James F. Buell: Thermally Pulsing Asymptotic Giant Branch Star Models and Globular Cluster Planetary Nebulae I: The Model, arxiv:1110.1396
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George H. Jacoby, Jon A. Morse, L. Kellar Fullton, K. B. Kwitter, R. B. C. Henry: Planetary Nebulae in the Globular Cluster PAL 6 and NGC 6441, bibcode:1997AJ....114.2611J