The abundance of carbon in three type I planetary nebulae.

Abstract

The three planetary nebulae of type I: IC 4673, Me 1-1, and M 1-7, have been observed with the IUE satellite and the chemical abundance of carbon was derived. For the sake of homogeneity, also the abundances of the other most abundant chemical elements have been redetermined using the best optical data from the literature. We have found C/O equal to 1.2, 0.40, and 1.1 for IC 4673, Me 1-1, and M 1-7, with uncertainties of a factor of two in the first nebula and of a 60 % in the other two. The ratio is, within the errors, similar to the solar value of 0.56. Helium and nitrogen are strongly enhanced in IC 4673. In Me 1-1 and M 1-7 N/O is enhanced by about an order of magnitude. According to the predictions of the stellar evolution theory, the masses of the progenitors, on the main sequence, of the studied nebulae should not be above 2-3 solar masses.