THE PROGENITORS AND LIFETIMES OF PLANETARY NEBULAE

Planetary nebulae (PNe) are among the most spectacular objects produced by stellar evolution, but the exact identity of their progenitors has never been established for a large and homogeneous sample. We investigate the relationship between PNe and their stellar progenitors in the LMC by means of a statistical comparison between a highly complete spectroscopic catalog of PNe and the spatially resolved age distribution of the underlying stellar populations. We find that most PN progenitors in the LMC have main-sequence lifetimes in a narrow range between 5 and 8 Gyr, which corresponds to masses between 1.2 and 1.0 M-circle dot, and produce PNe that are visible for 27 +/- 6 kyr. We tentatively detect a second population of PN progenitors, with main-sequence lifetimes between 35 and 800 Myr, masses between 8.2 and 2.1 M-circle dot, and average PN lifetimes of 11(-8)(+6) kyr. These two distinct and disjointed populations strongly suggest the existence of at least two physically distinct formation channels for PNe. Our determination of PN lifetimes and progenitor masses has implications for the understanding of PNe in the context of stellar evolution models, and for the role that rotation, magnetic fields, and binarity can play in the shaping of PN morphologies.