1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Poisson stats: signal to noise

  1. Oct 6, 2003 #1
    A star was measured to have an apparent magnitude m=16 with S/N=10 integrated over a minute. What is the uncertainty in the measurement?
    signal=flux*area*time
    noise=sqrt(signal)=sqrt(fAt)
    So, S/N=sqrt(fAt)
    How can I find fA?
    m=-2.5logfAt+K
    16=-2.5log(fAt)+K
    Hoping that K is arbitrary (please verify this), I choose K=0
    Then 16=-2.5log(fAt)
    So fA=3.98 e-7 J/s (units inconsequential)
    So, uncertainty =6.3 e-4
    ??
    HELP!
    edit:
    Or, I can get N=uncertainty=sqrt(S/10)=sqrtS <--- something VERY wrong here
     
    Last edited: Oct 6, 2003
  2. jcsd
  3. Oct 7, 2003 #2
  4. Oct 7, 2003 #3
    I think this is an exercise in error propagation.
    You could also write m=-2.5log(I)+K
    You have m, and I/dI=10. You want to find dm. (d means differential).

    m + dm = -2.5log(I + dI) + K.
    You could now substitute dI = I/10, and solve for m. That will work, since I will cancel.

    However, I suspect they talk about RMS noise.
    Which makes things a bit more complicated.
     
  5. Oct 7, 2003 #4
    Re: Re: Poisson stats: signal to noise

    No, actually. You're answer if perfect. We went over this today in class. It didn't make sense then, but I think it's finally making sense. I was trying to hard to find S.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?