Object of the Week, October 31, 2021 – A galaxy cluster next to M30

[Steve Gottlieb]

Name: ACO S963 (Abell-Corwin-Olewin)
R.A.: 21h 39m 56s Dec: -22°28'
Size: ~22', Distance: ~450 million l.y.

ACO S963 is little-known galaxy cluster at a similar distance as the much richer Hercules Galaxy Cluster (AGC 2151). What makes it of special interest is its location -- just 45' north of M30!

ACO S963 contains a couple of dozen galaxies centered around the cD galaxy NGC 7103, and also includes NGC 7104, IC 1393 and IC 5122. Most of the additional members have 2MASS designations with high LEDA numbers. A redshift survey in 1993 (http://articles.adsabs.harvard.edu/pdf/1993A%26AS..100...33G) by Garilli+ listed redshifts for 8 members and a labeled finder chart, but otherwise this cluster has not been studied.

The 2 NGC and 2 IC members were either discovered with the 26" Clark refractor at the Leander McCormick Observatory in Virginia or the 20" Clark refractor at the Chamberlin Observatory in Denver. Using a MegaStar finder chart, I logged a total of 10 members in my 18" (labeled on the DSS2 image below with my notes below at 225x and 286x).


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1) ESO 531-013
21 39 26.1 -22 26 01
Size 0.9'x0.6'; PA = 159°
Extremely faint, round, ~18" diameter. Required averted vision.

2) IC 5122
21 39 45.9 -22 24 23
V = 15.4; Size 0.8'x0.4'; Surf Br = 14.0; PA = 55°
Very faint and small, round, 12" diameter. Collinear with a mag 14 star 2' ENE and a mag 13.3 star 5’ ENE.

3) LEDA 93990
21 39 48.5 -22 35 04
Size 0.6'x0.4'
Extremely faint, round, 12" diameter. Nearly on a line with a mag 14.4 star 3’ NNW and a mag 15.5 star 5' NNW.

4) NGC 7103
21 39 51.4 -22 28 26
V = 13.8; Size 1.4'x1.2'
Brightest of 10 galaxies in ACO S963. At 225x appeared moderately faint, irregularly round, 40"x35", weak concentration with no core or zones. A mag 13.7 star lies 2' ENE.

5) LEDA 134285
21 39 52.3 -22 45 36; Cap
Size 0.6'x0.4'; PA = 95°
Extremely faint, round, 12" diameter. Situated 40" S of a mag 14 star.

6) LEDA 197842
21 39 55.9 -22 38 53
Size 0.4'x0.3'; PA = 120°
Threshold object, extremely small, round, 6" diameter. Located 2.7' N of MCG -04-51-007.

7) MCG -04-51-007
21 39 59.2 -22 41 32
Size 0.65'x0.60’
Very faint, round, 18" diameter. On a line with two mag 15.2 and 14.6 stars just 0.8' SW and 1.4' SW.

8) NGC 7104
21 40 03.2 -22 25 29
V = 14.2; Size 0.8'x0.7'; Surf Br = 13.7; PA = 51°
Faint, irregularly round, 25"x20", very weak even concentration.

9) IC 1393
21 40 14.2 -22 24 40
V = 14.6; Size 0.7'x0.5'; Surf Br = 13.5; PA = 172°
Very faint, elongated 3:2 N-S, 24"x16", very weak concentration. A mag 13 star is 2' NW and a mag 10 star 3' SE.

10) LEDA 93995
21 40 39.2 -22 29 21
Size 0.7'x0.6'
Very faint, round, 20" diameter. A mag 14.5 star lies 0.8' N.

So next time you're appreciating the beauty of M30, just slide your scope 45' north and see how many members you can identify.

Give it a go, and let us know!

[lamperti]

Saw NGC 7103 back in 2000 with an 18" at 256x: "Just about caught it with direct vision. Too low declination to see any other members." At the time. it was almost directly south, but only at a declination of only 22 degrees above the horizon.
Time for another look-see with a slightly larger telescope.

[Steve Gottlieb]

My observations, by the way, were made in the Sierras at an elevation 7100 ft and a latitude close to +40°.

The cluster (declination -22.5°) was close to the meridian at the time, so the altitude for me was ~ 27° above the horizon.

[Howard B]

My only view of this cluster was in 2003 with my 20-inch from Steens Mountain:

"To my surprise, I was able to see all seven galaxies in this group (as shown in the Astronomical League's Observing Galaxy Clusters book) but I suspect the faintest, IC 5124 is mislabeled as being magnitude 17.7 - it's much too easy to see! I'll check it out... But for now, I'm cautious about declaring it to be the faintest object I've ever seen. 359x to 500x."

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The eyepiece sketch also mentions that one of galaxies I observed wasn't visible until I removed the Paracorr, which happens sometimes with the faintest objects. Also, the galaxies I saw aren't all the same as in Steve's notes and the photo he included, but it is the same cluster!

[lamperti]

Took another look at this cluster from a different site than in 2000. Transparency was not that great (SQM 20.5) but I was able to see 3 members, including IC-1393, this time around.