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Homework Help: Star temperature from B-V color

  1. Oct 25, 2007 #1
    1. The problem statement, all variables and given/known data

    I need to know how to calculate the temperature of a star from it's B-V color

    2. Relevant equations

    B = -2.5log(F440)+C
    V = -2.5log(F550)+C
    B-V = -2.5log(F440/F550)

    3. The attempt at a solution

    Really no idea, all my textbooks say that B-V color is used to measure temperature but none of them say how. I also can't find anything linking flux ratios to temperature.

    Any help appreciated :)
  2. jcsd
  3. Oct 25, 2007 #2


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    Science Advisor
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    From my list of handy astronomy values
    B-V = -3.684 log(T) + 14.551 (for log(T) < 3.961)
    B-V = 0.344 (log(T))^2 -3.402 log(T) +8.037 (for log(T) >3.961)

    Note that B-V is also called the color-index of a star.

    These are experimental fits to the HR diagram for some cluster - you can probably derive it from Planck's law + stefan-boltzmann if you know the filter bandwidth.
    Last edited: Oct 25, 2007
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