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robin_astro

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About robin_astro

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    Star Forming

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    http://www.threehillsobservatory.co.uk

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  1. Hi Vlaiv, If you have not come across them already (thanks for the hat tip Andrew :-) ), here are my two configurations using the Star Analyser which can incorporate a slit : SEPSA. This keeps the converging beam but adds a focal plane to place the slit at http://www.threehillsobservatory.co.uk/astro/spectroscopy_18.htm Fully collimated "junk box"design (without slit though one could be added http://www.threehillsobservatory.co.uk/astro/spectroscopy_19.htm You might also be interested in this grism design (note the mirror slit guider which (almost) all commercial slit spectrographs use thse days) http://www.burwitz-astro.info/spectrographs/tragos/ and my modification of the similar Shelyak ALPY spectrograph using a 200 l/mm grism http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm As Andrew said though, adding a slit is the easy part, finding the target, focusing it and guiding it on the slit are the hard parts. With bright targets though you can get away with defocusing the target into a large blob so it is impossible to miss the slit. (See my Vega spectrum using the SEPSA for example) Cheers Robin
  2. Colours of (very) HOT Solids!

    The observation in the video that aluminium looks different from steel where the flame hits the surface is interesting though. The local surface temperature here could be much higher. I checked the thermal conductivities and steel has ~5x lower conductivity than aluminium so perhaps the heat is conducted away faster so you dont see a glowing hot spot like you do with steel. Also you never see the raw metal surface with aluminium as it immediately oxidises so perhaps the emissivity of the oxide layer has a part to play here. Robin
  3. Colours of (very) HOT Solids!

    Google Draper point. I would be surprised if glowing aluminium looks significantly different from any other glowing metal at the same temperature (but then again nothing really surprises me these days!) aluminium would melt before you would see any glow in a lit room. Robin
  4. Welcome to the spectroscopy board

    Hi Eric, I have just noticed your neon test graph shows the slit width as 5um. That is very tight. Is that correct? with your 8 inch f10 scope the star image FWHM will be around 30um FWHM with typical 3 arcsec seeing so you will need a slit of around 25-30um to get reasonable throughput. What camera are you planning to use? Because you have a 5/9 reduction in image scale through the spectrograph you will need to watch out for potential under sampling. For a 25um slit for example the pixel size will need to be < (25*5/9)/2 ie < 7um Cheers Robin
  5. Welcome to the spectroscopy board

    Hi Eric, The spectrograph looks good but dont underestimate the acqusition, focusing and guiding issues with slit spectrographs. Except for bright targets (where you can defocus) you will soon want to incorporate a mirror slit guider. Though not cheap, mirrors slits which can be used in self build guider designs are now commercially available, eg from Shelyak http://www.shelyak.com/produit.php?id_produit=122&id_rubrique=16 or Ovio http://www.ovio-optics.com/jetons-de-diffraction-interferences,fr,3,56.cfm for example. Cheers Robin
  6. Beginners Radio Astronamy

    Really?? Are you sure? Which one. The difference in signal between the sun and a pulsar is huge. What does your lunar signal look like? Here are some of my plots with a similar setup http://www.threehillsobservatory.co.uk/astro/radio_astronomy/radio_astronomy_1.htm Cheers Robin
  7. This masterflat ok?

    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.
  8. This masterflat ok?

    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
  9. This masterflat ok?

    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
  10. Supernova fireworks in NGC6946

    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
  11. Superluminal motion

    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
  12. 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
  13. SAO45590

    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.
  14. SAO45590

    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
  15. SAO45590

    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
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