Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983s%26w....22...68g&link_type=abstract
Sterne und Weltraum, vol. 22, Feb. 1983, p. 68-74. In German.
Astronomy and Astrophysics
Astronomy
Astronomical Spectroscopy, Interstellar Gas, Planetary Nebulae, Stellar Envelopes, Astronomical Photography, Emission Spectra, Morphology
Scientific paper
The first planetary nebula (PN) was discovered by Darquier in 1779. In 1981, a compilation of galactic PN listed a total of 1455 objects. Outside the Milky Way Galaxy, PN are currently known in the Magellanic Clouds and in several members of the local group of galaxies. The PN have a rich emission-line spectrum, which makes it possible to recognize them at large distances. A central stellar object can be observed within the nebula. In 1927, spectral lines at 4959 A and 5007 A emitted by the PN could finally be identified as 'forbidden lines' of O(++). The life expectancy of a PN, estimated on the basis of the observed expansion rate, is only about 30,000 years. The PN have a number of interesting characteristics which are partly related to the high effective temperature and luminosity of the central stars, the presence of a particle system under extreme physical conditions, and the stellar material provided by the PN for the interstellar medium. Attention is given to the determination of the distance of PN, the Shklovsky distances, and two mysterious aspects related to the spectrum
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