Multi-aperture photometry of extended IR sources with ISOPHOT - I. The nature of extended IR emission of planetary NebulaeU. Klaas, H. J. Walker, T. G. Müller, P. J. Richards and J. SchreiberA&A, 452 2 (2006) 523-535DOI: https://doi.org/10.1051/0004-6361:20053245
