Martin Meredith

Great shots and report Mike. Here's my Arp 82 from about a year ago with about double your exposure. I'm seeing more detail in the upper arm in your shot -- impressive!

I also took a look at SHK 280 last night (along with a bunch of Arps in Hydra and Sextans). Glad that Mike has already done the hard work labelling them!

Very nice Mike. SHK 280 is a lovely chain. Personally I think all SHKs are worth posting as they have their own individuality! I checked my lists and I have an example of SHK 346. I must have left this one stacking for quite a while so the exposure is quite a bit longer than yours, but it shows there are more galaxies in the surrounding area (Shakhbazian listed 8 members but I think equipment has moved on since she observed them). Martin

Hi Mike Glad you're having some clear nights. Here's mine from last year (6 minutes total exposure so more than 3 times yours). Looks like I turned the background up to allow my visual system to catch some of the faint stuff. Martin

Wonderful objects! Next time I carry the scope to the back of the house I will try to observe them. I looked them up and they are apparently both members of the Flat Galaxy Catalogue (FGC 133A and 134A) and close enough to be (potentially) interacting. The only clear reference to them that I can find is in this paper:

Just to add (I found the code). Suppose you are trying to detect a mag 20 point source (e.g. a very distant quasar) from skies of moderate quality (SQM 19, FWHM 3") using your existing scope and a Lodestar X2 mono. With 10 x 20s subs you obtain a signal-to-noise ratio of around 3.5, enough for detection. By comparison, my 8" f4 scope reaches that SNR in 6 x 20s subs. So in reality there is not that much difference, in the sense that by waiting a little longer you can obtain the same SNR. At the same time, an f5 scope is easier to keep in collimation and ought to produce better looking stars across the field. I know quasars are not what you asked about, but this kind of comparison is likely to give an indication also for how long it will take to acquire faint details in the Arps, for instance. Martin

Hi Marv I have been using a Lodestar X2 mono + 8" f4 reflector (800mm FL), mounted in alt-az, without guiding and without cooling, to do EEVA-style observing for the last 5 years and haven't felt more than a passing temptation to upgrade any of these components. Such a setup can reach to mag 20 and fainter on good nights from my observing site which is about 11km from a city with a population of 230,000, with best SQM measurements of around 20.5 on moonless nights (more typically around 20). For the occasions when I want colour (mainly for globs and open clusters) I use the same setup along with a Starlight Xpress electronic filter wheel with Baader filters, combined live in software. With a very similar FL of 750mm, your 150mm PDS would most likely show plenty of detail in the Arps. It is somewhat slower at f5, but still pretty fast and would be fine if paired with a sensitive sensor (i.e. with a high QE). Regarding sensors, I may well be in the minority here, but I see very little to be gained if you are mainly interested in galaxies by using a sensor that produces a large FOV, and plenty of disadvantages in terms of processing time and storage (as well as initial cost). My Lodestar coupled with the Quattro has a FOV of 0.44 x 0.35 degrees -- tiny by modern standards. Your 150mm scope would produce a slightly larger FOV of 0.47 x 0.37 degrees -- see https://astronomy.tools/calculators/field_of_view/ with the Lodestar or similar. What does this buy you in terms of visible DSOs? A surprising amount! Taking 20' as the maximum diameter of the DSO (i.e. leaving some space around it on the sensor), you get 100% of all quasars (million or so) 100% of the globulars (157) 100% of the Hicksons (100) all but 1 (very faint) planetary nebulae (2390) all but 4 galaxies (exceptions being M31, NGC 292, M33 and NGC 55, although I have managed decent images of M33 with my sensor) 99.8% of the VVs (2010) 99% of the Arps (335) 95% of the Abell galaxy clusters (though admittedly not the closer i.e. brighter ones) 86% of all open clusters (1847) 84% of reflection nebulae (134) 57% of dark nebulae (2850) 41% of bright nebulae (518) There is a tendency nowadays to promote CMOS cameras with low read noise and there is nothing wrong with that, but I would say that at 750mm or so FL you can easily get 20-30s sub-exposures even in alt-az mode with no guiding, so the advantages of low read noise are somewhat diminished. I still prefer CCDs like the Lodestar because the gain is fixed so that is one less parameter to mess around with. As a minimum for Arp hunting, I'd say you need a driven mount, a fast focal ratio scope, a modest pixel count but sensitive mono camera, a USB connection and a computer. And software of course, ideally capable of hot pixel removal as a minimum. I can't lay my hands on it at the moment but I have some code that will compute the signal to noise ratio for a given scope/camera combination to be able to see a point source of a given magnitude. Later I will plug in the details for your scope and see what it comes up with. Meanwhile, if you look at this thread you can see a comparison of mono cameras for EEVA: HTH, and feel free to ask more questions! Lots of fun to try to answer them. Martin

I'm glad you had some fun with them! I get as much pleasure during the observation as I do later reading about them and as much again looking afresh at the image. I did take a look myself for the quasar on the Arp 315 image and wasn't too sure, but checking again with the DSS image I can see it is there. The thing you've circled shows both a star and the quasar very close by at around 10 o'clock. Its interesting to compare the detail in the two images. Clearly the DSS2 has better resolution and goes deeper in some wavelengths, but it always surprises me how much one can obtain with a modest setup.

Nice write-up Mike. Arp 22 looks particularly intriguing. I was looking through my very disorganised collection of Arps to see if I have any of these three but could only find the Antennae. This needs a long exposure and a big stretch.... (preferable with a clean sensor). This is the best I've been able to achieve to date. I have the advantage of observing at a lower latitude of course....

There are actually 9 Arps in Lynx (6, 55, 143, 195, 202, 215, 250, 283, 315), just the right number for a single observing session if all goes well. Unfortunately, Arp 55 was just out of view during the time slot I was able to devote to it, but I managed to take a good look at the remaining 8. Here are 6 of them -- I posted about Arp 6, the Bear's Paw Galaxy, and Arp 143, the collisional ring galaxy, in other threads. Arp 195 is classified as a "Galaxy with material ejected from nuclei". It is a triple galaxy system with a very clear linear plume at the N. The lower galaxy has spiral arms that can be made out in the shot. I can't find much online about this specific galaxy group but one article refers to it an ultra-luminous infra red galaxy [1] resulting from galaxy merger. Arp 202 (NGC 2719, 2719A) is classified in the same way as Arp 195. A 2018 paper [2] devoted entirely to Arp 202 is worth a look as it contains multi-spectral images of this pair but also because it explores the formation of a 'tidal dwarf galaxy' resulting from stars stripped from each galaxy during the interaction -- presumably in sufficient number to spawn a new dwarf galaxy from the two parent galaxies. There is nothing visible at the proposed location of the tidal dwarf in my image (some way off to the right of the pair). I wonder whether it would be possible to capture it with a longer overall exposure in H-alpha. Arp 215 (NGC 2782) is well-described as a "galaxy with adjacent loops", very evident of to the left in this highly-stretched image. Apparently, this is the result of a minor merger and has tidal tails extending to both sides, only one of which is evident in my image (the other is very weak in the visible spectrum) [3]. Coincidentally, a tidal dwarf galaxy candidate was proposed in the brighter tail. A ripple structure referred to in the paper is clearly visible to the upper-right of the galaxy. These are very blue in the DSS2 image. Arp 250 is a "galaxy with the appearance of fission" and is also quite hard to spot in this image! These galaxies have magnitudes 16.6 and 17.5 so it has to be one of the more challenging Arps. The faintness is made up for by the presence in the same shot of the face-on spiral NGC 2415 towards the bottom-left which looks like it makes a nice pair with the nearby star. This (NGC 2415) is a blue compact galaxy (like the Bear's Paw, Arp 6). Arp 283 is categorised as "galaxies with infall and attraction". It consists of the pair NGC 2798 and 2799. There is a clear bend to the edge-on member (NGC 2799) and a curving plume towards the top of the brighter member NGC 2798. Lying almost at the 'four corners' point where Lynx meets Cancer, Leo and Leo Minor, Arp 315 is simply categorised as "groups of galaxies". In the central part is the triple making up the Arp group. But the field contains as many as 6 further NGC galaxies and is in fact the core part of Abell 779, a relatively nearby galaxy grouping. Cheers Martin [1] https://iopscience.iop.org/article/10.1088/0004-637X/784/2/140/pdf [2] https://arxiv.org/pdf/1712.04913 [3] https://arxiv.org/pdf/1712.00932.pdf

In case useful to others, the lower shot from the DSS2 shows the position of the quasar (bright green square); the upper shot without the square suggests it is in the plume, but seems to be surrounded by a dark circle (perhaps not so much gas in the plume at this point). I think I can see that dark region in your image Mike.

Mika and Bill, thanks for posting shots. Its great to compare FOV, resolution etc with our different setups. Martin

Great report! Sound like a powerful observational machine to go after the Hicksons with. I'm impressed you could pick off 18 in a session. Martin

A few days back I was observing some of the 9 Arps in Lynx. Arp 143 was the most peculiar of anything I saw during this session, and indeed one of the weirdest things I've ever seen. Verontsov-Velaminov called it a blue nest of galaxies while Arp used the understated description 'material emanating from elliptical'. De Vaucouleurs regarded it as an irregular ring galaxy. To me it looks like a small sack of frogspawn. Arp 143 (NGC 2444) is apparently a collisional ring galaxy still in formation, where the typical spiral structure is replaced by a ring of knots caused by collision of a spiral galaxy with an early type galaxy [2]. This other galaxy may well be the compact companion NGC 2445 which sits immediately to the north. Paper [1] is a fascinating read on many levels (not least to read about the technology available for these kind of studies as recently as 1992 compared to the sensors we use nowadays). It contains a mass of very detailed information about the individual regions which would complement an EEVA-style observation of these structures. Although [2] is primarily a radio wavelength study, it is well worth a look as it contains more recent hi-res mono and colour optical wavelength images of the pair. There is a lot of interesting structure to tease out here for the observer armed with a camera (see also [3]). NGC 2445 has a number of blue regions, indicating hot young recently formed stars (< 10 million years). I'd like to return to take a colour shot of this one. My observation is 17 x 15s subs = 4m15 (ignore the estimate on the photo). There is a mag 20.2 (B) quasar just above the very obvious curving plume arising from the upper galaxy which I haven't been able to capture, in case anyone fancies a challenge! [1] http://articles.adsabs.harvard.edu/pdf/1992ApJ...385..491A [2] https://arxiv.org/pdf/1407.7369.pdf [3] https://arxiv.org/pdf/astro-ph/9709134.pdf The other Lynx Arps are also well worth a look for the variety of structures to observe. cheers Martin

Yes, sorry I couldn't really help with Windows Mike. I'm hoping to have some time over Easter to work on the next version of Jocular (the one I'm using myself that is, to do the LRGB stuff). It needs a few weeks work and this year has been really busy so far... Martin

Here's mine. There is a tiny hint of the faint tail that comes out at the top and curves away to the left, but you can only see it if you have already seen the picture in the Arp book! I will reprocess to see if I can bring it out more using an extreme stretch.... Martin

That's a great shot of the comet Bill. I must admit this one has passed me by so far. I note you used the 'hyper' stretch, presumably to get the tail as well as you have captured it. I'd be interested to see your Arp 165 if you feel like posting it because I also took a look a few days back and it would be interesting to compare. To me it looks like a mini version of M87 with a jet although I imagine it is just a star in the wrong place. I did manage to get a hint of the faint curved tail, but barely. Martin

Very nicely-presented document Mike. I particularly appreciate the insets. It's surprising how many really interesting VV targets there are in one constellation. Certainly they give the already fascinating Arps a good run for their money. VV161 (AKA the inner part of Abell 539?) is one of my favourite parts of the sky. So many galaxies. Martin

These two objects lie around 17' apart in the central portion of Lynx. I've manually mosaiced a pair of images I took to show the configuration (lower part is mono...). I've observed the Bear's Paw Galaxy (Arp 6, NGC 2537) before without really looking into what kind of object it is. It certainly looks like no other galaxy I've seen before. This time, after observing in luminance only for a while I decided to add a few subs in each of R G and B, something I rarely do with galaxies unless they seem to demand it. In this case it helps to see some of the blue star-forming regions that make up the many knots in this peculiar galaxy. I later learnt that it is a Blue Compact Dwarf galaxy, about a 1/10 of the size of our galaxy, lit up by hot massive young stars, typically less than 10 million years old. I read that it is because it is formed of star clusters such as these that the galaxy lacks a typical 'galactic' shape. This paper [1] describes bubbles of ionized gas in the lower part of the central section. IC 2233 is classified as an ultra-thin type SBc galaxy (classifed as Sd in [2]). In my close-up there are lots of knots in both the central region and towards the lower part, which also shows a slight bend. N is up in this image. The possibility that these very different looking galaxies are physically related has been raised. Paper [2] suggests that they are not linked, but is a good read as it covers both of these interesting objects and contains some much more detailed images than those I obtained, particularly of the ultra-thin galaxy in the H-alpha band (which I think would be worth collecting some subs in -- next time). In [2] it is argued that a star-bursting galaxy like Arp 6 will never evolve into a 'normal' galaxy like IC 2233. An interesting part of the sky! cheers Martin [1] https://arxiv.org/pdf/astro-ph/9903060.pdf [2] https://arxiv.org/pdf/0709.4249.pdf

Nice shot. Definitely orange and blue! Here's a quick capture from a few nights back in the north of Spain. Martin

Beautiful shots Mike and an interesting write-up (and kudos for braving the post-midnight temperatures!). Its remarkable what you can achieve in under 100s. I'm looking forward to seeing your other Arps (second time round?). I was out looking at Arps over the weekend and Monday and a couple of Shakhbazians too which I'll post later. It is always fascinating to see what emerges as the stack progresses, especially for these ultra-faint galaxy groups. Martin

Hi Mike Noooooooo! On the plus side, it gives you the perfect excuse to start again. The log stretch is compressing the original intensity values in the image by taking their log, so faint areas are boosted relative to bright areas. The x / (x+c) stretch is something I came up with that does an even more extreme compression (I use it habitually when I invert the image, for instance). Here, x is the intensity of each pixel, and c is a constant value, which can be chosen to vary the degree of compression. I call it 'hyper' stretch on the Jocular interface because I haven't yet found the correct name for what is a very simple function to map the image brightness. I hope you manage to somehow recover your drives but I imagine you've tried all the usual approaches. In my only experience of a computer failure I was still able to extract the hard drive and recover stuff. Martin

I also love reading up on objects. This is what I sometimes do: 1. Go to Simbad: http://simbad.u-strasbg.fr/simbad/ 2. Type in the name of the object in the Basic Search box. This brings up some basic info on the object. 3. To find out more, scroll down to References and press the button marked 'display'. This brings up much of the known literature in which the object is mentioned, most-recent first. You need to be a bit selective here, but it can be interesting to look at the earliest such reference as well as some of the most recent. 4. To find out about a specific reference, after clicking on the title (which brings up an abstract), the best option is 'view the reference in ADS' (near the base of the page). 5. Once that page comes up, nearly always you'll find a free pdf on arXiv (link on the right go the page). Often going to the publishers website you get the abstract only. Hope this helps! Martin

Of course, the best-known object in Lepus is the constellation's only Messier object, M79. This globular cluster was long the subject of age estimates that put it beyond the accepted age of our galaxy, but the estimate seems to have stabilised recently at around 12 billion years. I was observing this for quite a while -- such a long exposure is not really required, as there is only 1 minute in each of RGB (4 x 15s subs each). As you can see, there is a lot of information in a single 15s luminosity capture even at just above 20 degrees above the horizon: but the colour version really brings out the contrast between the blue-white nucleus and the band of yellow-orange stars that appear to encircle the cluster like a scarf. I find log stretch works really well with globulars for some reason (I normally use arcsinh except for inverted displays where I use x/(x+c) stretch). There are a few galaxies in this image too, the brightest being around mag 16. Martin

Thanks Bill and Mike. Glad to hear it is observable (and being observed) from the UK! In the northern reaches of Lepus, not far from Orion, is the constellation's only Arp entry. The description is "Elliptical close to and perturbing spiral". In this case, the type SBc spiral (NGC 1888) has a clear tilt at the lower end, and appears to be almost in contact with the type S0 elliptical NGC 1889. They are listed at around 110 M Lyrs with mags 12.8 and 14.1 respectively. The challenge is to spot the 'faint parallel feature on the opposite side from the elliptical", which can be made out in the image as a very narrow hair-like structure. NGC 1888 was 'recently' host to supernova SN2018yu. The other bright galaxy to the upper-left of Arp 123 is entry 534 from the Flat Galaxy Catalog, a mag 15 S0-a type which, intriguingly, is at a similar distance to the Arp pair. At the top left is another edge-on, a mag 16.4 galaxy PGC 147414. Martin