Resumen

PHILLIPS, J. P.. Variation of central star masses in planetary nebulae with height above the galactic plane. Rev. mex. astron. astrofis [online]. 2004, vol.40, n.1, pp.25-30. ISSN 0185-1101.

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 |b_LOW| ≃ 2.0 x 10 ^-3 M_๏ deg ^-1 for nebulae having 1.0 < log(T_B/K)< 3.6, where | b_LOW | represents de lower latitude of the sources. This corresponds to a gradient d<M_CS> /d|z_LOW| ≃ 5.6x10 ^-2 kpc ^-1 for nebulae with heights |z|>|z_LOW|, and where one adopts the statistical distances of Phillips (2002).

Palabras llave : ISM [Jets and outflows]; Planetary nebulae [General]; Stars [Evolution].