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    Re: Star proper motion - thanks.
    From: Aubrey O´Callaghan
    Date: 2001 Nov 20, 6:27 PM

    All,
    Thank you for your assistance, you have given me an amount of pointers to
    continue with my little project.
    Robert's explanation of the conversion of the proper motion was perfect.
    The relationship between the different proper motions that was confusing
    me, is the 1/(15*cos(decl) )Robert referred to.
    For Sirius:
    0.0385  =.553/(15*cos(16d 42' 58"))
    
    Aubrey.
    
    Hi all,
    
    >The best source for stellar proper motions nowadays is the Hipparcos
    >catalogue that is now available at
    >
    >   http://astro.estec.esa.nl/Hipparcos/hipparcos.html
    >
    >First, you will need to know the Hipparcos number of your star.
    >
    >For that, go to
    >
    >   http://astro.estec.esa.nl/Hipparcos/HIPcatalogueSearch.html
    >
    >input the approximate J2000 co-ordinates, a tolerance (say 0.1 degree)
    >and a limiting magnitude (say 4). You will then obtain a short table of
    >all stars brighter than the limiting magnitude measured near to that
    >position with precise co-ordinates, magnitudes and proper motion
    >components with their errors - with a bit of luck there will be just one
    >star. Click on the star number for more details.
    >
    >You can also make a plot of your search region with
    >
    >
    >http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/apps/SelectArea.html
    >
    >but do not use it when the star is very close to one of the celestial
    >poles (you will not easily find Polaris in this way).
    >
    >Note that the proper motion components are given in milli-arcseconds per
    >year. For correcting the RA co-ordinate, divide the RA proper motion
    >component by 15 * cos(decl.) to obtain the proper motion in seconds of
    >time.
    >
    >In the case of Sirius there is also a 50-year oscillation in RA and
    >decl. due to the presence of a white dwarf companion (Sirius B).
    >
    >Regards,
    >
    >========================================================
    >* Robert H. van Gent * Tel/Fax:  00-31-30-2720269      *
    >* Zaagmolenkade 50   *                                 *
    >* 3515 AE Utrecht    * E-mail: r.h.vangent{at}astro.uu.nl *
    >* The Netherlands    *                                 *
    >********************************************************
    >* Homepage: http://www.phys.uu.nl/~vgent/homepage.htm  *
    >========================================================
    

       
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