|
Designations:
|
NGC 663 (Caldwell C10)
|
||
|
Object Type:
|
Open Star Cluster
|
||
|
Constellation:
|
Cassiopeia
|
||
|
01 hr 46.3 min
|
+61° 13 min
|
||
|
6.7
|
Size:
|
15 arcminutes
| |
|
Distance:
|
7,200 light years
|
||
|
Discoverer:
|
William Herschel, 1787
|
||
|
Designations:
|
NGC 659
|
||
|
Object Type:
|
Open Star Cluster
|
||
|
Constellation:
|
Cassiopeia
|
||
|
01 hr 44.5 min
|
+60° 40 min
|
||
|
7.9
|
Size:
|
||
|
Distance:
|
6,300 light years
|
||
|
Discoverer:
|
unknown
|
||
|
In the image above, NGC 663 is in the upper left corner and NGC 659 is in the lower right. The description below was written by Steven James O'Mera (see full credit below). To THE TELESCOPIC TRAVELER, the open clusters that adorn the Cassiopeia Milky Way are like pale wildflowers along a country road. Anyone with modest equipment can find some five dozens of them planted in the constellation's 598 square degrees of sky. Most congregate around that busy highway of stars, the galactic equator. One particularly rich section lies only 2-½ ° east-northeast of 3rd-magnitude Delta Cassiopeiae in the constellation's famous M (or W) asterism. Here you will find five dramatically different examples of these loosely packed stellar agglomerations. They are, in order of equinox 2000.0 right ascension: M103, Trumpler 1, NGC 654, NGC 659, and NGC 663. When seen through binoculars or a rich-field telescope, these clusters form an incomplete 2°-wide circle around a diamond of roughly 7th-magnitude stars. Glimmering at 7th magnitude, NGC 663 (Caldwell 10) is brighter, but not more famous, than MI03, itself a Christmas-tree-shaped cluster glistening with stellar ornaments about 1½° to the west-southwest. Messier objects have a powerful hold on observers. Like magnets, they immediately attract our gaze, pulling it away from nearby objects that might be equally interesting. So unless an observer feels adventurous, he or she will probably not seek out NGC 663 in lieu of M103 without reason (like this suggestion that you do so). I've been guilty of this oversight myself. NGC 663, as it turns out, is a wonderful object, being at least 0.3 magnitude (32 percent) brighter, 1,000 light-years closer, and 2 1/2 times larger than MI03. The cluster's 108 measured members (roughly 8th magnitude and fainter) fill an area of sky measuring ¼°, or 31 light-years, across. By comparison, MI03 packs some 172 suns in an area of sky only 6' across, which, at its distance of 8,100 light-years, is equal to 14 light-years of space. (This high concentration of stars in such a small area of sky is, of course, why MI03 packs such a visual punch.) From a dark sky NGC 663 can be seen with the naked eye, but you have to take the time to resolve it from the two roughly 6.5-magnitude stars about 1'20 west and south-southwest of it. While comparing the apparent brightnesses of these three objects, I realized that NGC 663's listed magnitude (7.1) is too faint. Using 7x35 binoculars, I estimated the cluster's apparent visual magnitude to be 6.7. Barbara Wilson independently deduced a value of 6.5. So NGC 663 is arguably at least half a magnitude brighter than commonly believed. (Wilson also wonders why William Herschel's description in his original Philosophical Transactions catalog differs from that in the General Catalogue, since John Herschel did not observe the cluster and William did so only once.) Viewed with the 4-inch at 23x the nearly 3° field centered on NGC 663 comes alive with clusters, double stars, patches of Milky Way, and streams of dark nebulosity. NGC 663 itself is immediately very well resolved. In fact, several of its brightest (8th-magnitude) members can be glimpsed in 7x35 binoculars. My visual impression with the 4-inch is one of an elliptical orb with snaking chains of 8th- and 9th-magnitude stars, all of which are projected against a lens-shaped backdrop of fainter suns. Similarly, Jere Kahanpaa (Jyvaskyla, Finland) used a 6- inch refractor at 52x to see a "beautiful cluster" with its major axis oriented east -west, In the Genesis at 23x the star chains radiating from the cluster's core seem to gravitate to the south; one especially long arm ends in a bright pair of stars that all but pinches NGC 659 1'20 to the southwest. At 72x the cluster's core is fragmentary, being composed of three stellar groupings shaped somewhat like a horseshoe. The horseshoe asterism is the result of a prominent north-south-trending dark lane that rips through the heart of the cluster, dividing it into two V-shaped stellar cities before tapering off into a triangular island of stars. Looking through a 20-inch f/4 reflector at 72x, Wilson notes that the horseshoe's dark lane is "very dark and devoid of stars, making the cluster appear [weakly] concentrated." Lining this dark lane like poorly shielded streetlights are several bright double stars. Christian Luginbuhl and Brian Skiff note that many of these doubles are faintly colored. Two distinct pairs punctuate the ends of the horseshoe asterism. Higher power in the 4-inch also brings out an attractive concentration of stars just south of the eastern pair; the scene looks like a sparkling mist trapped in a circlet of suns. And the eastern member of each wide pair is a telescopic double star with a separation just under 10". Within 15' of NGC 663's fractured core are 24 irregular variable stars of spectral class Be. These special stars display bright hydrogen emission lines superimposed on the normal absorption spectrum of a hot, B-type star. Be stars are believed to rotate so rapidly that they shed mass, forming an expanding shell and a disk around each star's equator. One of NGC 663's Be stars is already known as an X-ray source and may be associated with a neutron star, the result of a supernova explosion. Future X-ray observations may enable astronomers to detect other compact objects in the system. Stepping beyond the corridors of reality, one can imagine that the great rift tearing through the cluster's core was the result of an extraordinary supernova explosion, one whose supersonic winds pushed through the crust of stars lining the rift like some violent volcanic event. Finally, observers looking for a challenge might try spotting NGC 654 and NGC 659 in 7x35 binoculars. I did this with difficulty. NGC 654 is the most difficult, for it is but a breath of haze slightly offset from a yellowish 7th - magnitude star. NGC 659 is also difficult and is distinguishable from the background Milky Way only with averted vision. Telescopically, 7.9- magnitude NGC 659 is a small pack of stars - a C -shaped asterism -within a 5'-wide glow of partially resolved suns. NGC 654, on the other hand, is outstanding. The magnitude-6.5 cluster is tapered, and starlight drips off its tip like water off a needle. It's such an unusual gathering of irregularly bright suns that it stands out in the 4-inch. |
|
Telescope:
|
|
|
Focal Length:
|
900 mm (1201 * .75 Astro-Physics reducer/flattener)
|
|
Mount:
|
|
|
Camera
|
|
|
Guider:
|
|
|
Exposures:
|
10 5-minute exposures for each color (Red, Green and Blue)
|
|
Location:
|
Cicero, IN
|
|
Software:
|
CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
|
