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Homework Help: Eclipsing binary

  1. Apr 16, 2016 #1
    1. The problem statement, all variables and given/known data
    Two main sequence stars have the following properties:
    #1: apparent magnitude m_v=2.5, λ_eff = 551nm radius r=1.6R_sun
    #2: m_v = 5.77, r = 1.25R_sun

    1) Calculate the apparent brightness of the system when #2 is in front of #1. Assuming that #1 has constant apparent brightness, what radius is required for #1 to make the depth of the primary eclipse equal to that of the secondary eclipse (the properties of #2 don't change).

    2)Further: B-V colors of the two stars have to be calculated

    2. Relevant equations
    a) m_v1 - m_v2 = -2.5*log(F_1/F_2)
    b) λ_max = 2898/T
    c) B-V= m_b - m_v =-0.865+(8540/T)

    3. The attempt at a solution
    1)I already calculated the apparent brightness of the binary system, when there is no eclipse, using eq. a and the relation of fluxes (m_system=m_2+2.5*log(F_2/F_system).

    2)for #1 I did the following:
    using Wien's displacement law (eq. b) I calculated T (not sure if I can use the effective wavelength as max wavelength), and then calculated B-V using eq. c. From that I calculated m_b. But how to calculate B-V of #2 with only m_v given?

    Thanks for any suggestions!
  2. jcsd
  3. Apr 16, 2016 #2


    User Avatar
    2017 Award

    Staff: Mentor

    That's not what the question is asking.
    You also know the radius, and the star is at the same distance as the other star. You can find some relations to calculate λeff.
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