Object of the Week Apr 1, 2012 - Hickson 55 aka VV 172 - "Mr Galaxy-Chain" itself

[Uwe Glahn]

UGC 6514 (= PGC 35572-35576, Hickson 55, Arp 329, VV 172)
R.A. 11 32 07; DEC +70 48 56
Mag (NED): 15,2
Size: 1'

UGC 6514a = PGC 35573 = HCG 55c; Mag (bmag LEDA) 17,0; distance: 0,67 Gyr
UGC 6514b = PGC 35572 = HCG 55b; Mag (bmag LEDA) 16,4; distance: 0,68 Gyr
UGC 6514c = PGC 35575 = HCG 55a; Mag (bmag LEDA) 15,9; distance: 0,70 Gyr
UGC 6514d = PGC 35574 = HCG 55d; Mag (bmag LEDA) 17,1; distance: 0,70 Gyr
UGC 6514e = PGC 35576 = HCG 55e; Mag (bmag LEDA) 17,4; distance: 1,52 Gyr

1959 started the history of UGC 6514 - the Russian astronomer Vorontsov-Veljaminov found the object on the POSS plates and cataloged the group as VV 172. On year later Burbidge focused his interest to the group – the term "galaxy chain" was born. In later years the tension raises again, because the redshift measurements showed, that the faintest group member PGC 35576 has a discordant redshift. Later papers discussed the discordant member but the current knowledge believes that PGC 35576 physical belongs not to the group. Later the group became member of some more famous catalogs like Hickson (55) and Arp (329).

What can be seen?
With 16" the chain is visible as a 1' N-S elongated streak of light 25' NW of the fine edge-on NGC 3735. When seeing is good HCG 55a and HCG 55b glimpsed out as stellar peaks.
With 20"-24" the streak curved like an "S", components HCG a-d could be seen easily as stellar spots within the chain. Component e is still hard to resolve.
Bigger aperture shows the Hickson as a concatenation of five galaxies.

HCG55_5.jpg
POSS II blue plate

HCG55_27.jpg
sketch with my 27" at 586x (home with inverted version)

"GIVE IT A GO AND LET US KNOW"

GOOD LUCK AND GREAT VIEWING!

[Marko]

In NELM 6.9 skies of GSSP 2009 with SQM at 21.65 and seeing 5/5, transparency 5/5 my report is dismal in my 18" at 338x (5mm TakLE, no paracorr for my best 'less glass' view)

Reported as a line with at most seeing 3 cores but never all 3 at the same time and the cores only coming and going (averted of course). A second observation in lesser but still very good skies was even worse.

[reiner]

My observation with 22" is very similar to Mark's:

Starting from NGC 3735, the chain is quite obvious with indirect vision, though difficult to split into single galaxies. After
extended observation three, sometimes four knots could be separated with averted vision, but could not be held steadily.

Very difficult to nail down which is which galaxy, this group is considerably more difficult than Hickson 56.

[Steve Gottlieb]

My 17.5" observation from 16 years back is also similar to Mark's...

At 220x HCG 55 appears as a very faint, elongated string SSW-NNE about 1' in length with an irregular appearance. At 280x, a couple of individual components (A and either B or C) are sometimes resolved with the more obvious "knot" at the north end of the string (55A) appearing barely nonstellar.


As expected, the chain was not difficult to fully resolve at 700x in Jimi's 48" a couple of years back...

55A: Moderately bright, slightly elongated, small, ~15"x12". This galaxy is the brightest of in the 1.1' chain and bracketed by 55E 12" N and 55C 19" S.

55B: Southernmost member in the chain and second brightest. Easily visible as a fairly faint, very small knot, ~10" diameter.

55C: 4th of five in terms of visibility; very faint and small, with a low surface brightness halo that faded out into the background. Squeezed between 55A 19" N and 55B 15" S.

55D: Northernmost galaxy in the chain; faint, very small, round, ~8" diameter. In terms of visibility, I placed this member as 3rd of 5.

55E: Smallest and faintest (B = 17.4) member with a discordant redshift (over twice the redshift of the other 4 members); extremely faint and small, round, ~4" diameter. Sandwiched between 55D just 9" NNW and 55A 12" SSW!

[FaintFuzzies]

My observation was also like Mark's and Steve's. Picked up a "string" about 90" long but with only 3 components. The middle was a little fainter than the other two.

This was with my 22". I didn't observe it with my 30" yet.

[Marko]

A pattern is emerging in many of the threads here on DSF. Allow me to speculate:
Perhaps a 48" scope in deep Texas dark skies offers a better view than a 20" range dob.
Again, this is just a theory but several observations on DSF 'seem' to support that theory ... ;-)
(Thanks for the perspective SteveG)

[FaintFuzzies]

Marko,
Funny that you say that - this object is on my list for my next observing run with the 48" in two weeks.

[FaithJ]

I observed it with Larry Mitchell's 36" at TSP 2006, and here is the (rather rudimentary) sketch I made, with some (even more rudimentary) notes:

"These were faint but obvious. The galaxies showed up as an uneven chain of 5 tiny nuclei surrounded by a faint halo."


hickson55.jpg

[Uwe Glahn]

Thanks Marko, Reiner, Steve, Alvin and Faith. Very interesting observations without an discordant member like HCG55e I wonder how bis or better small is the minimum aperture to detect HCG55 as a faint streak - perhaps 12" under perfect skies?

[Steve Gottlieb]

A pattern is emerging in many of the threads here on DSF. Allow me to speculate:
Perhaps a 48" scope in deep Texas dark skies offers a better view than a 20" range dob.
Again, this is just a theory but several observations on DSF 'seem' to support that theory ... ;-)
(Thanks for the perspective SteveG)

You learn fast, (not so) young grasshopper

[RolandosCY]

Hi there,
a group of observers has observed Hickson 55 earlier this evening from the mountain site of the Cyprus Astronomical Society at Amiantos (alt approximately 4,500ft) with excellent transparency. The group was "easily" seen through a 16" Meade Lightbridge with direct vision, though I was not (yet) told how many of the individual galaxies were resolved. The galaxy string was described as "fascinating". It's kind of funny, I asked them to observe it since due to night shifts I was unable to get there myself. Hopefully I'll observe it later this week...

[FaintFuzzies]

Here is my latest observation with Jimi's 48" reflector under NELM 7.0 skies at 488x.

All five galaxies were well resolved in a curvy line aligned N-S.

The middle galaxy, component A, is the brightest of the bunch. It is the largest of the bunch and bright with a brighter core.

The southern most galaxy, component B, is the second brightest, appears as a small bright glow with a much brighter core.

The northern most member, component D, is third brightest and is a bit more compact than the two brighter ones. Much brighter center.

The second one down from the north, component E, end is fairly faint with a brighter core. It is also the smallest of the bunch.

The last one, component C, 2nd from the south, is pretty faint glow with a slightly brighter core.

[RolandosCY]

I did try for "The Worm" (as I like to call Hickson 55) with my 18" last Saturday night from my favorite dark sky site at Xyliatos, Cyprus. Unfortunately, although the transparency was good, the seeing was extremely unstable (one of the worst I have ever experienced). I did easily detect their soft glow, but the unsteady atmosphere transformed them into any imaginable longish shape, and at no time was I able to distinguish the various components. As a friend put it, it resembled a longish view of Stephan's Quintet via an 8"! Thankfully, their position is such that I should get a few more chances for them!

[RolandosCY]

Well, this little is "worm" is becoming an obsession for my 18" Obsession! I tried it again last Sunday evening, from a rather dark site near the village of Agglisides at Larnaca, Cyprus. Transparency was excellent, I could easily see ω Cen and M13 naked eye, but the seeing was rather unsteady (likely due to temps in the high 90s during the afternoon). I did not have any trouble locating the correct field, but seeing H55 itself was quite another story. Although the site was dark, it does not compare to our mountain sites, and apparently the "worm" needs steady and very dark skies. I finally saw a tiny bit of a trace of rather longish light that I could hold steady for about 30% of the time with averted vision at 297x obtained with a 7mm Nagler. The seeing could not support any greater magnification. I covered myself with a black blanket and things did improve a bit - I could now hold the tiny smudge about 75% of the time with averted vision and even glimpsed it momentarily with direct vision. I could only make out a tiny longish shape which seemed to be unsteady in its brightness profile, but could not detect any steady brightenings (which would be individual components). What I could detect was its direction which was a bit offset from the north-south line, pointing a bit east, towards a bright star with a nearby fainter companion.

I did produce a sketch, and after scanning it I did confirm with a DSS image that indeed the orientation of the tiny smudge was correct so I was really seeing the H55. During my previous attempt from darker skies the terrible seeing would not allow me to detect any shape or detail, to the extend that I was not 100% sure I was really seeing this object, so I did not sketch it. Keep in mind that I have managed to reproduce quite well its faintness on my sketch, it might be hard to spot!
HK55a1.jpg

[Faintandfuzzy]

Anyone know of any HST images of VV172? I'm curious as to how it would compare to old photos or my eyepiece view.