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GAL_UVW

GAL_UVW

Name


    GAL_UVW

Purpose


    Calculate the Galactic space velocity (U,V,W) of star

Explanation


    Calculates the Galactic space velocity U, V, W of star given its
    (1) coordinates, (2) proper motion, (3) distance (or parallax), and
    (4) radial velocity.

Calling Sequence


    GAL_UVW, U, V, W, [/LSR, RA=, DEC=, PMRA= ,PMDEC=, VRAD= , DISTANCE=
              PLX= ]

Output Parameters


      U - Velocity (km/s) positive toward the Galactic *anti*center
      V - Velocity (km/s) positive in the direction of Galactic rotation
      W - Velocity (km/s) positive toward the North Galactic Pole
  REQUIRED INPUT KEYWORDS:
      User must supply a position, proper motion,radial velocity and distance
      (or parallax). Either scalars or vectors can be supplied.
    (1) Position:
      RA - Right Ascension in *Degrees*
      Dec - Declination in *Degrees*
    (2) Proper Motion
      PMRA = Proper motion in RA in arc units (typically milli-arcseconds/yr)
            If given mu_alpha --proper motion in seconds of time/year - then
            this is equal to 15*mu_alpha*cos(dec)
      PMDEC = Proper motion in Declination (typically mas/yr)
    (3) Radial Velocity
      VRAD = radial velocity in km/s
    (4) Distance or Parallax
      DISTANCE - distance in parsecs
                or
      PLX - parallax with same distance units as proper motion measurements
            typically milliarcseconds (mas)

Optional Input Keyword


      /LSR - If this keyword is set, then the output velocities will be
            corrected for the solar motion (U,V,W)_Sun = (-8.5, 13.38, 6.49)
            (Coskunoglu et al. 2011 MNRAS) to the local standard of rest.
            Note that the value of the solar motion through the LSR remains
            poorly determined.

Example


      (1) Compute the U,V,W coordinates for the halo star HD 6755.
          Use values from Hipparcos catalog, and correct to the LSR
      ra = ten(1,9,42.3)*15. & dec = ten(61,32,49.5)
      pmra = 628.42 & pmdec = 76.65 ;mas/yr
      dis = 139 & vrad = -321.4
      gal_uvw,u,v,w,ra=ra,dec=dec,pmra=pmra,pmdec=pmdec,vrad=vrad,dis=dis,/lsr
          ===> u=141.2 v = -491.7 w = 93.9 ;km/s
      (2) Use the Hipparcos Input and Output Catalog IDL databases (see
      http://idlastro.gsfc.nasa.gov/ftp/zdbase/) to obtain space velocities
      for all stars within 10 pc with radial velocities > 10 km/s
      dbopen,'hipp_new,hic' ;Need Hipparcos output and input catalogs
      list = dbfind('plx>100,vrad>10') ;Plx > 100 mas, Vrad > 10 km/s
      dbext,list,'pmra,pmdec,vrad,ra,dec,plx',pmra,pmdec,vrad,ra,dec,plx
      ra = ra*15. ;Need right ascension in degrees
      GAL_UVW,u,v,w,ra=ra,dec=dec,pmra=pmra,pmdec=pmdec,vrad=vrad,plx = plx
      forprint,u,v,w ;Display results

Method


      Follows the general outline of Johnson & Soderblom (1987, AJ, 93,864)
      except that U is positive outward toward the Galactic *anti*center, and
      the J2000 transformation matrix to Galactic coordinates is taken from
      the introduction to the Hipparcos catalog.

Revision History


      Written, W. Landsman December 2000
      fix the bug occuring if the input arrays are longer than 32767
        and update the Sun velocity Sergey Koposov June 2008
vectorization of the loop -- performance on large arrays
        is now 10 times higher Sergey Koposov December 2008
      More recent value of solar motion WL/SK Jan 2011



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