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Finding an absolute magnitude

  1. May 24, 2015 #1
    1. The problem statement, all variables and given/known data
    1.2.png



    2. Relevant equations
    m1-m2[/SB]=2.5log(ι21)

    m-M=2.5log (d/10)2

    3. The attempt at a solution
    1.2 answer.png

    Not sure if my approach and answers are correct

    Please help
     
  2. jcsd
  3. May 24, 2015 #2

    nrqed

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    First question: In your very first line with an equation, you changed the factor of 2.5 to a factor of 5 in front of the log. Why did you do this? This seems to be a mistake.
     
  4. May 24, 2015 #3
    I forgot the exponential: m-M=2.5log(d/10)2
     
  5. May 24, 2015 #4

    nrqed

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    AH yes, Ok.

    EDIT: you seem to have made a sign mistake. In the exponential for the calculation of the luminosity, you should have

    M_1 - M_2 = M_1 - ( m +1.99) = 5 -m - 1.99


    Then your work looks good. You just need to plug in the value of m=2. The absolute magnitude of the star is smaller than the Sun's absolute magnitude (3.99 versus 5) so the star has a larger luminosity than the Sun's and your final expression agrees with this. All the steps look good.
     
  6. May 24, 2015 #5
    Thanks a bunch and sorry for the typo
     
  7. May 24, 2015 #6

    nrqed

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    You are welcome. And no problem about the typo, I make typos all the time :-)

    Patrick
     
    Last edited: May 24, 2015
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