Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....98...81l&link_type=abstract
Astronomy and Astrophysics, vol. 98, no. 1, May 1981, p. 81-84. In French.
Astronomy and Astrophysics
Astrophysics
3
Astronomical Photometry, Astronomical Spectroscopy, Electron Energy, Planetary Nebulae, Ring Structures, Stellar Envelopes, Astronomical Photography, Forbidden Bands, H Alpha Line, Monochromatic Radiation
Scientific paper
Observations of the double shell and the electron temperature distribution of the ring planetary nebula NGC 6720 in Lyra are presented. The double shell was photographed with narrowband interference filters centered on the H-alpha (6563 A) and forbidden N II (6584 A) lines using an image tube. Observations in H-alpha revealed practically no evidence of a double shell, while the filamentary structure of the second shell was detected in forbidden N II, indicating that the forbidden N II line is dominant in the second shell. Observations of the forbidden O III lines at 5007 and 4363 A were made with a Wray focal reducer camera to obtain an isothermal contour map of electron temperature in the nebula. The map reveals three major temperature zones within the shell, with temperature increasing towards the edge and center of the nebula and several cold globules situated in the ring itself. Both the higher temperature of the center of the nebula and the presence of cold regions are interpreted as manifestations of the projection of the second shell, in agreement with the model of Minkowski and Osterbrock (1960).
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