Integral Field Spectroscopy of Faint Halos of Planetary Nebulae

We present the first integral field spectroscopy observations of the two planetary nebulae NGC 3242 and NGC 4361 with the VIMOS instrument attached to VLT-UT3. By co-adding a large number of spaxels, we reach an emission-line detection limit of 5 × 10-18 ergs cm-2 s-1 arcsec-2. In the case of NGC 3242, we succeed in determining some properties of the halo. The radial surface brightness profile in [O III] implies increasing mass loss before the formation of the planetary nebula. Traces of the mysterious "rings" are clearly visible. We find for the first time an apparent temperature gradient across a halo: from about 16,000 K close to the shell/halo transition to 20,000 K at the halo's outer edge. No line emission is seen in the suspected halo region of NGC 4361 down to the sensitivity limit.