The seeing from my backyard has been good in recent weeks, usually on evenings where there is some moon. Small planetary nebula are good targets under these conditions, so I have been hunting down some small ones and even some proto-planetary nebulae.
Here is an example of one I just finished processing and analyzing. This is a very young planetary nebula, with Hubble Space Telescope results showing the outflows of gas visible here to be well less than 500 years old, and other recent papers discussing the results of radio observations (of water masers and such - its pretty "wet", possibly from evaporating icy objects) of the proto-planetary showing that the progenitor star has begun its post-AGB phase only a bit over 100 years ago (AGB = asymptotic giant branch star) with fusion stopping and it becoming a planetary nebula as the hot stellar core remnant is exposed (a brand new white dwarf!) and starts ionizes its surrounding nebula and lighting up the gas it has been ejecting for several 100 years.
The distance measurement listed in SIMBAD was a quite distant 3572 parsecs. This placed the size of the object at almost 1 light year - nearly the size of the inner bright ring of M57, which didn't make sense, since a proto-planetary nebula should be small. When I did a little more digging, more recent distance estimates put it at 900 parsecs away from us, only a little farther out than M57. This fit much better, as this meant its longest axis was only 1/4 of the diameter of M57. This made a lot more sense!
The circular magnified inset image shows a one light year radius around the object (at the 900 parsecs). The field of view in the circle is the same size as M57 if M57 was the same distance from us as CRL618. This gives a convenient sense of scale.
So, measuring the nebula visible in this image, I get a size of 0.22 x 0.06 light years given its distance of 900 parsecs. Compare this to M57 which is 787 parsecs away and its inner bright ring is about 0.8 x 1.0 light years. It does not appear that the progenitor star is visible right now, probably lost somewhere in the hazy glowing outflow that is rushing away from the new white dwarf at 40 to 300 kilometers per second (from spectral data reported in multiple papers). The different speeds are producing the asymmetric bipolar shape. A paper discussing a lot more and with links to other papers on the object can be found here:
https://iopscience.iop.org/article/10.3847/1538-4357/ab1f93The image here has 48 minutes of integration time. It was produced by stacking 6 images, each of which was an 8 minute live-stack (in SharpCap) of 320 x 1.5 second images.
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