EVOLUTIONARY TESTS OF THE PLANETARY-NEBULA LUMINOSITY FUNCTION

The planetary nebula luminosity function (PNLF) depends on the physica l characteristics and evolutionary paths of the components. Changes in the nebular and stellar parameters may influence the extragalactic di stance scale based on the PNLF. We aim at studying from a theoretical viewpoint how changes in the physical conditions of the parent galaxy and the evolutionary paths of the central stars and nebulae propagate into the PNLF. By means of synthesis of post-asymptotic giant branch e volution, we have tested the invariance of the distance scale based on the H beta PNLF for changes in the evolutionary timescales, in the in itial mass-final mass relation, and in the number of optically thick p lanetary nebulae (PNs) populating the PNLF. We start with a theoretica l H beta PNLF truncated at M(f) < 0.7 M., which we successfully check against its empirical homologue for SMC and LMC PNs. We obtain that sm all shifts in the transition time evolve into H beta magnitude shifts of the high-luminosity cutoff up to 0.75 mag for constant star formati on rate populations only, while intermediate/old populations are almos t invariant with respect to these evolutionary time differences. We al so obtain that a different initial mass-final mass relation does propa gate into shifts in the H beta PNLF, the effects being important only for young stellar populations. Finally, the high-luminosity cutoff of the H beta PNLF seems to be invariant to the number of PNs considered. Overall, our results indicate that extreme care should be taken when using H beta PNLF in the context of high-mass-high-luminosity PNs.