Continuum intensities in planetary nebulae
Abstract
Thirty-four planetaries are considered for which continuum intensities have been measured, Te may be calculated from the [0 `III] intensities and Ne may be calculated from forbidden line intensities or from the surface brightness. Values of Be/H8 measured by Aller (Be = Balmer continuum intensity) are in reasonable agreement with theory. About half of the nebulae considered appear to come closer to Case A than to Case B (A = optically thin, B = optically thick in Lyman lines). Total continuum intensities are calculated for H II regions allowing for: (I) all H and He II recombination and continua and (2) the H 25 15 two-quantum continuum, collisional deactivation of H 25 being taken into account. The calculated intensities, relative to H8, are compared with the measurements of Page for both sides of the Balmer limit. The mean results are in fair accord but there is a considerable scatter probably due to observational errors. Recently measured Balmer discontinuities (A) are in good agreement with theory for 6 nebulae, but for NGC 6826 A (obs) is significantly smaller than A (calc). This object is unusual in that it is surrounded by a faint outer envelope. The small value of A (obs) is probably due to the conversion of Ly into H 25 15 quanta in an extensive H I region. when such processes are not important A (obs) may be used to improve the estimates of Te and Ne.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- 1955
- DOI:
- 10.1093/mnras/115.3.279
- Bibcode:
- 1955MNRAS.115..279S