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Homework Help: Kinetic energy of gases in stars

  1. Nov 15, 2011 #1

    I have a conceptual and mathematical question about gases in stars.
    The information we have from stars is due to the motion of particles in one dimension: along our line of sight.
    We assume that this motion is isotropic and that regardless of where on the star we look, we'll get the same motion.
    So, when calculating the temperature of the star's chromosphere, do we use the one dimensional kinetic energy E=1/2kT, the three-dimensional kinetic energy E=3/2kT or the average kinetic energy E=kT to equate to 1/2mv^2, where v is the one dimensional velocity?

    (Note to mods: I posted this question in the Astrophysics section earlier today, but after 130 views with no replies, I think I may get a better response in this subforum. I know spread-posting is frowned upon but I do not intend to troll!)
  2. jcsd
  3. Nov 18, 2011 #2


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    We see the photons which arrive from the stars, and these photons are radiated out by the atoms (molecules, ions) of the chromosphere. The particles have rotational, vibrational and electronic degrees of freedom. The visible, UV and higher frequency radiation originates from the transition between the electronic states of the particles. We get information about the temperature of the stars from the frequency distribution of their radiation.
    Read about "black body radiation". http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html
    The wavelength of maximum intensity of radiation is proportional to the absolute temperature of the star, according to Wien's Law.

  4. Nov 18, 2011 #3
    Thank you.
    I should have said that I was working with velocities and temperatures of chromospheric winds, not just the temperature of the chromosphere. The wind would be anisotropic, as it is being ejected from the star, but the turbulent velocity of the particles within the wind would be isotropic.
    So how does that effect my original question?
  5. Nov 18, 2011 #4


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    I see. I do not know if those stellar winds are isotropic or not. The star can have magnetic field and I think it has its effect. I guess the velocity distribution in the chromosphere is described by the Maxwell-Boltzmann distribution, but the particles lose energy when escaping the star.

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