Available formats: HTML | PDF | (gzipped) PostScript
Letter to the Editor
Third-dredge-up oxygen in planetary nebulae *
D. Péquignot ** 1,
J.R. Walsh *** 2,
A.A. Zijlstra **** 3 and
G. Dudziak ***** 4
Received 22 March 2000 / Accepted 14 August 2000
The planetary nebulae He 2-436 and Wray 16-423 in the Sagittarius dwarf galaxy appear to result from nearly twin stars, except that third-dredge-up carbon is more abundant in He 2-436. A thorough photoionization-model analysis implies that ratios Ne/O, S/O and Ar/O are significantly smaller in He 2-436, indicative of third-dredge-up oxygen enrichment. The enrichment of oxygen with respect to carbon is (74)%. Excess nitrogen in Wray 16-423 suggests third dredge-up of late-CN-cycle products even in these low-mass, intermediate-metallicity stars.
Key words: nuclear reactions, nucleosynthesis, abundances ISM: planetary nebulae: general ISM: planetary nebulae: general ISM: planetary nebulae: general galaxies: dwarf galaxies: individual: Sagittarius
* Based on observations collected at ESO La Silla, Chile.
Send offprint requests to: D. Péquignot
Online publication: September 5, 2000