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Thread: Why do Am stars have slow rotations?

  1. #1
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    Why do Am stars have slow rotations?

    Are the metals in their atmospheres and their slow rotations related?
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  2. 2021-Aug-02, 01:14 AM

  3. #2
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    The Wikipedia article also makes the point that "Normally, A-type stars rotate quickly. Most Am stars form part of a binary system in which the rotation of the stars has been slowed by tidal braking.[5]"

    And from the David Darling Internet Encyclopedia referenced in the footnote:
    An Am star, also known as a metallic-line star, is a type of A star whose spectrum has strong and often variable absorption lines of some metals (hence the "m"), such as zinc, strontium, zirconium, and barium, more typical of an F star, and deficiencies of others, such as calcium and/or scandium. These abundance anomalies are due to some elements being pushed to the surface because they are better light-absorbers, while other elements sink to lower levels under gravity an effect that requires slow stellar rotation.

    Normal A stars spin quickly, but the vast majority of Am stars are known to be members of close binary systems, with orbital periods of less than 1,000 days, in which the two stars slow each other down by tidal action. Familiar examples include Sirius and Acubens (Alpha Cancri). An example of an Am star which is single is HD 8801. This star is also unusual for an Am star in that it pulsates, and it is unique among known stars in that it pulsates intrinsically with both gamma Doradus and Delta Scuti frequencies.

  4. #3
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    being pushed to the surface because they are better light-absorbers,
    I'm a little confused about this. How does absorbing light push a substance to the surface?
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  5. #4
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    Quote Originally Posted by parallaxicality View Post
    I'm a little confused about this. How does absorbing light push a substance to the surface?
    Photon pressure.

    Grant Hutchison
    Science Denier and Government Sponsored Propagandist. Here to help.
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  6. #5
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    So it's like an aerofoil? More pressure on bottom than top?
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

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