Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...377..210r&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 377, Aug. 10, 1991, p. 210-226. Research supported by University of Toronto
Astronomy and Astrophysics
Astrophysics
16
Astronomical Spectroscopy, Forbidden Transitions, Neutral Gases, Oxygen Spectra, Planetary Nebulae, Radiative Transfer, Diffuse Radiation, Massive Stars, Stellar Temperature
Scientific paper
For the first time, forbidden O I 5577 A and forbidden O I 6364 A have together been mapped across planetary nebulae, making possible direct measurement of transition zone temperatures. In NGC 2440, the neutral oxygen temperature is 10,400 + or - 600 K, compared with 10,200 + or - 200 K for the forbidden N II temperature and 14,100 + or - 300 K for the forbidden O III temperature. The forbidden O I temperature in NGC 3918 is 13,000 + or - 900 K, significantly different from that in NGC 2440. Models computed with the nebula code CLOUDY successfully reproduce the forbidden O I and forbidden O III temperatures observed in NGC 2440, indicating that the implemented blend of on-the-spot and outward-only approximations to the transfer of diffuse radiation is a reasonable representation of reality. Even though radiation hardening enhances the heating at large optical depths within a planetary nebula, an increase in the cooling efficiency can present a concomitant rise in temperature. It is predicted that hot transition zones, as observed in NGC 3918, should be restricted to nebulae with cooler central stars and metal abundances (particularly N) at or below solar.
Martin Peter G.
McCall Marshall L.
Richer Michael Gerard
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