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Determine body properties by visual spectrum?

  1. May 3, 2011 #1
    I'v been taking an interest to astronomical spectroscopy lately and I have some questions about that.

    In order to get myself going I wanted to get as much information about Sirius A and Sirius B using the distance, obtained by using parallax(I didn't do that but imagine I did) , and their visual spectra(nor did I obtain the spectra by myself, but again imagine that I did).

    If I used the information in the visual spectra to put in Wien's law, then the temperatures of the stars would be incorrect. Are there methods to get accurate information by using only the visual spectra, or does it only work for stars that have their lambda max in the visual spectra?

    Could I do something with the info in the visual spectra, i.e. an integral, and compare it to 'B-V color index', bolometric/apparent/absolute magnitude or something else?

    Thanks in advance, and I'm sorry if I´v understood astronomical spectrography completely wrong.
  2. jcsd
  3. May 4, 2011 #2


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    Staff: Mentor

    Hrmm, I wish I could help you. Maybe someone else can? I'd like to know also.
  4. May 4, 2011 #3


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    Staff: Mentor

    What are the temperatures you come up with if you use Wien's laws? How is the real star different?
  5. May 4, 2011 #4


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    A slightly more sophisticated thing to do would be to fit the spectrum to the black-body curve and get a best-fit value for temperature.
  6. May 6, 2011 #5
    If I use Wien's law of displacement(λmax=b/T) I get the temperature to be ~6,000K. That is because the λmax of the visual spectrum is ~4,800Å.
    However, the actual temperature of Sirius A is ~10,000K and so according to λmax=b/T the λmax should be ~2,800Å

    I read something like that on a site that I found whilst I goggled "determine temperature from visual spectrum" http://mysite.du.edu/~jcalvert/astro/magnitud.htm" [Broken]

    Do I perform some sort of extrapolating operation on the curve of the visual spectrum, compared to the black body curve?

    Again I must stress that I´m quite new to astronomy so there might be something fundamental that I have yet to understand.

    But all in all, Is there a way* to determine the temperature of a star from it's visual spectrum(even if the star is of a blue-white color, so it's spectrum is in the UV area) ??

    *That means any way what so ever; Calculus, algebra, comparing to whatnot and etc etc.
    Last edited by a moderator: May 5, 2017
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