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View Full Version : Object of the Week July 23rd, 2023 – Sharpless 2-27 in Ophiuchus



ScottH
July 23rd, 2023, 10:05 PM
Sharpless-Osterbrock 15, Stromlo (Gum) 73, Sharpless 2-27
Zeta Ophuchi Nebula
Ophiuchus
Shockwave Emission Nebula
RA 16:37:10
DEC -10:34:02
Mag --
Size 9°

(Note: Paul Alsing let me go a week early to alleviate a personal scheduling conflict)

I first learned of Sh 2-27’s existence quite a few years ago probably the way most of you did – some excellent, extremely wide-field image of the Sgr, Sco, Oph region. But I’ve never heard of any observations of it until I somehow stumbled upon Dr. Jiri Gardavsky’s last year.

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In January of 1952, while working together at the Yerkes Observatory, two young Northerners – Stewart L. Sharpless (age 25) and Donald E. Osterbrock (age 27) – got their The Nearest H II Regions (https://ui.adsabs.harvard.edu/abs/1952ApJ...115...89S/abstract) paper published. In it, they presented the results of their short Ha survey with the Greenstein-Henyey wide-angle camera, of which included some of the largest emission nebulae in the sky. Using a red filter and a Ha interference filter, they cataloged 16 nebulae, with all of them having been discovered previously…except for one. And that “one”, with an angular diameter of nearly 10°, is one of the largest emission nebulae in the sky. They found that it was nearly perfectly centered on Zeta Ophiuchi and in their paper, undertook a quick comparison of it to that of the Lambda Orionis, which they had also photographed.

The next paper published about it, titled A Description of Certain Galactic Nebulosities (https://ui.adsabs.harvard.edu/abs/1955ApJ...121..611M/abstract), was submitted for review in late 1954 by Morgan, Strömgren, and Johnson. Working at Yerkes but in conjunction with McDonald, they had photographed several regions of the sky in H II that they were interested in investigation further. They found the dimensions of the Zeta Oph Nebula to be approximately 7° x 10°, and included a surprisingly detailed image of it on both page 5 and 6.

In the first half of the 1950s, Colin S. Gum, working from Australia, created a catalog of southern H II nebula that he had managed to photograph. A Survey of Southern H II Regions (https://ui.adsabs.harvard.edu/abs/1955MmRAS..67..155G/abstract)was published in 1955 and included the Zeta Oph Nebula as Stromlo #73 (hereafter Gum 73). Four years later, in late 1959, Sharpless included the Zeta Oph Nebula in his second and final catalog. There it was cataloged as the 27 object (hereafter Sh 2-27).

At a distance of about 365 light-years, Zeta Oph (the third-brightest star in Ophiuchus) is a single, rapidly-rotating hot O-type star. It’s also a runaway or exile star (at least 25% of massive stars are ejected from their parent cluster) because it was actually born in the Scorpius OB2 association (Sco-Cen), which is the nearest OB association to the Sun and is composed of three subgroups (Upper Sco, Upper Cen-Lup, and Lower Cen-Cru). While Zeta Oph is only about 3 million years old, it’s been theorized that for the first half of its life it had a more massive companion. But then the “primary” was destroyed in a Type II supernova, possibly pushing Zeta Oph on its current course.

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In the image above (which I got from https://stellarscenes.net/object_e/zeta_oph.htm), you can see that the nebula is structured while there are dark nebulae in front of it (the white arrow indicates the direction Zeta Oph is traveling). Because of how much energy Zeta Oph is putting out, it’s ionizing a density-bound H II region around itself. Along with that, kinetic energy is generated in the surrounding Interstellar Medium (ISM) from the H II region’s expansion at a rate comparable to the mechanical luminosity of the stellar wind from Zeta Oph. The reason the H II region around it has remained quite spherical is because it’s always dynamically young, in contrast to the often-complex shapes of old H II regions around static stars. In the infrared wavelength, a distinct and impressive 1/2°-long bow shock is visible due to how fast the star is moving the dust-rich environment above the galactic plane.

Interestingly, against the odds, astrophotographer Mathew Ludgate managed to get the bow shock to show up in an image he posted last year on AstroBin (https://www.astrobin.com/39tu57/). He coaxed it out by focusing his efforts on the feeble amount of O III emissions produced in the bow shock.

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On the morning of March 20th of this year, I attempted to tackle this humongous nebula with best instrument for the job – a 6-inch f/5 reflector. With that and my Explore Scientific 30/82, I was able to operate at 26x and grab nearly 3.2° of sky. None of the nebula was visible, however, until I added a H-Beta filter and concentrated on the area northwest of Zeta. Then I got a great look at the largest, brightest streak and a smaller one farther above it. What was really exciting was when I was able to see the brightest little piece (LBN 35) with no filter by using an eyepiece yielding 59x and encompassing 1.5° of sky. I looked at it all again on May 1st and found that while both H-Beta and NPB showed the “wave” or “hotdog streak” of nebula NW of Zeta, I felt my eye caught site of it better with the NPB…something about the contrast boost.

Now I'd like to see it in binoculars like Gardavsky did!
Until then,
“Give it a go and let us know!”

akarsh
July 24th, 2023, 07:12 AM
Interesting timing. This past new moon weekend, I wrote a detailed naked-eye report on the Milky Way from the pristine skies of the Warner Mountains of northeastern California in my logbooks. Here's what I had to say about the "Ophiuchus loop" of the milky way:

"The visibility of [a certain] dark rift highlights the presence of brighter nebulosity near Dschubba, between it and [Al Niyat]. The bright rift appears to further continue up along the curve of Scorpius' head. It cuts over north[west] of zeta Ophiuchi. The region [north / northeast] of zeta Ophiuchi also seems bright, but less distinctly so. This vague nebulosity almost connects with the bright branch of the Milky Way ending at Taurus Poniatovii in an amorphous, vague, faint and thick third band. The vaguest section is between Taurus Poinatovii and zeta Oph"

Now, this has little relevance to the OOTW except for this vague illustrative sketch that I made:

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Coincidentally, the region that I mark as "strongest contrast around zeta Oph" corresponds squarely with the two strands of nebulosity Scott has marked in the second image. While making this observation, I had no idea which part of the zeta Oph nebulosity was brightest or which part was faintest. The coincidence of the location of the contrasty region is interesting... An imager friend (Tarun Kottary) who was with me informed me that there's a lot of faint dust clouds in that region of the sky, which is what constitutes the third "Ophiuchus loop" of the milky way. I quote what I wrote in my report to TAC (https://groups.google.com/g/sf-bay-tac/c/KB0O_qQt8Ak/m/EnFytGbmBAAJ):

"The region around zeta Ophiuchus appeared distinctly brighter, although I would not attribute this to the huge H-alpha nebulosity around zeta given how red it is; it could just be some aspect of the Milky Way in a band in which the night vision is more sensitive."

I wish I had pointed my binoculars at it, but I was sufficiently mesmerized by the naked eye view of the milky way that I did not think of reducing my field of view. The coincidence of the position makes me a little more likely to believe that I was picking up hints of the zeta Oph nebulosity naked eye, but I would hesitate to call it until there are more reproductions of this.

j.gardavsky
July 25th, 2023, 07:53 PM
Hello Scott,

and thank you very much for the review of the Zeta Ophiuci Nebula astrohysics, which is very interesting, and for sharing your visual observation.

Clear skies,
Jiri

j.gardavsky
July 27th, 2023, 10:36 AM
Hello Scott,

checking it with my notes, the bent ribbon well visible through the H-beta filters, as marked with the large oval, is home of the Lynds nebulae:
LBN 39 (east of the oval), LBN 32 and 35 (NW of the MBM 139 molecular cloud), and LBN 20, 21, 22 (south-west).

Clear skies,
Jiri

Uwe Glahn
August 20th, 2023, 10:22 AM
Tried the nebula last new moon with my 9° 8x30 binoculars and two Hß filters. Transparency was very good, NELM around 7mag. I could localized all boundaries of the whole nebula by pan into the nebula from outside. The boundaries were visible from all sides and I estimate the size to around 10° diameter. The brighter Sh 2-27 was not visible as a single object.

ScottH
August 20th, 2023, 07:27 PM
Hello Scott,

checking it with my notes, the bent ribbon well visible through the H-beta filters, as marked with the large oval, is home of the Lynds nebulae:
LBN 39 (east of the oval), LBN 32 and 35 (NW of the MBM 139 molecular cloud), and LBN 20, 21, 22 (south-west).

Clear skies,
Jiri

Thanks for that, Jiri. Where a Lynds Bright Nebula ends and another begins isn't easy to see or draw!

By the way, Victor van Wulfen has found (and SIMBAD agrees (https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=Dolidze+27&submit=SIMBAD+search)) that what you labeled as the open cluster Do 23 on your drawing should instead be Do 27 (with the "Do" standing for Dolidze). Here is the excellent chart he drew up and labeled (https://clearskies.eu/csog/downloads/dsfootw2023/#30).

Scott H.

j.gardavsky
August 21st, 2023, 05:02 PM
Hello Scott,

and thank you very much. Yes, the OC is Do 27, also according to the Star Guide Atlas, I am next to IDSA using.

Clear skies,
Jiri

Robin
August 28th, 2023, 05:11 PM
Hi everyone,


Wow, Uwe, even with 8x30 binoculars + H beta filters!! So did you see the whole nebula complex, including the long dark nebulae in the south east region?


In June I had a chance to observe Sh2-27 visually with my 20" Dobsonian at 74x magnification. I started with the brightest patch (LBN 35) near open cluster Doldize 27, where I saw a curved arc when using an H-beta filter. It was quite faint, but I could hold it with averted vision. With a UHC filter I also was able to detect it, but it was more difficult. I could not see it at all without filter.

I was also able to observe the LBN 20, 21 part, where I saw 3 separate nebulous patches with H-beta filter. However, I was not able to see any other parts of Sh2-27. So with LBN 30 I had a negative observation. I scanned the whole region for some more nebulosity, but couldn't see anything else.

This observation took me about 90 minutes. Here at 48° N there is darkness for a while in the middle of the night in June. However, I guess the observation should be easier at more southern latitudes, where Sh2-27 gets higher above the horizon.

Please find attached my sketches.



Clear skies

Robin

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