A new synthetic library of the Near-Infrared CaII triplet indices. I.Index Definition, Calibration and Relations with stellar atmospheric parameters

TL;DR

This paper presents a newly synthesized library of Near-Infrared CaII triplet indices, calibrated against observational data, and explores their relation to stellar parameters for improved stellar spectra analysis.

Contribution

The paper introduces a new synthetic library of NIR CaII triplet indices, defined and calibrated for SDSS and LAMOST spectra, with analysis of their dependence on stellar parameters and noise effects.

Findings

Little influence of alpha-element enhancement on CaII indices.

Good agreement between synthetic and observational indices.

Regression models linking CaII indices to stellar parameters.

Abstract

Adopting the SPECTRUM package, we have synthesized a set of 2,890 Near-InfraRed (NIR) synthetic spectra with a resolution and wavelength sampling similar to the SDSS and the forthcoming LAMOST spectra. During the synthesis, we have applied the `New grids of ATLAS9 Model Atmosphere' to provide a grid of local thermodynamic equilibrium (LTE) model atmospheres. This synthetic stellar library is composed of 1,350 solor scaled abundance (SSA) and 1,530 non-solar scaled abundance (NSSA) spectra, grounding on which we have defined a new set of NIR CaII triplet indices and an index CaT as the sum of the three. Then, these defined indices have been automatically measured on the synthetic spectra and calibrated with the indices computed on the observational spectra from the INDO-U.S. stellar library. In order to check the effect of alpha-element enhancement on the so-defined CaII indices, we have compared indices measured on the SSA spectra with those on the NSSA ones at the same terns of stellar parameters (Teff, log g, [Fe/H]), and luckily, little influences of alpha-element enhancement has been found. Furthermore, comparisons of synthetic indices with the observational ones from the INDO-U.S. spectra, the SDSS-DR7, and DR8 spectroscopic survey have been presented respectively for dwarfs and giants in detail. Finally, a new synthetic library of NIR CaII indices has been founded for deeper studies on the NIR waveband of stellar spectra, and is particularly appropriate for the SDSS and the forthcoming LAMOST stellar spectra. Later on, we have regressed the strength of the CaT index as a function of stellar parameters for both dwarfs and giants after a series of experimental investigations into relations of the indices with stellar parameters. Ultimately, a supplemental experimentation has been carried out to show that spectral noises do have effects on our set of NIR CaII indices.