Name

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    GAL_UVW

Purpose

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

Explanation

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    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

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

Output Parameters

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      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

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      /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

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      (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

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      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

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      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