The Lick-Index Calibration of the GEMINI Multi-Object Spectrographs

TL;DR

This paper calibrates the Lick/IDS line-index system for Gemini GMOS spectrographs, providing correction functions for 25 indices to facilitate stellar population analysis in distant systems.

Contribution

It introduces linear calibration functions for 25 Lick indices specific to GMOS instruments, enhancing their accuracy for stellar population diagnostics.

Findings

Small correction terms for Balmer and metallicity indices.

Indices with molecular bands or narrow passbands are less robustly calibrated.

Calibration improves the reliability of stellar population measurements using GMOS data.

Abstract

We present the calibration of the spectroscopic Lick/IDS standard line-index system for measurements obtained with the Gemini Multi-Object Spectrographs known as GMOS-North and GMOS- South. We provide linear correction functions for each of the 25 standard Lick line indices for the B600 grism and two instrumental setups, one with 0.5 arcsecond slit width and 1x1 CCD pixel binning (corresponding to ~2.5 Angstroem spectral resolution) and the other with 0.75 arcsecond slit width and 2x2 binning (~4 Angstroem). We find small and well-defined correction terms for the set of Balmer indices Hbeta, HgammaA, and HdeltaA along with the metallicity sensitive indices Fe5015, Fe5270, Fe5335, Fe5406, Mg2 and Mgb that are widely used for stellar population diagnostics of distant stellar systems. We find other indices that sample molecular absorption bands, such as TiO1 and TiO2, with very wide wavelength coverage or indices that sample very weak molecular and atomic absorption features, such as Mg1, as well as indices with particularly narrow passband definitions, such as Fe4384, Ca4455, Fe4531, Ca4227, and Fe5782, less robustly calibrated. These indices should be used with caution.