by Steve Gottlieb
HCG 5a and 5b = N190 form a double system which often appeared as an elongated glow, 40"x20", oriented N-S. With careful viewing, the system just resolved into two very small round knots, just 20" between centers. The northern component was ~20" diameter and the southern member ~15". The two knots both have faint stellar nuclei and appeared virtually tangent. A third member, HCG 5C, was occasionally visible as an extremely faint knot off the NW side.
HCG 6a is the brightest member of a faint trio in Cetus and at 225x appeared very faint, small, round, 20" diameter. The extremely faint glow of two fainter members (HCG 6B and 6C) was just detected ~50" WSW as an irregular, extremely faint elongated glow of very low surface brightness. Occasionally the components may have partially resolved (one visible or the other) as the object seemed to slightly jump around in position with averted vision.
A much easier group is HCG 7 which consists of 4 NGC galaxies. The brightest member, HCG 7a = NGC 192 appeared moderately bright, fairly small, very elongated 3:1 NNW-SSE, ~1.0'x0.3'. The center was well concentrated with a small very bright core that increased to a stellar nucleus. The second brightest was NGC 196 = HCG 7b, a moderately bright galaxy, with a fairly high surface brightness. The center was sharply concentrated with a bright, very small core surrounded by a much fainter oval halo 3:2 N-S, ~0.6'x0.4'. NGC 201 = = HCG 7c is situated 5' E of NGC 192 and is the largest in the HCG 7 quartet. At 225x it appeared faint, fairly large, round, ~1.6' diameter, low nearly even surface brigtness with only a very weak concentration. Finally, NGC 197 = HCG 7d was just a very faint, round spot of 20" diameter. This galaxy is the smallest and faintest in the HCG 7 quartet and was missed by both William and John Herschel (discovered by Albert Marth).
HCG 8 is another tough group with brightest member, HCG 8a appearing very faint, small, round, ~25" diameter with a low surface brightness. At 225x the appearance was irregular and confused with the immediate vicinity "clumpy" as occasionally several extremely faint nearby members of HCG 8 popped into view for moments. At the position of HCG 8b and 8c I found an extremely faint knot, ~10" diameter that was occasionally visible just 50" NNE of brighter HCG 8a. I may have only viewed only one of these tiny galaxies, though it's possibly both occasionally popped into view at different moments.
In 1957 an Armenian astronomer R. Shakhbazian reported the discovery of an amazingly compact group of 17 stellar red objects with individual magnitudes of 17-19 crammed into 50" x 100" of sky. Although this cluster was initially assumed to be a distant halo globular cluster, when recessional velocities were obtained 16 years later in 1973 by Halton Arp and others, they were surprised to find a very large redshift (z = .12) for all members corresponding to a distance of roughly 1.7 billion light years! Subsequent surveys for additional compact groups of compact galaxies by Shakhbazian and others netted 377 groups meeting the following criteria -
As a collection the Shakhbazians share similarities with the Hickson list, but are typically denser and roughly three times as distant. In fact, the notorious Hickson 50 (the toughest Hickson group) is also Shakhbazian 5! Some members of the Shkh catalogue are clearly the cores of larger groups including Abell clusters. Unfortunately, due to their distance and magnitude range, relatively few Shakhbazians are visually accessible to an 18-inch scope unlike the more user-friendly Hicksons and only five have revealed multiple members in my scope - Shkh 16, 30 = HCG 97, 166, 202 and 317. From Lake Sonoma on Wednesday night I tracked down the final cluster in this list, but if anyone is inspired to take on this challenge, I've also included my descriptions of Shkh 166 which is part of Abell Galaxy Cluster 2247.
In Cetus is a 6' chain of five galaxies forming Shkh 317 (position 2hr 10.7m +08 35). At the southwest end of the chain is Shkh 317-7 = PGC 08317. This small galaxy is probably the brightest in the group and appeared as a faint, 15" knot just 2' NNE of a mag 11.5 star. The double system Shkh 317-4 = PGC 08330 and 317-3 = PGC 08329 was immediately noticed 2.8' NE as a faint smudge. With careful viewing, two knots were resolved and both appeared very faint, very small, round and barely resolved (just 38" between centers), although 317-3 was slightly brighter. Often this close pair merged into a single image or only one member was visible at a time. Continuing to the NE I ran into a mag 12 star and just 40" SE of this star was Shkh 317-1 = PGC 8340. Although the star was not bright, it detracted from viewing the dim galaxy which appeared as a tiny 10" knot, roughly mag 15.5. Finally 2' SSE of the mag 12 star and 1.3' south of Shkh 317-1 was the final member viewed, Shkh 317-2 = PGC 96667, another tiny knot. This collection is not much at the eyepiece but a great challenge to catch dim photons that have been traveling this way for some 650 million years.
I've observed the Shakhbazian chain Shkh 166 in Ursa Minor twice from the Sierra Buttes and identified five members strung out in a similar 6.7' chain oriented SW to NE! Starting at the southwest end is Shkh 166-2 = PGC 59122, an extremely faint, round knot of 15"-20" diameter, located 1.5' NW of a mag 12 star. Next up is Shkh 166-3 = PGC 59179, located 2' NE, which appears slightly brighter than its neighbor. Continuing towards the NE, another compact member, Shkh 166-4 = PGC 2785443 is just a 10"-15" knot about 40" SW of a 13th magnitude star. Next up is perhaps the brightest member of the chain, Shkh 166-1 = PGC 59174. It's situated less than 1' following a mag 13 star and at the midpoint with Shkh 166-4 1.5' WSW and Shkh 166-7 just 1.4' NE. No real details were visible, just a faint, round spot of ~20" diameter with very weak concentration. Finally the last and furthest NE in the chain is Shkh 166-7 = PGC 59157. This one appeared extremely faint, very small, and required averted vision for a comfortably view. In moments of steady seeing the galaxy was clearly elongated 2:1 ~N-S with dimensions ~20"x10". Notes on some of the other groups I've observed can be found by searching the TAC observing archives on "Shakhbazian".
Posted on tac-sac Nov 27, 2005 17:21:16 PT
Converted by report.pm 1.2 Mar 16, 2006 20:35:13 PT