palRvgalc.c

/*
*+
*  Name:
*     palRvgalc

*  Purpose:
*     Velocity component in a given direction due to the rotation
*     of the Galaxy.

*  Language:
*     Starlink ANSI C

*  Type of Module:
*     Library routine

*  Invocation:
*     double palRvgalc( double r2000, double d2000 )

*  Arguments:
*     r2000 = double (Given)
*        J2000.0 mean RA (radians)
*     d2000 = double (Given)
*        J2000.0 mean Dec (radians)

*  Returned Value:
*     Component of dynamical LSR motion in direction R2000,D2000 (km/s).

*  Description:
*     This function returns the Component of dynamical LSR motion in
*     the direction of R2000,D2000. The result is +ve when the dynamical
*     LSR is receding from the given point on the sky.
*
*  Notes:
*     - The Local Standard of Rest used here is a point in the
*     vicinity of the Sun which is in a circular orbit around
*     the Galactic centre.  Sometimes called the "dynamical" LSR,
*     it is not to be confused with a "kinematical" LSR, which
*     is the mean standard of rest of star catalogues or stellar
*     populations.
*
*  Reference:
*     - The orbital speed of 220 km/s used here comes from Kerr &
*     Lynden-Bell (1986), MNRAS, 221, p1023.

*  Authors:
*     PTW: Pat Wallace (STFC)
*     DSB: David Berry (JAC, Hawaii)
*     {enter_new_authors_here}

*  History:
*     2012-02-16 (DSB):
*        Initial version.
*        Adapted with permission from the Fortran SLALIB library.
*     {enter_further_changes_here}

*  Copyright:
*     Copyright (C) 1995 Rutherford Appleton Laboratory
*     Copyright (C) 2012 Science and Technology Facilities Council.
*     All Rights Reserved.

*  Licence:
*     This program is free software: you can redistribute it and/or
*     modify it under the terms of the GNU Lesser General Public
*     License as published by the Free Software Foundation, either
*     version 3 of the License, or (at your option) any later
*     version.
*
*     This program is distributed in the hope that it will be useful,
*     but WITHOUT ANY WARRANTY; without even the implied warranty of
*     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*     GNU Lesser General Public License for more details.
*
*     You should have received a copy of the GNU Lesser General
*     License along with this program.  If not, see
*     <http://www.gnu.org/licenses/>.

*  Bugs:
*     {note_any_bugs_here}
*-
*/

#include "pal.h"
#include "pal1sofa.h"

double palRvgalc( double r2000, double d2000 ){

/* Local Variables: */
   double vb[ 3 ];

/*
*  LSR velocity due to Galactic rotation
*
*  Speed = 220 km/s
*  Apex  = L2,B2  90deg, 0deg
*        = RA,Dec  21 12 01.1  +48 19 47  J2000.0
*
*  This is expressed in the form of a J2000.0 x,y,z vector:
*
*      VA(1) = X = -SPEED*COS(RA)*COS(DEC)
*      VA(2) = Y = -SPEED*SIN(RA)*COS(DEC)
*      VA(3) = Z = -SPEED*SIN(DEC)
*/

   double va[ 3 ] = { -108.70408, +97.86251, -164.33610 };

/* Convert given J2000 RA,Dec to x,y,z. */
   eraS2c( r2000, d2000, vb );

/* Compute dot product with LSR motion vector. */
   return eraPdp( va, vb );
}