Abstract
There are various reasons for suspecting that the progenitor masses of planetary nebulae (PNe) decline with height z above the Galactic plane. This, if true, would also imply a similar decrease in mean central star masses <M[CS]>. We report here a further way in which such gradients may be determined. It will be shown that the distribution of planetary nebulae with respect to 5 GHz brightness temperature varies strongly with Galactic latitude. This variation is likely to arise from a change in the central star mass function N(M[CS]). High latitude sources appear to have a steeply varying function N(M[CS]), implying the presence of relatively few nebulae with high central star masses. By contrast, the low latitude sources have a much gentler fall-off in N(M[CS]), implying a larger proportion of high M[CS] nebulae. This is shown to imply significant gradients of mean mass <M[CS]> with latitude b. We find that d<M[CS]>/d |bLOW . b[LOW] . bLOW| ≃ .0×103M⊙ deg-1 for nebulae having 1.0<log(T[B]/K)< 3.6, where |bLOW . b[LOW] . bLOW| represents the lower limit latitude of the sources. This corresponds to a gradient d<M[CS]>/d |zLOW . z[LOW] . zLOW| ≃ .6×10-2 kpc-1 for nebulae with heights |z . z . z| > |zLOW . z[LOW] . zLOW| , and where one adopts the statistical distances of Phillips (2002).
