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M-dwarf metallicities: A high-resolution spectroscopic study in the near infrared
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
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2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 542, A33- p.Article in journal (Refereed) Published
Abstract [en]

The relativley large spread in the derived metallicities ([Fe/H]) of M dwarfs shows that various approaches have not yet converged to consistency. The presence of strong molecular features, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs diffcult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio suffcient for a detailed spectroscopic abundance analysis.

We present a high-resolution (R~50,000) spectroscopic study of a sample of eight single M dwarfs and three wide-binary systems observed in the infrared J-band.

The absence of large molecular contributions allow for a precise continuum placement. We derive metallicities based on the best fit synthetic spectra to the observed spectra. To verify the accuracy of the applied atmospheric models and test our synthetic spectrum approach, three binary systems with a K dwarf primary and an M dwarf companion were observed and analysed along with the single M dwarfs.

We obtain a good agreement between the metallicities derived for the primaries and secondaries of our test binaries and thereby confirm the reliability of our method of analysing M dwarfs. Our metallicities agree well with certain earlier determinations, and deviate from others.

We conclude that spectroscopic abundance analysis in the J band is a reliable method for establishing the metallicity scale for M dwarfs. We recommend its application to a larger sample covering lower as well as higher metallicities. Further prospectsof the method include abundance determinations for individual elements.

Place, publisher, year, edition, pages
2012. Vol. 542, A33- p.
Keyword [en]
stars: atmospheres, stars: binaries visual, stars: low-mass, stars: abundances, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:uu:diva-158847DOI: 10.1051/0004-6361/201118101ISI: 000305803300025OAI: oai:DiVA.org:uu-158847DiVA: diva2:441679
Available from: 2011-09-18 Created: 2011-09-18 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Solar Type Stars as Calibrators: A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars
Open this publication in new window or tab >>Solar Type Stars as Calibrators: A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed.

Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested.

Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter.

M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 855
Keyword
stars: atmospheres, stars: late-type, techniques: photometric, stars: abundances, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-158709 (URN)978-91-554-8161-2 (ISBN)
Public defence
2011-10-21, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
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Available from: 2011-09-30 Created: 2011-09-13 Last updated: 2011-11-03Bibliographically approved

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Önehag, AnnaHeiter, UlrikeGustafsson, BengtPiskunov, Nikolai

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