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Martin Meredith

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About Martin Meredith

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    Sub Dwarf

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  1. RGB Filter Exposure Ratio (ASI1600mm-c)

    In case anyone is interested the G2V approach and wonders if there is such a star in their image, the best source I've found for G2V stars is Skiff's Catalogue of Stellar Spectral Classifications which can be accessed here: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk Just stick G2V in the spectral type field and set the max to unlimited on the left menu and you'll get some 2400+ stars. Martin
  2. Last night's 'Grand Tour'

    Thanks Rob. After playing around a bit I can simulate the grainy look by setting the black point just a little too high combined with a fairly aggressive stretch. But the raw data is fine and it is possible (as you also found with DSS) to get smooth results. Here are a couple of attempts using 9 of the 11 subs (you had a satellite or plane fly thru one, and another had eggy stars, although they had remarkably little effect on the stacking). I used median as I don't yet have hot pixel removal. I was hoping to get some hint of the 'loop' from the inverse image but no joy. It really is exceedingly faint. [edit] Just to add. Something I hadn't realised before (though probably obvious ...) is that the black point setting is absolutely critical. I've implemented a fine control that allows shifting the black point by as little as 1 part in 2**16 and it reveals that the difference between a setting at say (arbitrarily chosen ADU number) 2000 and 2010 is remarkable. Martin
  3. Last night's 'Grand Tour'

    If you happen to have the complete set (for the Ambartsumian, say, simply because its a great grouping, but any DSO would be fine) I'd be very happy to have a go at restacking with my new tool (ulterior motive!) and checking whether median vs mean makes much of a difference ... Martin
  4. Last night's 'Grand Tour'

    Theoretically mean will deliver the best SNR and if you're using darks or hot pixel removal there is little benefit of median unless to get rid of transients like satellite trails. The difference is not so great but it might explain any lack of smoothness. Do you save FITs by any chance? If so, I'd be interested to have a play... Martin
  5. Last night's 'Grand Tour'

    A marvellous collection Rob! My favourite (hard to pick) is Ambartsumian's Knot. I'm fortunate in being able to make out the jet from my location (but only with a longish run of subs). I see you're using median throughout. Is this to avoid taking darks? Martin
  6. An unexpected discovery

    Nice report. Don't forget Hickson 92 AKA Stephan's Quintet ;-) Martin
  7. Jocular: a preview

    Messing around with different stretch functions I came across one that gives a very direct visual meaning to stacking subs. This is exactly like the pile of acetates I used to prepare my classes on... Interesting to see that a median stack destroys the effect completely: It makes sense when you think about it, but all the same I was quite surprised at the difference in information content between these two ways of combined subs (at least at the edges where it is most noticeable since the number of subs contributing varies).
  8. Seeing Red - A Selection Of Lesser-Known Carbon Stars

    Very interesting account, thanks. For later in the year V Corona Borealis with a B-V index of +4.4 is worth a look. David, I don't know for sure but I'd agree with your guess. What matters is the entire spectrum (or at least the part that overlaps with that of our visual system for eyepiece observing) and the B-V index is just a crude one-dimensional approach to classify colour, and other colour indices can be used. It would be interesting to dig out spectra for R Lep, W Ori etc and check this out. Also, I note that Wikipedia has the B-V for R Lep at +5.74 but presumably this is at or near minimum. The value in Stellarium I guess is some kind of average? Martin
  9. Distances to PGC Galaxies, available anywhere?

    Incidentally, the modz for the galaxy you're looking at (45+) must be an aberration as it results in a distance of 39 billion light years. There are errors in the LEDA catalogue as in all such enormous catalogues...
  10. Distances to PGC Galaxies, available anywhere?

    The formula I use for converting the distance modulus m as provided by LEDA parameter modz to million light years is 3.261633 * 10 ^ ((m - 25)/5) (the additional 25 term is based on the info here: http://leda.univ-lyon1.fr/leda/param/modz.html) Distances are given in the charts I sent too. Martin
  11. Distances to PGC Galaxies, available anywhere?

    Check out these (the full set of 6000+ is available...). Unfortunately M44 straddles a chart boundary. CNC4512.pdf CNC4513.pdf In general you can get distances for the entire PGC from the HyperLEDA database at the University of Lyon, but some conversion is required. cheers Martin
  12. Jocular: a preview

    I've been mainly working on the stack inspector this week. The idea is to be able to quickly inspect the entire stack, rejecting bad subs (this also applies to calibration frames, though fuller support for calibration is the main task for next week). The stack inspector also allows animation of the subs and/or stack, making it easy to diagnose tracking issues etc. There's the option to restack based on an arbitrary sub in case the keyframe chosen isn't too good. One thing I'm finding a great surprise when going back through some of my old captures is the proportion of 'bad' subs that nevertheless get stacked into something reasonable.
  13. Jocular -- a new tool for EAA

    Thanks Stub & Bruce!
  14. Jocular -- a new tool for EAA

    Thanks, and sure, this is the best place to ask. I'm using Kivy from kivy.org Whether you could call it suitable for rapid development is another matter. The learning curve is quite high I found and some layout aspects are not very logical, but it is very powerful in terms of designing one's own widgets etc and I think well worth the initial effort. The beauty is that it is cross-platform and based around touchscreen ideas, so quite easy to build more natural interfaces.
  15. Bit quiet on VA - hang overs,back skies ????????

    You might recognise the 'ocular' inspiration. Thanks for that! So one of my main requirements during EAA is to orient the image to line up exactly with my charts, and of course it is very ugly doing an arbitrary rotate with rectangle image... Martin