AKB

Just noticed this! Small problem... the slider control for sharpen appears to be missing: Running on Apple Mac. Tony

Exactly so. Found out the hard way when trying to do darks (which I normally do with the camera detached, of course, but I had spent ages collimating and arranging the cables, which I didn't want to redo.) There should be a 'dark' mode for these status lights. Tony

Is it just me, or does anyone else see a brontosaurus / apatosaurus / diplodocus ? Tony

There are, of course, some very well-known objects which are Arps... M51 and M101 perhaps the most popular. So whilst mooching around Canes Venatici at some other familiar favourites, I took a peek at NGC 4627, the dwarf elliptical galaxy, which is the 'calf' of NGC 4631, 'The Whale'. Together these form Arp 281 (also VV 1156), 'Double galaxies with infall and attraction.' Relatively featureless, NGC 4627 lies about 13,000 light-years from the wonderfully mottled NGC 4631, which is classed, now, as a barred spiral (used to be Sc?). The Arp atlas has a splendid image by Robert Gendler using a 12.5" RC and 100 minutes of exposure, but the 10 minutes here captures just a little of that grandeur. In the wide field, though, we also see NGCs 4656 [SBm(bar,mult) at a mere 17 Mly] and 4657, both part of the larger 4631 galaxy group (all part of VV 1560??.) Also visible here are FGC 1490 (towards the middle of the LHS) and PGC 42953 (middle of bottom LH quadrant.)

Well, I certainly hope so! Thanks for all that – I turn to many of your posts to gain insight into what are, otherwise, just nice sights, and I do so again in reference this post, a similarly clarifying view of Arp 25 and 114. Here's my observations of these objects from a recent night (April 1 – no joke.) I can do little to add to your contribution except offer a wider field, dominated my two mag 8 stars HD 51141 (centre) and HD 47976 (top edge) and, hiding off on the LHS, (mag 15) galaxy UCG 3715. Continuing the naming confusion, the Arp Atlas notes that some sources reverse the naming of NGC 2276 and NGC 2300. Outside of the Arp grouping, other galaxies include (mag 14) IC 455 at 111 Mly, nicely flatish UGC 3661, and many others.

That is absolutely amazing!

Two for the price of one... Arp 296 and 299. First of all, the wide field (1º x 0.75º) shows: CGCG291-076, top left, Sm(diffuse) mag 14 at 81 Mly multple star 11271+5905, half way down RHS, mag 12/13 PGC 35218, Sbc, mag 15.9 and PGC 2583396, mag 17.1 at 1300 Mly Arp 296 This is PGC 35345 'and companion' which is marked in the atlas as SDSS J1 12850.64+583336.7, but here shown as PGC 2580146 and also, curiously, outside the boundary marked here for the Arp. Ostensibly, 'double galaxies with long filaments' Arp notes a "straight filament almost to attachment with arm of spiral". There's nothing visible joining the on any of the plates but the smaller galaxy does at least align towards the other. Arp 299 Again, more confusion. The main components are shown in the atlas as NGC3690E, NGC 2690W, and IC 694 (to the top right of the group), respectively show there as VV 18a,b, and c. My worry is that these are labelled in Jocular as VV 118, so is something wrong here? Arp notes "bright internal knots", and others (Hibbard and Yun, 1999) have studied optical tails beyond Arp's field to the north and south-west. They're shown as quite extensive in the atlas, but the image there seems to be from a 24" f5 Newtonian, so absolutely no sign of that here.

Aha! Title: The nature of 'box' and 'peanut' shaped galactic bulges Authors: Shaw, M. A. Journal: Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 229, Dec. 15, 1987, p. 691-706. Bibliographic Code: 1987MNRAS.229..691S Many thanks! MUCH better than:

Not a chance! Here's Arp 162 / NGC 3414, also from last night. This is mag 11, classified as S0(bar,mult) and has a "diffuse, diagonal filament", clearly seen. Apparently considered to be 'a "box" or "X" galaxy by Whitmore and Bell (1988)' ... that's something I'm going to have to look up, unless someone here can shed more light on this. Nearby, we have other delights: NGC 3418, S0-a(bar), mag 14.2 at 66 Mly NGC 3400, SBa(bar,ring) off to the right in the wide field FGC 135A, mag 15.4 at 74 Mly a couple of quasars dozens of other PGC galaxies

Had a go at this last night... not observed it previously. Actually, I had two attempts: one at the start of the session; one towards the end. The wide field (1º x 0.76º) captures NGC 5205, and (centre bottom) flat-ish UGC 8491 Late evening (22:45) clearly shows the bridge, but it's pushing into the noise even at 15 minutes worth Early evening (21:05) the bridge is barely visible after 10 minutes. I think that the darker sky a bit later makes the main difference here. I enjoyed giving this a go, so thanks to @roelb for the inspiration. Tony

Yes, I’m OCD too!

I’m in exactly the same position, and have been wondering whether to do anything about it, since it has zero impact on image quality. I saw a post from Lucas once on how to calculate and set the necessary parameters, but don’t recall where that was …. 🙁 Tony

The EEVA folk have a dedicated Hickson thread…

Really nice, Mike. That big aperture is really working hard for you.

Arp 214 and friends Yet another Arp from my recent haul, and, again, so much to see. The wide-field landscape image covers about one degree across the diagonal. Before moving on to the narrower labelled eyepiece field, take a moment to spot FGC 1259, the little edge-on spiral at the middle of the bottom edge of the image. This is mag 17 at a distance of 483 Mly. For the larger objects, we have: Arp 214 / VV 1449 / NGC 3718 NGC 3729 Arp 322 / VV 150 / Hickson 56 / UGC 6527 Arp 214 Arp noted this as "Barred spiral, sharp nucleus, narrow absorption lanes through the centre" which is a pretty good summary. This image here compares favourably with that of Robert Gendler using a 12.5" RC, f9, with 150 minutes of exposure, as shown in the The Arp Atlas of Peculiar Galaxies. No hint, though, of the faint extended peripheral structure shown in a hand-drawn diagram along side that, which was based on a separate image from a larger scope. The notes in the atlas say: "NGC 3718 is mag 10.7, 9.2' x 4.4', and SB(s)a pec (Seyfert 2). It is a LINER (Low-Ionization Nuclear Emission-line Region) galaxy, possibly interacting with NGC 3729, following to the E. Called a barred spiral, but the bar is an absorption structure, not stars." NGC 3729 Classified as Sa(bar, ring, mult) this is mag 11.5 at a distance of 67 Mly. It shows really great structure. The labelled galaxy PGC 3400984 is mag 18 at some 2.2 Gly. Arp 322 Looks like every catalogue wanted to claim this group! As well as the galaxy chain (left to right A – E, components B,C,& D are Seyfert 2 galaxies), at a distance of about 400 Mly, there's a couple of quasars sitting in there too, apparently. Real value for money, this area. Tony

Thanks for that. Makes sense to me. Should I be worried that one of the stars directly below it, and at about 1 o'clock from the little galaxy which is PGC 2432364, has apparently moved a bit to the right ... ?

Yes. A smaller unsharp mask width increases the high frequencies in the image... ie. noisier. For the noise reduction, the window effectively defines the scale and amplitude of the background mottling that you can see if you raise the background level too high.

Arp 27 Another one from my recent Arp-fest. This reminded me of Arp 1. NGC 3631 is described as "spiral with one heavy arm" and Arp's notes include the comment "Note straight arms, absorbtion tube crossing from inside to outside of S arm." Not quite sure what I am looking for here, so if someone can point out or explain further, that would be great. I can only find two other galaxies in the wider field with discernable shapes: PGC 34523 – mag 15.6, type Sab(mult), 712 Mly CGCG268-023 – mag 14.7, type E(compact), 489 Mly, with two other galaxies of similar distance in the zoomed field and also a couple of quasars. What's not to like?

Frankly, I think that’s what most of us do! Wikipedia has a good page on unsharp masking: https://en.wikipedia.org/wiki/Unsharp_masking

Both smoothing (noise reduction) and sharpening an image requires the selection of an image ‘scale’ – essentially a length over which to average. Remarkably, unsharp masking is achieved by subtracting a smoothed version of an image from itself. All the more amazing because the technique was developed for analogue processing of image plates in a darkroom. So the unsharp mask radius is simply the half width of a window (probably a Gaussian function) used to smooth the data. The noise reduction approach I suggested that Martin implement, has a sound theoretical background in Bayesian statistics but has been much simplified and approximated to make it tractable for use in an interactive environment. It essentially adaptively mixes a smoothed version of the image (again!), an approximation to the background, with the image itself. There are two choices of smoothing – a Gaussian average, or a median – both of which require a width parameter. This is the noise reduction kernel size. The sharp and TNR (an acronym chosen by Martin to denote Tony’s Noise Reduction) sliders control the strength of the filtering in both cases. The scale parameters, somewhat less critical, are defined on the Configuration Monochrome settings page. Modern noise suppression and sharpening methods are almost all multi-scale implementations, with many more parameters, and much, much more computation time. The somewhat simplistic approaches here are probably as good a fit as any to the EEVA ethos, remarkably effective, and as far as many of us would care to go in the post-processing direction.

Lovely sights! Distances, though, should surely be mega- rather than giga- …?!

@catburglar was kind enough to share with me the raw stack of M51 (and the other images on his "Showpieces" thread, results of which I've shown there.) Here's a couple of attempts I've made, and the slider settings I used. Note that similar results are achievable with a variety of stretches (here using asinh and gamma) but with vastly different positions for the W and S sliders. The auto setting for B invariably makes an excellent choice. In this case, a very light touch on the NR slider gives good visibility of the dimmer parts of the image. Modest amounts of sharp and TNR settings generally suffice. I've used a median noise reduction kernel of size 16, and an unsharp mask radius of 9. Hope this helps. Tony

@catburglar was gracious enough to send me the raw stacks of the above images, in order to investigate the potential of Jocular's latest noise suppression. Here are the results which I managed to get, and which are arguably a small improvement on those he showed. I'll post some further guidance / suggestions for parameter settings on the Jocular thread itself. Tony

Would be most interested in seeing the FITs files of these captures (stacked). The noise looks of a slightly different nature from what I’m used to seeing (maybe pixel resolution?) and I’d be interested in using these as benchmarks for further noise suppression development. Thanks if possible to PM them. Tony

Arp 18 So much going on here. Arp 18 turns out to be NGC 4088, VV 357, and in the wider field we also have VV 1504 and NGC 4085, plus a host of more distant galaxies. The close-up of NGC 4088 shows why it is described as "spiral with detached segments". The catalogue shows it to be 40 Mly distant but 'nearby' galaxy PGC 38369 is much further away at 845 Mly. Even more distant are PGC 3411579 (mag 18, 1045 Mly) and PGC 3411583 (mag 18.7, 2663 Mly). NGC 4085 and vicinity 62 Mly away, classified as SABc(bar) is magnitude 12, and easily outshone by the magnitude 8/9/10 stars in the same field. PGC 3411573 is aroung 3.5 Gly away. VV 1504 This galaxy cluster is about 900 Mly distant, but PGC 3411607 is around 3.3 Gly and magnitude 19. All in all, another splendid area of sky (but there again, what isn't?) Tony