The Ca ii triplet in red giant spectra: [Fe/H] determinations and the role of [Ca/Fe]

Measurements are presented and analysed of the strength of the Ca ii triplet lines in red giants in Galactic globular and open clusters, and in a sample of red giants in the LMC disc that have significantly different [Ca/Fe] abundance ratios to the Galactic objects. The Galactic objects are used to...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2016-01, Vol.455 (1), p.199-206
Main Author: Da Costa, G. S.
Format: Article
Language:English
Subjects:
Abundance
Astronomy
Calibration
Chemical evolution
Dispersion
Estimates
Giant stars
Magellanic clouds
Red giant stars
Spectrum analysis
Stars & galaxies
Strength
Symbols
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Summary:Measurements are presented and analysed of the strength of the Ca ii triplet lines in red giants in Galactic globular and open clusters, and in a sample of red giants in the LMC disc that have significantly different [Ca/Fe] abundance ratios to the Galactic objects. The Galactic objects are used to generate a calibration between Ca ii triplet line strength and [Fe/H], which is then used to estimate [Fe/H]CaT for the LMC stars. The values are then compared with the [Fe/H]spec determinations from high-dispersion spectroscopy. After allowance for a small systematic offset, the two abundance determinations are in excellent agreement. Further, as found in earlier studies, the difference is only a very weak function of the [Ca/Fe] ratio. For example, changing [Ca/Fe] from +0.3 to −0.2 causes the Ca ii-based abundance to underestimate [Fe/H]spec by only ∼0.15 dex, assuming a Galactic calibration. Consequently, the Ca ii triplet approach to metallicity determinations can be used without significant bias to study stellar systems that have substantially different chemical evolution histories.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stv2315