Chemical Abundances and the Parameters of Planetary Nebulae
Abstract
All known ezisting observations of spectral4ine intensities of planetary nebulae have been compiled into a catalog which consists of 250 nebulae, including four well-observed H ii regions. New electron densities have been calculated for most of these nebulae, and revised electron temperatures from the [0 liii lines are given for 109 of them. The ratios He/H, 0/H, and 02+/H+ are given for 80,124, and nearly all the nebulae, respectively. A two-temperature model is assumed for the calculation of abundances, in which the low temperatures derived from the hydrogen lines and continuum are used for hydrogen and helium recombination coefficients, and the [0 iii] temperatures are used for the calculations involving forbidden lines. Various methods of calculating the abundance of the higher ionization stages of ozygen are evaluated, and the method of using the He2+/He+ ratio is found to give the most consistent results. The intensities of the [Ne ivi and [Ne v] lines suggest a high electron temperature near the central star. The [0 iii] electron temperatures are correlated negatively with the 0/H ratio and positively with the temperature of the central star in accord with the currently accepted ideas of nebular heating and cooling. The mean [0 iiij electron temperature is 11500 K for nebulae without He ii lines and 14000 K for those with He ii lines. The mean 0/H ratio is 5.35 X 10- and ranges from about 10- to 1.4 X l0- . The mean He/H ratio is 0.14 wfth a range of from 0.09 to greater than 0.2. The 0/H ratio is negatively correlated with the He/H ratio, and is also correlated with population indicators such as radial velocity and height above the galactic plane in the sense that objects with high 0/H have Population I characteristics and the nebulae of Population II have low 0/H. In view of these results it would appear difficult to interpret the data in terms of "cosmic abundances."
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1970
- DOI:
- 10.1086/150479
- Bibcode:
- 1970ApJ...160..887K