Some aspects of the chemical evolution of 4He in the Galaxy: the He/H abundance gradient and the Delta Y/Delta Z enrichment ratio
W. J. Maciel
Abstract
Two aspects of the chemical evolution of 4He in the Galaxy are considered on the basis of a sample of disk planetary nebulae by the application of corrections due to the contamination of 4He from the progenitor stars. First, the He/H radial gradient is analyzed, and then, the helium to heavy element enrichment ratio is determined for metallicities up to the solar value.
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