Object of the Week, November 1, 2015 - Stephan's Quintet, HCG 92, Arp 319

[Howard B]

Who was Stephan and why is a compact galaxy group named after him?

Édouard Jean-Marie Stephan (1837-1923) was Director of the Marseilles Observatory and was working on measuring the exact positions of as many deep sky objects as he could to use them as a fixed background reference system in order to determine the proper motions of stars within our Milky Way galaxy.

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In the process Stephan discovered 139 deep sky objects using the world’s first large silver-on-glass mirror (made by Leon Foucault) that was the heart of the 78.7cm (31 inch) Marseilles telescope shown below. In many respects, this is the first modern reflecting telescope.

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Stephan came across his quintet of galaxies on September 23, 1876 – the first compact galaxy group ever discovered - but at the time he saw only four of the five as he didn’t resolve the close pair of NGC 7318A and B, perhaps due to the light pollution from nearby Marseilles.

Even though he went on to discover several more compact galaxy groups, only this first one is named after him.

We now know that four of the five galaxies are physically interacting with each other, and a quick look at the NOAO photo below will show you which one isn’t – the light blue galaxy NGC 7320 is in the foreground and is a random alignment only 40 million light years away. The yellow-ish interacting galaxies of Stephan’s Quintet are all around 290 million years away and illustrate red shift at a glance.

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The galaxies range from 13.1 to 14.3. Physically associated with the main group but 17 arc seconds to the east is small NGC 7320C at magnitude 16.7.

The main five galaxies of the quintet all have NGC numbers and each one might be detected in an 8 inch scope under ideally dark and steady skies, and their combined glow would likely be visible with a 6 inch under the same conditions. With a 16 inch or larger scope you can use high powers to separate the individual galaxies for a view much like that shown in my sketch. My sketch was made with my 28 inch scope under dark but not great skies (21.47 Sky Quality Meter reading) using 408x. It’s similar to views I’ve had with my old 20 inch under better conditions.

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I could see the main five galaxies quite well but it took averted vision to see NGC 7320C at the far left of the sketch. Under truly dark skies it can pop out, but it’s quite faint and most observer's shouldn't expect to see it in anything smaller than a 16 inch.

Conveniently, Stephan’s Quintet is easy to find because it’s so close to the magnitude 9.4 galaxy NGC 7331 in northern Pegasus. Find 7331, move your scope less than a degree to the southwest, and you’re there.

GIVE IT A GO AND LET US KNOW!

[RolandosCY]

Hi Howard, great OOTW and a perrenial favorite. And yes, it IS readily visible in my 6" achromatic refractor under my SQM 21.0 backyard skies. The problem is that the Quintet at 128X appears as a tiny blur of an undefined shape (and of course no resolution to individual galaxies). In one occasion I did try 240X (Tak LE 7.5mm and 2X barlows) but the seeing did not support the magnification so I have to give it another go. At the same time, SQ is high on my list of targets to check with my 5" achro as well.

[wvreeven]

Hi Howard and Rolandos,

I, too, have spotted this galaxy group with my 6" several years ago. I didn't write down any notes of the observation though but I do remember it was in the south of France and probably in 1994 or 1995. I regularly observe the group with my 20" and one of my notes says that I observed NGC 7320C as well.


Clear skies!

[Howard B]

Hi wvreeven - so were you close to Marseilles when you saw Stephan's Quintet with your 6 inch? That would be poetic!

[wvreeven]

Howard, actually I was in Puimichel, which is about 115 km from Marseille, so yes I was close! That makes the observation even more special :)


Clear skies, Wouter

[Jimi Lowrey]

Nice OOTW and great read Howard.

I have had on my list for awhile to try for the high redshift quasar near the center of NGC 7319.

Link to paper http://arxiv.org/abs/astro-ph/0409215

With a Z of 2.114 its way out there! It will be fun to try for this unusual object with its unusual alignment.

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[Uwe Glahn]

Nice OOTW Howard and important reminder that this telescope was a real quantum leap in the telescope development. I think it was Foucault who calls Lord Rosse Leviathan "a joke" against his modern glass/silver spaceship.

Here is my quick and dirty translation of my HCG 92 observations:

4", 88x, NELM 6m5+
from 44x visible as a faint glow 30'SW of NGC 7331; from 63x separation visible; best power 88x; two clearly separated plobs visible; a shows as a laminar glow; 1,5'NW another glow from the both not separated b and d


8", 160x, Seeing III, NELM 6m5+
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not separated glow visible even in the searching eyepiece; best view with 160x; a visible as a 1:2 SE-NW elongated glow with concentration to its middle, can hold it with averted vision, SE of the center faint star; b+d direct vision and easy to separate, no elongation; c a little bit more difficult than a but visible with averted vision, round, concentrated; e very difficult, direct neighbor of a NW 13mag star, together visible as a "double star"; NGC 7320C not visible


16", 257x, NELM 7m0+
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Under perfect alpine skies remarkable even in the searching eyepiece; with high magnification all five members are visible; a as faint, 3:2 SE-NW glow without brighter center; near SE of the center faint star; b+d brightest members; b as 2:1 NW-SE elongated; d 2:1 N-S elongated; halos of both touching each other; c bright center with NW-SE elongation, faint glow SE following; e as bright, small and round glow SE of a star; NGC 7320c visible as very faint glow somewhat deposed of the group


27", 419x, NELM 7m0+
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Impressive with big aperture and very good transparency; all galaxies direct vision objects even in the searching eyepiece (113x); with higher magnification some galaxies with details and first glimpse of the tidal tails; a 1:2 elongated with brighter center and surface faint halo, NW part of the halo seems to be brighter and shows a beginning of a spiral arm, E of the center faint and stellar HII region; b brightest member of the group, shows N-S elongated bar, from the N end a spiral arm started to the S with a brighter spot at the S end; c also shows a SE-NW elongated bar, at the E side a closed spiral arm can be detected; SW of c a very faint tidal arm is visible; d only a few arc seconds W from b, 3:2 E-W elongated; 1’ N of this double system a noticeable glow can be detected which seems to be in contact with b/d but without showing any spiral arm form; e compact with high surface brightness, a little bit elongated to a 13mag star NW; NGC 7320c direct vision as a round glow 4’ NE, shows a faint round halo around the bright small center, halo can not be detected as a ring

[RolandosCY]

Uwe, confirm you could readily see them AND separate them in only 4" at 63X?

Under SQM 21.1 skies (lm 6.6) about 90 minutes ago I could readily detect the Quintet in my 6" as an unresolved very faint glow of undefined shape at 128X, and they were all but gone by doubling the magnification. Using an Ethos 13mm at 69X I could see there was "something" at the correct position but I could not hold it enough time, and I could not see them at all in my 31mm Nagler at 29X.

Also, last night I was unable to get a confirmed sighting of SQ using my 120mm f5 refractor. I did suspect something at 85X but I could not hold it even with averted vision except for fleeting moments, could be a case of averted imagination!

[Uwe Glahn]

Rolandos, just checked my original written records from 2008 and yes, I confirm the separation. I wrote "from 63x feeling of separation, 88x clearly see two plobs (which I could confirm later as "a" and "b+d" because of a rough sketch) between three 12-13mag stars in a row"

Transparency was very good at an alpine location with very dry "Föhn" wind. Telescope was a 114mm Newton. I measured the mirror (minus fase) with 108mm. Because of the obstruction and the normal coating I always called it 4".

[Howard B]

I have had on my list for awhile to try for the high redshift quasar near the center of NGC 7319.

Link to paper http://arxiv.org/abs/astro-ph/0409215

With a Z of 2.114 its way out there! It will be fun to try for this unusual object with its unusual alignment.



Hey Jimi,

A quick read through the paper shows it's supportive of the quasar being physically associated with NGC 7319, so Halton Arp must be smiling somewhere. Do you have a visual magnitide for this thing?

Howard

[Ivan Maly]

Never thought the 31" had a lumber tube! But then, of course, it wasn't physically that big. Incidentally, I wonder what W. Herschel meant to coat his glass mirrors with. Be that as it may, here is my description of the OOTW in 16".

Stephan’s Quintet observed at 225x when culminating near zenith. Only slightly tighter than the NE group [the UGC 12127 group "balancing" the Quintet NE of NGC 7331]. The most conspicuous at this magnification is NGC 7318. The A and B cores are fully resolved. The pair is oriented EW and embedded in a common halo. To its E, NGC 7317 is a compact glow just S of a star. NGC 7320 in the S corner of the group has a star on its SE end and is large, diffuse, and elliptical. It is extended NW toward NGC 7318. NGC 7319 on the NE end of the group is comparatively thin and oriented NW-SE. There is a faint star about its major axis length to its E.

[Howard B]

Hi Ivan,

The Herschel's mirrors were all made from speculum metal and weren't coated, which is a big part of why the Marseilles 31 inch was such a big step forward for reflectors - speculum mirrors at best were 66% reflective, and when they tarnished had to be refigured while restoring their reflectivity.

[Ivan Maly]

I suspected they were a) meant to remain uncoated, and b) were never used, and this is what I've just found, a museum page that seems to take the same view without indicating any sources:

http://www.sciencemuseum.org.uk/online_science/explore_our_collections/objects/index/smxg-56844

It looks like it was some sort of nontransparent glass.

[Howard B]

How about that - I'd never read that WH tried a glass mirror - thanks for the info Ivan!