Analysis of the dependence of the CaT callibrations with the magnitude

B. DIAS; M.C. PARISI

Seúl

Congreso; Gemini Observatory Science Meeting; 2022

Gemini Observatory

The line strength of the near-infrared Ca II triplet (CaT) lines are a proxy for measuring metallicity from integrated and individual stellar spectra of bright red giant stars. In the latter case it is a mandatory step to remove the magnitude (proxy for gravity, temperature, and luminosity) dependence from the equivalent width (EW) of the lines before converting them into metallicities. For decades the working empirical procedure has been to use the relative magnitude with respect to the horizontal branch level or red clump, with the advantage that it is independent from distance and extinction. In this work we investigate the dependence of the CaT calibration using the griz filters from the Dark Energy Camera (DECam) and the Gemini Multi-Object Spectrograph (GMOS), the G filter from Gaia, the BVI filters from the Magellanic Clouds photometric survey (MCPS), and the YJKs filters from the Visible and Infrared Survey Telescope for Astronomy (VISTA) InfraRed CAMera (VIRCAM). We found that the magnitude dependence of the CaT EWs is well described by a linear relation using any analysed filter and the slope increases with wavelength of the filters. The zero point (i.e. reduced EW), which is the metallicity indicator, remains the same. In conclusion, if the same line profile function is used with the same bandpasses and continuum regions, and the total EW comes from the same number of lines (2 or 3), then the reduced EW is the same regardless the used filter.