The chemical structure of bipolar planetary nebulae .1. IC 4406

Long slit spectrophotometry of the bipolar planetary nebula IC 4406, in the range from 360 to 930 nm, has been used to study the chemical structure along its major axis. We find that: - the He, O, N, Ne, and Ar abundances are constant, within errors, along the major axis of the nebula. Average values for He/H, O/H, N/H, Ne/H, and Ar/H are: 0.126, 5.6x10(-4), 2.0x10(-4), 1.7x10(-4) and 3.2x10(-6), respectively. The N and He abundances of IC 4406 are quite modest for objects in this morphological class. - The computed abundances of sulphur indicate an increase of S/H towards the external parts of the nebula, which may likely reflect inaccuracies in the available ionization correction factors. Within the accuracy of the present data and analysis method, IC 4406 appears therefore to be a chemically homogeneous object.