Revisiting the near infrared Calcium triplet as metallicity indicator

Abstract

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 $K_s$ 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 $\sim$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.

References in corpus (20)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Painting a portrait of the Galactic disc with its stellar clusters
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• Analysis and calibration of CaII triplet spectroscopy of Red Giant Branch stars from VLT/FLAMES observations
• Farthest Neighbor: The Distant Milky Way Satellite Eridanus II
• The Chemical Enrichment History of the Large Magellanic Cloud
• The Chemical Enrichment History of the Small Magellanic Cloud and Its Gradients
• The chemical abundance of the very metal rich old Open Clusters NGC 6253 and NGC 6791
• The Infrared Ca II triplet as metallicity indicator
• The Open Cluster Chemical Abundances and Mapping Survey: VI. Galactic Chemical Gradient Analysis from APOGEE DR17
• Metallicity Evolution of the Six Most Luminous M31 Dwarf Satellites
• The Magellanic Inter-Cloud Project (MAGIC) III: First spectroscopic evidence of a dwarf stripping a dwarf
• A chemical confirmation of the faint Bootes II dwarf Spheroidal Galaxy
• OCCASO V. Chemical-abundance trends with Galactocentric distance and age
• Titans metal-poor reference stars II. Red giants and CEMP stars
• Updated properties of the old open cluster Melotte 66: Searching for multiple stellar populations
• Radial velocities and metallicities from infrared Ca II triplet spectroscopy of open clusters II. Berkeley 23, King 1, NGC 559, NGC 6603 and NGC 7245
• Metallicities of Outer Halo M31 Globular Clusters from Integrated Light Calcium-II Triplet Spectroscopy
• Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362