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The images of the three planetary nebulae
displayed on the following page were obtained by Romano Corradi at the INT with the
Wide Field Camera, that covers a field of view of 34×34 arcmin. They
are very deep exposures (one to three hours exposure time) obtained through
an Hα+[NII] narrow-band filter, and were aimed at studying the faint haloes
that are known to surround a large fraction of planetary nebulae. We believe
that these haloes are the trace of the last episodes of mass loss from the
stellar progenitors of the nebulae, occurred a few 104 years ago when they
were in the pulsating red-giant phase that eventually leads to the complete
ejection of the stellar envelope and the formation of a planetary nebula.
In the case of two of the nebulae (Sh 2–200 and NGC 3242) displayed in the
figure, however, the extended and structured emission revealed by the WFC
images might not be material lost by the stars in the recent past, but simply
interstellar gas located in the proximity of the planetary nebulae and ionized
by the energetic radiation from their central stars.
