The exciting stars of low-excitation planetary and diffuse nebulae.

Abstract

view Abstract Citations (60) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The exciting stars of low-excitation planetary and diffuse nebulae. Kaler, J. B. Abstract Effective temperatures of the exciting stars of 35 low-excitation planetary and five diffuse nebulae have been computed under both of the alternate assumptions that the stars radiate according to Hummer and Mihalas's flux models, and that they behave as blackbodies. The method used employs the ratio of the sum of the nebular forbidden-line fluxes to the flux of H (Stoy's method), with modification for the observed electron temperature and helium content. The present analysis is restricted to nebulae with very weak or absent He ii emission, which are therefore expected to be optically thick. Both sets of temperatures correlate very well with measured O2 + /0+ ratios. The temperatures calculated from the flux models are systematically lower than those calculated under the blackbody assumption, the discrepancy increasing with increasing T. The onset of He ii emission is about 46,000 K for the models, and 60,000 K for the blackbodies. The latter is consistent with the predicted He ii Lyman continuum emission at 228 A, whereas the former is not, and it is concluded that the blackbody assumption is superior to that of the set of flux models. The method provides an independent calibration of effective ultraviolet temperatures on the upper main sequence, in that Teff for 61 Ori C (an O6 star) is found to be 37,000 K. Peimbert's finding of a low mass for the planetary in the globular cluster Ml 5 is confirmed. Finally, in accord with earlier studies, it appears likely that cooler planetary nebula nuclei (T < 70,000 K) are as a class less luminous than the maximum luminosity found for the hotter stars. Subject headings: nebulae: planetary - stars: atmospheres - stars: early-type Publication: The Astrophysical Journal Pub Date: December 1976 DOI: 10.1086/154894 Bibcode: 1976ApJ...210..843K full text sources ADS | data products SIMBAD (35)