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Thread: Do Sirius A and B have opposite spin ?

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    Default Re: Do Sirius A and B have opposite spin ?



    Thank you again not_Fritz_Argelander,

    it's very appreciated.

    regards,

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    Default Re: Do Sirius A and B have opposite spin ?

    Quote Originally Posted by not_Fritz_Argelander View Post
    The only hope of doing that is for stars close enough to have their disks resolved by interferometry for instance. Achernar is one example. There aren't many others! If any! (See link at end.)
    But wait a second... how come astronomers can resolve by interferometry Achernar (situated at 140 ly) and not Sirius (situated at ~ 8 ly) ?

    Did I miss something ?

    regards,

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    Default Re: Do Sirius A and B have opposite spin ?

    Hi !
    About spin broadening of lines in the spectrum due to Doppler effect, it can't indicate the spinning direction, because half of the star is approaching (the left or the right one) and the other is moving away so in both cases of spinning, the spectral line is broadening the same way.
    That was, during a long time, the same case for the galaxies : were they winding or unwinding their arms ?
    Arsène
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    Default Re: Do Sirius A and B have opposite spin ?

    What a very interesting question and although my knowledge of the above is next to zero and from what I can tell you have come to a brick wall, try asking the question to this chap...

    https://www.lpl.arizona.edu/faculty/holberg

    Maybe he could shed some light on the question??

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    Default Re: Do Sirius A and B have opposite spin ?

    Quote Originally Posted by Pluto2006 View Post
    What a very interesting question and although my knowledge of the above is next to zero and from what I can tell you have come to a brick wall, try asking the question to this chap...

    https://www.lpl.arizona.edu/faculty/holberg

    Maybe he could shed some light on the question??
    The "brick wall" is that it is in principle unobservable as detailed in this thread. The formation of Sirius A and B from the same gas cloud along with conservation of angular momentum argues most likely the spins are aligned. It would be a surprise if the spins were opposite but there is no way to tell observationally. There's no additional light to be shed.
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    Default Re: Do Sirius A and B have opposite spin ?

    Quote Originally Posted by fractalrocks View Post
    But wait a second... how come astronomers can resolve by interferometry Achernar (situated at 140 ly) and not Sirius (situated at ~ 8 ly) ?

    Did I miss something ?

    regards,
    What you missed is that Sirius B is much smaller than Sirius A.
    Radius of Sirius B is 0.008 solar, unresolved interferometricaly.
    Sirius A radius is 1.711 solar, resolved interferometricaly.
    Achernar has a polar radius that is 7 times solar and an Equatorial radius that is 11 solar.

    To answer your question BOTH Sirius A and B need to be resolved and that isn't happening.
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