Méndez, R. H., Thomas, D., Saglia, R. P., Maraston, C., Kudritzki, R. P., & Bender, R. (2005). Oxygen and neon abundances of planetary nebulae in the elliptical galaxy NGC 4697. The Astrophysical Journal, 627(2), 767-781. doi:10.1086/430498.