Abstract
We present O2 +/H+ abundances derived from echelle spectroscopy of four planetary nebulae, NGC 6210, NGC 6826, Hu2-1, NGC 6543, from the forbidden, collisionally excited lines, and from the permitted recombination lines. We find that the ratio of the recombination line to collisional line abundances ranges from essentially unity (1.2 for Hu 2-1) to 6.6, for an offset position of NGC 6826, and corresponding t2 values range from 0.016 to 0.087.
