2025/12/23 by M. Navabi, R. Carrera, Navabi, M. +9
Physics and Astronomy · #Stellar, planetary, and galactic studies #Astronomy and Astrophysical Research #Scientific Research and Discoveries
paper · doi:10.48550/arxiv.2512.20574
The near-infrared Calcium II Triplet (CaT), around 850nm, is a key metallicity indicator for red giant stars. We present a revised [Fe/H] calibration as a function of CaT line strengths and four luminosity indicators, including the Gaia G-band, together with the classical V, I, and Ks bandpasses. For this purpose, we used a sample of 366 red giant stars belonging to 25 globular and open clusters, complemented by 52 extremely metal-poor field giant stars. The CaT line strengths are determined by fitting Gaussian-Lorentzian combination profiles using the Python lmfit package, which utilises the algorithms implemented therein. The derived calibration is valid for a wide metallicity range, -4 dex \lesssim [Fe/H] \lesssim +0.15, and for ages older than ∼200 Myr. In addition, we performed a detailed assessment of how factors such as spectral resolution, spectral quality (expressed through the signal-to-noise ratio), and the algorithms used to constrain the line profiles affect the measured line strengths and the resulting metallicities.