A precessing collimated outflow in the quadrupolar planetary nebula NGC 6881

We present high-quality (subarcsecond) optical narrowband CCD images of the planetary nebula NGC 6881, which reveal a highly collimated bipolar struct ure. A careful examination of the [N II] image and of the [N II]/[O III] an d [N II]/H alpha ratio images shows that NGC 6881 is a quadrupolar planetar y nebula, that is, a twice bipolar planetary nebula, each pair of lobes hav ing a different symmetry axis. In addition, a striking knotty, looplike structure has been discovered in t he southeast extreme of the nebula. Its appearance strongly suggests a prec essing jetlike structure. Kinematical information of the different morphological features confirms th e proposed nature of this nebula. The bright core is a ring that is collima ting the bipolar lobes, while the looplike structure turns out to be a prec essing jet. Assuming a simple ballistic model, an age of 7400d yr (d is the distance in kpc) is worked out, which can be compared with the computed ag e of the inner lobes of 400d yr. The precession period is 3800d yr. An uppe r limit of the ionized mass ejected (1.8 x 10(-5) d(5/2) M.) in the precess ing jet has also been calculated.