![[M22 Globular Star Cluster in Sagittarius]](../JpgSm/m22.jpg)
By Doug Snyder
Extraordinary Efforts And Results!
Near the heart of this magnificant globular cluster lies a very unusual
planetary nebula first noted as a strong infrared radiation source in the
IRAS catalog of 1985. The purpose of this web page is to provide some
background information on this PNe and also supply enough information so
that observers with the appropiate telescopic equipment along with the
passion to search out seemingly
impossible objects can get a 'hand-hold' on just exactly what they are
looking for and where. We lead off this quest with an article written by
Rich Jakiel, who often seeks the ultimate in deep sky challenges, and
often succeeds!
The following information has been extracted from a longer article entitled "Seven Ultimate Challenges" written by Rich Jakiel, which can be found on the web site of Jim Shields (Adventures in Deep Space). I have embedded some updated information within the text that I have obtained from other web sites.
The 7th Ultimate Challenge. Planetary Nebula PK 009-07.1 (J2000.0: 18h 36m 22.82s -23d 55m 18.3s)
If any object is impossible to see, this small planetary nebula comes close! Located deep in the heart of the great globular cluster M22, this object has defied every observing attempt. And yet, there may be some hope. This most unusual planetary nebula was first recorded in the IRAS Point Source Catalogue (1985). It is a member of a rare class of halo planetary nebulae and bears certain similarities with Pease 1 (K 648) the only other PN in a globular cluster. (Doug's note: there are now at least 4 known PNe's within globular clusters - Pease1, GJJC1, and one each in NGC6441 and PAL 6) This peculiar object lacks the characteristic H and He emission lines, with only [O III] and [Ne III] present (1991, ApJ 379 168 ). There is a substantial amount of dust accounting for the distinct infrared emission.
Courtesy of Brian Skiff at Lowell Observatory: "...standardized photometry. The cluster was studied by Monaco et al (2004MNRAS.349.1278M), who provided BVI data for 186,000 stars in the cluster. They give RA/Dec for the stars, so once the precise position is in hand, then it was easy to look it up. The data imply that they resolved the northern/southern components of the planetary. They give: V = 14.67 (N) and 14.53 (S). Assuming there is no bleeding of flux between these determinations, I get a sum of V = 13.8 for the combined light. The bright background of the cluster is surely the reason it is a difficult object visually, but the implication here is that it is quite a bit brighter than everyone seems to be assuming. This magnitude seems to be consistent with the I-band magnitude, which is 12.4 as measured both by Monaco et al and the completely independent DENIS near-IR survey."
Measuring 10" x 7", the PN forms part of an optical triplet only 1' (arc-minute) from the core of M22.
Before attempting this object, try Pease 1 in M15. It is visually at 13th magnitude and located several arc-minutes north of the globular's core center. Alister Ling (1990, Deep Sky 32 36) gives a good write-up on how he finally succeeded in locating this PN. (Doug's note: There is a Pease 1 page on this site with finder charts.)
Unfortunately, our little PN in M22 is a much more difficult customer. Many serious observers have attempted with apertures up to 25-inches with NO success. I have tried this several times, the last at the Chiefland Starfest in 1996. Using a detailed finder chart of M22 and Vic Menard's superb 20-inch f/6.2 dobsonian we gave it our best for almost an hour. Using magnifications over 400x, and an O III filter we just could not pick out this PN from the haze of unresolved stars in the core. And that's the paradox. Its emission is the strongest in [O III] lines, but this type of filter is best used at lower magnifications. However, to separate the nebula from the extremely dense stellar background high power is required. The O III filter "mushes" out the very faint stars turning it into a diffuse background haze. Perhaps a very large scope ( > 30-inches), coupled with very dark and steady skies an observer may be able to ferret this nebula. A sliding filter bar with both UHC and O III filters would be an invaluable tool.
THE BELOW INFORMATION WAS OBTAINED FROM THE
ADS SERVICE FOR DeNIS ON THIS PNe:
THE PN G DESIGNATION IS PN G009.8-07.5 and the IRAS DESIGNATION IS 18333-2357.
Title: The optical/infrared counterpart(s) of IRAS 18333-2357
Authors: GILLETT, F. C.; JACOBY, G. H.; JOYCE, R. R.; COHEN, J. G.;
NEUGEBAUER, G.; SOIFER, B. T.; NAKAJIMA, T.; MATTHEWS, K.
Affiliation: AC(Kitt Peak National Observatory, Tucson, AZ),
AE(Palomar Observatory, Pasadena, CA)
Journal: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 338,
March 15, 1989, p. 862-874.
Publication Date: 03/1989 Category: Astrophysics Origin: STI
NASA/STI Keywords:
BLUE STARS, GLOBULAR CLUSTERS, INFRARED SOURCES (ASTRONOMY), PLANETARY
NEBULAE, RED GIANT STARS, ABSORPTION SPECTRA, ABUNDANCE, EMISSION SPECTRA,
INFRARED ASTRONOMY SATELLITE, IONIZED GASES, STELLAR SPECTROPHOTOMETRY
Bibliographic Code: 1989ApJ...338..862G
Abstract
Observations of the potential optical counterparts of the unusual source
IRAS 18333-2357 are reported. There are three distinct optical objects
located within roughly 2 arcsec of the IR source: a red star, a very blue
star, and an extended emission line nebulosity. IRAS 18333-2357 indeed
appears to be physically associated with the Galactic globular cluster M22,
and while it probably should be considered a PN, its very small nebular
mass and extreme abundance anomalies are very unusual among known PNe.
IRAS 18333-2357 does not appear to be at an early stage of PN evolution,
but instead may be in a late stage. The lack of an associated radio or
H-alpha source is the result of abundance anomalies in the source.
It should be brought to your attention that the following page may take considerable time to load. There are a few images which are over 20KB each, and the page may take over a minute to load.
AND NOW, ONTO THE FINDER CHARTS AND IMAGES
I returned recently from a very productive ten-night stay at Cherry Springs State Park - http://www.dcnr.state.pa.us/stateparks/findapark/cherrysprings/index.htm - in north central Pennsylvania. My friend Tony Donnangelo and I observed many celestial objects both new and old during that time but the most memorable highlight for me by far was successfully observing a certain planetary nebula.
The sky was beginning to cloud up completely early Saturday morning, June 23, so I packed up my dew-soaked gear and was ready to crawl into my sleeping bag when conditions began to improve dramatically. I walked over to Tony's 24" f/3.3 Starmaster Sky Tracker Dob as he was making an attempt at one of the classic observing challenge objects, GJJC1, the planetary nebula located within the globular cluster M22. We had never actually seen it before but with great seeing, the dark skies of Cherry Springs, a very detailed finder chart, an aperture of 24 inches, and a magnification approaching 800x, Tony, Dr. Elliott McKinley (a fellow Cherry Springs regular), and I all caught glimpses of the very elusive DSO.
The conditions were superb after midnight on Sunday morning and Tony, Elliott, and I had an even better view of GJJC1 through the 24" Starmaster. Stars were surprisingly sharp at 771x (3-6mm Tele Vue Nagler zoom set at 3mm) and the transparency was excellent. Even so, the tiny and dim planetary nebula was nothing more than a slightly fuzzy star when seen with averted vision. GJJC1 did not respond when I blinked it with a Lumicon OIII filter.
Pease 1 in M15 is a piece of cake compared to GJJC1.
Dave Mitsky
On the NNE border of the central concentration of the globular, there is a distinct wedge shaped asterism that points almost directly to the location of the PNe, which is located in the SW quadrant of the globular. In this sector, there is now an asterism that takes the shape of a baseball diamond (see photo below). Directly ENE of the baseball diamond and on the opposite side of the M22, there are 2 more stars w/ a 30" separation extending along a NE/SW axis that are of relatively equal magnitude (roughly 12th V) that served as my field markers. GJJC1 is located a third of the way between 2nd base of the diamond and the southern most star of the two addressed above.
Pinpointing the specific area at 376x and no filter, I noticed a 13th to 14th mag star in the +/- 10" general location of the Pne. I knew this star would practically butt up to the planetary. Reading the few observations that there are of ths object, I immediately understood what the task before me would entail: to successfully confirm this PNe, I had to split this small star and the PNe itself. If successful, the southern most object would be GJJC1!
I immediately switched to 501x and took out my O-III and UHC filters. The seeing, though not great, was relatively steady every few seconds. Still I could not discern that there was anything else there but a relatively faint star. Underneath a velveteen cloth, I began blinking the O-III filter. The field was rendered very dark - almost too dark for me to keep my bearings in my non-tracking instrument. Then I switched to the UHC. After quickly blinking the filter over and over for 20 seconds or so, I began to notice GJJC1 blinking like a distant beacon every time the filter passed in front of it. It is interesting to note that once observed, it was actually not that difficult to keep it w/ averted vision - even direct vision every now and again.
Then, I switched to 864x (3mm Radian) w/out a filter and though the stars were quite soft, I believe that this was the power (and higher if allowed) to really exploit this planetary. I discerned the object as not disk shaped rather, highly elongated whereas the stars were still round (well, round blobs). At times I noticed a very faint stellaring within GJJC1 which is what had to be the CS. It was not always visible but with my eye at the eyepiece constantly at 864x for over 45 min's straight, it would definitely come and go w/ the seeing conditions. The CS was much more difficult than the CS in M57 but seemingly not as difficult as the CS in Abell 39, for example.
Overall, this was a very tough observation that quite honestly took a lot out of me. The skies are still very dark with phenomenal structure in the Milky Way from horizon to horizon and the seeing is pretty darn good for the Appalachian mountains.
On June 22-23, 2001, I was at Fremont Peak, mostly to look at Mars. When I got tired of that I decided to look for GJJC 1 and Pease 1, planetary nebulae associated with M22 and M15 respectively. I seem to have been successful, and with relatively modest aperture, so I thought people might be interested in the details.
CIRCUMSTANCES OF OBSERVATIONS:
Equipment: Astro-Physics 10-inch f/14.6 Maksutov-Cassegrain, with the "small" (23 percent of diameter) central baffle, MaxBright diagonal, 8 mm Brandon and 6 mm Pentax SMC-ED orthoscopic eyepieces (464x and 618x), Orion "Ultrablock" narrow-band filter, used as described below.
Seeing: Looking at Mars made us much aware of seeing during the evening. It was episodic, with intervals a few tens of seconds to a minute long when little Martian surface detail showed, yet there were comparable intervals of much better conditions. During the latter, the diffraction pattern of a suitable star at similar elevation to Mars (and to M22 -- M15 was higher) showed the Airy disc continuously visible but mostly in motion, and the first diffraction ring continuously visible, always in motion, and mostly interrupted; that is, I could not see it as a continuous whole. I observed at 309x (12 mm Brandon) and used the brighter, closer pair of nu Sco for this test; it was well resolved, with much dark space between the two stars. Results with the planetaries were in intervals of good seeing; when seeing got bad, not only the planetaries but also many of the guide stars in the clusters, that I was using, simply disappeared. Except where explicitly stated, the notes that follow are based on moments of good seeing.
Sky conditions: Fremont Peak is not dark like the Sierra Nevada, but transparency was good, and the fog was in on the coastal plain, which much diminished local city lights. These cities have cut back their nighttime lighting considerably -- hurrah for the California power crisis! In any case, sky background brightness was not a factor in these observations, considering the magnifications used.
Aids to navigation: Some time ago, I downloaded the finder charts and images that then existed on Doug Snyder's web site, the home page of which is http://www.blackskies.org. I checked that site while preparing this posting. Doug now has lots more stuff. I have no way to prepare and append graphics to this missive, so I will describe star-hopping and so on with reference to Doug's current images.
GJJC 1:
I started with GJJC 1 because M15 hadn't cleared the tree line. Doug has
five images with increasing amounts of detail. The one with the bar 60
arc-seconds long is most useful for describing star-hopping. I found star
"FC1" easily, as the west point of a right isosceles triangle whose other
stars, about as bright as FC1, lie about 40" east and 60" northeast of FC1.
These stars were easy with direct vision.
Centered about 60" toward position angle 100 degrees from the right-angle
star of this triangle, is a star pattern I would describe as a narrow bow
tie or butterfly. It comprises a skewed rectangle, about 10" by 50", with
a star about as bright as FC1 at each corner, with the long axis running
about in position angle 030/210, with a pair of fainter stars at the center.
Star "V8" is about 100" east of the south end of the rectangle. V8 is one
of an obvious quadrilateral of stars, about 30" high and wide. The other
three stars (actually more) are a single star about 30" toward position
angle 160 from V8, a tight group
about 20" toward position angle 250 from V8, and another tight group about
30" toward position angle 225 from V8. All stars mentioned so far were
easy with direct vision at 464x with no filter, and I could tell that the
two tight groups were not single stars. The quadrilateral was very useful,
for it established both scale and orientation at the eyepiece, and GJJC 1
is less than an arc-minute away.
Look now at the "tilted" image on Doug's pages, from a 1989 issue of
_Astrophysical_Journal_. The star whose disc is cut in two at the bottom
corner of that image, is the southeast star of the quadrilateral just
mentioned. Stretching about 25" toward position angle 50 from it, and
including it, is a long, narrow kite or diamond shape of stars, whose long
axis is in position angle 050/230. GJJC 1 is about 20" north of the
northeast end of the diamond, and is the southernmost of a pair of "stars"
(actually, both have companions) that lie some 10" apart on a north-south
line. Another easily identified star in this area was about 30" toward 030
from GJJC 1; on the "tilted" image it appears as a bright star flanked by
three fainter ones 120 degrees apart. I could see it with direct vision,
and could tell it was not merely a single star.
The "cut-in-two-at-the-corner" star was easy with direct vision at 464x. The other three stars of the diamond were more difficult with direct vision, but easy with averted vision. There was no sign of GJJC 1 with direct vision, or of the star 10" north of it, but with averted vision, I occasionally saw stars at the correct positions for this pair -- sometimes one, sometimes two equally bright. The proportion of time at the eyepiece during which I could see stars at or near the position of GJJC 1 was no more than a few percent, but that proportion includes times of poor seeing; in good seeing I believe I would have seen the averted-vision stars in a much higher proportion of the time. In any case, with patience, the averted-vision observation was repeatable.
The two "stars" at or near GJJC 1's position were so hard to see that there was no hope of "blinking" the usual way, by interposing a filter between eyepiece and eye, so I took the star diagonal off the back of the telescope, attached my Orion Ultrablock to it, and put it back. Here I must give due credit to Scott Losmandy -- I use a G-11, which many consider too little mount for 40 pounds of OTA and fittings plus two 21-pound counterweights, but after all the fumbling with the filter, when I looked through the eyepiece again, the line of sight was within a few tens of arc seconds of where it had been before. Stellar images were much dimmer, but the stars of the quadrilateral were still detectable, so there was no issue of not knowing where to look.
In this configuration, during several minutes of observation, I several times saw a single star by averted vision at the position of GJJC 1 -- never two stars, always just one. The averted vision image was noticeably brighter, compared to the "blinked out" stellar images nearby, than had been the averted-vision images that I had seen without the Ultrablock in the optical path; that is, the image that I was seeing clearly had not had its brightness as much diminished by the filter as the other stars. (If it had, I probably would not have seen it at all.)
All averted-vision images appeared entirely stellar, at least in good seeing. There was no trace of anything I would call "nebulosity".
The processed image on Doug's pages, with continuum removed, shows that GJJC 1 has a small, nearly stellar component that is quite bright in OIII. I believe that is what I saw. I think this is a reasonably convincing observation of GJJC 1, though it wasn't as much fun as if I could have pointed at something and said "Wow, there it is!" Instead, I had to make lengthy observations with two different configurations of the telescope, and then think carefully about what I had seen.
CONCLUDING COMMENTS:
I mentioned what I was doing to a couple of people present, but no one was much interested in looking at the planetaries. Most of the local crew aren't as craz- er, enthusiastic, about deep-sky work as I am. Anyhow, it would be difficult to show these targets to a line of people. Each observer would have to spend much time comparing finder images to the eyepiece view, to determine where to look, and would then have to wait for good enough seeing to see the objects.
Without the excellent finder images on Doug's web site, I wouldn't have had a ghost of a chance at finding either Pease 1 or GJJC 1. Furthermore, I cannot overemphasize the importance of good seeing in finding them -- without conditions that made stellar images small enough to see the Airy disc, I am sure that the star-like core of GJJC 1 would have been smeared out and undetectable, even with averted vision, and that the brighter and broader glow of Pease 1 would have merged in with the fuzzy images of nearby stars. I am sure that a lot of credit also goes to the high quality, excellent polish, and freedom from scattering of Astro-Physics's optics -- you can't see the corrector plate on the AP-10 even when you are shining a light on it, the secondary spot just seems to hang there in space.
I hope my remarks are encouraging and helpful to others who may try to view these faint planetary nebulae. It is probably true, that if it were easy, everybody would do it. Yet just because it's not easy doesn't mean it's not possible. - JAY REYNOLDS FREEMAN.
Kent Wallace, Navaho Flats, California, 20" f/5 reflector.
... I must add that I have seen this object once. After literally eating, sleeping, and breathing PNe for about 6 months to prepare Megastar's database, I arrived at TSP ' 96 with a new 16" and a suitcase full of charts for "never before seen" PNe. One of these happened to be GJJC 1 located in M 22. Of course, I had long before seen Ps 1 in M 15, but I really got some strange looks when I threw this chart on the table amongst some fairly experienced observers. I had cross-referenced the coordinates and other data as much as possible for accuracy, and my position was as good as one could get (or at least I thought so). I played around with the field with my 16" in "not so good" seeing the first couple of nights to no avail. Then, on a night when the seeing was truly steady, I tried again with the 16. After about an hour and a half of fumbling around inside the core of this monster globular at 427x, I came to the realization that I needed more aperture in order to better resolve the inner most stars where the nebula lies. Onto the scene steps a good friend of mine, David Tosteson--aka-"Minnesota Dave" and his 25" f/ 5 Dob. He and I quickly had the cluster's core at 661x, and the core stars separated completely and fit my chart wonderfully. Since I already knew that the PN's emission characteristics were very odd to say the least, we sampled a number of filters, but most had too narrow of a bandpass for this power and added too much contrast for the field stars. When the field was blinked, however, with a Lumicon UHC filter, a faint non-stellar (well, of course EVERYTHING is non-stellar at this point) object popped into view at the exact position of my charting. The object was just advertedly visible without the filter, but definitely reacted to the UHC. I would assume it would react likewise to the Orion Ultrablock, which has a similar bandpass. And, hey, all of this was being done while everyone else was screaming across the field about how good some "planet"looked through their giant scope!
More power seemed useless on this particular night with the 25", and much less power was definitely useless in the observation. I've tried repeating the observation a couple of times with various scopes (including a buddy's awesome 36" f/ 5) to no avail. I've actually become quite good at acquiring the field of the PN, since the object resides just inside the NE corner of a small (27" high by 23" wide) inverted pentagon composed of 5 mag 13.0-13.6 stars. I call the structure the "house" when describing the area to others when at the scope. Ironically, the very next day at TSP, I had the entire field etched into my memory as I went digging for high-resolution pictures of M 22, and guess what I found??? On page 195 of John Vicker's Northern CCD Atlas Vol. 1, there's a rather serious image of the innermost 3.6' by 4.35' of the core of M 22. With a good magnifier, our tricky little PN is plainly visible!!! You ought to check it out.
On my PN web site, I have a series of finder charts, information, and one
positive observation report (Jay McNeil's) on this PN. I had not previously
even attempted this one, as not having a telescope with enough aperture kept
me away from anything this challenging (But now with the 20", I'll try
anything!). A challenge it is, and does make the list on Jim Shield's site.
Since M22 would not transit until around 4 AM, I decided to follow its
journey up, and dig into the necessary star fields as it approached its
highest point of 34.7 degrees above the southern horizon here in Palominas,
Arizona (latitude of 31 degrees). Using the finder chart printed out from
my web page and Jay's notes, I soon found myself (well, within half an hour!)
in the region of where the PN resides (the PN is about 8" in size and about
mag 15). Over the next hour, I went from 149X to 605X using various eyepieces
and filters (both O-III and UHC). I was also trying out two different
Barlows, one a 2X from a well known popular telescope maker, and a 2.5X
Televue. With the same eyepiece (10.5mm), I found the Televue to deliver
a considerably sharper image in spite of the higher magnification. At about
2:40 AM, I got my first confirmation of the PN with the O-III after
suspecting it initially without a filter, and that was difficult enough,
having to use averted vision in both cases. I also blinked with the UHC,
and maybe saw a slightly better response than with the O-III, but its hard
to say. Taking a break from the eyepiece, while still maintaining night
vision, I returned to go over the entire sequence again about 40 minutes
later when M22 had reached an altitude of about 34 degrees, about a half
hour before transiting. Like Jay says in his report, the field stars and
their positions seem to get etched into your memory, and it did not take
nearly as long to zero in on the coordinates of the PN. I don't know if
it was because of the higher position in the sky of M22 or the sky
conditions had improved more, or a combination, but at 605X, I was able
to directly view the PN for about 50% of the time as a very faint (almost)
stellar object. This time I blinked first with the UHC and then with the
O-III. I definitely could see a more positive response with the UHC, but
still could confirm the PN with the O-III. Everything else in the field
either became unobservable or a dark gray smudge. The fun part of this
at 605X was doing the blinking, moving the scope (not motorized), and
making sure the focus was continually precise. I'd like to see positive
or negative reports on this PN with scopes in the 13" to 18" range - I
think its doable under the right sky conditions, and from mid latitude
locations, but of course the more southerly one is, the better the chances.
It'll be a pleasure for me to be able to put in my own observing report
of GJJC1 next to Jay's, and move on to the next PN challenge - in my
case, I'll wait for Pease 1 in M15. For those really wanting the ultimate
PN challenge (besides GJJC1), there is JaFu1, confirmed to be a outlying
member of Pal 6 in Ophiuchus. So there is a challenge within a challenge!
Information and charts on both JaFu1 and JaFu2 (in NGC 6441) can be found
on my site at http://www.blackskies.org/JaFu_challenge.htm .
What a night of observing Larry Mitchell and I had last Saturday Night at
the Columbus Observing Site west of Houston. The seeing allowed powers of
up to 950x and the transparency was excellent in the hours up to 1:00 am.
That the night was going to be exceptional was apparent from nightfall,
with Mars steady as a rock. Larry immediately went to M22 in Sagittarius,
to attempt PK 009-07.1 (IRAS 18333-2357) in M22, a "holy grail" of deep
sky observers.
At 808X in Larry's 36" driven Obsession using charts he obtained from Brent Archinal, and special charts Larry made over the past several weeks, (using a edit version of MegaStar to add appropriate stars to the M22 charts using a Real Sky Overlay), Larry spent much time carefully starhopping across the cluster, then saw the planetary. But it would not "blink" with the O3 filter.
My turn, using his wider field chart, then the IRAS zoomed in chart, it
took me about 15 minutes, to rectify the starfield with the wide, then
the zoom chart, even with Larry's careful guidance.
I noticed that the nearest star to the planetary would harden, as Brian
would call a "stellaring" but the planetary never did. It remained
nebulous. Wow. I mentioned this to Larry, then he went back up the ladder,
and also noticed the same phenomena. Again the stars would harden, but
the planetary never did, and Larry noted that he might have seen a disk.
I then with the starfield memorized, went to my 20" using a 6 mm Radian eyepiece and a 2.8 Klee barlow, effective power of 950x with tracking platform working perfectly, also observed the planetary, with Larry confirming the observation.
My congratulations to my friend, and observing buddy, Larry Mitchell for
the observation of this "ultimate challenge"!! And I can confirm it is
visible in a 20" using "obnoxious powers". The sub arc second seeing was
what I believe made the real difference. I made a drawing at the eyepiece
of the starfield at 950X with the planetary. The nearest star to the
planetary is very similar in magnitude to the planetary itself.
--
Barbara Wilson
Author: Doug Snyder
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