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 & OIII = 240 min. each - SII = 220 min.  -   20 min. sub-exposures binned 2x2
Red, Green, & Blue = 60 min. each filter  -   3 min. sub-exposures binned 2x2
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 radiation excites the surrounding nebula and causes it to glow.  The brownish/gold portions of the nebula are primarily composed of ionized hydrogen[2].  The blue is mainly from doubly 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 ionized Sulfur (SII), hydrogen alpha (Ha) and doubly ionized oxygen (OIII) filtered images.  The SII image was mapped to the Red channel, the Ha was mapped to the Green channel, and OIII was mapped to the Blue channel.  This mapping scheme is known as the Hubble Palette.  The stars were overlaid with data from a separate RGB filtered image.  A bi-color (HOO near true color) 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