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Martin Meredith

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About Martin Meredith

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    Sub Dwarf
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    Mountains, cycling, growing stuff
  • Location
    Northern Spain

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  1. Back in December I posted about extreme runaway and hypervelocity stars, which are stars that have somehow reached a velocity that will allow them to escape the clutches of our galaxy one day. There I focusing on one called HVS 5 which is believed to have gained exit velocity by an encounter with the super-massive black hole at the centre of the galaxy. Out of the 20 or so HVS that have been identified, one stands out as different from the rest: HVS 2. This star is also known as US 708 due to its radial velocity of 708 km/s. At an overall velocity of 2.6 million miles per hour it is the fastest known star in the galaxy. Apart from this claim to fame (and somehow related to it!) HVS2 is special because it is thought not to have been caused by an encounter with the black hole, but instead is believed to be the result of a supernova explosion. Models predict that HVS 2 was a member of a binary star system, one of whose components exploded, sending it out at the enormous speed we now observe. HVS 2 is in Ursa Major, not far from galaxy UGC 5091. It is pretty faint at Vmag = 18.8 but is within reach of EAA techniques. You can find it at 9h 33' 21" +44 17 06. Here's a shot from earlier this year. I waited until this week to complete the story in order to capture another object that links to the HVS 2 story. The favoured ejection scenario for HVS 2 is actually a double-detonation of a white dwarf. The mechanism suggested is that helium is deposited on the white dwarf surface by accretion; this ignites, triggering the explosion of the white dwarf and leading to the ejection at hypervelocity of the helium star. Remarkably, a candidate system capable of such double detonation has been discovered. This is known as CD-30 11223 and lies in Centaurus at a declination of -30 degrees not too far from NGC 5494 (exact position: 14h 11' 16" -30 53 4). The star is quite bright (Vmag 11.9) and is shown on this single 30s shot from earlier this week: Admittedly, it is not much to look at, but consider a fascinating paragraph in the discovery article linked to above, pointing out that it is by far the nearest known SN Ia progenitor to Earth, and that when this star explodes (in an estimated 42 million years time), it will be visible from Earth with an apparent magnitude as high as -7.6, as bright as the 1006 supernovae, which itself was the 'brightest stellar event in recorded history'. One for future generations to look forward to. For more details, I recommend the web page of Warren Brown, who discovered the first HVS. It includes a link to his 2015 HVS article in the Annual Review of Astronomy and Astrophysics. Martin
  2. M51

    Thanks Jannis. I typically don't post-process, but on this occasion I did look at the effect of noise reduction in Nebulosity, but I didn't like the result...
  3. M51

    Skywatcher Quattro 8" f4 mounted in alt-az on AzEQ6 + Lodestar x2 mono camera. Due to field rotation I was forced into short exposures on this one (24x10s). This is unprocessed (captured at the scope using StarlightLive). There is some noise in there (probably read noise) but I left it in to show what is possible without processing if you don't mind that kind of thing! Martin
  4. I've found that I need much more RGB than L, plus increasing saturation helps. I've more or less given up the LRGB experiment for the moment because I think it takes too much time and takes away from the live element. But I'm a firm believer that it is possible in principle to do it live with the appropriate algorithms that treat luminosity and chrominance separately. For certain applications like the H-alpha+L combination I think it works well, although again quite a lot of H-alpha is needed to overcome the dominance of the L signal.... You could experiment with laying a base of a small amount of luminance and then add RGB.
  5. Excellent clear night yesterday even though it didn't get fully dark until 11.30 (pretty tired today at work...). The SQM reading reached 20.5, which is unusual for where I live. I had a long session looking at galaxies, galaxy clusters, globulars, an open cluster and Tabby's Star. Here are a few flat galaxies (all members of the Flat Galaxy Catalogue, FGC) in Virgo. NGC 4437 = FGC 1455 is quite bright and bears some resemblance to the Whale but without the Pup NGC 4430 = FGC 1423 is quite a bit fainter. With time the core became visible as a brightish spot NGC 5170 = FGC 1626 is my favourite of the lot, not just because of the almost perfect shape and bright core, but because of the 'ear-ring' like asterism to the lower right. Usual kit: alt-az mounted Quattro 8" f4 Newt, Lodestar X2 mono, StarlightLive software Thanks for looking Martin
  6. Welcome to the club! It will be interesting to hear your experience with RGB, esp. with respect to the nonlinear modes. Do you have an electronic filter wheel? Luminance can be overwhelming, its true. Laying down a luminance base first then adding quite a lot of colour seems to work, as does turning the saturation up (although for best colour in RGB mode I leave the saturation and hue controls alone). Martin
  7. Great work Bill. I'm inspired to take a look for this comet tonight if the forecast holds out. There are a bunch of other brightish (well, EAA-accessible) supernovae out at the moment. BTW I've noticed the same kind of diagonal banding (only when the contrast is turned up) on my shots when I use short exposures and don't use darks. Did you take darks? I suspect it is the bias signal that will be eliminated as part of dark subtraction. Martin
  8. M5

    Thanks Rob. I was looking for a target with some good colour contrasts for live RGB imaging and it is little early for the likes of M9, so I was glad to see a few yellow suns in the globular. Very short subs worked well here. Next time I will collect more data.
  9. M5

    This is M5 in Serpens, using 5s subs, 18 in total (6 = 30s in each of RGB, Baader filters), with live spectral combination (i.e. at the scope, no post-processing) using Paul Shear's StarlightLive software. Alt-az mounted 8" f/4 Skywatcher Quattro, Lodestar X2 mono camera. Perhaps a bit on the dark side.... Martin
  10. Thanks David for your informative feedback which I'm sure will be helpful to many people considering entering this area. Looking forward to some pics! Martin
  11. Just as a laugh, I tried out the new 1ms minimum exposure tonight on Jupiter and it was still far too bright. Even with RGB filters I couldn't make out any details. So I used an H-alpha filter and lo-and-behold managed to see the belts! Martin
  12. Nice shots, both. Nonlinear is definitely the way to go for globulars. I tend to use nonlin for everything, although perversely I've found dark nebula sometimes respond best to linear... Martin
  13. Great work Don! That looks like a bright one (and maybe relatively brighter in your shot than the discovery image?) Martin
  14. Hi Miguel A warm welcome from just up the road in Vitoria (where today it snowed ;-) Martin
  15. Check out this matrix here which Dr D sent me some years ago. Martin