Willow Springs Ayers site 10/21/06

by Steve Gottlieb

In the early part of the evening I easily resolved a few test doubles down to 0.8" separation, Comet Swan and Neptune/Triton in Bill Cone's scope. But by 8:30 I switched gears, pulled out my MegaStar charts and spent the rest of the evening (quitting around 4:15) observing galaxy clusters and groups. Mark and I worked on a number of these clusters at the same time in our 18-inch scopes, confirming sightings and chasing down the fainter members. Here's a breakdown of the main targets:

HCG 16: One of the better Hickson groups was discovered by William Herschel in November of 1785 with his 18.5-inch f/13 (20-foot focal length) speculum reflector. The group consists of four galaxies (N833/835/838/839) with similar magnitudes in a 6' crooked chain. A more distant member, N838, lies 17' SE. Two low surface brightness edge-ons, IC 210 and MCG -02-06-035, are less than 30' N.

HCG 90: This Hickson group would likely be better known if located further north, but it's well worth a visit down to -32° dec in Pisces Austrinus. The group was a bit too far south to be picked up by William Herschel but his son, John, visited the group several times during his stay at the Cape of Good Hope beginning in 1834. NGC 7173, 7174 and 7176 are crammed into a mere 1.5' of sky with N7174 and 7176 consisting of an interacting elliptical and disturbed spiral. NGC 7172, a spiral with a difficult dust lane, lies 6' N of the trio. An 8-inch scope will show the group though the double system may appear merged.

Abell Galaxy Cluster 14: This faint cluster is located one degree south-southeast of NGC 45, a low surface brightness Magellanic-type system. Although the integrated magnitude of NGC 45 is 10.6V, it's spread out over a large area and a nearby 7th magnitude star (and superimposed 10th mag star) makes it a challenging galaxy. The cluster itself has no NGC or IC members but with some effort I could tease out 15th magnitude ESO 473-2, 473-4, 473-5 and 473-6 at 325x.

Abell Galaxy Cluster 71 and 77: NGC 181, 183 and 184 are a trio of galaxies discovered by Edouard Stephen (of Stephen's Quintet fame) with the 31.5-inch Foucalt silvered glass reflector at Marseilles Observatory. The brightest member, NGC 183, is easy to locate just 12' north of 4.4-magnitude Epsilon (30) Andromedae with NGC 181 and 184 nearby to the south (3' and 4'). The other members (including MCG +5-2-31 and UGC 400) are more difficult at roughly mag 15.5B. I also picked up UGC 428 less than half a degree east, but this galaxy is a member of Abell Galaxy Cluster 77.

Abell Galaxy Cluster 539: Orion is an unusual location for an Abell Galaxy Cluster, but just two degrees west of 1.6-magnitude Bellatrix lies the rich cluster AGC 539. The centerpiece of the cluster is the galaxy chain UGC 3274 (of the four components, two were resolved) and within my 280x field (14 arcminutes), 7 additional members were tracked down. The identifications of this nest of galaxies are a mess in various catalogues but NED identifies these galaxies as CGCG 421-015, -016, -017, MCG +01-14-014, MCG +01-14-019, 2MASX J05164149 +0629376 and 2MASX J05164699+0629536. All of these appeared as dim, tiny knots (15" diameter) just 15-16th magnitude.

NGC 7184 Group: NGC 7184 is a photogenic spiral in Aquarius (see http://www.noao.edu/outreach/aop/observers/n7184.html) and brightest in a small group of galaxies. In my 18-inch, I logged it as "bright, large, elongated 4:1 WSW-ENE, 4.5'x1.1'. The halo extends to a mag 11.5 star at the tip of the ENE arm. The core is fairly sharply concentrated, round, ~20" in diameter with a stellar nucleus. The extensions have a grainy appearance. Two wide pairs of mag 12 stars (~1' separation) lie 2' W and 7' NW." To the north is a trio of fainter NGC galaxies making a quartet; 7180, 7184 and 7185. About 5' N of NGC 7185 was an extremely difficult galaxy, 2MASX J22022039-2027096, that was only momentarily visible at 280x.

NGC 7385 Group: This field of 7 NGC galaxies was first seen by William Herschel, although he only picked up the two brightest members - NGC 7385 and 7386. NGC 7386 is a cD type galaxy, a supermassive elliptical typically found in the core of galaxy clusters and formed through cannibilizing nearby cluster members. I logged it as "moderately bright and large, elongated 4:3 SW-NE. Contains a bright, 25" core and a much fainter halo. A mag 10.8 star hugs the NW side, 1' from the center. Appears slightly larger and brighter than NGC 7386, located 6' to the north." John Herschel revisited the field a couple of times but ony logged these two galaxies again. The fainter cluster members were discovered using William Parsons' (Third Earl of Rosse) 72-inch speculum reflector at Birr Castle in Ireland. Although the cluster was examined a number of times, the identity of NGC 7384 is in doubt and may refer to PGC 69819 or else a faint field star that was mistakenly thought to be nebulous. PGC 69819 is by far the faintest member and I only noted it as "extremely faint and small, round, 10" diameter, requires averted to glimpse".

NGC 3 Group: This field includes several of the last entries in the NGC (7834, 7835, 7837, 7838, 7840) but spills over to the start of the NGC with 3 and 4. This entire cluster of faint galaxies was found by Albert Marth on November 29, 1864 observing from Malta with a 48-inch fork-mounted equatorial reflector. Even with this impressive scope, Marth described all the members as "extremely faint" except for NGC 3 which was described as "faint, very small, round, almost stellar". In my 18-inch I recorded NGC 3 as "faint, very small, elongated 3:2 WNW-ESE, 0.4'x0.25', very small slightly brighter core, faint stellar nucleus with direct vision. A mag 11.5 star lies 1' SW." The group includes some nasty challenges including a very tight pair, NGC 7837/7838, that are separated by only 0.6' between their centers and 16th-magnitude NGC 7840 and NGC 4.

NGC 1016 Group: Marth and Stephan both contributed to the discovery of the NGC 1016 cluster, located 1.7 degrees southwest of 3.5- magnitude Gamma Ceti (excellent 2" double star BTW). I logged NGC 1016 as "moderately bright, fairly large, round. A bright 30" core increases to the center. Surrounding the core is a fairly large, low surface brightness halo, roughly 2' in diameter. This is the dominant galaxy in the cluster. A parallelogram of four mag 14 stars is just south." The group also includes NGC 993, 1004, 1007, 1008, 1009, 1019, 1020 and 1021. Most of these faint galaxies were not difficult in my 18-inch with the exception of NGC 1007 and 2MASX J02364057+0208445.

NGC 2290 Group: The last group I took a look at was a curving chain of 5 NGC galaxies in Gemini - NGC 2288, 2289, 2290, 2291 and 2291 - located just 35' southwest of 3.6-magnitude Theta Geminorum. At the south end of the chain is a spiral galaxy, NGC 2290 (another William Herschel discovery), that appeared "fairly faint, fairly small, slightly elongated SW to NE, 40"x30", increases to a very small bright core." The northeast end is marked by NGC 2294 (a William Parsons discovery), a fairly faint galaxy appearing "small, elongated 2:1 ~N-S, 0.6'x0.3', very weak concentration. A 40" pair of mag 10.5-11.5 stars lies 2' SE."

By this point, I had taken notes on 75 galaxies and had run out of steam, so crawled into my sleeping bag, photon-satiated from the views of many distant clusters.
Steve