iansmith

Hello, I’ve been using the ONAG now for 5 years or so with my Edge HD11 at prime focus. Typically I get PHD2 rms figures of 0.5”, but that is a much due to the mount as the ONAG. Guiding works very well. In general you will not lack for guide stars. I would recommend the use of a CMOS camera as the near IR view of stars can make them quite faint and CCD cameras with their fixed gain can struggle. Having said that I used a Starlight Xpress Ultrastar for years, but then I have a mount that can image without needing corrections every few seconds so I just upped the exposure time. You can also bin. I would recommend a CMOS camera as you can wack the gain up to max to help as well as bin the pixels. I have just change from the Ultrastar to a Player One Apollo Max: 9um pixels and a much larger field of view compared to the Ultrastar. The backfocus can be an issue, but (on an Edge HD at least) the distortions that come from being too far back work their way from the edge of the field in, so it depends on how far out your are and how big an imaging camera you are using. A full field camera might have issues, a 1 inch chip, not so much. It is one of my most favourite pieces of astro kit. Guiding the Edge HD with it has been easy and the ability to focus continuously in real time is absolutely great. Expensive, yes, but worth every penny as far as I’m concerned. Cheers, Ian.

Thanks all. For your suggestions. I was indeed worried about oil dripping onto the mirror, grease/Vaseline sounds like a great idea. Cheers, Ian

Hello All, I have an Edge HD11 which I’ve been using for about 5 years now. It lives on a permanent mount in the observatory in the back garden and rarely needs much work done on it. Recently, I checked the collimation and decided a few adjustments were required. I noticed that the collimation screws are hard to turn and I have been wondering if it would be a good idea to put a drip of oil onto them. Has anyone done this, or done something else to help them loosen up a bit? Cheers, Ian

Hello, this is my version of the planetary nebula Abell 16 in the constellation of Lynx. Imaged with the Edge HD11 and QSI 6120 camera at prime focus, binned 2x2. In this image north is to the right and east is to the bottom. Astrodon 3nm narrow band filters: 60x1200s for each of Ha, N2 and O3 making 30 hours in all. The narrow band channels have been blended according to the following scheme: Red = 0.9*Ha+0.1*N2, Green = 0.5*(Red + O3), Blue = O3. The background stars are 30x60s each in red, green and blue. At a distance of 2413 lightyears, Abell 16 is one of the few examples of a spherical planetary nebula. Assuming that the distance is accurate (which is rarely the case for planetary nebula) it's actual diameter is ~3 lightyears with the gasses expanding at speeds of ~37km/s. Planetary nebula are the result of a slowly expanding shell of gas ejected by the progenitor star in its AGB phase, interacting with the faster stellar wind given off when the progenitor star’s core is exposed. Often these winds are shaped by magnetic fields, companion stars, the interstellar medium and other effects, but in this case the gases appeared to have expanded equally in all directions. Given that this interaction results in the turbulent mixing of bubbles of hot gas, I have deliberately highlighted the layers containing structures with a size similar to the FHWM (corresponding to a resolution of 2.2" ) of the image to give the impression of a roiling, boiling sphere of expanding gasses. I hope you like it.

Thanks Mick. There are so many objects out there (and not just obscure planetary nebula) waiting to be imaged that it seems a shame to just stick to the usual suspects. I find it quite exciting to image something new and see what’s there. It is, as much as anything else, a voyage of discovery 🙂 Cheers, Ian.

Hello all, This is my latest project M 2-55: M 2-55 is a planetary nebula in the constellation of Cepheus, some 2254 light years away. Imaged with the Edge HD11 and QSI 6120 camera at prime focus, binned 3x3. Astrodon 3nm narrow band filters: 40x900s for each of Ha, N2 and O3 making 30 hours in all. In this image north is to the right and east is to the bottom. The image is composed of Ha for the red, N2 for the green and O3 for the blue channels for the whole image. I didn’t really have time to get RGB data for the stars. After linear fitting the Ha and N2 to the O3 I have blended the images according to the following scheme: Red = Ha * (1-N2), Green = N2*(1-Ha), Blue = O3. The idea here is to make the Ha strong in the red, where the N2 is weak and the N2 strong in the green where, the Ha is weak. Hopefully, this has allowed the N2 and Ha structures to be seen together, rather than having the N2 swamped by the Ha. The arc of material that runs from the SE to the SSW is extremely faint in my raw data, but it does exist. Its presence has been detected by professional astronomers (Chih-Hao Hsia et. al, March 13th 2020, “Discovery of Extended Structures around Two Evolved Planetary Nebulae M 2-55 and Abell 2”). Because it was so faint (just barely above the noise in my data) its presentation here has used a bit of artistic license. It shows up (just about) in the Ha, weaker in the N2 and not at all in the O3. I wanted to show this structure as it is believed to be formed from the earlier AGB wind material being compressed by the motion of the PNe through space. On the PNe itself you can clearly see the two bipolar lobes. The lobe aligned approx. NE to SW is approx. 67.2” x 36.6” and the other, aligned approx. NW to SE is 65.5” x 34.3”. This suggests they formed within a short period of time. Where the two cross one and other we can see lumpy features, esp. in the four corners. These regions may be projection features where the two lobes interact. For some reason, the NW to SE lobe is more prominent in O3 than either Ha or N2, the opposite to the other lobe. In either case, both have a well-defined edge. The central region is large and probably carved out by increasing thermal pressure as the PNe evolved. This object is thought to be quite old. Gaia DR2 data suggests an age of 92,191 years old. IR observations show the central cavity to be full of dust. This may be why its so difficult to make out the central star which has a mass of ~0.5 solar with a surface temperature of 55,000 K and is about 35 times brighter than our own Sun. You can find it on my astrobin page: Hope you like it. Cheers, Ian

Also known as IPHASX J205527.2+390359 it canbe found in the constellation of Cygnus. In this image north is to the right and east is to the bottom. The insert shows the PNe at x2 the original. This little PNe appears as #141 in the 1st release of the IPHAS catalogue of new extended PNe published in Jul 2014 by L.Sabin, Q.A.Parker,R.L.M.Corradi, et al. (https://academic.oup.com/mnras/article/443/4/3388/1019117) This paper publishes the results of a survey of new PNe extracted from the much larger IPHAS catalogue. IPHAS stands for the Isaac Newton Telescope Photometric Ha survey of the Northern Galactic Plane. The image is composed of N2 for the red, Ha for the green and O3 for the blue channels for the nebulosity. The starts are LRGB, where the luminance was taken from a combination of the narrow band channels. This PNe does not make many appearances in the professional literature with only 3 entries in SAMBA, one of which is the paper referenced above. Another paper, https://academic.oup.com/mnras/article/470/3/3707/3869624, suggests that PNe such as PN G081.1-03.9 have a higher H2 molecular content than narrower waisted PNe, but the reasons for this are unknown. On the sky the PNe is only 23” across. This paper gives it a diameter of 2.74 light years at a distance of 28,050 light years, so it’s actually quite a large structure (compare to the Dumbbell nebula which has a diameter of 2.88 light years). PN G081.1-03.9 is a bipolar PNe with an open barrel structure with the tips protruding slightly from the ends of the barrel. I have tried to bring out some of the inner structure inside the barrel. The bright pink arc at the bottom of the central ring structure, in my image, appears to be an N2 feature. The rest of that ring is, I think, Ha but covered by O3 emission, so it takes on a bluer appearance. The O3 forms a brighter central oval of material inside the barrel, that covers this ring and is also coincident with the central portion of the Ha. The Ha extends below the N2 to the east (bottom) of my image and extends slightly to the west (top) as well but is generally quite diffuse. There also some knots of material in the arcs to the east and west in both the N2 and Ha. The Ha is brighter in the central regions compared to the eastern and western arcs, which ties in nicely with the general observation that the broad ring PNe have brighter H2 emission in the central regions compared to their lobes. The H2 tends to be confined to the edges of this region, with more ionised material closer to the central star. This suggests that the ionised H is protecting the molecular H gas.

Thanks Knight of Clear Skies and x6gas. The outer halo is very faint compared to the main nebula so you have to go deep to get it. Narrow band filters help as well 😀 Cheers, Ian

Thanks MarkAR.

A bright PNe from the Messier catalogue is this famous one: M 97 or NGC 3587, also known as the Owl Nebula. It lies about 2869 light years away in the constellation of Ursa Major. It is about 8000 years old and 0.91 light years in diameter. The image is composed of 7 hours each of Ha, N2 and O3 images and 50 minutes each for red, green and blue broadband images taken with an Edge HD 11 and QSI 6120 binned 3x3 for all filters at f/10. Ha: 28 x 900s; O3: 28 x 900s;, N2: 28 x 900s. Red: 25 x 120s; green: 25 x 120s; blue: 25 x 120s. The narrowband filters were assigned to the RGB channels as Red: 100% N2, Green: 100% Ha, Blue: 100% O3. North is roughly to the right on this image and east approx. to the top. The goal of the longer subs was to try and capture the outer halo which you can see in this image as a diffuse blue ring. On the northern edge, almost opposite a bright feature on the edge of the outer shell the halo becomes a bit redder. This is due to a faint glow from N2 gas. After calibration and stacking the nebula and stars have been processed separately. In this image the nebula is composed solely of the narrowband data and the stars and background galaxies/nebula from just the RGB data. I hope you like the image: The two darker “eye’s” have given the nebula its name and it has long been supposed that this planetary nebula was a form of bipolar nebula. Recent studies suggest that it has a much more complicated structure. A 2018 paper ( https://arxiv.org/abs/1806.04676 ) shows that the Owl nebula has a tri polar structure with multipolar “fingers”. In fact, the authors propose that the Owl nebula be a prototype for a new class of PNe, called strigiform nebula (Strigiformes being the scientific name for owls). Three others have been suggested as members of this new group: K 1-22, Abel 33 and Abel 50. These are old PNe, with complex, multipolar cavities within a nearly spherical nebula that is otherwise filled with gas. Within the gas is a complex pattern of cavities. For M 97 there is, as yet, no explanation as to how these cavities have formed and no observations to indicate how they are evolving. A previous paper ( https://iopscience.iop.org/article/10.1086/316800/fulltext/ ) suggests that the Owl nebula consist of 4 concentric shells. An inner, barrel shaped shell surrounded by three spherical shells of decreasing ionisation energy as you move away from the central star. This inner structure is responsible for giving the Owl its famous face. The authors suggest that the barrel shaped shell is unusual for a PNe like the Owl, so perhaps they were just starting to make out the structure described in the 2018 paper, but at a much lower resolution and hence misinterpreted it? The inner spherical shell of gas is mainly of high energy ionised gas (in my image this is mostly blue, associated with O3). Its mass is thought to be about 0.36 solar. The outer shell is composed of low energy ionised gas (shown as mostly orange in my image, associated with Ha and N2). The mass of the outer shell is about 0.41 solar. The diffused halo (blue in my image, so again mainly O3. There is some N2 that shows as a purple patch at about the 4 o’clock position and close to a bright feature in the outer shell) has a mass of approx. 0.22 solar. The central star has an approx. surface temperature of 100,000K and a mass of 0.65 solar. The star does not appear to be generating a significant stellar wind, consistent with the PNe being classified as highly evolved PNe. Adding all this up gives a 1.6 solar mass progenitor star which had a luminosity of between 40x to 140x the Sun’s luminosity. Cheers, Ian

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

Thanks MarkAR, glad you liked it. Cheers, Ian

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

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

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

Thank you tooth_dr. Cheers, Ian

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.

Thanks x6gas. It’s 7 hours per narrow band channel, so 22.5 hours in total. Cheers, Ian.

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.

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

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

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

Thank you tooth_dr and MarsG76. Cheers, Ian

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

Very nice image. Cheers, Ian.