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robin_astro

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About robin_astro

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    http://www.threehillsobservatory.co.uk

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  1. Ah yes, sn2004et. Another type II, around the same magnitude. I was imaging with a modified video camera back then and just starting to do spectroscopy. http://www.threehillsobservatory.co.uk/astro/spectra_8.htm Tonight I am collecting photons from this latest one for a spectrum using considerably more sophisticated (and more expensive !) kit Robin
  2. I remember following this phenomenon with modified video and webcams back in 2003-2005. http://www.threehillsobservatory.co.uk/astro/astro_image_37.htm I knew about it being a light echo but didn't realise the geometry made the echo appear to be moving outwards faster than light. Thanks for posting ! Robin
  3. Here is a more complete description of where the stuff that makes up solar system came from http://blog.sdss.org/2017/01/09/origin-of-the-elements-in-the-solar-system/ Robin
  4. Hi Peter, Notice how the Balmer lines become progressively sharper as they crowd together at the blue end just before the camera runs out of sensitivity. (H epsilon is really clear and sharp compared with H beta for example) The features at the far red end are beyond the sensitivity of the camera and are just noise.
  5. Hi Peter, I think it is the other way round. The Balmer lines are very sharp at the short wavelength end and I suspect your best focus could be actually in the UV beyond the range of the spectrum. I think you will get a better result if you focus to make the H beta/gamma lines as sharp as possible. Cheers Robin
  6. Hi Andrew, There are some discussions on this on the RSpec forum too where Peter has posted the fits image. I independently processed the spectrum (using Vspec) covering a wider spectral range (attached) The line visible in the red in spectrum image is the telluric O2 band at 7620A. (You can also see it in the adjacent K star). H alpha is indeed quite weak and out of focus. There is some Chromatic Aberration with this ED refractor so the focus varies along the spectrum. The spectrum here is in best focus at the UV end where the lines are very sharp but H beta, gamma are not so well focused and should be much sharper with this small aperture refractor. I think the spectrum would benefit overall from moving the best focus point away from the UV end to the H beta/gamma lines. Cheers Robin
  7. Hi Steve, By your definition an image would be 3D as each X,Y location has an intensity (It is actually a 2D matrix of intensity values) fits file spectrum profiles usually are strict 1D arrays (a single list of intensities, the relationship between wavelength and index being defined separately) but in general it is a useful way to distinguish between a 2D raw spectrum image and a 1D spectrum image generated from the profile in which the rows are repeated. Cheers Robin
  8. Yep the C11 is my workhorse too with a focal reducer to match spectrograph focal ratio where needed 1. With the LHIRES III at f10 2. With the ALPY at ~f5 3. With the Star Analyser at ~f5 Robin
  9. Yes you can get a bit sharper spectra with the grating mounted on a camera lens but it is much less sensitive compared with mounting it behind a telescope as you effectively only have a ~25mm diameter aperture (Even an 80mm aperture telescope will collect ~10x more light), so it only works for brighter targets. Cheers Robin
  10. Hi Louise, Using the video mode is good to start with as it helps with focusing. Choose a main sequence A or B type star to start with (type Av/Bv) There is a list of bright stars with their spectral type in the back of the manual. Check you have the grating orientated with the star on the left and the brightest spectrum horizontal across the field (There are spectra on both sides of the star image, one is much brighter). Focus first on the zero order star image to start with, then reduce the exposure until the spectrum looks on the under exposed side all the way along the spectrum and then wind the focuser in a touch until you see a dark absorption line appear sharpest about 1/3 the way along the spectrum (The Hydrogen beta line) You should then be able to other Hydrogen lines crowding together towards the blue end nearest the zero order. ( It is a good idea to always start an observing session this way as this star can be used to both wavelength calibrate and adjust your spectrum for the response of your instrument.) Once you are in good focus you can move to other targets. Perhaps try a cool M type star for example, noting the broad molecular bands and an emission line star like Gamma Cas for example, looking for the bright spot towards the right hand end of the spectrum which is Hydrogen alpha emission from the disc around this star, or later in the year, P Cygni, a luminous blue variable supergiant which shows Hydrogen and Helium emission lines. Wolf Rayet stars, although fainter show spectacular emission lines too in the stellar wind. You can get an idea of what the raw spectra should look like here. (Yours will be clearer as these were taken with a smaller camera sensor so the spectrum is not very long) http://www.threehillsobservatory.co.uk/astro/spectra_12.htm http://www.threehillsobservatory.co.uk/astro/spectra_14.htm Cheers Robin
  11. Perfect ! That will be a very nice setup. Good resolution and plenty of room to fit the spectrum in the frame. Can't wait to see first light Good Luck Robin
  12. Hi Louise Small aperture APO's work really well with the Star Analyser. See Jim Ferreira's work for example http://www.lafterhall.com/spectroscopy.html I ran your setup using an SA100 and minicam5 through the calculator. With 5arcsec seeing, distances 20-46mm give all ok. For best resolution aim for the top end. For the faintest objects at lower resolution you might want to reduce the spacing. Larger distances (up to 60mm when it gets difficult to fit the spectrum in the frame) will still work ok though Cheers Robin
  13. I see the minicam5s is cooled and can do long exposures too. That makes it ideal for spectroscopy with the Star Analyser and will allow you to go fainter. Cheers Robin
  14. Hi Louise, Using the Star Analyser at too large a distance is a bit like using too high a magnification eyepiece. You get to a point where you dont see any more detail, things just get fainter. The calculator is just warning you that you have reached that limit. Colour cameras are not ideal for spectroscopy because in some regions of the spectrum (red and blue) only 1 in 4 of the pixels are sensitive due to the Bayer pattern. Also the red green and blue filter responses dont match perfectly so you get humps and bumps in the overlapping regions in the spectrum which should not be there. As a beginner you will find the mono minicam5 easier to get to grips with using the Star Analyser 100 (It was designed exactly for this kind of camera) Focusing is critical to getting good resolution but is tricky to learn and a fast updating webcam type camera is ideal for this. Being monochrome is an extra bonus too. (Software like RSpec can even give you a live view of the spectrum profile) With cameras like the minicam5 it is usual to just screw the grating onto the end of the 1.25 inch nosepiece (with spacers if needed to get the distance optimum) and put it directly into an eyepiece holder. The same is usually done with DSLR, using a T2 converter and a 1.25 inch nosepiece I know it sounds a bit counter intuitive but when used behind a telescope, the SA100 used at twice the distance works better than the SA200. This is because the angle the beam is deflected is less which gives less aberration and less focus shift along the spectrum. This is why I chose a 100l/mm grating for the original Star Analyser 100. The SA200 was developed later for situations where the larger distance cannot be achieved. (Note in the case where the grating is positioned in front of a camera lens, the aberrations are less so the spectrum can be spread out more to gain resolution. Here SA200 can have some advantages over the SA100. See here for list of pluses and minuses in that case http://www.threehillsobservatory.co.uk/astro/spectroscopy_17.htm ) Cheers Robin
  15. Hi Peter, Which camera are you using now? Is this with the colour camera or the monochrome Lodestar? Your spectrum is ok but the line identification is not right. See here on this RSpec forum thread for more information on the problem of identifying lines in cool stars like Betelgeuse https://groups.yahoo.com/neo/groups/RSpec_Real_Time_Spectroscopy/conversations/messages/6188 Robin