Pregalactic helium abundance and abundance gradients across our Galaxy from planetary nebulae.
Abstract
Observations of planetary nebulae are used to study the radial gradients across our galaxy of the helium, oxygen, and nitrogen abundances relative to hydrogen. The increase in the oxygen-to-hydrogen abundance ratio from a radial distance to the galactic center of 14 to 8 kpc is about a factor of 3, while that in the nitrogen-to-hydrogen ratio is about twice as large. By adopting oxygen as representative of the heavy elements, it is found that helium enrichment is coupled to heavy-metal enrichment by a factor of 2.9, in close agreement with the value derived from H II regions. The pregalactic N(He)/N(H) value derived from planetary nebulae is 0.073 plus or minus 0.008, also in agreement with the value derived from H II regions.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 1976
- Bibcode:
- 1976A&A....47..341D
- Keywords:
-
- Abundance;
- Galactic Evolution;
- Helium;
- Milky Way Galaxy;
- Planetary Nebulae;
- Galactic Nuclei;
- H Ii Regions;
- Hydrogen;
- Interstellar Gas;
- Nitrogen;
- Oxygen;
- Astrophysics