Object of the Week July 17th, 2022 - NGC 6537 The Red Spider Nebula

NGC6537
Sanduleak 2-294
PK10+0.1

Planetary Nebula

Sagittarius

RA: 18 05 13.1
Dec: -19 50 35

Mag: 13

Size: 10.0”

CS mag: 18.8

As I began writing a list of targets for my 25” at next week’s Nebraska Star Party, I came across this object – NGC 6537 The Red Spider Nebula. Not only was I surprised that I had never observed this object, but I have no recollection of ever having heard of it!

Discovered July 15^th, 1882 by Harvard University astronomer Edward Charles Pickering, NGC 6537 is a small, irregular dual-lobed planetary in northwestern Sagittarius. In images, these lobes appear rather rippled or striated as opposed to smooth – something attributable to the nebula’s 300km/s winds!

Having no observing logs of this object, I reverted to trying to find online reports by other observers. Best I can tell, this object, although appearing stellar, can be seen in scopes as small as 11”. In larger scopes, the lobes tend to present themselves giving the planetary an overall elongated appearance. Some reports even claim having seen an overall “s” shape. I found no reports of observers claiming any red as seen in photographs but larger scopes do tend to reveal an overall blueish tint.

As I mentioned above. I’ve never seen this object and I hope that next week at NSP will be my first time. I hope anyone with experience with the Red Spider can chime in giving us with no experience a little insight.

And I’ll be sure to let you know once I…

…give it a go!



Attachment 4799

Attachment 4800

Hi, here's my observation from 7/26/2008: Ngc 6537 aka the Red Spider nebula in Sagittarius ; mag: 13 ; size: 10" ; small, elongated, responds to OIII, two faint stars nearby. I used a 10mm Radian at 198x with my 14.5 Starstructure f/4.3Attachment 4801

I observed this nebula with my 6" homemade Newton telescope. My notes state that it is only visible at high magnification using an OIII filter. At 170x I was able to see a tiny disk. I'll need to revisit this one with my 20" telescope!

With a 20" at 272x: A slightly brighter center to a disc. Easy to find, no central star or color.
With an 18" at 286x: There was a faint, relatively large glow.
Sounds like an O-III may be slightly better than a UHC.

Not surprisingly, the N-II emission strength in this one is higher than O-III, though.
Very strong signals are N-II, S-II, H-alpha though there is a lot of energy in the IR.
I attach a spectrum from 0 to 1000nmAttachment 4802

I observed the Red Spider again last night at 610X I got a good response to the NPB filter. I could see the faint streamers with the filter. Cool little PN!

My notes:

20" scope: After a little bit of searching, this is the very tiny but distinctly not stellar NGC 6537, the Red Spider Nebula, which in the 14mm has very much a “vagueness” to it; I want to say the extensions are SP and NF, but that might be a trick of the light (so to speak). The nebula’s absolutely tiny, just a fraction above stellar—maybe 4”. It forms the SF vertex of a flat isosceles triangle; P very very slightly N of the nebula by 1.5’ is an 11.5-magnitude star; there’s a 12.5-magnitude star 1.25’ N very very slightly P that star, and that last star is about 2.25’ NP the nebula. NF the nebula by 7’ is a 7.5-magnitude star; due N of the nebula by 4.5’ is a pair separated by 0.3’, with the brighter star N very very slightly P the fainter (a satellite crosses the S end of the field) and those two stars are both 13th-magnitude; the one on the S is just a shade fainter than the first. Even further N of the nebula by 15’ is the brighter of a very unequal pair; that star is 9.5 magnitude and has SF by 0.67’ an 11.5-magnitude star. With the 7mm Nagler, I’m not getting a good focus tonight, because the seeing’s pretty crappy; but with the 7mm the nebula’s even more obviously non-stellar. I’m not sure if there’s a central star visible at all, but there’s almost a hint that there could be, an implication. It helps to get that star out of the field, the 7.5-magnitude one. There’s a curious line of bright stars in the 10th– to 11th-magnitude range that run roughly P-F along the S end of the field. The extensions seem to still be there, running SP-NF; the nebula itself seems very very slightly elongated P-F. I’ll go ahead with the nebula filter here and see what turns up. Oh, wow– with the UHC filter in, the nebula brightens considerably, and really impressive how much it does so. And the impression that I had earlier of it with directions of tendrils and things like that are all enhanced quite a bit at this magnification with the filter (this is still the 7mm). It really is brightish with the filter in, with the extensions and the elongation, everything being as read earlier, but man, it’s a neat little object, just letting it drift across the view there. Using the O-III filter, though, really just kills everything there; the two other stars in the little triangle with the nebula are almost gone. The nebula’s considerably bright but I’m not picking any extra detail with the O-III.

12.5" scope: I didn’t expect to take notes tonight, due to the skyglow and smoke and poor-looking transparency. This is the Red Spider Nebula, and I’m using the 10mm Delos for this miniscule planetary. The nebula is just barely distinguishable from a star because of its perimeter fuzziness, and is grey rather than even the slightest tinge reddish (of course). It’s very very small–even with the OIII filter, it’s no more than 5” across. It appears that the central star may just be visible; the nebula comes to a very sharp central point, and the outer fuzz is mostly visible in averted vision. It also, at some moments, seems to be slightly elongated SP-NF. The nebula is the SF vertex of a triangle that includes two 12th-magnitude stars, one of which is P very slightly N of the nebula by 1.5’ and the other which is N very very slightly P that star by 1.5’. Also visible NF the nebula by 0.75’ is a 14th-magnitude star; there’s another 14th-magnitude star NP that star by 1’; the nebula is therefore at the juncture of two triangles. Due N of the nebula by 4.25’ is a double/close pair: the slightly-brighter star is S slightly F the fainter by 0.25’, and these are approximately 13.5 magnitude. Due NF the nebula by 7’ is the brightest star in the field, which is 7th magnitude; F very slightly N of that star by 6’ is a 9th-magnitude star.

Found two itself interesting observation with different results concerning the red tails.

27", 586x, without filter, NELM 6m5+, Seeing II-III
faint, small and elongated ring; north side of the ring somewhat brighter; to the southeast a faint and broad extension becomes visible; [OIII] and Hß don't bring any positive reaction; thin arms are not visible

sketch:
Attachment 4803
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20", 1000x, without filter, NELM 7m0+, Seeing I
under much better conditions but smaller aperture, two arms becomes visible; one wide arm to the southeast and a thinner arm to the northwest; the PN itself is presented as a very small but open oval body