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We present spectroscopy of nine planetary nebulae (PNe) in the outskirts ofM31, all but one obtained with the 10.4m GTC telescope. These sources extendour previous study of the oxygen abundance gradient of M31 to galactocentricradii as large as 100 kpc. None of the targets are bona fide members of aclassical, metal-poor and ancient halo. Two of the outermost PNe have solaroxygen abundances, as well as radial velocities consistent with the kinematicsof the extended disk of M31. The other PNe have a slightly lower oxygen content([O/H] ~ -0.4) and in some cases large deviations from the disk kinematics.These PNe support the current view that the external regions of M31 are theresult of a complex interaction and merger process, with evidence for awidespread population of solar-metallicity stars produced in a starburst thatoccurred ~2 Gyr ago.

The chemistry of planetary nebulae in the outer regions of M31