NGC 6337

Scorpius

RA
17h 22m 15.65s

DEC
-38º 29' 01.4"

MAG 12.3, central star mag 14.9

Type: Planetary nebula, size 49” x 45”

NGC 6337, the Cheerio Nebula is our focus this week. A lovely annular planetary nebula very much like M57, it’s located in southern Scorpius a few degrees west and south of the Stinger stars. At magnitude 12.3 and 49” x 45” arc seconds in size it’s reasonably bright and large and will take magnification well. Its central star’s magnitude is 14.9.

dss_searchNGC6337crop.jpg

6337 is special because of all its central stars – check out the DSS image and you’ll see a straight line of five stars bisecting the very round ring of NGC 6337, and they’re the visual challenge here. Of course only one is the physical central star of 6337 – it’s the one closest to the bright star that’s just inside the southern edge of the ring.

I've found the non-filtered view to be the most satisfying mostly because it’s the only way to see the three faint central stars. The two brighter stars on the end of the five star line are seen fairly easily, but the three in the middle are about as difficult to see as the single central star in M57 during poor seeing. The nebula stands out with higher contrast using either UHC (good) or OIII (better) filters but they do dim the stars and erase any hope of seeing the faint triple. My sketch is a composite – the nebula was drawn using an OIII filter and the stars added without a filter, all using 408x. You’ll note that I've seen only two of the three faint central stars so far. Has anyone seen all three?

NGC6337 sketch.jpg NGC6337 inverted sketch.jpg

I've observed 6337 from the Golden State Star Party at about +40 degrees latitude with my 28 inch scope, and had similar views through my 13 inch from the Big Island of Hawaii at around +19 degrees latitude, so elevation above the horizon really matters. My best view was with the 28 inch – see the sketches above - but it was only slightly better than with the 13 inch.

In the paper “The Outflows and Three-Dimensional Structure of NGC 6337: A Planetary Nebula with a Close Binary Nucleus”, Ma. T. García-Díaz, D. M. Clark, J. A. López, W. Steffen and M. G. Richer (http://iopscience.iop.org/0004-637X/...1633.text.html) discuss the three dimensional structure of 6337 as being greatly influenced by the true central star being a tight double star. The other four stars just happen to lay in our line of sight.
The discussion of how the authors constructed a 3D map of 6337 is worth the effort to read their paper. Having some idea of 6337’s internal dynamics brings it to life, making knowledge of its physical nature as powerful an observing tool as a nebula filter or averted vision.


“Give it a go and let us know!”

Good luck and great viewing!