Other
Scientific paper
Feb 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983prhe.work..267p&link_type=abstract
IN: ESO Workshop on Primordial Helium, Garching, West Germany, February 2, 3, 1983, Proceedings (A83-50030 24-90). Garching, Wes
Other
11
Abundance, Astronomical Models, Galactic Evolution, Helium, Hydrogen, Planetary Nebulae, Chemical Evolution, Galactic Structure, Stellar Evolution
Scientific paper
Three determinations of the pregalactic helium abundance Y(p) are made by combining observations of planetary nebulae (PN) with stellar evolution models. From disk PN and assuming that the chemical evolution of galaxies is characterized by a ratio of helium to metal enrichment due to galactic chemical evolution dY/Z = 3 + or -1, it is found that Y(p) = 0.227 + or -0.012 where the main source of error is the adopted dY/dZ value. Using a different set of disk PN and other assumptions it is found that Y(p) = 0.220 + or -0.010 where the error is given by a linear regression fitted to the data. Using halo PN and assuming that their excess carbon abundance comes from the convective helium burning shell (CSH), with Y(CSH)/Z(CSH) = 3.3 +3.3 or -2.3 for Z dredged up in the first two dredge-up episodes, it is found that Y(p) = 0.218 +0.026 or -0.037 where the main source of error is the adopted (CSH)/Z(CSH) value.
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