Waid Observatory

Object: Sh2-290 / Abell 31
Date: Mar./Apr., 2024   -   Location: Davis Mountains west of Fort Davis, TX
Telescope: 10 in. RC   Mount: Paramount MX   Camera: Apogee U8300M
Exposure: Ha = 240 min   OIII = 120 min.  -   20 min. sub-exposures  -   RGB = 60 min. each filter
Click on the image below to view at higher resolution.




Sh2-290 / Abell 31 1,2

Discovered in 1955 by George Abell[1]

Sh2-290, also designated as Abell 31, is a planetary nebula approximately 2,000 light years distant[1] located in the constellation of Cancer[1].  As viewed from the Earth, this planetary nebula is one of the largest in our sky[2].  It is almost as large as the Helix planetary nebula[1].

The nebula is very faint and requires long exposures to bring out nebular detail and the extent of its extended halo[1].  The progenitor star that formed the nebula is believed to have been about twice as massive as our Sun[2].  As it aged, it evolved into a Red Giant and began expelling the outer shells of its atmosphere until only a compact core remained.  This core, no longer capable of fusing elements, has evolved into a white dwarf star.  It is extremely hot and produces prodigious amounts of ultra violet radiation.  This excites the surrounding nebula and causes it to glow in the vivid colors you see in the image above.  The red portions of the nebula are primarily composed of hydrogen[2] and the blue is mainly from ionized oxygen[2].

The above image is oriented with north toward the top and east to the left.  The nebula is moving toward the south and the sharp bow wave is being compressed by interaction with the interstellar medium[2].  The fainter northern portion is on the down wind side and is probably a better representation of the primordial nebula as it was expelled during the Red Giant phase.  The nebula is expanding, and dispersing, into interstellar space.  Over a period of many thousands of years, the nebula will disappear and only the dying white dwarf will remain.

The image above was assembled using hydrogen alpha (Ha) and doubly ionized oxygen (OIII) filtered images.  The Ha image was mapped to the Red channel and the OIII was mapped to the Green and Blue channels.  The stars were overlaid with data from a separate RGB filtered image.  This method produces a near true color image that more closely portrays the natural color of the subject object.  A full narrowband (Hubble Palette - SHO) version of the image may be viewed here.

1Astrodon Imaging: https://astrodonimaging.com/gallery/sharpless-290-abell-31/
2Anne's Astronomy News: http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/abell-31-by-adam-block/

Copyright Donald P. Waid