Abell 33 ~ The Diamond Ring Nebula
Optics:   Ritchey–Chrétien 20" F/8.2 (4166mm FL) Processing:   PixInsight, Photoshop
Camera:   SBIG STXL-11000 with Adaptive Optics Date:   January-March 2022
11 Megapixel (4008 x 2672 16-bit sensor) Location:   Columbus, Texas
Exposure:   LRGB = 580:80:100:140 minutes Imager:   Kent E. Biggs
A ring, a star, and a cross are all together in one place. What has caused this phenomenon? Abell 33 is also known as PLN 238+34.1 and is a Planetary Nebula located in the direction of the constellation Hydra, one of two Babylonian constellations to remain in use (the other is the split constellation Serpens), both adopted by the Greeks. It is a mythological creature with serpentine features that may also have multiple heads, sometimes of a lion, as well as wings.

The ring in this image is the material being blown off by an aging central star seen in the image above as bluish white. Note the second star next to the central star is likely a companion star. The Abell 33 ring is about 2700 light years away from earth. It just happens to optically align with the star HD 83535 responsible for creating this "diamond ring" effect. The blue “diamond” star is in front of Abell 33 at only about 800 light years away. It is about magnitude 7, almost bright enough to be seen with the naked eye. By knowing it is a blue A0 spectral class, we automatically know it is twice as massive, twice as large, almost twice as hot, and 40 times as luminous as our own sun. The astrophysics of stars predicts this quite accurately.  

Finally the cross or spikes seen are much closer to earth and has nothing at all to do with the star or the ring. It is an optical effect caused by the telescope’s 24 inch long spider vanes responsible for holding the secondary mirror in place precisely above the primary mirror. In this image those vanes happen to line up with the rotation angle of the camera so they are parallel to the camera edges.

Two additional bright colorful stars are visible. The yellow G8 star, SAO 137031, is 6 times fainter than the blue “diamond” star. By classifying it as a G star, we know it has similar mass, luminosity, and size as our own sun. The red K5 star is about 2 times fainter than the blue star, with about 70% the mass and size and less than 20% the luminosity of our own sun.

Hundreds of additional very faint galaxies are visible in the image. Two of the brightest galaxies are PGC 1087949 and 1088161. They are 10s of millions, perhaps a 100 million light years away! That is up to 40,000 times further from us that the planetary nebula!