Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...461.1019g&link_type=abstract
Astronomy and Astrophysics, Volume 461, Issue 3, January III 2007, pp.1019-1025
Astronomy and Astrophysics
Astrophysics
2
Ism: Planetary Nebulae: General, Radio-Continuum: Ism
Scientific paper
Context: Radio-continuum spectra are frequently used to infer the density distribution of ionized gaseous regions, while observed correlations between the brightness temperature and other distance-independent parameters are used to test evolutionary models of planetary nebulae. Aims: We check empirical correlations among features derived from the observed radio data and the inferred conclusions available in the literature, using self-consistent photoionization models. Methods: Photoionization models are computed for the physical conditions of planetary nebulae in order to derive self-consistent radio-continuum spectra, as well as the brightness temperature. Results: The temperature and ionization distributions throughout the nebulae explain the observed range of spectral indexes in the thick region of the spectrum, even for a uniform density distribution, usually challenged in the literature. The obtained models fit the observed radio spectra for planetary nebulae in a large range of spectral indexes. Our calculations show a correlation between the spectral index obtained in a given frequency range and the nebula size, as well as reproduce the observed relations between the brightness temperature and other distance-independent parameters. Such diagrams are frequently used to check evolutionary models of the central star and/or of the nebula. Conclusions: .Since PNe images clearly show that the density is not constant inside the nebulae, and models with uniform and non-uniform density distributions can both reproduce the observed radio spectra, we conclude that it is not possible to favour one of them from the radio data, or to infer a particular density distribution for planetary nebulae.
Aleman Alexandru
Gruenwald Ruth
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