An Etymological Dictionary of Astronomy and Astrophysics
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An evolved → hot star which is responsible for the ionization of a → planetary nebula. Planetary nebulae result from mass ejection by evolved stars undergoing violent instabilities. CSPNe are extremely hot, with → effective temperatures ranging from 30,000 to 120,000 K. They evolve rapidly toward the → white dwarf stage, while the planetary nebulae continue expanding with a small expansion velocity of about 25 km s^-1, becoming progressively thinner and thus eventually invisible after some 10⁴ years. The initial masses of these stars range from about 1 to 8 solar masses. CSPNe are not a homogeneous group and present a large variety of spectral characteristics. Many of CSPNe display emission lines, some of them with spectra resembling those of → WC Wolf-Rayet. Although superficially similar, they differ from classical W-R stars in their degenerate structure, much lower masses, a wider range of temperatures, and limitation almost exclusively to carbon-rich stars. Some CSPNe show → weak emission-lines (wels). A considerable fraction of both groups are hydrogen deficient. However, some wels may be H-rich despite having emission lines. The evolutionary status of the [WR]-type stars is still very uncertain, and it is unclear whether there is any evolutionary relation to the wels. CSPNe have a strong → stellar wind composed of helium, carbon, and oxygen. Some of them are binary systems. The study of CSPNe is important for understanding of → post-AGB stellar evolution.

CSPN, short for → Central, → Star of → Planetary Nebula.