Jacoby, G.H., & Ciardullo, R. 1999, ``Chemical Abundances of Planetary Nebulae in the Bulge and Disk of M31,'' Ap. J., 515, 169. [ADS - Abstract and Full Paper]
Ciardullo, R., & Jacoby, G.H. 1999, ``The Circumstellar Extinction of Planetary Nebulae,'' Ap. J., 515, 191. [ADS - Abstract and Full Paper]