Zeroing in on cassiopeia: many fascinating but rarely visited treasures lurk among this constellation's dazzling star clusters.
We'll start at the beginning of the zero-hour zone near Beta ([beta]) Cassiopeiae, also known as Caph. Just 26' south-southeast you'll find a skinny little triangle of 8th- and 9th-magnitude stars enshrined in the reflection nebula van den Bergh 1. Most reflection nebulae are quite faint in a small telescope, but vdB 1 is relatively bright through my 105-mm (4.1-inch) refractor. I prefer a magnification that places dazzling Caph out of the field of view while keeping vdB 1 near the center. The nebula covers about 3' and is most intense near the embedded stars, which are the source of its illumination.
Star-gilded vdB 1 is the first entry in a catalog of 158 reflection nebulae compiled in 1966 by the Dutch-born Canadian astronomer Sidney van den Bergh.
Deep images of vdB 1 expose two small reflection nebulae northeast. The larger one has an unusual, oval-loop shape. The star couched in its northwestern end is the primary source of illumination, but the nebula itself was probably sculpted by outflow from another nearby star. A fainter ring, offset southeast, may indicate a previous outflow episode. The illuminating star is designated LkHa 198 (a Lick Observatory hydrogen-alpha emission star), and its nebula shares the name. I don't know of any visual observations of this nebula, but it might be possible for observers pushing the envelope with some of today's impressively large amateur telescopes.
Now we'll turn to the Local Group galaxy IC 10, located 1.4[degrees] east of Caph. My 105-mm refractor shows a very faint star at the western end of a little patch of fuzz about 1' across. It grows twice as large with averted vision. My 10-inch reflector reveals that this is merely the brightest, southeastern region of the galaxy. At low power, IC 10 is an easily visible, uneven glow at the northern end of a 12'-long chain of 7th- to 12th-magnitude field stars. At 188x the galaxy is 3 1/2' long and leans northwest. Two faint stars are superposed on the northern reaches of the galaxy, one on each flank. Little spots that look non-stellar lie southeast of the eastern flank star and east of the star in the bright region. Images unmask them as foreground stars juxtaposed with star-forming regions in the galaxy.
IC 10 is approximately 2.6 million light-years distant and belongs to the small group of galaxies dominated by the Milky Way and the Andromeda Galaxy. It's a dwarf irregular galaxy and is heavily obscured because we see it through the dusty plane of our galaxy.
Sweeping 1.6[degrees] northwest of Caph takes us to the semiregular variable star WZ Cassiopeiae. The star is thought to have superposed periods of variability. The two main cycles, roughly one year and a half year, are due to radial pulsations of the star. WZ Cas is a deeply red-orange carbon star, which makes estimates of its magnitude so challenging that some observers call it the Red Beast. Most of the time the star ranges between visual magnitude 7 and 8 1/2.
As a welcome bonus, WZ Cas is a double star with a blue-white, 8.3-magnitude companion a spacious 58" east of the ruddy primary. The designation of the pair is O [SIGMA] [SIGMA] 254, the Greek letters signifying its place in Otto Struve's Supplement to the Pulkovo catalog. Although only a chance alignment of unrelated stars, it's a lovely duo when viewed through a telescope.
The nicely contrasting colors of O [SIGMA] [SIGMA] 254 show well through my little refractor at 28x. When observing the pair through my 10-inch scope at 44x, I also noticed the nearly equal double Stein 1248 about 7.6' northwest. The 10th-magnitude primary appears yellow, and its companion 12" northeast shines with a yellow-orange hue.
Residing 1[degrees] east of WZ Cas, the open cluster Berkeley 1 is a little sprinkling of extremely faint stars through my 105-mm refractor at 127x. Two brighter stars, 11th magnitude, lie in the group's western side. Through my 10-inch reflector at 115x, this pair is part of a U of stars that dominates the cluster's eastern side and opens northward. The U overlays a 4' mist glittering with faint sparks of light. A bowl-shaped group of stars, 10th to 12th magnitude, is balanced atop the cluster.
Berkeley 1 is the first object in a catalog published in 1960 by Arthur Setteducati and Harold Weaver, astronomers at the University of California, Berkeley. Of the 104 objects on the list, 85 were original discoveries.
Climbing 42' north brings us to the open cluster King 13. My little refractor at 127x displays a 5' foggy patch holding several faint to extremely faint stars. The fog is enshrined in a parallelogram formed by a row of three stars that clips its southwestern edge and a parallel line of two stars on the opposite side, all 10th or 11th magnitude.
Since we've visited the first of the van den Bergh nebulae and the first of the Berkeley clusters, let's rocket 3.5[degrees] north-northeast to King 1. In my 105-mm scope at 76x, this open cluster is a very faint, slightly mottled haze 5 1/2' across. A 10th-magnitude star guards the northeastern edge, and another is nestled in the opposite side. When viewed at 122x, the latter is revealed as a double star (Stein 40) with a 12th-magnitude companion 13" south east of its primary. At least a half dozen pinprick stars are entangled in the haze.
King 1 is delicately pretty through my 10-inch scope at 115x. Many minute flecks are irregularly scattered over 7 1/2' of sky. At 187x I count 45 stars, 13th-magnitude and fainter. King 1 and King 13 were discovered by Ivan R. King on sky survey plates taken with the 16-inch Metcalf and 24-inch Bruce refractors at Harvard College Observatory. King enjoyed looking at the plates and began to notice uncataloged clusters. In 1949 he published a list of 21 clusters either found by him or marked on the plates by previous workers. Two subsequent papers added six more clusters to the roster. Of the 27 King clusters, 22 were original discoveries.
Our final target is the little emission nebula Sharpless 2-175, which rests 40' east-northeast of King 1. It's framed by an 8th-magnitude golden star 14' west-southwest and a 7th- and 8th-magnitude pair 20' east-northeast. With my 105-mm scope at 47x, I see a small nimbus of light haloing an 11thmagnitude star. Sh 2-175 is also noticeable when I use a narrowband nebula filter, but the star is dim and the nebula little improved. Boosting the power to 76x, I estimate the nebula's size as 1 1/2'. Seen through my 10-inch scope at 187x, this subtle glow is slightly elongated northwest-southeast and brighter on its northeastern side.
The second Sharpless (Sh 2) catalog was published in 1959 by Stewart Sharpless of the U.S. Naval Observatory Flagstaff Station. It listed 313 objects thought to be H II regions (clouds of ionized hydrogen). If seemingly detached portions of nebulosity were thought to be ionized by the same stars, they were deemed to be a single H II region.
Sue French welcomes your comments at email@example.com.
Lesser-Known Treasures of Cassiopeia Object Type Mag. Size/Sep. RA vdB 1 Reflection nebula -- 5' 0h 10.7m IC 10 Local Group galaxy 10.4 6.3' x 5.1' 0h 20.3m WZ Cas Carbon/Dbl. star 6.9-8.5, 8.3 58" 0h 01.3m Stein 1248 Double star 10.4, 10.8 12" 0h 00.4m Berkeley 1 Open cluster -- 5' 0h 09.7m King 13 Open cluster -- 5' 0h 10.2m King 1 Open cluster -- 9' 0h 21.9m Sh 2-175 Emission nebula -- 2' 0h 27.3m Object Dec. vdB 1 +58[degrees] 46' IC 10 +59[degrees] 18' WZ Cas +60[degrees] 21' Stein 1248 +60[degrees] 26' Berkeley 1 +60[degrees] 29' King 13 +61[degrees] 11' King 1 +64[degrees] 23' Sh 2-175 +64[degrees] 42' Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than the cataloged value and varies according to the aperture and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0.
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|Title Annotation:||Deep-Sky Wonders|
|Publication:||Sky & Telescope|
|Date:||Dec 1, 2009|
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