Object of the Week, August 3, 2014 - Seyfert's Sextet

[Howard B]

Seyfert’s Sextet
(NGC 6027 group, HCG 79, UGC 10116, VV115, VII Zw 631)

Galaxy Cluster
Serpens
RA 15h 59m 12s
DEC +20 45’ 31”

Magnitude: ~14.8 to ~16.5

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There are so many galaxy clusters in the August sky, but this is one of my favorites. One reason is that there are a couple of enjoyable observing challenges in this compact group, and another is that all the members are not actually galaxies. And a third supposed member is actually a line of sight object far in the background.

When I first started observing Seyfert’s Sextet, the first appeal was the name – named objects are usually interesting. This one was the tightest galaxy group when Carl Seyfert published his research about them in 1951. The group also has a distinctive flying wing shape that sets it off visually, with NGC’s 6027 c and e forming the wing tips.

The tidal tail, NGC 6027e, is the first observational challenge because it’s diffuse without a brighter core, and I’ve found it difficult to see unless conditions are quite good. 6027e shoots out to the upper left in my sketch (as seen through Jimi’s 48 inch) and the HST image in black and white. It’s listed as two magnitudes brighter than 6027c, the galaxy that’s aligned straight up and down in the bottom center of the images here. Oddly, I’ve found them to be more or less equally visible – if I can see one I can see both.

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The most difficult galaxy to see for me has always been 6027d, the background galaxy. I’ve seen it only once with my 28 inch, using averted vision and 700x on a great night, but it was easily and satisfyingly seen through Jimi’s 48 inch with direct vision at about half that magnification.

I didn’t think to try for the very thin dark lane is 6027a then, but that can be a challenge for another night.

Members of Seyfert's Sextet
Name Type Distance (million ly) ~ Magnitude
NGC 6027 S0 pec. ~190 +14.8
NGC 6027a Sa pec. ~190 +15.3
NGC 6027b S0 pec. ~190 +15.3
NGC 6027c SB(S)c ~190 +16.5
NGC 6027d SB(S)bc pec. ~877 (background galaxy) +16.5
NGC 6027e SB0 pec. ~190 (tidal tail) +14.4

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“GIVE IT A GO AND LET US KNOW"

[Bgman]

Hi Howard,

This one has been on "my list" this year and I finally was able to see them all during the new moon at the end of June. I was observing in south east Ohio and the SQM was 21.54 that night according to a fellow observer at the site. I was using my 25" Obsession and looking nearly straight up into unusually cool and very transparent skies for this time of year. Our altitude was only about 750 feet above sea level there. Anyway, I was exploring what the sky would allow for magnification as the seeing was quite good at the time I was observing it. I finally got 6027e to pop in for me with averted vision using an ortho at 488x.
More magnification made it worse and lower magnification just wouldn't allow 6027e to show for me. I could only hold it with averted vision, but I could hold it. I must say that I spent some time trying to see it before it became visible. I am sure my observing skills are not as good as most of you guys but I really enjoyed marking this one down as a positive viewing!

Will

[Clear Skies]

One observation logged using a 12" SCT, 8 July 2010, SQM 21.26:

Difficult, many galaxies close in a very faint group. A "patchy patch" without use of AV, using AV individual galaxies can be discerned.

179x / 27': The central galaxy (NGC6027A - Hickson 79A) and the two brightest northern galaxies (NGC6027 - Hickson 79B and NGC6027B - Hickson 79C) are visible.
Directly SE is a mag. 14 star, slightly farther to the WNW is a mag. 13.5 star.
NGC6027C - Hickson 79D, NGC6027D - Hickson 79E and NGC6027E - Hickson 79F are not visible.

254x / 19' : Using this magnification NGC6027D - Hickson 79E is visible, a small, round patch. The group remains faint and difficult.

http://www.clearskies.eu/webfiles/temp/DSF/Hickson79.jpg

[Jimi Lowrey]

This with out a doubt is my most favorite compact galaxy group. year after year I revisit it.

It is interesting that in the 1951 discovery paper that in a private communication from Dr. Baade to Dr. Seyfert that after imaging the Sextet with the 200" Hale telescope that Baade thought that two of the nebulous patches were tidal distortions. http://adsabs.harvard.edu/cgi-bin/bib_query?1951PASP...63...72S
Even then there was a question if it was a true sextet of galaxies.

To see the dust lane in A it takes a night of really good to excellent seeing from my experience and 600X to 800X. The first time I was able to catch it I did not know that it was there. I was surprised that the next day after view the dust lane I was able to confirm it on deep images of the the Sextet.

Great OOTW Howard keep after that dust lane. I am sure that one night you we catch it!

[Uwe Glahn]

Beside HCG 55 I'm with Jimi - my most favorite compact galaxy group, great OOTW Howard.

The "fight" began in my 16" times when I tried to see as much as I could. Even under very good conditions the separation was always a tough challenge. My best observation was in the High Austrian Alps, when I could catch 5 of the 6 galaxies. Like Howard wrote I missed NGC 6027D. I suspected f, the NE end but was not sure.

16", 450x, NELM 7m+
http://www.deepsky-visuell.de/Zeichnungen/HCG79_16.jpg

But the fight gave me so much fun that I fall in love with that group. My wish was to see all galaxies without any problems. No sooner said than done, I selected this group as my first light object for my 27" and I was shocked how beautiful this group looks like in big telescopes.

27", 419x, NELM 7m+
http://www.deepsky-visuell.de/Zeichnungen/HCG79_27.jpg

[akarsh]

I remember the view of this through skyraider's 25" dob at TSP 2012. His happened to be the only dob > 18" on the middle field. We were easily able to resolve all 6 members.

[Marko]

This group was observed in 21.7 sqm sky with excellent transparency and very good seeing in my StarMaster 18" f/3.7 scope.

I'll leave off prior partial observations and just discuss the July 7, 2013 observation from a north California GSSP star party. The 6027A observation gives general group look and feel and then individual members are listed.


Ser NGC 6027A MltG 15 59 11.1 +20 45 17 mag 14.8
Date: 07/07/13 Time: 12:45am Site: AdinCa
Scope: 18SmF3.7 Eyepiece: 8mmSm Power: 211.0x
NELM: 6.7 SQM: 21.72 Seeing: 4 Transparency: 5
'Hick_79_SeyfertsSextet: N is around 5:30 in the field. The L sort of shape was obvious where one side points south and one side points east from corner or B member. One of the brightest members that is just below [E] of the corner galaxy or B member. The 8mm SuperMono gave a better view than 8mmDelos. Jimi Lowery confirmed these and shared his 6mm Zeiss II eyepiece with 42deg Fov which gave maybe even a better contrast in the view and of course greater magnification. The Zeiss seemed to bring out the cores better than the 8mm SuperMono. Gotta get one of those but very hard to find.'

er NGC 6027B MltG 15 59 10.9 +20 45 45 mag 15.3
Date: 07/07/13 Time: 12:45am Site: AdinCa
Scope: 18SmF3.7 Eyepiece: 8mmSm Power: 211.0x
NELM: 6.7 SQM: 21.72 Seeing: 4 Transparency: 5
'Hick_79_SeyfertsSextet: This is the 'corner' of the 'L' and was easily spotted as a small member. '

Ser NGC 6027C MltG 15 59 11.9 +20 44 50 mag 16.5
Date: 07/07/13 Time: 12:45am Site: AdinCa
Scope: 18SmF3.7 Eyepiece: 8mmSm Power: 211.0x
NELM: 6.7 SQM: 21.72 Seeing: 4 Transparency: 5
'Hick_79_SeyfertsSextet: This is the far southern one and was the most difficult. The 8mm SuperMono gave a better view than 8mmDelos. '

Ser NGC 6027D MltG 15 59 13.0 +20 45 36 mag 16.5
Date: 07/07/13 Time: 12:45am Site: AdinCa
Scope: 18SmF3.7 Eyepiece: 8mmSm Power: 211.0x
NELM: 6.7 SQM: 21.72 Seeing: 4 Transparency: 5
'Hick_79_SeyfertsSextet: This member is very small and separating it from the A member just north takes patience to see it dims down between the two cores.'

Ser NGC 6027E MltG 15 59 14.7 +20 46 00 mag 14.4
Date: 07/07/13 Time: 12:45am Site: AdinCa
Scope: 18SmF3.7 Eyepiece: 8mmSm Power: 211.0x
NELM: 6.7 SQM: 21.72 Seeing: 4 Transparency: 5
'Hick_79_SeyfertsSextet: Second to most difficult member. Jimi says the far right [east] is actually a tidal tale where we only saw it 3-4 sec averted in better transparency. '

[Bob Douglas]

At the Golden State Star Party in Northern California this past June I looked at HCG 79 using a 28" f/3.6 Starstructure. Using a 5 Nagler (513x), A, B, & C were obvious as expected. I saw the tidal tail (F) several times. and caught a couple of glimpses of D. The spiral E was not seen. Steve Gottlieb told me that the tidal tail is actually easier to see than D. I believe it. Jimi's seeing the dust lane in A in his 48" certainly promotes aperture fever.
I note that the letter designations of the six components in Victor's image are the same as in a Hubble image I have seen. But some other sources unfortunately attach the letters differently--including the Night Sky Observers Guide and also an image from noao: http://www.noao.edu/image_gallery/html/im0407.html .

[Marko]

Too bad the NGC A-E are all jumbled up with the Hickson A-F designations but for the purposes of this post so far all those stating simply the letter are referring to the Hickson letter designations. I'm only stating this so those who read this post don't get too confused.

Howard: It might be nice if the initial post added to the mini-table the Hickson letters to help ease this for those who read in the future especially in light of what Bob has just mentioned in some references being jumbled themselves. MegaStar seems to have the Hickson F member as Hickson79B and does not even say that Ngc6027 is even a Hickson member (which it is the official B).

[Jim Chandler]

I'm curious about something. I'm traveling and don't have my Hickson book with me, but here's Hickson's labeling of 79 from his 1982 paper. I fail to see an f component. Does anyone know whether Hickson revised 79 later, or, if not, when/where the f component label was added? It's pretty clear that in 1982 Hickson considered b to be one galaxy.

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[Steve Gottlieb]

Very interesting question, Jim!

There were three primary papers by Paul Hickson and collaborators and none of these include a listing for HCG 79f.

1) Systematic properties of compact groups of galaxies (1982)
http://articles.adsabs.harvard.edu/full/1982ApJ...255..382H

2) A photometric catalog of compact groups of galaxies (1989)
http://articles.adsabs.harvard.edu/full/1989ApJS...70..687H

3) Dynamical properties of compact groups of galaxies (1992)
http://articles.adsabs.harvard.edu/full/1992ApJ...399..353H

In fact, the 2002 study (http://arxiv.org/abs/astro-ph/0201178) of HCG 79b "A Multi-band Photometric Study of Tidal Debris in A Compact Group of Galaxies: Seyfert's Sextet" does not refer to this object as HCG 79f. So, I'm guessing this designation was introduced in a later paper. Can anyone track down the source?

To confuse the issue further, in 1959 Vorontsov-Velyaminov introduced his own letter designations for VV 115 with both a capital "A" and a lower case "a"!

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[Ciel Extreme]

Paul Hickson published a book called Atlas of Compact Groups of Galaxies in 1994, which was my introduction to Hickson objects. A friend of mine had the book, which I borrowed. It had data on all 100 compact galaxy groups. Perhaps this is where 79f can be found. The book is long out of print, and a quick search shows no second hand copies for sale. Does anyone on this list have the book? Perhaps you can look up the data for Hickson 79.

[Ciel Extreme]

Just downloaded the book from the SAO/NASA Astrophysics Data System. There is no “f” listed for group 79.

[Steve Gottlieb]

I didn't know you can download the entire contents of 1994 spiral-bound book? In any case, I checked my copy of the book earlier (I bought it when it first came out) and like you found no 79f, though Hickson mentions "The diffuse extension northwest of b was thought by Seyfert to be a sixth galaxy." So, it appears Hickson didn't introduce this designation for the diffuse tail as he didn't consider it a separate object.

[Ciel Extreme]

The version available at the ADS was originally published in Astrophysics Letters and Communications, 1993, Volume 29. Someone at the StScI went to the trouble of scanning the entire 207 page paper. Those interested in downloading should note that it is a 164 meg file and takes a few minutes.