Martin Meredith

As I see it, the problem here is that Montage consists of binaries (as opposed to source code) for Linux/OSX (these binaries being created from the original Montage C code). So even with a Python distribution (+/- Anaconda) on Windows there is no way to run the code without going back to the original C and going through the build process. BTW Anaconda is a distribution containing lots of mainly scientific Python code (plus a few tools to help install new stuff). I used to use it but it is rather bloated. An alternative is miniconda, or -- my preference these days -- just download/install the required stuff as and when you need it, using pip. Martin

Just catching up on other observations from April... Here's a 5-minute-ish capture of a field in Coma containing VV 61 and much else besides. VV61 is the pair type Sab NGC 4098 and a mag 15 PGC companion, at around 360 million light-years. There are 5 other NGC galaxies in the field. NGC 4092 is a nearly face-on Sab type at 326 MLyrs, so perhaps part of the grouping. NGC 4093 is an elliptical, also at around 344 MLyrs, as is the compact elliptical NGC 4095 (346 MLyrs). The pair NGC 4091 and 4089 are also listed as being in the 350-370 MLyr range. This latter pair is also a member of the catalog of overlapping galaxies, important astrophysically as they allow estimates of the foreground galaxy's structure to be determined based on the appearance of the background galaxy. Completing the interest in this rather small field (we're looking at around 15 x 15 arc mins) is a Palomar Compact Group which is listed as having 4 members, though there are at least 6 galaxies in the general area circled. The brightest of the group is mag 17.8. I don't have a distance estimate for the PCG group but I suspect it is rather further away than the NGC grouping. The rather unprepossessing VV 62 is just outside the field for those with larger sensors. cheers Martin

If you search for fringe killer filters there are a few threads here and elsewhere that cover the specifics. I must admit I moved on to a reflector and gave the achromat away so I never explored these filters myself. Gain is a simple multiplier that can be thought of as spreading the count of photons captured at each photosite (~pixel) across the bit range of the camera. Setting the gain is analogous to setting the recording level on a microphone amplifier. Set it too low and your recording occupies just the lower bit range, so you are not making effective use of the bits; while you can boost the resulting digital signal after you capture it, you are boosting a highly-quantised signal, which ends up sounding louder but also noisy. Set the gain too high and you are in danger of saturating. Setting the gain is a bit of an art. [Aside: forcing a user to set the gain is a hack due to the low bit depth of most CMOS sensors.... personally, I prefer 16-bit CCD cameras with fixed gain -- one fewer decision ;-)]

Are you using an achromat refractor for these? If so, you can cut out some of the star bloat (eg in the last shot -- M103?) by using a filter. I started with an achromat and eventually switched to a Newt to get tighter stars. Darks will help if you have either amp glow or hot pixels. I don't see much of either in your images. You can also do hot pixel removal without taking darks. Flat will help if you have dust shadows or vignetting. I see some vignetting so I'm guessing flats will help, though many find them a bit of a pain. If you do take flats, remember to take bias frames too. Having said that, I think the results you're getting are pretty good. Possibly you could cut back on the black point (ie darken the background) a little. Could you say more about your equipment and the current exposure times (number of subs and total exposure) you're using? Martin

It won't be a total washout. One of the benefits of EAA is that reasonable results can be obtained in conditions that would be considered marginal or near-impossible visually. To give an idea, I generally align my scope during twilight and then do a goto to a nearby object to check alignment, and it is surprising how good the view is even though the sky is nowhere near dark. It's worth choosing your objects carefully though, as faint galaxies may indeed be washed out, though brighter ones will still show structure. Good targets are open clusters -- fortunately plentiful during the summer -- and globs, also in season. (I use alt-az too) good luck!

Its a while since we had a VV entry, so here's one: VV 179 in Coma The VV pair (or triplet) designates the two obvious ellipticals lined up vertically near the base of the image. The starlike object to the right of the upper galaxy is also a suspected elliptical with a similar distance estimate. What makes the field compelling is the number of other 'major' galaxies present (although they are nearly all ellipticals), as well as a flat galaxy catalogue member and a host of faint galaxies. This north-up annotated shot shows some of them. The PGC galaxy labelled has a B-band magnitude of 20.0 and I can just about make out one at mag 20.6 at around 6.5 billion light years distance, so it must have been a reasonable night for seeing and transparency. All in all an interesting part of the sky to visit.

Another great haul Bill. I dug out my Arp 335 and turned the stretch well up to see if I could extract a bit more from the cores as well as the lower curved tail. There does seem to be quite a bit of detail though some might be foreground stars. There are loads of galaxies in the field, the labelled ones having mags ranging from 16.2 to 18.6. They seem to belong to very different groupings judging by their distance estimates, some around 360 MLyrs (same as the Arp galaxy itself) and others up to 1.6 billion Lyrs. The Saturn-like galaxy (PGC 93108) looks to be part of the Arp group, physically-speaking.

I was intending to focus on Arps last night but as usual when browsing the charts I got distracted by this very thin sliver of a galaxy in Coma that stands out not just for its fine linear appearance but also for its relative isolation. Not surprisingly, it is a member of the Flat Galaxy Catalogue and also denoted UGC 7321. We're seeing this galaxy very nearly edge-on. There is some clear mottling visible along its length. According to Simbad it is a well-studied galaxy as its edge-on nature allows a good estimation of the luminosity profile which in turn feeds theories of galaxy evolution https://simbad.u-strasbg.fr/simbad/sim-basic?Ident=fgc+1403&submit=SIMBAD+search

Here is Arp 242 from last night, one of several I observed in Coma. Better known perhaps as The Mice, this pair of galaxies is classified as 'appearance of fission'. The two galaxy cores have some structure in the shot, and the fainter tail of NGC 4676B is an interesting challenge to pull out in this 5 minute view. (Info on shot except for binning, which was 2x2; and ignore seeing estimate in favour of automatically estimated FWHM value)

What a fantastic session (and great to see the Lodestar X2 delivering such excellent results -- it must be at around 10 years since it was released). I haven't done much EEVA recently, preferring some simple 10x50 binocular views, but your post inspires me to get the kit out under the stars again. Arp 283 is a particular favourite due to the placement of the pair of bright stars, echoing the galaxies and somehow emphasising the differential in distance. Martin

It isn't often I get down as low as Fornax, but the opportunity arose this evening to observe NGC 1360 just after transit at around 18 degrees above the horizon. I had no idea what to expect and could barely believe what appeared -- a large and relatively bright blue oval, the likes of which I've not seen anywhere in the sky. This is known as the Robin's Egg Nebula, and is a strong radiator of Oiii. I'd love to see this from lower latitudes. It is rather noisy looking through the murk (check out the FWHM) and I had to turn the gain up which meant I hadn't any suitable darks to cancel the amp glow at bottom left, but this is EEVA... There's a great image here: https://en.wikipedia.org/wiki/NGC_1360

From an hour ago (sequence of 15s subs)

I found this photogenic configuration by accident earlier tonight. IC 239 is a delicate face on spiral surrounded by a lovely asterism of mag 10-12 stars (not part of a cluster as far as I can tell -- very different parallaxes but they happen to glow at a similar apparent magnitude). The galaxy is of type Scd, hence the evident far-flung arms.

Not sure if we've had Arp 135 (NGC 1023 + 1023A) yet but here is a 5m capture from tonight. This is now thought to be an interacting pair (Arp classified it as "nearby fragments" and it had also been hypothesised as an asymmetric spiral arm). See [1] for an early paper. The main galaxy is type SB(rs)0, and its companion (irregular Magellanic type?) lies at the right hand end in this shot. In Aladin the companion has a distinctly blue/grey tinge, making me wish I'd added some colour to this capture. A 2022 paper [2] found 523 globular cluster candidates in NGC 1023, finds 2 spiral arms, and suggests that the centre has been displaced due to the interaction. Following the chain of stars beyond at the right hand end there is a star which appears to be bathed in a fuzzy glow which, according to Aladin, is the mag 16.3 9(R) galaxy PGC 10169. [1] [2] https://www.aanda.org/articles/aa/full_html/2022/08/aa42402-21/aa42402-21.html

I caught that too. Fascinating topic that I knew little about. There was only one point where Melvin was a bit lost for words... Next week's should be equally interesting. I visited Brahe's observatory on Hven many years ago. Its a great day trip (boat then cycle on the island) from Copenhagen.

I'll repeat my regular caveat that Jocular isn't really designed for OSC cameras. As you've probably gathered, the temporary solution currently implemented is to split each RGB into 3 subs so that it can go on to treat them as coming from separate filters and flip into LAB-space. I guess there are better ways of doing this (less memory/compute intensive) but I haven't had the time to investigate as yet. cheers Martin

The alternative forum has more traffic and posts, and is a great place for equipment advice. Oddly though, I've always found that -- even accounting for fewer posts -- SGL has more information on, and discussion about, the DSOs being 'observed' using EEVA techniques. Its good to have complementary fora!

The modified gamma function is worth considering perhaps s = g / (a0 * (g - 1) + a0 ** (1 - g)) d = (1 / (a0 ** g * (g - 1) + 1)) - 1 y[x < a0] = x[x < a0] * s y[x >= a0] = (1 + d) * (x[x >= a0] ** g) - d where g is the exponent and a0 is the x-value below which the regularised part comes in (s is the slope). This is Python code so ** is ^ I use this in my EEVA software to stretch the RGB channels semi-automatically (user supplies g only) so that the user doesn't have to mess around with the individual channels and can focus on stretching luminosity.

Nice work Simon -- I'll take a look at 'Auntie' myself. Yes, fierce is the word. It really brings out faint galaxy features/tidal tails etc when used interactively in an EEVA-observing context but you wouldn't want it in a prize-winning AP situation, and most likely does crazy things to colour too.

After some experimentation I've been using b = (1.02 - y) / 50 where y varies from 0 to 1 to control the degree of stretch (1 being most) and a = (1 + b) to ensure the output goes from 0-1 too These values give a pretty aggressive stretch for my (EEVA) purposes, but I suspect if the goal is to match arcsinh other values will be needed. No doubt some optimisation routine could be used to find the best match, or perhaps even some progress could be made analytically.

An exceedingly simple function I use for stretching is f(x) = a * x / (x + b) for suitable choice of a and b. I've not seen it used elsewhere in an image context (*). A quick comment on the x^p family: it gets noisy near x=0 due to the gradient going to infinity. There is a modified gamma function that handles this by linearising the low intensity part of the range, although it adds a little to the computational complexity. I believe this also addresses the point Olly is making to some extent. Martin (*) This function was inspired by a 1985 approximation to the input-output function of the turtle cochlea hair cell that I picked up in the course of my doctoral research decades ago. The auditory system has to solve a similar problem to AP: compressing an enormous range of values into more meaningful equally-discriminable units.

Just checked my observations and I've not seen either of these. You've managed to resolve some interesting detail in the individual members, especially member 6 of SHK 365 and member 8 of SHK 142. BTW I'd always believed that the numbers were ordered by decreasing magnitude but that doesn't appear to be true for the 365 group.

Its a value-for-money field, that's for sure. Here's mine from 2020 (doesn't add anything to yours but interesting to see what a smaller scope can do, albeit with a longer exposure)

Good advice on aperture Geoff. I'd add that even with a bigger scope / longer focal length there is no guarantee that seeing will be good enough to resolve the additional detail.

Ah, you're right, no it doesn't. ROI is implemented at the point of capture at present (in fact, I use the zwoasi function to set the ROI). It is possible in principle to do it with incoming subs but it will be important for consistency to do it prior to the main capture ie using framing subs, which doesn't necessarily fit with Dan's workflow.