Mass Distribution Of Central Stars Research Articles

White dwarf masses derived from planetary nebula modelling

Aims. We compare the mass distribution of central stars of planetary nebulae (CSPNe) with those of their progeny, white dwarfs (WD). Methods. We use a dynamical method to measure masses with an uncertainty of 0.02 M� . Results. The CSPN mass distribution is sharply peaked at 0.61 M� . The WD distribution peaks at lower masses (0.58 M� )a nd shows a much broader range of masses. Some of the difference can be explained if the early post-AGB evolution is faster than predicted by the Blocker tracks. Between 30 and 50 per cent of WD may avoid the PN phase because they have too low a mass. However, the discrepancy cannot be fully resolved and WD mass distributions may have been broadened by observational or model uncertainties.

Mass Distribution and Birth Rate of Central Stars of Planetary Nebulae: Comparison with White Dwarfs, and Influence of Selection Effects

The mass distribution of central stars (CPN) as derived by the Schönberner method (1981) M⊙ vs. age, v(exp) = const, for an enlarged local ensemble, as presented at the London Symposium, 1983, appears to be much narrower and more strongly peaked towards smaller masses than the one recently derived by Heap and Augensen (1987) (HA) using the same method, but IUE data and M⊙ (λ 1300) vs. age, corrected for individual v(exp). Whereas according to Schönberner 65% of all CPN have M < 0.64 M⊙, HA find only 44% below the same limit. We demonstrate that this discrepancy is entirely due to the fact, that HA use Daub and 0.9 × Cahn/Kaler distances, whereas Schönberner used 1.3 × CK. We list a number of arguments which favor the larger distances, especially the recent work by Méndez et al. (preprint, 1987) (Teff/g determinations) and investigations of Magellanic Cloud PN by Aller et al. (1987), Wood et al. (1987) and Barlow (1987) which all indicate a scale ≥. 1.4 × CK. If one uses Barlow's recalibration formula for optically thick PN, the distances for those - which mainly contribute to the massive CPN in the HA analysis - are increased so much as to remove most of them from the local ensemble. We thus obtain for the revised IUE ensemble 84% CPN with M < 0.64 M⊙, in better agreement with results for white dwarfs (70%) (cf. Weidemann, 1987).

Evolution and Mass Distribution of Central Stars of Planetary Nebulae

Considerable progress has been made in our understanding of the evolution of the central stars of planetary nebulae (NPN) compared to the situation five years ago at the Ithaca Symposium where Shaviv (1978) and Paczynski (1978) reviewed the subject. Shaviv stressed the necessity to start theoretical calculations with realistic initial models but doubted - in view of the loops in the HR diagram made by flashing stars - if the Harman-Seaton sequence could be taken as a single evolutionary sequence. Paczynski pointed out how strongly the theoretical rate of evolution depends on the stellar mass - a result which had appeared in his earlier calculations (1971) - and expected the existence of more flashing NPN's of the FG Sagittae type among the luminous (L > 104 L⊙) central stars, for which the core mass luminosity relation (Mc > 0.7 M⊙) combined with the core mass interpulse time relation predicts fairly short (2.10 yrs) intervals between flashing events. Weidemann, however, at the Symposium and shortly thereafter (1977a) concluded in view of the lower effective temperature derived by Pottasch et al. (1978) and the observed narrow mass distribution of white dwarfs around a 0.6 Mo. combined with the theoretical predicted horizontal tracks from the red giant branch towards the NPN region at a luminosity given by the core mass luminosity relation that the high luminosity part (and also the “upturn”) of the Harman-Seaton sequence does not exist. He also proposed an increase in the distances by an average factor of 1.3 compared to the Seaton/Webster (Seaton, 1968) or Cahn/Kaler (1971) scale in order to bring the observed NPN on the 0.6 M⊙ track in the HR diagram and to lower the NPN birth rates to a value compatible with white dwarf birth rates.