GAL_UVW
Calculate the Galactic space velocity (U,V,W) of star
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.
GAL_UVW, U, V, W, [/LSR, RA=, DEC=, PMRA= ,PMDEC=, VRAD= , DISTANCE= PLX= ]
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
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)
/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. PLE: (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
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.
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