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GAL_UVW

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

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)
(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
===> 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
ra = ra*15. ;Need right ascension in degrees
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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