Analysis and calibration of Ca ii triplet spectroscopy of red giant branch stars from VLT/FLAMES observations

Battaglia, G. ; Irwin, M. ; Tolstoy, E. ; Hill, V. ; Helmi, A. ; Letarte, B. ; Jablonka, P.

In: Monthly Notices of the Royal Astronomical Society, 2008, vol. 383, no. 1, p. 183-199

Add to personal list
    We demonstrate that low-resolution Ca ii triplet (CaT) spectroscopic estimates of the overall metallicity ([Fe/H]) of individual red giant branch (RGB) stars in two nearby dwarf spheroidal galaxies (dSphs) agree to ±0.1-0.2 dex with detailed high-resolution spectroscopic determinations for the same stars over the range −2.5 < [Fe/H] < −0.5. For this study, we used a sample of 129 stars observed in low- and high-resolution modes with VLT/FLAMES in the Sculptor and Fornax dSphs. We also present the data-reduction steps we used in our low-resolution analysis and show that the typical accuracy of our velocity and CaT [Fe/H] measurement is ∼2 km s−1 and 0.1 dex, respectively. We conclude that CaT-[Fe/H] relations calibrated on globular clusters can be applied with confidence to RGB stars in composite stellar populations over the range −2.5 < [Fe/H] < −0.5