NGC 7331 and Stephan's Qunittet

[callump]

A fairly cloud free sky last night, but not very transparent. But a good opportunity to tackle a dozen or so targets in Pegasus. 

Here are the first two - NGC 7331 (the Deer Lick Galaxy), with the four 'fleas' visible, and Stephan's Quintet (NGC 7320 and friends) which is also known as Hickson Compact Group 92, Arp 319, and VV 28.

Taken with Celestron C11 on G11 mount, with ASI174MM mini camera. 6 x 20s exposures. Processed with bias and darks subtracted in Siril.

Probably need a few more exposures on these for more signal.

Callum

 

[Martin Meredith]

Excellent shots of these great targets. Funnily enough I was also looking at them the night before last. There is an awful lot going on in Hickson 92  and the longer you look the more of the wispy tails become visible. You're getting great detail for 2 minutes total exposure.

Martin

 

[Mike JW]

These are favourites both visually and using the EEVA technique. Plenty of detail in your shots.

Below are shots using my 7" Mak Cas and the Ultrastar for comparison. Taken back in July 2020.

Mike

 

[Mike JW]

Hi all,

Callum's post of 7331 and 7320 fired me up to take another look at these well known objects but this time I used the 15" Dob, to give a comparison between a 7", 11" and a 15" scope.

During yesterday I thought I would read up about 7331, rather than just post yet another image.

NGC 7331 (mag 10) also known as Caldwell 30, is an unbarred spiral about 50 million lyrs away (One article said 40 mlyrs) and is similar in size (120,000 lyrs across) to the Milky Way. Its four companions are known as the fleas and on a good night I see all four of them with my 20". Like the Milky Way it has a super massive black hole at the centre. Strangely the central bulge (describe as being 'boxy') spins slowly in the opposite direction to the rest of the galactic disc (which spins relatively fast). I could not find any information as to the origin of this retrograde spinning bulge. Infra-red studies reveal there is a warm disc (ring) of small grained dust surrounding the bulge. Overall the galaxy has a low rate of star formation (a quiet galaxy). However detailed studies show two tidal streams which, suggests past interactions. Quite possibly consuming dwarf galaxies. Currently six dwarf galaxies have been located orbiting 7331 (not the so called fleas).

A = mag 19, B= mag 20, C = mag 18.5, D= mag 20.5, E = 19.5 and M = 16.15 (no idea why it was called M!). Now this set me pondering whether I would be able to locate any of them. See reference image below.

First up A and B. Below is a close up. No sign of B. My circle indicates where A would be. I adjusted the settings to remove as much noise as possible and this leaves two tiny specks of fuzz, the right hand one being the brighter. I am not claiming this as a definite for A. I should probably revisit on a very good night.

Next up is my attempt for companion M. Happy with my ID for this one - top left fuzz of the image below.

Now to C and D. The circle at the top is where C lurks - nothing to be seen. The lower circle is D - reducing the noise and something very faint lurks. See zoomed in shot - the fuzz could well be noise but it does not quite have that 'noise' feel about it.

I forgot to try for E.

A fun and absorbing look at again at 7331 and always something to learn.

Mike

[Martin Meredith]

Fantastic amount of info there Mike and a wonderful challenge for us all! That is just the kind of evening the EEVA techniques are made for. It has me wondering if I managed to capture any of these in my LRGB shot from the other night. I doubt it but here it is. I will reload it later and take a more definitive look (and stretch it as far as I can...). Colour often doesn't add much but I think in this case the galaxy is bright enough to support fairly clean colour in EEVA length exposures.

 

[Mike JW]

Hi Martin, I like the wider fov but I would be amazed if you have captured any companions. It is pushing the limits of the 15/camera set up. I re visited 7331 again last night to have another go for companion A, Happy to say I have just got something, having eliminated the noise. The close up shot - I have removed several of the poorer subs to try to improve the sharpness. 

Have fun looking for these companions. Mike

[Martin Meredith]

Indeed you are right, Mike. I stretched just the luminance to within an inch of its life and had a matching patch of noise in position A, as well as 100s of other matching patches of noise in the vicinity 😉. So no clear ID there. But a definite challenge for another night. Mag 19 ought to be possible but I found this region to be somewhat obscured by the outer arms of NGC 7331 in my shot. 

Is there a link to any resources describing the 6 dwarves?

Thanks again, and to Callum for reminding us what a great galaxy this is.

Martin

 

[Mike JW]

Hi Martin,

https://arxiv.org/ftp/arxiv/papers/1701/1701.00615.pdf is where I got the info.

Last night I tried for 'E' but despite the power of my set up I did not get a hint of it. Conditions were not good.

Mike

[Martin Meredith]

Thanks for the paper. The information on exposures is very useful and I see we are in the 27 mags/arcsec^2 range for surface brightness, so well done on getting one (or more) of these! 

It appears that galaxy M as it has been known about since at least 2015 (it is on my charts, with ID LEDA 2051985) so I guess the M was to distinguish it from new discoveries? They seem to have included it because of their new radial velocity data that suggests it is a true satellite of NGC 7331.

Martin