Object of the Week November 02, 2014 - NGC1535

NGC1535

Eridanus

Planetary Nebula

04 14 15.8
-12 44 21

Mag: 10.5

CS Mag: 11.6

Size: 30"

(I swear it seems every object I select as an OOTW is discovered by William Herschel. Did he EVER have a cloudy night??)

Using his newly acquired 18.7" f/13 speculum mirror telescope, NGC1535 was discovered by Herschel on February 1st, 1785. The only notes of his I was able to find are these. He describes NGC1535 as "a very bright, planetary nebula, about half a minute in diameter, but the edges are not very well defined. It is perfectly round, or perhaps a very little elliptical, and all over of an uniform brightness: with higher powers it becomes proportionally magnified."

Visually, this PN makes for a fantastic object in all manner of scope sizes. Scopes down in the 4"-6" range will show the nebula as a small non-stellar disk that may or may not reveal is blue-ish green color depending on conditions and observer. Near the 10" to 12" range, observers may start to make out a feature not seen in many other PN's, an outer halo or double shell. Breaking the 18" aperture range will reveal the central star as a steady glow as well as a more prominent blue/green color. Its outer halo will also become more apparent giving the overall appearance of NGC1535 an elliptical feel. Within the inner shell observers may catch a glimpse of a 14th magnitude star located to the south of its central star. Another unique feature of NGC1535 I enjoy is its very defined edges (for lack of better description). The edges of the planetary are quite defined by its abrupt brightness changes within its annular shape. In other words, the inner ring is much brighter and denser than its outer shel giving itself wonderful contrasts. The object reminds me very much of the Ghost of Jupiter or the Eskimo in that the PN really offers the observer some contrasts in brightness all within itself. And of course, the higher the power and larger the aperture NGC1535 becomes a great object offering a wealth of fine intricate detail. Some observers using larger scopes may make out a pink/reddish hue on the outer edges.

I do offer two challenges.
1. At what aperture does the other shell become apparent? Can you see it with a scope smaller than 8-10"?
2. Sherburne Wesley Burnham reported in 1894 that faint stars within the nebula itself were visible. I quote, "Besides the central star, there are other fainter stars within the nebula .The most prominent of these is near the northern edge of the circular disc." Burnham used the 36" Lick Observatory scope for this observation. Is he referring to the 14th mag star imbedded within the inner ring or are there other fainter stars to be seen? And if there are, I wonder just how many of these stars Burnham refers to are able to be seen in today's large aperture telescopes? Have any DSF members seen any? Its definitely something I will strive for next time out.

And as always,

"Give it a go and let us know!
Good luck and great viewing!"

Attachment 1414
Image by Adam Block/AURA/NOAO/NSF

I looked up this planetary nebula with my 20" telescope from southern France in September 2010. I only looked at it briefly at a magnification of 160x. My notes say "it appears as a bright, round spot. Didn't try higher magnifications." I guess it is time I had another look :)


Clear skies,

Wouter

Cool object Dragan,

I often visit this PN, especially as night-bouncer object.

With 16" and 20" I could easily see the outer shell but I never noticed the star within the shell.

With 27" I could pick up the star. The challenge was to detect the inner structure from the inner shell to the CS. Under perfect seeing some structures were visible but not the extremely faint streaks.

27", 837x, NELM 7m+, Seeing I
Attachment 1415

I don't know which stars Burnham refer. Even in the Block photo only the "bright" 14mag star is visible. I searched after a photo and found the HST picture. Perhaps Burnham refer to the both marked stars in the cropped rough HST picture? I could never see these stars but is could be a target for the CS filter? Perhaps Jimi could try these stars?

HST crop
Attachment 1416

The star that Burnham measured (16" separation from the central star in PA 324°) is at the north-northwest edge of the outer shell and is shown on Uwe's sketch. I didn't mention in my 18-inch observations, but I've seen it in my 24-inch.