source: trunk/MagicSoft/slalib/rvlsrk.c

#include "slalib.h"
#include "slamac.h"
float slaRvlsrk ( float r2000, float d2000 )
/*
**  - - - - - - - - - -
**   s l a R v l s r k
**  - - - - - - - - - -
**
**  Velocity component in a given direction due to the Sun's motion
**  with respect to an adopted kinematic Local Standard of Rest.
**
**  (single precision)
**
**  Given:
**     r2000,d2000   float    J2000.0 mean RA,Dec (radians)
**
**  Result:
**     Component of "standard" solar motion in direction R2000,D2000 (km/s)
**
**  Sign convention:
**     The result is +ve when the Sun is receding from the given point on
**     the sky.
**
**  Note:  The Local Standard of Rest used here is one of several
**         "kinematical" LSRs in common use.  A kinematical LSR is the
**         mean standard of rest of specified star catalogues or stellar
**         populations.  The Sun's motion with respect to a kinematical
**         LSR is known as the "standard" solar motion.
**
**         There is another sort of LSR, the "dynamical" LSR, which is a
**         point in the vicinity of the Sun which is in a circular orbit
**         around the Galactic centre.  The Sun's motion with respect to
**         the dynamical LSR is called the "peculiar" solar motion.  To
**         obtain a radial velocity correction with respect to the
**         dynamical LSR use the routine slaRvlsrd.
**
**  Reference:  Delhaye (1965), in "Stars and Stellar Systems", vol 5, p73.
**
**  Called:  slaCs2c, slaVdv
**
**  Last revision:   27 November 1994
**
**  Copyright P.T.Wallace.  All rights reserved.
*/
{
/*
**
**  Standard solar motion (from Methods of Experimental Physics, ed Meeks,
**  vol 12, part C, sec 6.1.5.2, p281):
**
**  20 km/s towards RA 18h Dec +30d (1900).
**
**  The solar motion is expressed here in the form of a J2000.0
**  equatorial Cartesian vector:
**
**      va(1) = x = -speed*cos(ra)*cos(dec)
**      va(2) = y = -speed*sin(ra)*cos(dec)
**      va(3) = z = -speed*sin(dec)
*/
   static float va[3] = { -0.29000f, 17.31726f, -10.00141f };
   float vb[3];

/* Convert given J2000 RA,dec to x,y,z */
   slaCs2c ( r2000, d2000, vb );

/* Compute dot product with solar motion vector */
   return slaVdv ( va, vb );
}