The exciting stars of low-excitation planetary and diffuse nebulae

Journal Article · Wed Dec 15 04:00:00 EST 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154894· OSTI ID:7323782

Kaler, J B

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..beta.. (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 O/sup 2 +//O/sup +/ 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 T/sub eff/ for THETA/sup 1/ 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 M15 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. (AIP)

• Research Organization: University of Illinois Observatory
• OSTI ID: 7323782
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 210:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
CRYOGENIC FLUIDS
ELECTRON TEMPERATURE
ELEMENTS
EMISSION SPECTRA
ENERGY-LEVEL TRANSITIONS
FINE STRUCTURE
FLUIDS
FORBIDDEN TRANSITIONS
HELIUM
HYDROGEN
IONIZATION
MATHEMATICAL MODELS
NEBULAE
NONMETALS
NUCLEAR REACTIONS
PLANETARY NEBULAE
RARE GASES
SPECTRA
STAR MODELS
STELLAR ATMOSPHERES
STELLAR RADIATION