NGC 3184

[Martin Meredith]

Over the years my approach to planning an EEVA session has changed. Until a few years ago I used to scour books like the Night Sky Observer's Guide for interesting-looking objects and prepare a list based around such gems. Nowadays I try not to peek beforehand, and prefer to leave the selection of objects to near-chance. What I've found is that there is nearly always one object that takes my breath away when it appears on the screen -- the unexpected object of the night. Sometimes it is an object from a list I'm working my way through; at other times it is something that looks intriguing on the charts. 

That was the case here -- the charts showed a large galaxy with a perfectly circular disc, suggesting either an everyday elliptical or an exciting face-on spiral. The charts classify it as SABc, so a spiral it was...

The scene is balanced by the bright star, mag 6.6 variable GP UMa.  

I started off in mono but then added some colour both to reveal the nature of the acompanying star (which turns out to have a colour index of 1.6) and to see if I could get any further information on the galaxy core and star-forming regions. The core shows well, glowing orange-yellow in sympathy with the foreground star, and I think the arms have a pale blue look to them. 

The spiral arms of the galaxy are actually quite hard to tease out -- they needed a far more extreme stretch than I'd expected -- being uniformly faint compared to the bright core. There are a fewer obvious bright spots in the arms than in some face-on spirals. The bright spot that coincides with the galaxy label is a foreground star.

A mono image stretched even further better shows the multitude of arms. The outermost arms are harder to see but reach as far as the two stars at the top. The area around the core is visually complex.

 

The de Vaucouleurs Atlas of Galaxies classifies NGC 3184 as SAB(rs)c, ie spiral, of intermediate type between ordinary (A) and barred (B), and with characteristics of an inner ring (r) and yet also of spiral arms leading directly from the core (s). This is a kind of double-hybrid and sits right in the centre of the de Vaucouleurs scheme. I really recommend this book for anyone interested in galaxy types. The 'c' corresponds to a relatively 'late' type, with moderately unwound arms (some books call it 'cd' ie slightly later still). The bar is described in the de Vaucouleurs atlas as being a broad oval bounded by two bright inner arms. 

In common with several of the DSOs I've observed recently, NGC 3184 was discovered in 1787 by William Herschel.

cheers

Martin

 

 

 

[Adreneline]

Brilliant write-up Martin and an excellent result.

You've made me want to get into EEVA but maybe my 6" RC is too slow.

Inspiring.

Adrian

[Martin Meredith]

Thanks Adrian. If your RC is f/9 then it would be great for some types of objects that we observe in EEVA time scales, such as the brighter planetary nebulae, but it would struggle with low surface brightness objects like this one. However, if you could reduce it down to f/6 or ideally lower it would be fine. I'm not very familiar with the RC design so I don't know how easy that would be.

Cheers

Martin

[Adreneline]

2 hours ago, Martin Meredith said:

if you could reduce it down to f/6 or ideally lower it would be fine.

Hi Martin,

I do have the 0.75x  F/R for the RC which takes it from 1370mm to 1030mm and from f9 to I believe f6 so might be worth a try. I presume my ASI120MM guide camera would be ok to start with too. I also have a colour ALTAIR IMX224 - would that be worth a go?

Adrian

 

[RobertI]

Great report Martin, a very interesting galaxy, nicely captured and researched.

 

3 hours ago, Adreneline said:

Brilliant write-up Martin and an excellent result.

You've made me want to get into EEVA but maybe my 6" RC is too slow.

Inspiring.

Adrian

Adrian, I have been using an RC6 for EAA for a few years and have been very happy with it. I use a F3.3 SCT reducer to reduce it down to F4.5 ish, I imagine other reducers would also work with the small chips of EAA cameras, perhaps the ubiquitous F6.3 reducer? Some examples of what the setup is capable of can be found on my rather out of date website http://www.ipernity.com/home/robivory

Hope that helps.

[Adreneline]

2 hours ago, RobertI said:

Hope that helps.

Thanks Rob, it does help.

I think I'll have a go and see how I get on.

Thanks again.

Adrian

[Martin Meredith]

The reduced RC6 with the ASI 120 or the IMX224 seem like a good fit in terms of pixel scale, especially when binned 2x2, but the FOV is quite small (0.27 x 0.21 is what I make it). There are no shortage of interesting objects for that FOV but you might have difficulty getting enough stars to live stack, and getting the objects on the sensor could be a problem and/or issues with platesolving. My FOV is 0.44 x 0.35 which I regard as being fine but on the small side (I never have stacking or platesolving issues with this -- at least, for non-blind platesolving).

On the other hand, your ASI 1600 gives a large FOV. Binned 2x2 the image size is not too large for live stacking. Likewise for the ASI 294. Main imaging cameras can make good EAA cameras esp. when used binned. In fact, quite a few people seem to use these cameras solely for EAA.

Cheers

Martin

[Mike JW]

I keep meaning to visit  3184 but get side tracked. A classic galaxy. I am not sure colour really works for it but I do like the yellow star. 

Mike

Edited March 7, 2021 by Mike JW

[Adreneline]

2 hours ago, Martin Meredith said:

On the other hand, your ASI 1600 gives a large FOV. Binned 2x2 the image size is not too large for live stacking. Likewise for the ASI 294. Main imaging cameras can make good EAA cameras esp. when used binned. In fact, quite a few people seem to use these cameras solely for EAA.

Thanks Martin.

The 1600 is installed on my RedCat + EFW + EAF and is 'sealed' but the 294 "floats' between the RC and my Canon 200/Samyang 135 so I'll give it a go and see how I get on.

Thanks again for your advice and help.

Adrian

[Martin Meredith]

To be honest, the colour version looks a lot better on my screen than in the image here where it isn't very bright. I hope you get a chance to visit it with your 15" as there is a lot of structure to be seen.

Martin

 

[Mike JW]

At last I pointed the 15 at it.  So much detail picked up. Mike

Below is the same shot (different stretch) but labelled up to show two star forming area with NGC numbers and what I think is the ring structure. This galaxy is not especially large - 50,000 lyrs across and about 40,000 million lyrs away. Apparently it is high in heavy elements (yet to find out why/significance) and has fewer blue stars than what you might think from the blue appearance in colour images'

Edited March 10, 2021 by Mike JW
more info

[Bill S]

Excellent detail.

[vlaiv]

On 09/03/2021 at 22:37, Mike JW said:

Apparently it is high in heavy elements (yet to find out why/significance)

I guess that means that there were a lot of supernovae going off in that galaxy as heavier elements are only formed in such cataclysmic events? 

[Paul M]

I've only just seen this one Martin, it's a great subject.

I'll never be a hard core image processor, neither the patience, skill nor equipment. Just the other night, on my last session, I was trying to remember some of your recent targets. The Arp's in particular interest me greatly. But this one is just my bag.

I should keep a notebook so I can plan better.

[Martin Meredith]

Thanks Paul. I'm definitely not a hard or even soft core imager either.  If it can't be done at the scope then I don't do it. That isn't to say that I don't enjoy 're'-observing by reloading the sequence the next day or in the future and messing around with it, but anything that takes more than a few seconds of adjustment isn't for me. I'm mainly interested in seeing what I missed during the near-live experience...

One thing we've being trying to do is group things into threads by catalogue or object type so that things are easier to find in the future. I think we need one for interesting NGC galaxies as there are so many. 

Martin

[Mike JW]

I will spend time re-looking at my shots and tweaking them in Jocular. Sometimes I will then put the snapshots into photoshop to brighten a bit or soften the images to give a better look to the shot - no more than about a minute to do this.

Mike