arXiv subjects
Publications and source records attributed to R. H. Méndez.
We present a summary of current research on planetary nebulae and their central stars, and related subjects such as atomic processes in ionized nebulae, AGB and post-AGB evolution. Future advances are discussed that will be essential to substantial improvements in our knowledge in the field.
Recent advances in the modelling of stellar winds driven by radiation pressure make it possible to fit many wind-sensitive features in the UV spectra of hot stars, opening the way for a hydrodynamically consistent determination of stellar radii, masses, and luminosities from the UV spectrum alone. It is thus no longer necessary to assume a theoretical mass-luminosity relation. As the method has been shown to work for massive O-stars, we are now able to test predictions from the post-AGB evolutionary calculations quantitatively for the first time. Here we present the first rather surprising consequences of using the new generation of model atmospheres for the analysis of a sample of central stars of planetary nebulae.
We have developed a new procedure for the generation of a planetary nebula luminosity function (PNLF), improving on previous work. The procedure is based, as before, on an exponential central star mass distribution, on H-burning post-AGB evolutionary tracks, and on the avoidance of nebular models for the calculation of nebular fluxes. We have added new post-AGB evolutionary tracks and introduced the following improvements: (1) the imperfect analytical representation of post-AGB evolutionary tracks has been replaced by an interpolation routine giving a better approximation; (2) we have modified the distribution of the intensities of [O III] lambda 5007 relative to Hbeta, so that it better imitates the observed distribution, which we have taken from data in the Strasbourg-ESO catalogue of Galactic PNs and other sources; (3) we have adjusted the absorbing factor mu along the white dwarf cooling tracks, so as to reproduce the observed PNLF of the Magellanic Clouds and M 31 at fainter magnitudes. In this way we have produced a PNLF which is more consistent with observed PN properties. We use this randomly generated PNLF to: (1) show as convincingly as possible that most PNs in any real population must leak stellar H-ionizing photons; (2) revise our determinations of the parameter mu(max); (3) discuss the shape of the PNLF, hinting at the possible existence of a distinct feature 2 magnitudes fainter than the brightest PNs; (4) attempt estimates of maximum final masses from fits to the PNLFs of the LMC and M 31. There is marginal evidence of a higher maximum final mass in the LMC, but this should be confirmed in other galaxies with recent star formation. A convincing confirmation will require to increase the sample sizes and to extend the PNLFs to at least 1.5 mag fainter than the brightest PNs.