Physics – Optics
Scientific paper
Apr 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977jrasc..71...67a&link_type=abstract
Journal of the Royal Astronomical Society of Canada, vol. 71, Apr. 1977, p. 67-107.
Physics
Optics
32
Infrared Spectra, Light Emission, Near Infrared Radiation, Planetary Nebulae, Stellar Spectra, Cassegrain Optics, Emission Spectra, Helium, Image Tubes, Line Spectra, Optical Thickness, Wolf-Rayet Stars
Scientific paper
Spectra of the central stars of a number of planetary nebulae have been investigated with the image-tube scanner at the Cassegrain focus of the Lick 3-metre telescope. Emphasis has been placed on a search for emission-line features between 5000 and 8600A. With the aid of observations of suitable comparison stars, measured line fluxes can be converted to approximate relative fluxes, often normalised to the flux from 5802,12A of C IV. The discordance between the He II Zanstra temperatures (which are often taken as the bona fide temperatures of these central stars) and excitation and ionization temperatures derived from the appearance of the spectra in the visual region is attributed to the existence of hot stellar coronae which may be optically thick shortward of 228A. Such ultraviolet excesses are not confined to stars of the Wolf-Rayet type but may include objects that show only absorption lines in the normal observed spectral regions.
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