ARP GALAXIES

[Martin Meredith]

Definitely a clearer image, and in a 3rd the exposure time.

Last night with an even brighter moon I looked at the Horsehead in H-alpha, M74, Abell Galaxy Cluster 151 (containing VV 935), a rather startling planetary nebular NGC 246 (which I'll post in the other thread) and just to get an idea of magnitude reach, a Shakhbazian group (SHK 265). What it demonstrated to me (yet again) is that observing using EEVA techniques can take place on any clear night regardless of the moon (though for those with an artistic bent perhaps lunar sketching makes more sense...)

Martin

[Mike JW]

Hi Martin, you are firing me up to get back out there under bright moonlight with the camera but I do find that under strong moonlight I get much more noise (amplified by being a large Dob).

Well done.

Mike

[catburglar]

I recently picked up a copy of the Cambridge Photographic Atlas of Galaxies which has prompted me to get out and step off the beaten track of showpiece galaxies...

Here's my first dwarf galaxy- Arp 268 (Holmberg II) 11M light years away in Ursa Major. It's an iregular galaxy with some prominent star forming regions- most notably to the left of the triangle of bright stars in the centre of the field.

I'd tweaked my setup to see if I could get a filter wheel in the imaging train - which pushed out my spacing and gave even more focal ratio reduction but a bit more coma. In the end I didn't add any colour here because some light clouds/haze started to appear...Perhaps another day.

[Mike JW]

Hi 'Catburglar'

You chose a hard one for your first Arp. My first attempt was not worth posting. The low surface brightness of the galaxy really means it is best to wait until there is a transparent night to get the required contrast and then as you did go for at least 30 subs to reduce the noise. My second attempt is posted earlier in this thread. Great to see you getting into the spirit of EEVA with the additional info you have provided - makes for added interest and also adds an observational flavour to the post.

You mention colour - for star clusters and PNs it adds a great deal, also for star forming regions in galaxies. My feeling is colour is best left for true imaging although as software/cameras advance colour EEVA for galaxies is getting more worthwhile.

Have fun

Mike

[catburglar]

A very blustery night here in North Wales. Gusting winds meant that I was limited to 5sec exposures and even then ended up excluding approx 30% of the images from the stacks.

Arp 6 (NGC 2537)- The Bear Paw...a blue compact dwarf galaxy- type SBm. Regions of star formation 

Arp 337 (M82)- The nearest starburst galaxy at approx 12m light years. Just a hint of the outflows perpendicular to the disk in the stacked image on the left had side of the galaxy. Might try again with a h-alpha filter to see if I can capture these features.

Arp 210 (NGC 1569) - A dwarf galaxy irregular galaxy- with high rates of start formation. 

I removed the filter wheel today because it wasn't going to work but I didn't get the spacing right when i put everything back together and ended up imaging at approx 1 arcsec per pixel. I'll try again to reduce the spacing from the reducer so I can get a slightly wider FoV without introducing coma or vignetting. Jocular couldn't solve some of these fields- but at approx 18arcmin x 12 arcmin that's not surprising.

[Martin Meredith]

Lovely shots of some fascinating galaxies. Holmberg II is still on my list. Arp 210 is an intriguing galaxy with so many clear knots. Here's my attempt which I think is worth comparison if only because the large Lodestar pixels resulted in undersampling on this occasion.

When I use ROI in the new version of Jocular with my ASI 290MM I can get down to quite small FOVs and its pot luck as to whether they get solved. I currently go down to GAIA G mag 15.5 only so perhaps I need to introduce a few more stars into the platesolving procedure.

BTW are you using your ASI via Jocular or via the watched folder?

 

 

[catburglar]

5 minutes ago, Martin Meredith said:

BTW are you using your ASI via Jocular or via the watched folder?

Martin- I’m controlling the camera via jocular…it’s worked perfectly for the three sessions I’ve tried with it… It means I only have two programs running (SkyTools for planning / goto and Jocular for ‘observing’) so there’s less to go wrong during a session.

I was planning on getting an ultrastar, but the introduction of control for ASI cams into jocular made me rethink…I thought I could reduce the EFL of my scope to around 8-900mm which is a good match for the ASI at bin x2.
 

[catburglar]

On 26/02/2022 at 08:12, Mike JW said:

You chose a hard one for your first Arp. My first attempt was not worth posting. The low surface brightness of the galaxy really means it is best to wait until there is a transparent night to get the required contrast and then as you did go for at least 30 subs to reduce the noise.

Mike- Thanks for the comment. I think some of my ‘transparency’ issues may have been few on the corrector too- It looked pretty misty when I was packing up, so I’ll have another go next clear and calm night with the dew heater turned up a notch or two 😁.

It was the posts by you and Martin that got me interested in this- even though the images don’t look ‘pretty’ in the conventional sense- it’s a great opportunity to be able to detect and try to understand a little more about what’s in the FoV.

I’d like to have the option of colour primarily for the PN’s and clusters, but also to help delineate the different colours of stellar populations that the interactions between these galaxies often produce…but for now that’s not feasible with my current set up. However there’s lot’s more to find - even with an FoV of less than 0.5 degrees- so I won’t run out of things to observe.

[Mike JW]

2 hours ago, catburglar said:

It was the posts by you and Martin that got me interested in this- even though the images don’t look ‘pretty’ in the conventional sense- it’s a great opportunity to be able to detect and try to understand a little more about what’s in the FoV.

Thanks for your kind and encouraging comments - as to the pleasure of EEVA, you have summed it exactly.

I have just posted Abell 1185 in the Abell thread and as this cluster contains Arp 105, below is the Arp part of it.

There is much happening in this area. Arp classified the main galaxies as Elliptical and Elliptical like galaxies that are interacting and in this case elliptical connected to a spiral. The tidal stream is extensive and there is likely to be three interacting galaxies. The whole structure is known as the Guitar. The tiny fuzz right at the bottom is blue dwarf galaxy and is known as Ambarzumian's Knott. The Knot and two other tiny blue galaxies just above it (not visible in my shot) are known as a Zwicky Multiple - intereacting?

The upper bright galaxy is NGC 3561A - SA(r) pec, the lower one NGC 3561 is also SA(r) pec,Liner, Sy3.

Finally the group is a VV 237 with 6 members.

Mike

 

 

[Martin Meredith]

Indeed, this is a fascinating group of objects. Thanks for your description. With the benefit of a slightly larger FOV it is possible to include yet another intriguing object: VV 1419 (which is in your Abell thread image). This is the brightest member of the cluster. I'm not sure what the apparent triple-nucleus signifies. The SDSS (9) image of this region is marvellous and suggests this part of the sky would make a great AP target.

Here's an article about the Abell group

 

[Mike JW]

Hi Martin

I had spotted the triple nucleus galaxy and then got side tracked with the Arp group, so thanks for adding this info in - I do like it when there are so many objects of interest in the fov.

Mike

[Mike JW]

Arp 165 - NGC 2418,(Gemini/Cancer border) at first glance looks fairly standard until you look closer. It has just one low contrast spiral arm, which just shows up in my shot (going up). Then further observing reveals a faint/diffuse tidal extension more or less opposite the arm - I started to get a hint of it. The question is, what caused this tidal extension? Presumably some sort of interaction in the past. Arp classified this galaxy as not spiral or elliptical with diffuse elements. Officially it is E-pec - certainly it is peculiar. This large galaxy lies 240 million lyrs away.  Note the two other galaxy just to the north of it - no redshift data available.

At about  8 o clock and close to NGC2 418 are two stars, the one further away is in fact a galaxy (no data).

Mike

[Mike JW]

and here are 4 Arps located in Cancer.

Arp 243 (NGC 2423)

A classic S - shaped due to a merger/interaction. It is thought that a merger may well have taken place a long time a go and the galaxy has now settled down. It lacks a well defined core. It is classified as Peculiar galaxy and Seyfert 2 (active core). There are some great images out there, especially the Hubble image.

Arp 82 is a pair of galaxies interacting. NGC 2535 is the big one and its companion is NGC 2536. Once again we see the S-shape due to the interaction. NGC 2535 is classified as SA(r)c pec. I was pleased to get a hint of the ring and star forming knots. Wonderful curving tidal stream curving up from 2535

Arp 287  (NGC 2735) is yet another pair of interacting galaxies with the S -shape

and finally Arp 247 (IC 2339/2338) are an interacting pair but this time no S shape.

This is not all the Cancer Arps, so another rewarding session beckons. This session was difficult due to unsteady seeing. At times I was dumping every sub as the stars wobbled in all directions. Persistence paid off.

Mike

 

[catburglar]

Here's where it all started- Arp 1 (NGC2857)..I don't think we've seen this one in the thread so far and I wonder why?

Arps 1-6 are in the section "Low surface brightness" . This example looks like a perfectly normal face on spiral galaxy (Type: SA)- most out of place in an atlas of peculiar galaxies. Whilst there's nothing peculiar visually, Arp 1 is a LINER  (Low-Ionisation Narrow Emmision Line Regions) - part of a class of Low luminosity AGN's characterised by lower levels of OII ionisation than typical AGN's.

The two bright galaxies at lower left (NGC2854 & 2856) are unrelated to Arp 1 at just over half the distance (circa 120Mly) and just to complete the long distance leg of the journey- the two PGC galaxies marked on the zoomed in shot are around 10x more distant at 2.2 and 2.9 Gly.

 

I thought it might be interesting to compare my shot with the one from the catalogue- for anyone that's not sure, mine is on the right 😉 . Whilst the Palomar 200 inch clearly has the edge in resolution, it's still possible to see hints of the condensations in the spiral arms and the prominent bridge between the two spiral arms below the nucleus in my shot with altogether more modest equipment.

[Mike JW]

Hi,

Great idea to post the Palomar for comparison. A good point to make re not expecting to see such a standard spiral in the Arp catalogue. A good result using your set up, especially getting a hint of the bridge.

My shot below is 24 x 10sec subs, using my 15 @ f4.5, back in 2020. This was before I went over to using Jocular to process the SLL images. It would be interesting to re-visit this Arp again and process in Jocular.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mike

[catburglar]

Mike

Your image is a bit less noisy and the bridge is more clearly seen- I guess in part this is the benefit of greater aperture and large pixels leading to a "faster" system. How is your 15 inch mounted - is it an alt-az goto like Skywatcher or an equatorial platform? I seem to recall that the SW flextube tracking doesn't cut it for even 10 second exposures but if it could be fettled, then I might see a big dob in my future...although I do like the images that @AKBgets with his hyperstar and ultrastar camera... so that's also a consideration.

 

 

Edited March 5, 2022 by catburglar

[AKB]

19 minutes ago, catburglar said:

although I do like the images that @AKBgets with his hyperstar and ultrastar camera... so that's also a consideration.

 

Thanks for that.  If I was starting again I might just go for a RASA.  

On the camera front I am thinking of trying an ASI294MM, a cooled CMOS mono camera with slightly smaller pixels than the Ultrastar, which I believe to be under sampling currently at 2.5”.  The ASI would give me 1.8”, but really low read noise and high sensitivity.

Tony

PS: I’ll be adding Arp 1 to the observation list!

Edited March 5, 2022 by AKB

[Mike JW]

7 hours ago, catburglar said:

Your image is a bit less noisy and the bridge is more clearly seen- I guess in part this is the benefit of greater aperture and large pixels leading to a "faster" system. How is your 15 inch mounted - is it an alt-az goto like Skywatcher or an equatorial platform? I seem to recall that the SW flextube tracking doesn't cut it for even 10 second exposures but if it could be fettled, then I might see a big dob in my future...although I do like the images that @AKBgets with his hyperstar and ultrastar camera... so that's also a consideration.

My Dob is a 15" Obsession, to which I fitted encoders and the servocat motors. It can track Ok for up to about 15 seconds and I can fine tune the tracking but unless a Dob is built to 'cabinet maker' standards, i.e it is totally orthogonal then alignment/tracking are likely to always be an issue. The Obsession is well built but it is not truly square hence tracking limitations. It seems to track better at certain altitudes. If I could have in set up permanently under a run off shed then to have it permanently placed on a high quality equatorial platform might be a better option .

I have done EEVA using 5", 7", 9.25", 11" 15" (and just once on a 24") scopes. There is no ideal size aperture.  It seems to me that best aperture for EEVA is somewhere in the 10 -12" range. In this range you get quicker captures and better resolution due to the aperture. However one has to accept the decreasing fov. AKB's (Tony) set up is an excellent compromise - fast, wide fov, sufficient resolution. However this sort of set up with the hyperstar is best used in an observatory. With my interest in galaxies and the small SHK/PCG groups then my size scope/set up is excellent but I immediately lose out for Abell Clusters. Also Dobs have the problems of reaching focus, hence I stick with the Ultrastar which is eyepiece size. As we know SCT scopes are so versatile, although for visual use they give such soft views due to their lack of contrast.

As to your set up - probably close to being ideal. Their is no single scope that will do it all.

Look forward to your next post.

Mike

[Martin Meredith]

Great to see a spate of new Arp postings. Looking thru some of mine of the recent ones, here's Arp 243 with the Lodestar from 2019 on a decent night, although at 30s I was getting some trailing in alt-az mode. There's a lot of structure in the 'interaction zone' here.

[Martin Meredith]

Excellent images of Arp 1. No idea why I've not looked at this (except in my case the scope is much easier to set up facing south...). Posting the image from the 200" is a good idea -- let's see how much we can tease out.

 

[AKB]

On 05/03/2022 at 23:27, AKB said:

PS: I’ll be adding Arp 1 to the observation list!

I was so keen to take a look that, seeing a short clear window forecast last night, albeit with high winds and some high cloud, I flung open the observatory roof and with no opportunity to let the scope cool properly, or to focus (which is a bit of a killer for a Hyperstar), I captured 10 minutes-worth. 

This is a spectacular region of space.  The widefield view (nearly one degree across the diagonal) gives agreat panoramic vista, with Arp 1 as the centrepiece.  The bright star is 39 Lyn / HD 80608 and the two galaxies to the lower left of it are NGC 2854 and 2856.  But this field has so many galaxies, especially towards the top of the frame, there are too many to label and the Jocular display becomes peppered with markers if you try. 

The haze around the stars and the general fuzziness is probably a combination of high cloud, poor focus, and inadequate cooling time.  As a result, perhaps, I'm unable to resolve the bridge between the arms, but I've tried to emulate the FOVs from @catburglar to see the comparison.  What a great galaxy, though!

Tony

 

 

 

  

 

[AKB]

Reading further, I see that NGC 2854 and 2856, captured above, are parts of Arp 285.

The spiral arms of NGC 2854 are clearly visible, but look more closely at NGC 2856 and you can see evidence of the jet leaving at a right angle to the main body of the galaxy (a barred spiral, although I couldn't tell).

 

 

[Mike JW]

Hi Tony, a superb addition to the current  Arp 1 post. I have spent 10 minutes just absorbing your wide field view - such interest and beauty. I have checked back on my Arp 285 - no sign of the jet that you mention. I was geared up for tonight to look at Arp1 and Arp 285 but too windy and very unsteady skies. 

It works so well when we have various contributions from different size scopes/set ups with the associated comments/observations.

Below is a close up of Arp 285 (from 2 years ago) and no jet from NGC 2856 but note the three bright patches in a line. The two outer ones are at the end of the bar and where the spiral arms leave the bar.

Interesting article: https://faculty.etsu.edu/smithbj/research/sg/arp285/arp285.html

Yet another one to revisit........

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mike

[catburglar]

When I first looked at these two galaxies in my capture I didn’t notice any sign of interaction- although they’re at the same distance and sure a common recession velocity, so I’d been hopeful of spotting something. I’m away for a few days so won’t get another chance to look at this for a while.

Mike -your image seems to correspond with the bright patches shown in the 4.5micron band…And (this may be the eye of faith) Tony’s image seems to show the triangular knot that is the second of 4 regions within the jet.

So there’s definitely a lot more than a first glance might suggest.

[Mike JW]

I am reasonably hopeful of being able to pick up the tidal stream between the two and the 'jet' given a decent night.

Mike