Object of the Week March 17, 2013 - The MKW 3 Compact Septet

MKW 3, WBL 360, CGCG Septet

Virgo

RA
11 49 39
DEC
-03 31 42

Size: 6'
Mag: each 15-16B

Type: Compact Group

Any fan of compact groups is familiar with Stephan's Quintet (HCG 92), Seyfert's Sextet (HCG 79) and Copeland's Septet (HCG 57). But MKW 3, another excellent septet challenge, seems to have flown below amateur radar! Just like the more famous Copeland's Septet, this compact septet is squeezed into a mere 6' of sky and even the magnitude range is similar (MKW 3 is a bit fainter). Furthermore, 4 of the members are arranged equally spaced in a neat 3' chain!

Attachment 502

So why has MKW 3 escaped notice? The other groups were discovered visually and contain NGC numbers. Furthermore, Paul Hickson included them in his famous catalogue of compact groups. But MKW 3 was discovered on the POSS and contains only CGCG, MCG and PGC designations. The labeled image above gives all the CGCG designations. As far as catching my attention...

In 1974 W.W. Morgan, Susan Kayser and Richard White carried out a search of 73 northern POSS plates looking for potential giant cD galaxies lurking in poor clusters, where they are not generally found. Their paper titled "cD galaxies in poor clusters" was published in the Astrophysical Journal, Vol. 199, p. 545 - 548 and included 12 northern candidates (MKW 1-12) as well as 4 supplementary groups. Their search continued and a second paper ("cD galaxies in poor clusters. II") by Albert, White, and Morgan was published in 1977, resulting in AWM 1-7. In March 2011, I highlighted AWM 1 in a Sky & Tel "Going Deep" article.

As far as MKW 3, the entire septet fits nicely in a 11' field using my 24-inch at 375x (6mm Delos) and requires just enough work to be a little challenging to capture all 7 members. CGCG 12-95 is the brightest member and appeared fairly faint, elongated 3:2 WNW-ESE, 25"x16", brighter core. Visually, the faintest couple of galaxies seem a bit below the usual CGCG limit (15.7pg), with CGCG 12-97, a thin edge-on at the south end of the group, the most challenging.

I'm surprised Hickson didn't include this group in his catalogue, though perhaps it didn't quite meet the isolation criteria. What the smallest aperture that can capture the entire septet? (Image below from the MKW paper)

Attachment 503

“GIVE IT A GO AND LET US KNOW”
GOOD LUCK AND GREAT VIEWING!

This is a great group Steve. I too have wondered why it is not in the Hickson catalog.

Its been a few years since I last viewed this group. Larry Mitchell had MKW 3 on his Texas Star Party Advanced Observing list in 2009. I remember much discussion about this fairly bright group at that time.

All you galaxy group fans should give this one a go, I am sure you will like it.

I'm down for this one next time. From the megastar magnitudes it seems doable in my 18" with small mag 15.3 as the dimest two. The elongated CGCG 12-97 could be beyond my reach but what the heck, 'give it a go' I will.

In any case it is a good one Steve, Thanks!
Marko

Looks like an interesting one.

Just added it to my April list for (hopefully) a return to Pettigrew or Cherry Springs.

I agree with Marko, the 7 brightest all seem to be well within reach of Ursa. Plus will definitely be trying for some of the other, fainter galaxies in the area.

Thanks, Steve...

Looking forward to hearing your results, Marko and Lou. The members of MKW 3 are only 18" to 25" in diameter, so it really helps to pump up the magnification. I'd suggest at least 270x in your 18-inch scopes.

Also, like a number of groups MKW 3 has a higher redshift member -- CGCG 12-91, which may be in the background of the remaining sextet, which have nearly identical redshifts.

I had to dig this out!

This had been on my list since it had been posted here, but I never made it to observe it (I had made wrong finder charts for it :-( ). Two day ago, I finally made it.

This is a very interesting group with three brighter members, which are DV objects with my 22". The others are more difficult and it took some patience to pin them down, using 275x. Finally, I was able to see 7 galaxies, the three easy ones (1, 3 and CGCG 012-091), two more difficult ones (5 and 4), and two very difficult ones (2 and the one in the middle between 2, 4, and 5).