M 2-9: moving dust in a fast bipolar outflow.

Using optical images and spectra of the bipolar nebula M 2-9 we show that, in addition to the well-known bright inner nebula, the object has fast, highly collimated outflows reaching a total extent of 115". These radially opposed and point-symmetric outer lobes are both redshifted, leading us to model the radiation from them in terms of light reflected from moving dust, rather than intrinsic emission. Our polarization images show that the lobes are 60% linearly polarized in a direction perpendicular to the long axis of M 2-9. This high polarization indicates optically thin scattering, and lends weight to our dust scattering model. Use of this model then allows us to determine the distance to M 2-9 directly from the measured proper motions on images taken over a period of more than 16 yrs. The physical and geometrical parameters of the nebula then follow. M 2-9 is at a distance of 650pc, is 0.4pc long, has a luminosity of 550L_sun_, and its outer nebula has a dynamical age of 1200yrs, in round numbers. Using the fact that the central object has been constrained to be of low luminosity but of a sufficiently high temperature to make the observed OIII, we argue that the central object of M 2-9 has to contain a compact, hot source, and is probably a binary.