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iansmith

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About iansmith

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    Star Forming

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    Swindon
  1. Thanks. I would agree that the 10s exposures aren’t enough to affect the blurring due to seeing and on a mount like the Mesu they don’t really help with tracking errors either. But it’s nice to know that, rather than suspect it, which was the point of trying the experiment Cheers, Ian
  2. Thanks MarkAR, glad you liked it. Cheers, Ian
  3. Also known as the Eskimo Nebula, Clown Nebula, PNG197.8+17.3, and a great many other names, I used this nebula as an experiment in short exposure imaging. Instead of exposing for 5 or 10 minutes I thought I would try with 10s exposures in each of the narrow band channels to see if I could get any higher resolution. After calibration and stacking the nebula and stars have been processed separately. For the nebula exposures were: Ha: 720 x 10s; O3: 720 x 10s; N2: 720 x 10s The N2, Ha and O3 images for the nebular were assigned to the RGB channels as: red: 50% Ha and 50% N2; green: 50% Ha and 50% O3; blue: 50% O3 and 50% Ha which is kind of weird, but it produced a pleasing (to my eyes) colour combination. For the stars they were: red: 15 x 120s; green: 15 x 120s; blue: 15 x 120s Did the experiment work? In a word: no. The 10s exposures were too long to freeze the seeing, but I had wondered if they would reduce the blurring caused by other errors, such as tracking. However, I don’t think this image is any better than I could have produced with 5- or 10-minute subs. The Mesu is a good mount and can be easily guided for 20 or 30 minutes if required. I suspect it could go for an hour, but I’ve never had the patience for that test. In fact, I suspect that the longer subs would have produced a better image as I would have gone for a much longer integration time: 8 to 10 hours per filter rather than 2. That would have increased the SNR and given a much nicer image. I didn’t go for so long with the 10s exposures as that would have left me with a huge number of subs to process and it was tedious enough as it was with 720 per narrow band channel. As it was, processing the short exposure subs proved to be a lot of effort. PI complained that there weren't enough stars for it to register the subs. In the end I found and used SIRIL to stack them into a single sub which I then processed in PI. But even SIRIL could only register one on star. In short, I think short exposure imaging would be of benefit for people with mounts that cannot handle 5 minute plus exposures (and have cameras with better gain control), but it offers little benefit to me and is definitely not worth the extra hassle involved. But at least now I know that! Anyway, here is the image, I hope you like it: And do please do let me know if you have had any better success with this style of imaging. Cheers, Ian
  4. Hello, Below is a link to my image of the little PNe Haro 3-75. Details are on the astrobin page. I hope you like it. Cheers, Ian
  5. I go with Ha and N2 if the Moon isn’t too close to my target. If I already have those, or the Moon is too close then I pick another target. Don’t want to waste the clear nights if I can avoid it. Cheers, Ian
  6. Thank you tooth_dr. Cheers, Ian
  7. This is my image of NGC 40, a planetary nebula in the constellation of Cepheus, put at between 1100 and 4077 light years. North is to the left, east to the top of the image. NGC 40 is an interesting planetary nebula. The central star is classed as a WC8 star. This is a Wolf Rayet class star, that has had high mass loss in the past, generating fast winds of 1800km/s to 2370km/s. It has a high surface temperature but the gasses in the planetary nebula show low temperature ionisation features. The suggestion is that there is a shell of Carbon material that is blocking some of the ionising radiation. Visually I’m told that the nebula doesn’t respond well to O3 filters, so it was surprising to see a quite strong O3 signal when I used that filter. You can’t really see that in the image, except for a small part that peaks out on the southern (right hand side) of the image. It is there but it is hidden (quite literally according to some professional data) by other larger shells of material. To add further interest to this object, the jet like feature on the southern side, does not behave as expected when it is studied spectroscopically. Exactly what is going on with this is still unexplained. Part of my interest in this object stems from the fact that it has not one but two haloes that surround the main barrel like structure. These halos are very faint: the inner one is about 200 times dimmer than the main structure. I have captured some of this halo, but there is more to get. Professional images measure this as being at least 90” in diameter, but I have only ~68”. The suggestion is that this is material from a fast wind that has broken through the main structure and is now escaping into space. Spectroscopic studies show this structure to be quite complicated and possibly a hollow shell. Beyond this halo is an even fainter one, about 4’ in diameter. This is thought to be the material ejected from the stars Red Giant/AGB phase. I have only been able to capture the bright, knotty parts of this halo to the north and east. The rest of it is too dim to be seen in this image, even with some extreme stretching. I will have to come back to this object later this year to capture another 8 to 10 hours per filter, in the hope I can get more of these halos. Maybe even 2021 as well! Further to the south you can see some of the brighter knots of the supernova remnant CTA 1. This structure is much further away than NGC 40 at a distance of 4500 light years. My image was taken between September and December of 2019 using an Edge HD11 and a QSI6120 camera at prime focus, binned 3x3, mounted on a Mesu 200. NB: 160x180s in Hα, 20x180s in OIII, 42x600s in OIII and 48x600s in NII blended as: NII, Hα and OIII for red, green and blue respectively. BB: 15x120s in red, green and blue. The wacky selection of exposure times was just down to me experimenting a bit to see what worked well. I think from this that although the 180s images produce usable images there is just too many of them. The 600s images work best and I think that I will stick with that or longer in future as seems appropriate. The stars were removed from the NB images and the PNe was removed from the RGB images. These two images were processed separately before being combined to create the final picture. Normally I would process all the NB to a finished linear image for each filter and then combine those into a narrow band colour image. This worked fine for bi colour images but has given me a great deal of trouble with 3 filters. This time I tried combining them into a colour image after just a little linear processing: gradient removal, deconvolution and a linear fit on the N2 and O3 images. This worked out much better. I hope you enjoy, comments and criticism welcome.
  8. Thanks x6gas. It’s 7 hours per narrow band channel, so 22.5 hours in total. Cheers, Ian.
  9. Thanks for the info MartinB. I doubt I will pursue this idea much further. For me there are other issues as well. For example, one reason for using ONAG was to avoid having to fiddle around finding a suitable guide star which I would have to do with an OAG. Having said that, does anyone have some real world performance figures with it? My current system gives me ~0.4” to ~0.7” rms with ~0.7” to ~1.3” peak to peak (depend on seeing conditions). Would an AO unit improve on that? If there was a chance of significant improvement then I would be willing to reconsider an OAG. Cheers, Ian.
  10. Thanks DaveS. I like to go deep with these objects to see if there is anything interesting surrounding the PN such as a faint halo or some such. I have so far only tried N2 on this and NGC 6058, which you can also find in my astrobin page. I’ve not had it very long and with the poor weather we’ve been having I haven’t had much chance to use it. Currently imaging NGC 40 with it, but not enough data yet to present it. Cheers, Ian
  11. Thanks MartinB. I have thought about adaptive optics, but as you say I’d need to find a bright guide star for it to work on. I have been wondering about if it could work, looking at a star from a larger field of view. In other words, could it work if I had a separate guide scope that was looking in the same direction, but was viewing a square degree of sky and then adjusted based on that. Will have to think more on that. Cheers, Ian
  12. This is my image of K1-16, a planetary nebula in the constellation of Draco, between 5200 to 7000 light years away. I have yet to come across much information about the PNe itself, other than its size which is put at between 1.6’ to 2’ across. It lies in front of a very distant galaxy cluster and to the south (left in my image) there is a bright 14th mag quasar, HB89 1821+643 which is part of the cluster. The quasar is 3.3 billion light years away but almost as bright as the central star of K1-16 which puts the power of quasars into perspective. The central star is DS Dra and judging by the number of professional papers it is of great interest to professional astronomers. It is classed as a PG1159 variable star, one of 20 such stars and only one of 7 which are the central star of PNe. These types of stars exhibit a small amount of variability (~±0.01 magnitudes) which comes and goes. It’s also hydrogen deficient and carbon rich, showing the same kind of spectra as WR stars. WR stars are normally very heavy, but as the central star of a PNe (CSPN), DS Dra must have been below 8 solar masses to start with, which is much lighter than most WR stars. It is thought to have just finished it’s AGB phase and is now transitioning to a white dwarf. There is a suggestion that it underwent a late Helium flash which dredged up and expelled a load of Carbon into the surrounding environment. The current mass is reckoned to be about 0.65 solar, with a surface temperature of 140,000K. This high surface temperature probably explains the high terminal velocity of the winds blown off this star. They have been measured at about 3800km/s. The mass loss rate is now fairly low, estimated at ~10-8 solar/year. This fits in with the expected behaviour of a post AGB star. My image was taken between July and September of 2019 using an Edge HD11 at prime focus and a QSI6120 camera, binned 3x3, mounted on a Mesu 200. NB: 42x600s in Hα, OIII, NII blended as: NII, Hα and OIII for red, green and blue respectively and then spent ages messing about with saturation, hues, etc to try and get a pleasing colour image. BB: 15x120s in red, green and blue. The stars were removed from the NB images and the PNe was removed from the RGB images. These two images were processed separately before being combined to create the final picture. I would welcome any comments or criticisms, especially on how to improve. Cheers, Ian
  13. Thank you tooth_dr and MarsG76. Cheers, Ian
  14. NGC 6058 is a small PNe in the constellation of Hercules at a distance of 3.5kpc (11,415.47 lightyears) with a maximum diameter of ~45". I have found one paper that has done a detailed study of this PNe: https://arxiv.org/abs/1304.3248 According to the paper, there are 3 elliptical outflows, more or less in the plane of the sky. These show strong OIII emission (coloured blue in my image) indicating the presence of shocks at these locations. This suggests they are related to collimated outflows from the central star that occurred ~4800 years ago, ~4400 years ago and ~5900 years ago and currently have have polar velocities of ~68kms-1. The bright central arcs appear to be a ring, but spectroscopic studies show it to be a limb brightened barrel like shell similar to NGC 7354. It does appear to be more difficult to analyse so it’s position angle, relative velocities, etc are less certain than the other outflows. Its inclination to the plane of the sky might be anywhere from 50° to 130°. Its age is estimated to be ~3400 years old making it the youngest of the outflows, but this may be an upper estimate. The bright ring like structure is probably where it is interacting with the earlier outflows particularly their equatorial regions and is protruding through them and this is causing the gasses to slow down which would make it younger than suggested. These separate outflows suggest that the star underwent 4 different ejection episodes, with the collimation axis precessing between episodes. There are also two regions of enhance emission and some faint structure within the bright ring. As this is also present in the pro’s image I don’t think it is an artefact of my processing. On a purely speculative note of my own, this reminds me of the filamentary structure that can be seen in HST images of the Eskimo Nebula. In that PNe the filaments are thought to be the edges of bubbles of gas created by shocks as the outflow breaks out from the polar direction. https://www.astro.umd.edu/~jph/eskimo.html shows this for the Eskimo Nebula. Perhaps something similar is going on here? The image is composed of narrow band data for the PNe and broadband data for the stars: NB: 60x300s in Hα, OIII, NII blended as: 0.5* Hα + 0.5*NII, 0.4* Hα + 0.6*OIII and 0.15* Hα + 0.85*OIII for red, green and blue respectively. BB: 15x120s in red, green and blue. The stars were removed from the NB image and the PNe was removed from the RGB image. These two images were processed separately before being combined to create the final picture. I hope you like the picture. Cheers, Ian
  15. Very nice image. Cheers, Ian.
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