The structural features of certain planetary nebulae.
Abstract
Guided slitless spectrograms obtained with the aid of an image rotator at the coude' focus of the 100-inch reflector are used for a study of the structure of NGC 6572 and NGC 7662. The outer portions of NGC 6572 possess an amorphous structure. The nebula is not at all elliptically symmetrical as earlier observations with smaller telescopes indicated. Mg I X457I and S ii show a shell structure, whereas N iii X4640 and A iv X4740 apparently do not. The intensity distribution across the nebula, corrected for bad seeing and guiding, has been obtained for lines of hydrogen and helium. Isophotal contours of 0 iii X4959, Ne iii X3865, Hp, and Heii X4686 in NGC7662 have been drawn. The two forbidden lines show similar contours whereas the distribution of H and He ii is similar in the inner portions of the nebula. A three-night exposure shows that He ii does not appear in the outer shell at all. On the assumption that the structure of the nebula, in the first approximation, can be represented as circularly symmetrical in the plane containing the major axis of the ring and the observer, the radial emission distribution is derived by a method employed by Wallenquist in his study of star clusters. The hydrogen and Ne iii shells appear to be hollow, whereas there is some suggestion that He ii emission appears within the inner shell. Similar studies are in progress for other planetary nebulae, among them XGC62Io, 7009, and IC 418 and 4543. Observatory, University of Michigan, Ann Arbor, Mich. and Mt. Wilson and Palomar Observatories, Pasadena, Ca 1sf.
- Publication:
-
The Astronomical Journal
- Pub Date:
- April 1950
- DOI:
- 10.1086/106338
- Bibcode:
- 1950AJ.....55...70A