] < 0.0) by a factor two on average. Furthermore, a tendency is found for Rb-but not for other heavy elements (Sr, Zr)-to increase with increasing metallicity such that [Rb/Fe] ≳ 0.0 is attained at metallicities higher than solar. These are surprising results, never seen for any other heavy element, and are difficult to understand within the formulation of the s-and r-processes, both contributing sources to the Galactic Rb abundance. We discuss the reliability of these findings for Rb in terms of non-LTE (local thermodynamic equilibrium) effects, stellar activity, or an anomalous Rb abundance in the Solar System, but no explanation is found. We then interpret the full observed [Rb/Fe] versus [Fe/H] trend within the framework of theoretical predictions from state-of-the-art chemical evolution models for heavy elements, but a simple interpretation is not found either. In particular, the possible secondary behaviour of the [Rb/Fe] ratio at super-solar metallicities would require a much larger production of Rb than currently predicted in AGB stars through the s-process without overproducing Sr and Zr. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)
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ISSN: 1557-850X
In: Progress in nuclear energy: the international review journal covering all aspects of nuclear energy, Band 47, Heft 1-4, S. 389-396
ISSN: 0149-1970
In: Revue roumaine de chimie: Romanian journal of chemistry, Band 65, Heft 2, S. 141-147
In: HELIYON-D-22-18884
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