Author Topic: Sharpless 2-71, an unusual planetary in Aquila  (Read 3009 times)

sgottlieb

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Sharpless 2-71, an unusual planetary in Aquila
« on: August 03, 2015, 12:21:10 PM »
I posted this report on the http://www.deepskyforum.com/ yesterday.  If you're looking for an unusual object to observe this month, here's the scoop on Sh 2-71

Sharpless 2-71 (Sh 2-71) = PN G035.9-01.1 = PK 36-1.1 = LBN 103 = M 1-90
RA: 19 01 59.3
Dec: +02 09 18
Constellation: Aquila

Type: Planetary Nebula
Class: 3b(3)
Size: 124" x 75"
Magnitude: ~12.3V
Central Star Magnitude: 13.5-14 or ?

This planetary has a strange morphology and certainly deserves to be better known! It is one of my favorite large "obscure" summer planetaries and I return to it every year. Interestingly, my descriptions are slightly differently each time, probably due to its subtle structure.



Sh 2-71 was discovered in 1946 by Rudolph Minkowski and included in a table of "Diffuse and Peculiar Nebulosities" (designation M 1-90). Stewart Sharpless included it as object #71 in his 1959 paper "Catalogue of H II Regions". Sharpless added the note "May be planetary".

It's been long assumed the 14th magnitude star near its center in this Gemini North image is the CS. In 1979 Czech astronomer Luboš Kohoutek announced that this "central star" was variable (period = 68 days). His photometry showed a V magnitude range of 13.2 - 14.0. But he also noted "The observed central star of Sh 2-71 cannot be responsible for the radiation of the surrounding nebula." as the central star is not hot enough based on its B8 spectral type. It has been assumed the variability is caused by the orbiting hot companion.

In 2008, Aussie astronomers David Frew and Quentin Parker noticed a much fainter hot star in the geometric center of the PN with a magnitude consistent with it being the central star. If this is the REAL central star, the star that Kohoutek studied back in 1979 could be a very peculiar and rare chance alignment of a PN and a short period binary. More details are available on this Gemini Observatory announcement.

So, what can you see? In a dark sky, an 8-inch may reveal the original "central star" and the nebula, though a larger aperture may be necessary to see structure. A challenging, close pair of faint stars is just to its north and my 18-inch marginally splits this pair. As far as details, here is a sampling of my notes --

24" (7/20/12): at 200x and NPB filter, this large relatively bright planetary is elongated ~3:2 N-S and extends ~1.8'x1.3'. The northern portion of the planetary is clearly brighter with the south side having a lower surface brightness and more irregular. With careful viewing, a faint extension or irregular filament extends south on the west side. The filament increases the N-S direction to 2.2' along the west side.

18" (8/1/08): easily picked up unfiltered at 175x surrounding a 14th magnitude central star. Also an extremely faint star was resolved just north of the brighter central star. Good contrast gain using an OIII filter. The planetary is large and elongated N-S or NNW-SSE, ~3:2. The outline is not sharply defined but it does have a better defined linear edge (N-S) on the east side. The northern half is brighter without the filter, but less so using the filter and the southeast corner is slightly brighter.

18" (7/14/07): viewed at 174x with an OIII filter as a roughly rectangular glow, elongated 3:2 N-S with a size of roughly 1.8'x1.2'. Appears slightly brighter along the eastern edge with a small knot or brightening at the southeast corner. The west and southwest edges are slightly weaker and less defined with perhaps indentations or a scalloped edge.

18" (8/25/06): very impressive non-NGC/IC planetary at 140x and UHC filter. With this combination, Sh 2-71 appeared fairly faint, fairly large, elongated at least 3:2 N-S, ~1.6'x1.0'. Appears sharply defined with a straight border along the eastern edge that runs N-S. The south side has a lower, irregular surface brightness and is the faintest section but appears to extend just as far as the north end. Without a filter the 14th magnitude central star was easy and a fainter star was close north of the central star, appearing to be a double. A trio of mag 10.5-12 stars extending beyond the planetary are off the western side. Located 6' E of a mag 9.5 star.

If you try to track down this object in August or September, also try for the challenging, highly obscured globular cluster NGC 6749 just 50' east-southeast. And what about the huge (roughly 25' in size), low surface brightness HII region Sh 2-72? Is this a visual object?

Here's a colorized DSS view of the surrounding region ---


DDK

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #1 on: August 04, 2015, 12:19:43 AM »
Haven't seen Sh 2-71, but I can discern your mood by your mention of ngc 6749. Here are my notes with Felix my 11", from the Peak 10 years ago. Your name came up then.
"SGNB and no kidding. Peter Natscher and I both worked on this puppy. A discrete patch of mottling, at 126x and 210x. Same at 252x."
SGNB being the abbreviation for Steve Gottlieb Nut Buster.
TAC - astro anarchy at work <*>

sgottlieb

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #2 on: August 04, 2015, 08:28:50 AM »
Sh 2-71 is an easier nut to crack than NGC 6749 -- an OIII or UHC filter should do the trick.  Let me know the results if you check it out this month.

DDK

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #3 on: September 01, 2015, 08:18:51 PM »
Steve, did catch that odd PN at Lassen, just posted the OR. Fun tip, thanks.
TAC - astro anarchy at work <*>

mccarthymark

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #4 on: July 23, 2017, 11:18:05 AM »
"And what about the huge (roughly 25' in size), low surface brightness HII region Sh 2-72? Is this a visual object?"

Yes, it is. 

I observed it last night from the Pinnacles with my 20-inch, after first observing NGC 6749 (@ 205x a fairly large but very faint irregularly round glow, with slightly more concentration in the middle, just distinguished from rest of field) & Sh 2-71 (205x w/ OIII, pretty large 3:2 N-S, fairly bright, with ragged edges; presumed central star noticed with averted vision then held direct.)

Sh 2-72: Using HBeta filter at 101x 3.1 exit pupil, I could discern very faint mottling in the field and scanning about the adjacent areas, with a line of distinct crenellations along the eastern edge of the glow -- the edges of the nebula set off against the darker sky background.  Averted needed to brighten the view but it could be seen direct vision.  At 87x 4.4 ep, the mottling was maintained within the larger 1° field.  UHC had a similar but somewhat weaker effect.  Surprisingly not too difficult, considering transparency and seeing were about average.

Thanks to Mark Wagner for the confirming view
Mark

DDK

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #5 on: July 23, 2017, 06:13:49 PM »
I was privileged to see and overhear that confirmation. "You saw it and I caught a hint, you can log it."
McCarthy you have become a maven of subtle pleasures.
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Mark

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Re: Sharpless 2-71, an unusual planetary in Aquila
« Reply #6 on: July 25, 2017, 11:09:59 AM »
What I saw could be best described as "Lumpy Darkness".  On the subtle side of subtle mottling.  I chuckled when McCarthy told me he was looking at Sh-2, which I spent a few years chasing down.  Its a world of eye-torture. :o