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Brown Dwarfs on the H-R diagram

  1. Dec 2, 2012 #1
    Do Brown Dwarfs appear on the lower right hand "tail" of the main sequence of the H-R diagram?

    Or are they separate from the main sequence?

    The location here:
    https://en.wikipedia.org/w/index.php?title=File:HR-diag-instability-strip.svg&page=1
    appeared to show them in that location, but I wasn't sure if they are actually separate from the main sequence as the diagram isn't that clear on their location.

    Thank you.
     
  2. jcsd
  3. Dec 2, 2012 #2

    Drakkith

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    Staff: Mentor

    Brown dwarfs are not main sequence stars, as they never perform hydrogen fusion, but they appear on your link at the bottom right. I don't know how accurate that particular graph is.
     
  4. Dec 2, 2012 #3
    Thanks Drakkith.

    So if I was drawing a sketch of the H-R diagram, and labelling the position of the brown dwarfs, would I just point out that they are on the lower right-hand tail of the main sequence.

    Or should they be indicated as being completely separate from the main sequence in the way that white dwarfs are?
     
  5. Dec 2, 2012 #4

    Drakkith

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    Staff: Mentor

    If you are going to plot them, you have to plot them according to the parameters of the graph. This necessarily puts them at the lower right I believe.
     
  6. Dec 2, 2012 #5

    Chronos

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    A couple extra spectral classes past M were invented for brown dwarfs - L and T, so they technically are on the HR diagram, but, not considered main sequence. They can fuse deuterium if they can achieve a core temperature of about 1 million degrees. The ones too small to fuse deuterium may as well be called orphan planets.
     
  7. Dec 2, 2012 #6
    Brown dwarfs, as previously stated, are not on the main sequence. They are small and relatively cool and fall in the lower right hand corner of the HR diagram.
     
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