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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. Talking extremely long term (10^31 years), according to some Grand Unified Theories, protons (Hydrogen nuclei) may decay into other particles, though currently there is no experimental evidence for this.
  2. robin_astro

    One for any electronics experts

    Do you tear down completely every night or leave the OTA, camera and filter wheel connected? If the latter a flat should last a fair while Robin
  3. robin_astro

    One for any electronics experts

    I can see this wavelength in the daylight sky with my spectrographs. How long exposure does a daylight sky "T shirt" flat need at this wavelength? (Unless it is ridiculously high and as long as you can keep stray light out, exposure time does not matter for flats as long as you expose long enough and average enough exposures to beat the noise down (and correct with suitable bias and darks of course which you should do any way) Robin
  4. robin_astro

    One for any electronics experts

    Actually the power dissipated in the series resistor decreases as you increase it. ie for a 5v supply, the power dissipated in the resistor is always 1.4V * the current flowing through the circuit because the voltage drop across the LED remains constant at 3.6V
  5. robin_astro

    One for any electronics experts

    The wavelength does not change with voltage. The table is for different versions of the LED with different wavelengths (Actually strictly speaking the voltage across an LED is always constant provided the voltage source is above the specified value) Robin
  6. robin_astro

    One for any electronics experts

    Indeed, hence the pointer to the eye safety in the datasheet which says to not look directly into the beam and wear eye protection if there is a risk of reflections
  7. robin_astro

    One for any electronics experts

    The datasheet also has advice on eye safety. The eye is insensitive to this wavelength so you will not see it. Robin
  8. robin_astro

    One for any electronics experts

    The manufacturer's datasheet on that page says peak at 385nm (actually there is a tolerance so it could be anywhere from 380-390) There is also a spectrum plot there showing how wide the emission line is. https://docs-emea.rs-online.com/webdocs/1427/0900766b81427cb7.pdf The LED will drop 3.6V and will pass 0.5A current so if you plan to use a 5V supply for example you would need a series resistor which would drop the voltage by 1.4v at 0.5A. Ohms law says R=V/I so R = 2.8 ohm. (Go for the nearest next highest standard value) The resistor would need a rating of at least 1.4 x 0.5 = 0.7 Watts. Make sure to connect the LED up the right way round Cheers Robin
  9. There is no point in taking the inductor out of the circuit now if you have already removed the MOSFET (That was just my suggestion as the easiest way to isolate the fault) If the zener is ok and the mosfet has been removed and it is still not working then there are faults elsewhere.
  10. robin_astro

    Spectrum of Altair

    50 sec is an extremely long exposure on such bright stars at this resolution. With my similar resolution ALPY setup and a 280mm aperture, a spectrum of Vega is saturated in about a second or less. Was the star well focused and positioned on the slit? Have you checked that no part of the spectrum image was saturated ? Robin
  11. robin_astro

    Spectrum of Altair

    Yes that is ok but you could use your relco lamp to get a more accurate calibration. Robin
  12. robin_astro

    Spectrum of Altair

    Hi Andy, You have sort of got the idea but there are a couple of things you need to do first. 1. You need to subtract the sky background by selecting areas above and below the spectrum and subtracting them from the region where the spectrum is. It is important how you select these regions. Make sure the region you select for the spectrum is wide enough to cover the full height of the spectrum, turn up the brightness in the image to make sure. Then select regions above and below this for background subtraction, far enough away that there is no contamination from the star spectrum. 2. your camera/spectrograph is only sensitive between about 3700 and 8000A (After background subtraction your spectrum should read ~zero below 3600A and the spectrum above 8000A is not valid because it overlaps with the 2nd order spectrum) So you first need to crop your spectrum from 3700-8000. EDIT: - 3700-7400 in your case as this is the edge of your camera field. You can then divide this by the library spectrum, remove any features which did not exactly cancel and smooth the result to produce your instrument response. As a check you can then apply it to your uncorrected spectrum. The result should look like the library version. Again you can see the steps in my workshop tutorial Cheers Robin
  13. robin_astro

    Spectrum of Altair

    Hi Andy, A dark subtraction will probably deal with them. (The first step with processing spectrum images is the same as with astro imaging ie bias, dark subtraction, flat field correction) You then make any geometric corrections needed eg slant and tilt, remove the sky background and bin the region containing the spectrum to produce the digital data. You then wavelength calibrate and correct for the instrument response/atmospheric extinction to produce the final fully calibrated spectrum. You can see examples of these steps in the presentation "Low Resolution Slit spectroscopy (ALPY) - Confirming and classifying a Supernova " I gave at a BAA workshop a couple of years back for example. Cheers Robin
  14. robin_astro

    Spectrum of Altair

    Looking good Andy. Was this wavelength calibrated using your RELCO lamp? It looks like you have a few hot pixels/cosmic ray hits (The sharp "emission lines" You might be interested to know that the reference spectrum you used in Rspec (and also Visual Spec, ISIS and BASS) comes from the Pickles library, downloadable from here for example http://www.eso.org/sci/facilities/paranal/decommissioned/isaac/tools/lib.html It is one of many libraries of spectra though the pickles spectra are generic of the spectral type rather than of a particular star so do not always perfectly match actual spectra Vega is nice and easy to identify features as there is not many strong lines other than the Balmer and telluric lines. Christian Buil has a nice annotated higher resolution (~3A)spectrum of Vega here which can help you identify some of the weaker lines, including all the Telluric bands http://www.astrosurf.com/buil/us/vatlas/vatlas.htm ( Spectra of cooler stars like the G/K stars are much more complex so most lines cannot be uniquely identified at the resolution of your spectrograph as they are blended) Next step is to correct your spectrum for the effect of the instrument and our atmosphere. You can use your Vega or Altair spectra for this and then use it for other stars provided they are at similar height in the sky. The continuum will then show the same overall shape as your reference spectrum. Doing this for a few known stars and comparing them with professionally measured spectra is a good test of your technique, as I have done here for example using spectra of stars from the MILES database http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm Cheers Robin
  15. robin_astro

    Neon lamp to set spectroscope

    I guess the different sensitivities of the CCD in the two cameras (Sony ICX259AL compared with ICX674) could also be having an effect. (The ICX674 in my ATK 428 camera is known for its high sensitivity in the blue but the difference is perhaps greater than I would have expected.) We will see better when you move on to instrument response correcting your star spectra. Robin
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