Small Wonders: Aquila a Monthly Sky Guide for the Beginning to Intermediate Amateur Astronomer Tom Trusock 23-Aug-2006

Small Wonders: Aquila A monthly sky guide for the beginning to intermediate amateur astronomer Tom Trusock 23-Aug-2006

Figure 1. W idefield map 2/11 Small Wonders: Aquila

Target List Object Type Size Mag RA DEC B142-3 Dark Nebula 80.0'x50.0' 19h 41m 02.0s +10° 57' 58" NGC 6709 Open Cluster 15.0' 6.7 18h 51m 49.8s +10° 21' 30" NGC 6738 Open Cluster 15.0' 8.3 19h 01m 43.7s +11° 36' 36" NGC 6751 Planetary Nebula 26" 11.9 19h 06m 17.9s Þ05° 58' 55" NGC 6755 Open Cluster 15.0' 7.5 19h 08m 09.9s +04° 16' 37" NGC 6756 Open Cluster 4.0' 10.6 19h 09m 03.3s +04° 43' 00" NGC 6760 Globular Cluster 9.6' 9 19h 11m 33.5s +01° 02' 31" NGC 6781 Planetary Nebula 1.9' 11.4 19h 18m 48.9s +06° 33' 10" NGC 6804 Planetary Nebula 1.1' 12 19h 31m 55.6s +09° 14' 25" NGC 6814 Galaxy 3.0'x2.8' 11.3 19h 43m 03.7s Þ10° 18' 33"

Challenge Objects Object Type Size Mag RA DEC Palomar 11 Globular Cluster 3.2‘ 11.9 19h 45m 40.8s Þ08° 01' 03"

Aquila quila œ the stellar eagle and pet of Zeus, is probably one of the more interesting constella- tions that Messier and his contemporaries overlooked. Yes, that‘s right, there are no Mess- A ier objects in Aquila, but that doesn‘t mean there aren‘t any interesting targets œ quite the opposite! Aquila offers something for nearly everyone, and as a large scope owner and lover of planetary nebulae, it‘s one of my favorite constellations.

Figure 2: Aquila - Region 1 Tom Trusock 23-Aug-2006 Small Wonders: Aquila 3/11 Crossen (in Binocular Astronomy) tells us that Aquila is one of the many constellations that the Greeks received from earlier civilizations in Mesopotamia. He states that the Sumerian Eagle con- sisted only of the Alpha, Beta, Gamma trio, and notes that the Bedouin called this asterism Al- Nasr al-Tair, —the Flying Eagle“, and writes that the ancient Greek version of the Eagle was flying perpendicular to the way it is today. Aquila occupies some prime summer real estate. Lying astride the Milky Way and bordered Scu- tum and Sagitta it‘s a fantastic area to pull through with a rich field scope or pair of binoculars. It‘s home to a number of significant and interesting stars œ Altair, the bright Cepheid Eta, the long period variable R Aquilae, the —local“ red dwarf Van Biesbroeck‘s Star and V603 Aquilae which, in 1918, was one of most brilliant novae recorded in the last 300 years. E. E. Barnard and a young 17 year old Leslie Peltier were the co-discovers. Burnham‘s indicates that at discovery it was al- ready brighter than Altair, and soon outshone nearly every star in the sky reaching a peak bril- liance of magnitude Þ1.4 Blue tinted Altair (Alpha) forms one corner of the summer triangle (Vega, Deneb and Altair) and is the 11th brightest star in the night sky. It has a distance of around 16 light years and an apparent magnitude of 0.77. It also has an optical companion of around 10th magnitude. If you happen to gaze at Altair with a small scope or set of binoculars, take a minute to check out the color contrast with red /orange Gamma just two degrees to the northwest. But it‘s not the stars that are the primary attraction in Aquila œ it‘s the deep sky objects. Although it sits nearly neatly the summer milky way, it‘s surprisingly deficient in open clusters (only 17 cataloged) and diffuse nebulae (only 1). On the other hand, there are 112 planetary nebulae, 133 dark nebulae, 3762 galaxies, 4 quasars and even three globulars. Although Messier didn‘t find anything to include in his catalog, rest assured there‘s plenty here.

Barnard 142 & 143, NGC 6803 & 6804 Let‘s start with a couple of wide field or binocular ob- jects; the dark nebulae Barnard 142 and 143. Begin by looking just over a degree northwest from magnitude 2.72 Gamma Aql (Tarazed) for a couple of strangely shaped dark blotches. Known as the —Fish on the Platter Nebula“ these two are not difficult to spot even through small binoculars when sky conditions are good. Next drop about 3 degrees south west to pick up the planetary nebula NGC 6804. Sometimes called the —Snowball Nebula“ this should be visible in scopes as small as six inches. In a medium sized telescope, this is an impressive planetary and should yield it‘s magnitude 13 central star to most observers. One of the things that stood out for me in my 12.1“ was the chain of 3-4 stars Figure 3: B142-3 visible right across the face. Look closely for mottling and changes in brightness in the outer shell. Carl Burton contributed the wonderful NGC 6804 image of figure 4. He took this with a C14 oper- ating at f12.4 mounted on an AP 1200 and an ST-8XE/AO-7 combo. While we‘re in the area, you might take some time to scan about a degree north for NGC 6803. You'll need a good set of finder charts though, as NGC 6803 is a good contrast to NGC 6804. Al- though it‘s located nearby, the two couldn‘t be more dissimilar. NGC 6803 is a difficult catch on the best of nights, appearing stellar at all but very high magnifications. To nab NGC 6803, you might try the time honored technique of —blinking“ using an OIII filter and flipping it in and out of the optical chain. Planetaries respond so well to this type of filter because it has the effect of im- proving the contrast between the planetary and the rest of the field. Look for a —star“ that doesn‘t dim when the OIII filter is in your field of vision.

23-Aug-2006 Tom Trusock 4/11 Small Wonders: Aquila

Figure 4: NGC 6804 image courtesy Carl Burton

NGC 6871

Since we‘re hunting planetaries, keep that OIII filter ready and head another 4 deg south west of NGC 6804 to find NGC 6781. In a medium sized telescope I found this planetary to be quite bright and very im- pressive. A chain of similar magnitude stars leads right into this planetary, giving it the illusion of being a lake at the bottom of some stellar waterfall. The planetary itself is a near perfect spatial bubble and in larger scopes, I find it reminds me somewhat of M57 in Lyra. This is my favorite planetary nebula in Aquila.

Figure 5: NGC 6871

NGC 6738 & 6709 Now let‘s check out a couple of open clusters; NGC 6738 and 6709. Although classified as an open cluster in the NGC catalog, a new study by Boeche, Barbon, Henden, Munari and Agnolin has shown NGC 6738 to be an apparent concentration of a few bright stars and not a real cluster at all. Visually, it‘s a poorly concentrated grouping of stars of multiple magnitudes. There is a chain of stars running roughly north south through the proposed center of the —cluster“, and my mind connects these with another short chain running perpendicular and terminating on the N-S chain. In a 12“ scope, the —cluster“ looks a bit like an intersection with the brighter stars defining the roads. This object should be visible to moderate sized binoculars on a decent night.

Tom Trusock 23-Aug-2006 Small Wonders: Aquila 5/11

Figure 6: NGC 6738 Figure 7: NGC 6709 By nearly any measure, I find NGC 6709 2.75 deg south west to be a —prettier“ open cluster. Visi- ble to the slightest optical aid, an 80mm resolves a significant number of stars, while larger scopes simply improve on the view. Carol Lakomiak provides us with this excellent sketch made through her 8“ SCT.

Figure 8: Sketch of NGC 6709 courtesy Carol Lakomiak

23-Aug-2006 Tom Trusock 6/11 Small Wonders: Aquila

Figure 9: Aquila - Region 2

NGC 6755 & 6756 Where you‘re finished here, head down to NGC 6756 and 6755. Located near each other, these clusters can be seen in the same field of view if your 6 inch (or larger) tele- scope will give you a ² deg (or better) field of view. In a small scope, these two clusters provide a nice contrast to one another, while the view thorough large telescopes begins to remind me of the Double Cluster. In any case NGC 6755 is clearly the larger and brighter. When studying NGC 6755, take care to look for a lane bisecting the cluster roughly North to South, and look for strings of stars radiat- ing out from the center. Figure 10: NGC 6755 & 6756

Tom Trusock 23-Aug-2006 Small Wonders: Aquila 7/11

NGC 6960

Dropping down to NGC 6760, this globular is a bright target and should be a fairly —easy“ catch even in small telescopes. A 12“ scope at high power just begins to hint at resolution of the globular, so don‘t expect M13 type experience. Still, this is a nice catch. Keep this image in mind when you look for the challenge object this eve- ning œ it‘s an excellent illustration on how differ- ent globulars can appear.

Figure 11: NGC 6960

Figure 12: Aquila - Region 3

23-Aug-2006 Tom Trusock 8/11 Small Wonders: Aquila

NGC 6751 Just off the tip of the Eagle, we find our last planetary for the night œ NGC 6751. This small but bright planetary can be detected in smaller scopes, but I find I prefer moderate aperture as it provides more detail. In my 12“, I found the magnitude 13.5 central star easy, and counted sev- eral stars along the outer edge of the planetary. In a large scope, look for mottling on the south- ern side of the nebula. Rodger Raubach writes: Started at lambda Aquilae, and used a TMB Para- gon 40 to move due South. 1 1/2 fields of view. I then switched to a higher magnification to make the planetary stand out from the stars. It took 142x in a Pentax 10 XW to accomplish this. Even at 142x, this is an awfully small object. I increased to 203x (Pentax 7 XW), which made the planetary look like a slightly oval disk with fuzzy edges. Since it was still fairly bright (only by planetary standards), I stuck in the UWAN 4 for 355x. There was too much haze in the at- mosphere, attenuating the image brightness enough to make a sighting of the central star impossible. This is a tiny object, and is easily

mistaken for a star at any magnification <100x. I would suggest using an O-III filter to ”blink‘ Figure 13: NGC 6751 this one.

NGC 6814 On to our only galaxy this evening; NGC 6814. This is a beautiful little face on galaxy, that can be spotted in a 4-6 in scope, looks great in a 10 or 12“ telescope, and (like many targets) just keeps getting better the larger the more aperture you throw at it. In my 12.1" scope I found definite mottling and hints of the spiral arms. The core is brighter than the arms, and there is a definite hint of a stellar nucleus. NGC 6814 must be a very bright galaxy to show so well through the intervening gas and dust in our own Milky Way. Adam Block has an excellent image of this galaxy on the NOAO site at: http://www.noao.edu/outreach/aop/observers/n6814.html He also notes that interestingly enough, the nuclear region Figure 14: NGC 6814 changes brightness on the order of weeks and months.

Tom Trusock 23-Aug-2006 Small Wonders: Aquila 9/11

Challenge Object Finally, we come to our challenge object œ Palomar 11.

Figure 15: Palomar 11 There are 15 Palomar Globulars discovered while viewing the DSS plates created at the Mt. Palo- mar observatory. Such a small number makes for a very tempting list œ albeit something of an extreme one. ID Other ID Constellation RA DEC Mag Palomar 1 Cep 03h33m21.0s +79°34'54" 13.6 Palomar 2 Aur 04h46m06.0s +31°22'54" 13 Palomar 3 Sex 10h05m31.0s +00°04'18" 13.9 Palomar 4 UMa 11h29m16.0s +28°58'24" 14.2 Palomar 5 Ser 15h16m05.0s Þ00°06'42" 11.8 Palomar 6 Oph 17h43m42.0s Þ26°13'24" 11.6 Palomar 7 IC 1276 Ser 18h10m45.0s Þ07°12'48" 10.3 Palomar 8 Sgr 18h41m30.0s Þ19°49'36" 10.9 Palomar 9 NGC 6717 Sgr 18h55m06.0s Þ22°42'06" 8.4 Palomar 10 Sge 19h18m02.0s +18°34'18" 13.2 Palomar 11 Aql 19h45m14.0s Þ08°00'24" 9.8 Palomar 12 Cap 21h46m39.0s Þ21°15'06" 11.7 Palomar 13 Peg 23h06m44.0s +12°46'18" 13.8 Palomar 14 Her 16h10m59.0s +14°57'48" 14.7 Palomar 15 Oph 16h59m51.0s Þ00°32'30" 14.2 I‘ve seen Pal 11 both in my 12.1“ and my 18“. In the 12.1“ it was a very loose concentration of stars, appearing more like a dense open cluster with a haze of unresolved stars. The 18“ obviously showed more, but I still had a similar impression. I found lower powers provided the best view (~75x or so). Rodger Raubach writes: I did another slew from a known star, using my setting circles to move to the correct posi- tion, and this was my fourth try for Pal 11. While scanning slowly, I noticed a very dim haze in just about the right spot; I scanned past this hazy spot, and then returned going the other direction. Same spot again. I stopped and did a —tube tap“, and the hazy patch wiggled nicely. I pulled a coat over my head and tried to get even better dark adapted while taking some deep breaths, keeping my eyes closed at the same time. After a bit the patch became more distinct, and I could see some very faint and tiny field stars across the face by using averted vision. Checking a chart showed that I was in the right place, so I claim an observation of Pal 11 with a 6.9" APO refractor. The sight was definitely —under-

23-Aug-2006 Tom Trusock 10/11 Small Wonders: Aquila whelming“, but I was pretty pleased with my self for finding my 4th Palomar globular using the TMB 175. And well pleased he should be.

Figure 16: Position of Palomar 11 in our galaxy Figure 16 from —Where is M13?“ shows our relationship to Pal 11. The circled dot is the globular, while the one embedded in the arm of the milky way, is œ well, you and I. Bill Tschumy‘s program also tells us that Pal 11 shines with the luminosity of 18,375 suns, is 126 light years in diameter and lies 43,358 light years from where you sit reading this.

Figure 17: Palomar 11 (DSS negative) As with any difficult target, you‘ll need to prepare; particularly if your scope is on the smaller (IE normal) side. I‘d suggest making use of the Mast DSS to print out images, taking them into a photo editing program and making negatives. You can also take the time to orient the photo so it will match the view through the eyepiece. The image shown above was generated in Sky Map Pro using Real Sky, then edited in a photo editor.

Tom Trusock 23-Aug-2006 Small Wonders: Aquila 11/11 Till next time -

Tom T.

Additional Links o NGC 6738: Not a real open cluster: http://arxiv.org/abs/astro-ph/0306093 o Best of APO: NGC 6814: http://www.noao.edu/outreach/aop/observers/n6814.html o Observing Handbook and Catalogue of Deep-Sky Objects (Christen B. Luginbuhl and Brian A. Skiff): http://www.amazon.com/gp/product/0521625564/ref=nosim/002-2026076- 3463249?n=283155

If you liked this article, you may want to check out the rest of the series. I‘d love to hear of your experiences under the night sky – please feel free to e-mail me or send any observing reports to: [email protected] Please indicate if I can cite your observations in future columns. Photographic Images Courtesy DSS (except where noted): copyright notice http://archive.stsci.edu/dss/acknowledging.html Star Charts Courtesy Chris Marriott, SkyMap Pro 10 Printed with Permission http://www.skymap.com Locational Images Courtesy Bill Tschumy, W here is M13? Used with Permission http://www.thinkastronomy.com/

Special Thanks to Collin Smith for his editorial assistance, Olivier Biot for assistance with the PDF‘s and all those who take the time to read and contribute to this series.

23-Aug-2006 Tom Trusock