Planetary nebulae have recently been shown to be useful as standard candles (Ciardullo et al. 1989, ApJ, 339,53; Jacoby 1989, ApJ, 339, 39). Distances to many galaxies have been determined by fitting a planetary nebula luminosity function (PNLF) to observations of the OUI 5007À line of PNe. Here, the effect of the core mass distribution on the determination of the luminosity function is investigated and a technique for interpolating between model evolutionary tracks is discussed. Four

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... er tracks with central star masses of 0.565, 0.6, 0.644 and 0.835 Μ Θ are used to generate normalized curves of luminosity versus time and effective temperature versus time. The normalized functions are found to be remarkably similar, giving us confidence that more evolutionary tracks can be derived by interpolation. Each track consists of 16 grid points in each of the time, luminosity and temperature coordinates, and values between successive points are obtained by linear interpolation. Seven tracks were generated using this method for the following core masses: 0.6,0.62,0.63,0.64,0.65,0.66 and 0.68 MQ.