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G Magnitude to V magnitude stars in a CCD

  1. Feb 5, 2014 #1
    I have astronomical images taken using a CCD camera and telescope using a g filter. In the images I have stars with what is called instrumental magnitudes (from the photon count in each pixel). My question is if there is a way to change this g instrumental magnitude to a real V magnitude.

    I have found this:
    V = g - 0.03 - 0.42*(g-r)

    from
    Windhorst, R. W., et al. 1991, ApJ, 380, 362
    and http://www.astro.umd.edu/~ssm/ASTR620/mags.html

    This is telling me that I needed to have used an r filter on the same images. Is there another way to find the V magnitudes of the stars by only having images taken with a g filter?


    Thank you
     
  2. jcsd
  3. Feb 5, 2014 #2
    Not, with any precision. It would help if you told us what your background in photometry is?
     
  4. Feb 5, 2014 #3
    does it matter what the background is if all images were taken with a g filter? I don't understand the question.
     
  5. Feb 5, 2014 #4
    When I say "your background in photometry" I'm talking about your personal prior knowledge about the topics covered in the scientific field of photometry.
     
  6. Feb 5, 2014 #5

    phyzguy

    User Avatar
    Science Advisor

    Since the two filters have different wavelength bands, the conversion will depend on the color of the object. That is why you need two different measurements with two different filters to do a conversion. You might find this paper useful. Figure 1 shows the comparison of the filter bands.
     
  7. Feb 5, 2014 #6
    Great!!
     
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