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Homework Help: Calculating luminosity density of the universe

  1. Mar 12, 2009 #1
    1. The problem statement, all variables and given/known data

    l = Phi*L*Gamma(a+2)


    The Sloan Digital Sky Survey (SDSS) has recently measured the following Schechter
    parameters in the r passband: a = -1.16 +/- 0.03, M*= -20.80 +/- 0.03, Phi* = (1.50 +/-0.13). Given that the sun has absolute magnitude M = 4.62 in the SDSS r band, calculate the luminosity density in this band in solar units. Estimate the error on this quantity.
    Gamma(0.84) = 1.122, Gamma(0.81) = 1.153, Gamma(0.87) = 1.094.

    2. Relevant equations

    3. The attempt at a solution

    I done the entire question and then realised i had made a grave error. And this is what I think it is; I took L* as being -20.80 +/- 0.03 ie M*, and im pretty sure this is wrong. Luminosity confuses me and I'm not sure how to relate the absolute magnitude M* to the Luminosity L*. I know that L* is supposed to be in the order of 10^10. Can anyone out there help? Its kind of urgent (due in tomorrow!).
  2. jcsd
  3. Mar 16, 2009 #2
    Never mind. Problem solved
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