Metal Abundance Calibration of the Ca II Triplet Lines in RR Lyrae Stars
George Wallerstein (1), Thomas Gomez (1,2), and Wenjin Huang (1,3), ((1) Department of Astronomy, University of Washington, Seattle (2), Department of Astronomy, University of Texas at Austin (3) Brion, Inc.)
TL;DR
This study calibrates the relationship between Ca II triplet line strengths and metallicity in RR Lyrae stars, aiding Gaia's metallicity measurements using high-resolution spectra.
Contribution
It introduces a new calibration method linking Ca II triplet lines to metallicity specifically for RR Lyrae stars, based on high-resolution spectral data.
Findings
The Ca II line at 8498A provides the best correlation with metallicity.
A calibration between Ca II line strength and metallicity was established.
The method supports Gaia's low-resolution spectral metallicity estimates.
Abstract
The GAIA satellite is likely to observe thousands of RR Lyrae stars within a small spectral window, between 8470A and 8750A, at a resolution of 11,500. In order to derive the metallicity of RR Lyrae stars from Gaia, we have obtained numerous spectra of RR Lyrae stars at a resolution of 35,000 with the Apache Point Observatory 3.5 m echelle spectrograph. We have correlated the Ca II triplet line strengths with metallicity as derived from Fe II abundances, analogous to Preston's (1959) use of the Ca II K line to estimate the metallicity of RR Lyrae stars. The Ca II line at 8498A is the least blended with neighboring Paschen lines and thus provides the best correlation.
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