@inproceedings{inproceedingsc9980c88,
title   = {Chemical abundances for a planetary nebulae sample located outside the solar circle},
author = {Costa, Roberto Dell'Aglio Dias da and Chiappini, C. and Maciel, Walter Junqueira and Freitas Pacheco, José Antonio},
year = {1997},
publisher = {Cambridge University Press},
booktitle   = {Workshop stellar Ecology}
}