Small Wonders: Sagitta and Vulpecula 1/18 Small Wonders: Sagitta and Vulpecula A monthly sky guide for the beginning to intermediate amateur astronomer Tom Trusock 18-Sep-2006 Figure 1: W idefield map 18-Sep-2006 Tom Trusock 2/18 Small Wonders: Sagitta and Vulpecula Target List Object Type Con Size Mag RA DEC Cr 399 Open Cluster Vul 140.0‘x50.0‘ 3.6 19h 25m 42.2s +20° 11‘ 54“ IC 4997 Planetary Nebula Sge 13“ 10.5 20h 20m 28.0s +16° 45‘ 18“ M 27 Planetary Nebula Vul 6.7‘ 7.4 19h 59m 54.4s +22° 44‘ 31“ M 71 Globular Cluster Sge 7.2‘ 8.4 19h 54m 04.8s +18° 47‘ 53“ NGC 6823 Open Cluster Vul 7.0‘ 7.1 19h 43m 27.6s +23° 19‘ 04“ NGC 6885 Open Cluster Vul 20.0‘ 8.1 20h 12m 15.7s +26° 30‘ 20“ NGC 6886 Planetary Nebula Sge 10“ 11.4 20h 13m 01.5s +20° 00‘ 43“ NGC 6940 Open Cluster Vul 25.0‘ 6.3 20h 34m 44.3s +28° 17‘ 59“ Challenge Objects Object Type Con Size Mag RA DEC Palomar 10 Globular Cluster Sge 3.5‘ 13.2 19h 18m 30.4s +18° 34‘ 49“ Vulpecula and Sagitta His month we‘ve got two tiny constellations to look at: Vulpecula and Sagitta. The fox and the arrow seem to be a match made in heaven, but on investigation we find that while the T arrow has been around for thousands of years, the fox is a fairly recent creation. The constellation Vulpecula was initially known as Vulpecula et Anser, which literally means —the little fox with the goose“, and the constellation was an invention of 17th century astronomer Jo- hannes Hevelius to fill an area left blank on prior star maps. The goose must have been a short meal œ all that‘s left is Anser (Alpha Vulpecula) caught between the teeth like a leftover morsel. It‘s far too late to save this goose. So if it‘s too late to save the goose, why shoot the fox? That presumes the unknown archer is ac- tually shooting at the fox. Given the timeline, we see we have a bit of a chicken and egg problem. Obviously, since it was shot well before the fox came on the scene, the arrow can‘t be targeting Vulpecula. Who shot the arrow? And at what? Taking a look at the summer Milky Way, one celestial archer screams out œ but unless he‘s a truly horrid shot, it most likely wasn‘t Sagittarius œ he‘s facing the wrong way. Casting about the sky, we latch onto another likely suspect setting in the west œ Hercules. But if it was Hercules, whom was he shooting at? If not the fox, we‘ve got two other prime suspects, ei- ther Aquila (the eagle) or Cygnus (the swan). Both have just taken flight, undoubtedly shocked into action by the unexpected attack. Whatever the target, it looks like poor Vulpecula is going to go hungry for a while. Vulpecula and Sagitta lie on the edge of the summer Milky Way, and as such are rich in open clus- ters and planetary nebulae. Sagitta contains M71 œ a cluster with a history of identity crisis (but more on that later), while Vulpecula harbors M27 and the spectacular association Cr399 œ better known as the Coat Hanger. In addition, this area is home to a couple of cases of galactic identity crisis, several appear on the list this month. Another, not on the target list, is Merrill‘s star. This object is misclassified in most catalogs as a planetary nebula. In reality it appears to be a cool Wolf-Rayet star with an associ- ated nebula and thus it‘s a ”young‘ object. Interestingly enough, its velocity is considerable, and it‘s also thought to be a ”runaway‘ object. Tom Trusock 18-Sep-2006 Small Wonders: Sagitta and Vulpecula 3/18 Figure 2: Merrill‘s star (image courtesy Carl Burton) Carl Burton has done an excellent job of capturing it with the above image. And Bill Warden con- tributed the following. Figure 3: Merrill‘s star (image courtesy Bill W arden) This isn‘t much in the way of a visual target - at least in the average amateur telescope. But if you‘re so inclined, don‘t let that stop you. You‘ll never know what you are going to see until you look. Merrill‘s star can be found at: 19h 11m 30.9s RA, +16° 51‘ 38“ Dec. Note, the coordinates are in epoch 2000.0. As per the rest of the area, interesting targets abound. There are some 69 planetary nebulae, an amazing 2030 galaxies, 9 quasars (the brightest at magnitude 16.4), 8 diffuse nebulae, 102 dark nebulae, 21 open clusters, and two globular clusters (both of which are in this month‘s edition). In fact, some of you will probably want to take a set of binoculars and just scan the region. As per the rest: shall we get started? 18-Sep-2006 Tom Trusock 4/18 Small Wonders: Sagitta and Vulpecula Figure 4: Area map of M71 Let‘s begin with a good old fashioned Messier - M71. M71 Most likely discovered by Philippe Loys de Cheseaux in 1746, it was cataloged by Messier on the 4th of October in 1780. If you‘re reading this in September, you‘ve got a chance to observe it on the anniversary of its being added to the Messier catalog! For a long time, M71 suffered from some fundamental identity confusion. We weren‘t quite certain what it was. We had it pegged as some form of cluster, but the jury was out on it being either a dense open cluster or a loose globular. Confusion reigned as least as late as the 50‘s and 60‘s. We‘ve finally seemed to come to a general consensus (thanks to a re-examination of the HR dia- gram). M71 does, in fact, belong with the rest of the globulars in the Milky Way. It‘s probably so loose because it‘s a mere 13,000 light years away. Indeed, it‘s one of the closer globular clusters. I‘m sure it‘s relieved to know its status is no longer in doubt. Tom Trusock 18-Sep-2006 Small Wonders: Sagitta and Vulpecula 5/18 Figure 5: M71 (image courtesy John Graham) John Graham‘s photo of M71 is an excellent approximation of what I see in a large scope. I‘ve al- ways thought of this as the angelfish, can you see it, or do I have an overactive imagination? I‘ve seen M71 with scopes as small as 66mm, and various people have managed to pick out its subtle glow with binoculars. Larger scopes tend to give a more impressive view, but whatever you use, this is one pretty cluster. I‘ve found it takes an 80mm to really begin resolving stars on the outskirts. Observing with a 6“ from dark skies in California, Eric Graff has this to say: ...this object appears as a bright nebulous patch over strewn with numerous faint stars in an exceedingly rich field at 30x. To the west is a bright grouping of stars including 6th magnitude 9 Sagittae arranged in a Y-shaped pattern with the prongs pointing northward. The indistinct haze of H20 is also included in the wide field view of this globular star clus- ter. At 60x this object is seen to be elongated north-northeast to south-southwest with many stars resolved around the edges, particularly in the directions of elongation as well as across the face of the cluster. At 120x M-71 displays a bright triangular patch to stars near the center, pointing toward the south-southwest. The cluster is pretty well resolved across the entire face of the cluster, an indication of its loose structure compared with many other clusters of this type. A distinctive arc of bright stars to the northeast and a bright star on the south side of the cluster complete the scene at high power. M71 shines with the light of 6,576 suns. While you‘re in the area, take a peek ² degree south for the sparse open cluster Harvard 20. Now haul out those small scopes and binoculars, next up we‘re headed to Cr 399. 18-Sep-2006 Tom Trusock 6/18 Small Wonders: Sagitta and Vulpecula Cr 399 Figure 6: Cr 399 —The Coat Hanger“ (image courtesy Keith Geary) This photo by Keith Geary shows this famous grouping of stars. Cr 399 goes by several different names: Brocchi‘s Cluster, Al Sufi‘s Cluster and most recognizably, the Coat Hanger. Brent Archinal and Steven Hynes have an excellent section on Cr 399 in their book —Star Clus- ters“, where they note that historically we should probably refer to this as Al Sufi‘s Cluster, as the Persian astronomer discovered it in the 10th century AD. Sufi noted that it was —...a little cloud situated to the north of the two stars of the notch of Vulpecula.“ One supposed that Vulpecula was inserted by the translator as a positional reference as it wasn‘t actually a constellation for some time to come. —Star Clusters“ further notes that Brian Skiff has shown the group to be an asterism instead of a true galactic cluster. Our challenge object for the evening lies nearby so we‘ll return here at the end of the night. Can‘t see a Coat Hanger in the stars above? It can be difficult to pick out the asterism from the field stars without a size reference.