The CARMENES search for exoplanets around M dwarfs: rubidium abundances in nearby cool stars
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 de...
Saved in:
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article (Journal) |
| Language: | English |
| Published: |
23 October 2020
|
| In: |
Astronomy and astrophysics
Year: 2020, Volume: 642, Pages: 1-15 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202039032 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/202039032 Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2020/10/aa39032-20/aa39032-20.html 
|
| Author Notes: | C. Abia, H.M. Tabernero, S.A. Korotin, D. Montes, E. Marfil, J.A. Caballero, O. Straniero, N. Prantzos, I. Ribas, A. Reiners, A. Quirrenbach, P.J. Amado, V.J.S. Béjar, M. Cortés-Contreras, S. Dreizler, Th Henning, S.V. Jeffers, A. Kaminski, M. Kürster, M. Lafarga, Á López-Gallifa, J.C. Morales, E. Nagel, V.M. Passegger, S. Pedraz, C. Rodríguez López, A. Schweitzer, and M. Zechmeister |
| Summary: | 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. |
|---|---|
| Item Description: | Gesehen am 19.04.2021 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202039032 |