Nuclei of planetary nebulae as hot liquefying white dwarfs
Journal Article
·
· Nature (London) Phys. Sci., v. 244, no. 139, pp. 133-135
It is stated that none of the recently proposed models for the central stars of planetary nebulae, before and after ejection of mass, appears to be in good agreement with observations. The present masses of these central stars are not known, nor whether the amount of preplanetary mass loss is negligible or considerable. The following picture is here suggested: (i) the central stars of planetary nebulae in the diagonal branch of the H-R diagram are hot white dwarfs whose core is undergoing liquefaction; (ii) the cores of the stars are chemically pure and the envelopes are thin and composed of elements of mean charge Z < l0; (iii) the masses of the stars are in the range 0.45 to 1.3 M/sup sub solar /, which means that nebula ejection has to occur before the star reaches the diagonal branch, that is, in the horizontal branch; (iv) no neutrino luminosity is present and the cooling times are those for a gaseous core liquefying with emission of latent heat. This picture is based on latest results on gas-liquid phase transitions and the cooling of white dwarfs, which are briefly summarized. The following model is introduced for a hot white dwarf the core of which will eventually liquefy: an extended core, very dense and isothermal, where the electrons are completely diagnostio and relativistic, surrounded by a thin envelope where the temperature and density decrease towards the surface and the electrons are partially degenerate and partially relativistic. The dense core accounts for the total mass and luminosity of the star and is composed of pure C (or heavier elements) and the envelope acts as a thermal blanket, its opacity regulating the energy radiated by the hot core. Agreement was found between this model and previous calculations. (UK)
- Research Organization:
- Observatorio Astronomico de Capodimonte, Naples
- NSA Number:
- NSA-29-013417
- OSTI ID:
- 4380976
- Journal Information:
- Nature (London) Phys. Sci., v. 244, no. 139, pp. 133-135, Journal Name: Nature (London) Phys. Sci., v. 244, no. 139, pp. 133-135; ISSN NPSCA
- Country of Publication:
- United Kingdom
- Language:
- English
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