Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106.1954v&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 106, no. 5, p. 1954-1964
Astronomy and Astrophysics
Astronomy
6
Algorithms, Planetary Nebulae, Radio Emission, Stellar Evolution, Stellar Mass Ejection, Visible Spectrum, Emissivity, H Alpha Line, Imagery, Red Giant Stars, Ring Galaxies
Scientific paper
Several optical or radio images of planetary nebulae have been deprojected using the algorithm described in Leahy & Volk (1993). For each image 16 radial cuts from the center of the nebula were independently deprojected assuming either spherical symmetry or a weighting of the emissivity distribution towards the plane of the sky. The deprojection was carried out using the optical line images of Balick (1987) for the Ring Nebula (NGC 6720, PN G063.1+13.9) and NGC 40 (PN G120.0+09.8) and for the 15 GHz radio image of M3-35 (PN G071.6-02.3) from Aaquist & Kwok (1991). These three nebulae were chosen due to their generally ellipsoidal shapes as seen projected on the sky, but in all three cases the deprojection indicates that the nebuale are neither oblate or prolate ellipsoidal shells. Instead, these nebulae have two main regions of emission roughly oppositely positioned around the central star each of which covers a solid angle of approximately pi steradians, and most of the emission is in more or less cylindrical bands with very little emissivity at the 'poles' of the nebulae. The nebulae are therefore more barrel-shaped than ellipsoid-shaped. While the possibility that planetary nebulae are cylindrical in shape has been studied in the past, these results indicate that the body of the nebula is far more patchy than had been postulated which may resolve some of the difficulties that the hypothesis of cylindrical symmetry has had. Such shapes are more complicated than the simplest form of the interacting winds model of planetary nebula formation predicts, but can be explained if the progenitor red giant wind was rather asymmetrical.
Leahy Denis A.
Volk Kevin
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