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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. I feel your pain. The obs control computer is Win XP but has been getting increasingly flaky electronically for some time so I decided to retire it this week. I have a reserve computer also running XP which should have simplified matters but even so I am still having problems getting things working properly after re-installing everything.
  2. As an aside, it is recommended that with the ALPY at least 20 well exposed (ie ~50% in the maximum intensity region) flats are averaged to produce the master flat (I normally take ~30). This ensures a good SNR in the blue where the flat counts are much lower Robin
  3. Yes it is typical with the ALPY, though the steep hump and drop off in the blue is perhaps more severe than I have seen before. If you use ISIS, once the wavelength calibration is done, it applies an assumed black body curve (at 2700K I think) which calms it down quite a bit and makes it easier to get a good fit to the reference star spectrum in this region when calculating the instrument response. The flat is a combination of the instrument response and the flat light source spectrum but the exact origin of the hump is unknown as far as I am aware and apparently varies between setups. I had speculated that it might be due to the colour of the "white" reflective diffuser used in the ALPY/LISA but the fact that you are seeing it with a different setup suggests it might be more universal. You can see my typical instrument response for the ALPY here (corrected by ISIS for the black body curve so responses produced by other software may not look the same) What does your ISIS instrument response using your flat light source look like ? Robin
  4. 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
  5. 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
  6. 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
  7. 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.
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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