An Improved Bandstrength Index for the CH G Band of Globular Cluster Giants

Abstract

Spectral indices are useful tools for quantifying the strengths of features in moderate-resolution spectra and relating them to intrinsic stellar parameters. This paper focuses on the 4300AA CH G-band, a classic example of a feature interpreted through use of spectral indices. G-band index definitions, as applied to globular clusters of different metallicity, abound in the literature, and transformations between the various systems, or comparisons between different authors' work, are difficult and not always useful. We present a method for formulating an optimized G-band index, using a large grid of synthetic spectra. To make our new index a reliable measure of carbon abundance, we minimize its dependence on [N/Fe] and simultaneously maximize its sensitivity to [C/Fe]. We present a definition for the new index S2(CH), along with estimates of the errors inherent in using it for [C/Fe] determination, and conclude that it is valid for use with spectra of bright globular cluster red giants over a large range in [Fe/H], [C/Fe], and [N/Fe].

arXiv comment8 pages, emulateapj, accepted by PASP

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Cited by in corpus (12)

• Light-element Abundance Variations in the Milky Way Halo
• Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies
• Stellar Population Models and Individual Element Abundances II: Stellar Spectra and Integrated Light Models
• Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
• Masses and Ages for 230,000 LAMOST Giants, via Their Carbon and Nitrogen Abundances
• A Survey of CN and CH Variations in Galactic Globular Clusters from SDSS Spectroscopy
• Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo build-up with SDSS-IV
• CN Anomalies in the Halo System and the Origin of Globular Clusters in the Milky Way
• Light-Element Abundance Variations at Low Metallicity: the Globular Cluster NGC 5466
• A broad perspective on multiple abundance populations in the globular cluster NGC 1851
• Light Element Abundances and Multiple Populations in M10
• Light Element Abundances and Multiple Populations in M53