This
Astrobin Debut Object is an elliptical planetary nebula located 11,000 light years away in the constellation of Puppis at a declination of -19 degrees. It is a magnitude 13.7 PN which spans 45 arc-seconds in our apparent view. This corresponds to a diameter of 3 light years.
This is a difficult object to image because of the proximity, 4 arc-minutes away, of the bright 4th magnitude blue star 16 Puppis.
The full name of this object is Sanduleak 2-21, discovered in 1975 by Nicholas Sanduleak.
Like many PN, the outer rim is stronger in HII while the inner section is stronger in OIII. This is an
owl-type PN, with 2 darker void areas in the central region and other common traits as described in the link. I do not see a central progenitor star. The structure and color remind me of
M97 (as shown in the mouseover), but this object is over 5x smaller.
The scalloped nature of the outer rim HII signal is interesting, with strong signal at the orthogonal 12, 3, 6, and 9 o’clock positions. One paper suggests that this is due to an unusual occurrence of 2 HII mid-latitude rings, which if true would be the first time that such a structure is found in an elliptical PN. But since M97 looks somewhat similar in this respect, but not quite similar enough to seem to have two rings, I am not convinced of the dual ring HII theory.
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