SIMBAD references

Imaging Fourier transform spectroscopy is used to obtain multiwavelength observations of the M27 planetary nebula's optical gas complex. The data set allows a complete cartography of the nebula's morphological properties, of its density and temperature structures in its low-excitation zone, and of its gas excitation. Radial profiles in peak intensity indicate that the nebula is radiation-bounded along its highly inhomogeneous and clumpy minor axis. The diffuse major axis show a monotonic decrease with increasing distance from the central star and appears to be matter-bounded. Clumps, said to be formed of numerous small-scale features referred as `knots' in the literature, are mostly located in the low-excitation outer shell. The standard low-excitation [Sii] and [Nii] diagnostics reveal mean density and temperature, respectively, estimated at 80/ cm3 and 10 115 K in the nebula's outer layers. Temperature fluctuations, on the plane of the sky, show a decreasing trend with increasing angular scale. A lower limit of 0.023 is obtained for the amplitude t^2_V of the volumetric temperature fluctuations. This indicates that temperature inhomogeneities could play a role in the solution of the abundance discrepancy problem.