Martin Meredith

I came across these when looking for VV 1487 (which I believe is NGC 3997), not realising this is also WBL 368 (ignore the placement of the WBL 368 label/circle -- still under development!). It really is a lovely field. My shot was not really framed to maximise the galaxy field, though I notice that I caught NGC 4018 -- yet another lovely edge-on.

I see IC 2938 is classified as a Palomar Compact Group too. I think you did get the mag 20 gx. One of the Hickson groups (HCG 50 in UMA) has a mag 20.0 member which is quite tough to get. I just checked my observations and don't have any on that list, unless they're listed under a different name as part of another capture. Martin

Beautiful observation. It's great when you come across something different and better than expected. It happens to me about once a session and is part of the pleasure of this hobby. Great idea for a thread. There's nothing like pushing the equipment as far and deep as it can go. I look forward to checking some of my observations against this list. Martin

Hi Mike I was taking 'stock' (OC aficionados will have to excuse the pun) last night and although I've observed 87 of the 104, some are in mono and others are quite poor, so in reality I have about 20 to go. My plan is to produce a document of some kind recording all the Berkeleys once I've finished them, and try to relate them to the GAIA data release and recent research on which are likely clusters, etc. perhaps organising them in a 2D grid by Trumpler criteria. And of course to correct the RA/Decs. Martin

I had a chance to observe a further 11 Berkeley clusters on Monday, all in Perseus and Auriga. Here are 5 of them, all from Auriga, which itself contains 8 Be clusters. They display some subtle differences as reflected in their Trumpler classifications. In the main I used a minute each in LRGB, in 15s subs. Berkeley 71 is an obvious cluster and the RA/Dec values are in the right place for once. This is a Trumpler-class 2-1-m-* cluster, meaning 'detached, slight concentration; most stars of the same brightness; medium rich'. Be 71 is one of the 3 clusters studied in this article: http://articles.adsabs.harvard.edu/pdf/2004BASI...32..371L There are some interesting stars and groupings in the surrounding field. At around 1 oclock outside the cluster itself is a rather red Mira-type variable, ranging from 12.2 to 14.1 over a 145 day period. At around 3 oclock is a colour-contrast close pair with similar magnitudes (no data as to whether this is just a visual alignment), and near the base at around 5 oclock is an unequal pair of nearly white and orange stars. Berkeley 69 (just below-right of centre here) is somewhat similar in appearance, with a Trumpler classification 2-2-m-*, differing from Be 71 in having a medium range of brightness. This cluster is just a degree or so SE of the much larger open cluster NGC 1893. Be 69 is described in more detail here: https://aas.aanda.org/articles/aas/pdf/1997/04/ds1154.pdf What about Berkeley 70? This one isn't as clear cut as the earlier two, with a classification of 3-1-m-*, the initial 3 meaning 'detached, no concentration' (I sometimes know the feeling...) There is something of a denser stellar field NE of the centre (E meaning left) -- actually more like a river of stars. Archinal & Hynes report a comment that this may not be a genuine cluster. However, more recent studies suggest it is indeed a cluster e.g. see https://arxiv.org/pdf/1207.3244.pdf and that it contains a number of blue stragglers. When I complete the Berkeley catalogue I intend to check with GAIA-based studies for all the Be clusters to see what the latest state of play is. Berkeley 19 is different again. This is a very faint but rich (~150 stars) grouping in the centre of the shot. Perhaps surprisingly, it has the same Trumpler class, 2-1-m, as Be 71, but then the classification scheme appears not to distinguish overall cluster brightness. Really, it needs a longer exposure to bring out more of the colour. I've said on other occasions that I really like these faint clusters. In part it is for the same reason as I like their much more distant 'visual cousins', the Shakhbazian galaxy clusters (I just read that SHK 1 has been mistaken for an OC in the past, and its easy to see why). This one is faint because it is one of the more distant OCs known (an older estimate is around 26000 light years; but GAIA might have updated that). Be 19 is one of two clusters described in this article http://articles.adsabs.harvard.edu/pdf/1984ApJ...286..552C Finally, here is Berkeley 17, class 3-1-r. The richness (~100 stars) is perhaps hard to see in this shot (a little easier in the negative view). The second most interesting thing about this one is the line of very red stars running near-horizontally across the centre of the cluster (some or all may be field stars). But what's really interesting about Be 17 is that it is the oldest known galactic cluster, with an age of around 10 billion years (unfortunately I wasn't aware of this when I observed it otherwise I would have given it more respect (and photons)). As such it has been much-studied. This very recent article is dedicated solely to Be 17 which I look forward to reading soon. https://arxiv.org/pdf/1902.05891.pdf . Thanks for looking Martin

Here's SHK 147 from a couple of nights back. This one looks like either a cross or an arrow, pointing almost due North as it happens (or maybe pointing at the dust shadow on my sensor). The lowest element is clearly stellar. It is hard to find any magnitude or distance estimates. The galaxy at 4 oclock just outside the circle is apparently at 2.5 billion LYs and mag 19.2 and the faintest SHK member galaxy of this 7-strong group is at the head of the arrow, and looks somewhat fainter.

Here's a completely new one for me, found by accident last night as I was continuing my Berkeley collecting... I've been playing around with automatic annotation, so the first surprise was finding not only Be 68 but also part of the larger and supremely unconvincing open cluster Majaess 50. (Note that the positions for many of the Berkeleys in the catalogue I'm using are somewhat 'off' -- I believe the Be cluster to be to the upper right of where it is indicated; but that's a matter for another thread). However, this is the reflection nebular thread, and the odd smudge in the centre of Majaess 50 is indeed such an object. It isn't on my charts so I had to visit Aladin to find its designation: GN 04.41.8. There is only one reference to it in Simbad, namely Magakian's Merged Catalogue of Reflection Nebulae from 2003 but I read the GN refers to the Atlas of Galactic Nebulae published in 1985-1990 by Vehrenberg and Neckel. This latter book sounds like a wonderful thing to examine (I believe it was published in German and English). The close-up suggests that the RN contains a range of tendrils emanating from its centre (I count at least 6). I've no idea if these are artefacts and so if anybody is in the vicinity of Perseus I would appreciate further observations! (I also need to deal with the black stellar artefacts that are present on some of the subs ie not a stacking issue...) cheers Martin

Last night was the first chance I had for a month to test out a new feature in Jocular which detects the presence of L plus narrowband subs, and allows the contribution of the narrowband component to be visualised as a separate layer. The user has control over blending via the saturation slider and also the degree of stretch (modifed gamma function) applied to the narrowband signal, but the rest is automatic (i.e. choose L and Ha from the sequencer and hit capture). While it isn't possible to demonstrate the live effect, here's what the ends of the saturation continuum look like for the Crab (8 x 15s in L + 8 x 15s in Ha) and the Horsehead (11 x 15s in L + 12 x 15s in Ha). The software has to subtract any gradient and the background on the Ha signal in order to avoid producing an overall pink cast, but it is hard to avoid getting pink stars because there is plenty of Ha signal there, so in a sense this is the 'right' result, although visually unappealing.... If there is a chance tonight I'll see if I can produce any results in galaxies with star-forming regions, which was one of my main motivations in implementing this feature. Cheers Martin

Minor point, but I noticed when doing a web search there are at least 4 ways to spell the author's surname that appear in the literature (Shakhbazian, Shakbazian, Shahbazian and Shahbazyan), often with two forms appearing on the same web page or article! Judging from the article I cited it seems the preferred one is Shahbazian, which unfortunately doesn't sit easily with the widely-adopted SHK designation... Martin

Tracking these things down even with 'artificial aids' is a great part of the challenge. It would be no fun at all with a big sensor 😉 Its great to see the Shakhbazian thread building up too. I'd like to think we could observe them all between us over the next few years. The minimum declination is quite modest at -15. I'd love to get hold of the original 1957 article which I believe has been translated. Martin PS Here's an interesting relatively early article in English: http://articles.adsabs.harvard.edu/pdf/1976sgov.meet..251A

Nice observations Mike. Triangulum really is a great constellation. Thanks Mark for that list. The group around NGC 1060 and 1066 that you've observed is a wonderful sight in EEVA and is known as WBL 085. Here's a shot I took a couple of months ago. There's quite a few unlabelled objects that really merit the term 'fuzzy' in this picture.

If you're using Python I imagine you're using SciPy? There are various functions there but this one allows different loss functions (so not exactly custom distance functions, but at least some variations on least squares): https://docs.scipy.org/doc/scipy/reference/generated/scipy.optimize.least_squares.html#scipy.optimize.least_squares Have you checked out various libraries of stellar spectra to use instead of a uniform distribution (these could be weighted by frequency of occurrence) e.g. http://www.phys.unm.edu/~tw/spectra/mk.html No doubt vizier has some to download.

Discuss! 🙂 See also Hubble image from 1999 I believe, which helps identify some of the above structures https://en.wikipedia.org/wiki/NGC_2261#/media/File:Hubble's_Variable_Nebula_-_NGC_2261.png Plus two images from late 2016 and early 2018: https://britastro.org/sites/default/files/styles/xl_image/public/member_images/ngc2261comp.jpg?itok=wnSByP4S Plus an animated gif demonstrating variability between 2013 and 2016: https://www.cloudynights.com/topic/528106-ngc-2261-hubbles-variable-nebula-ver2016/ check out post 7 in the last link re the high proper motion star

Looking forward to seeing the rest of the results. (Love the legends 🙂) Quick question: what underlying distribution are you assuming for your random spectra? Uniform? Martin

Sure, but this is zoomed in from the png (capture predates Jocular), so no interpolation:

Here's a shot from 4 years ago to compare with. I do see some differences, especially on the 'left-hand' (in my picture) edge. I must revisit this soon. Thanks for the visual reminder! Martin

Happy new year everyone! We haven't had any posts in the observing section in 2021 so I thought I'd add one of mine from last November in Triangulum. This is NGC 925, a type Scd barred spiral with very clear, loose, flowing arms, both containing knots of star formation. There is more than a hint of a dust lane to the left of the bright streak at the centre. When this first popped up on the screen my comment to self was 'how come Messier missed this one?' After M33, NGC 925 is the second brightest galaxy in Triangulum. A surface brightness of 23.3 overstates the case I feel, and I suppose comes from dividing by a relatively large area. Mike or others, have you observed this visually? Martin .

There is a huge loss of information when going from any given spectrum to the outputs of a small set of filters. All filter systems are going to be doing a pretty bad job of representing carefully selected edge cases like pure monochromatic sources. Look how 'terrible' the Sloan system is with its near lack of overlap and G-R gap... 😉 https://astrodon.com/products/astrodon-photometrics-sloan-filters/ Given the infinite number of spectra that can, in theory, produce the same output value in any one of these filters, calibration is really the only practical way to use a photometric system. I bring up the Sloan system (and I could equally bring up the GAIA or any other 'science' system) for a reason, because it raises the question of what is the end goal of AP for any particular practitioner (as this will affect filter set choice). Is the goal to restrict colour information to the range and sensitivity of human vision, or is it to take advantage of the wider range/sensitivity of astronomical sensors, and then remap this information into the visible colour space? If it is the latter, then issues of correct colour balance and colour 'reproduction' are moot. Put another way, maybe a quantised rainbow is a fair price to pay for detecting L type stars, to give just one example? We are talking astrophotography (and not spectroscopy and not terrestrial photography) after all. Martin

A few comments 1. We are recording pseudo-continuous spectra in the main 2. The same argument can be made of the Astronomik filters by judicious choice of emission lines, right? 3. This assumes that the filter responses we see are actually accurate or just approximate. I imagine it is quite hard to design a filter with exactly zero transmissivity. 4. The instrument spectral response may well not be uniform. In the domain of AP and to address whether filter sets make much or any perceivable different, we still need to do a proper experiment.

Remember that we are not generating an entire spectral profile for each pixel but instead creating just a single intensity value per filter that is a multiplicative function of the stellar energy spectrum, the filter spectral transfer function and the sensor's spectral sensitivity. A single value. So, for instance, differences in the peak region of the passband (which are very clear in the OSC figure above and the IDAS figure) will also have an impact -- perhaps even a larger impact -- than differences in the amount of overlap at the edges. Baader make it pretty clear why they leave a gap in the G/R region. Other manufacturers will make other design choices. Ultimately, whether any of this makes much of a difference (after correct calibration) remains to be demonstrated by a proper visual psychophysics experiment -- don't hold your breath. Personally, I very much doubt it does make a noticeable difference. Martin

Ah, ok. I'm using a Newt so am spared that issue. I used to use an achromat and the star bloat (particularly at the UV end) was terrible even in an EEVA context. My 7 position EFW currently has RGBC, H-alpha, dark and a spectral grating. I've kicked out the OIII and SII for now 😉. Martin

Some additional Winter targets that are favourites of mine (usually in 10x50s) are M41 just below Sirius and the highly constrasting close pair of clusters, M46 and M47 in Puppis. These are a little low down perhaps but worth seeking out. There are a number of bright NGC open clusters in Puppis too. Martin

Hi I have the Baader set and am very happy with them, although I have not compared them to anything else, and my only use is in an EEVA setting rather than AP. One comment: I don't know if the Antlia set has a C filter, but I find the C filter very useful in the Baader set. The L filter cuts off quite a bit of energy in the IR range , and this can contribute useful photons to galactic imaging. Of course, how much extra energy is available to be picked depends on your sensor characteristics in this region too. cheers Martin

If you apply your (non-contentious) statement that our atmosphere reddens ('de-blues') by scattering, is it so hard to accept that the same scattering of shorter wavelengths by dust beyond our atmosphere leads to reddening (browning, and not greying) in Olly's image? Martin

https://clarkvision.com/articles/color.of.nebulae.and.interstellar.dust/ is quite interesting (it aint brown enough!). Also this: https://clarkvision.com/articles/astrophotography-color-and-critics/ Martin