binradvel

         compute radial velocity of a binary system as a function of
         orbital phase or time (if t0 or t90 are given)

         astronomy

         vel=binradvel(phase,k=k,period=period,asini=asini,eccen=eccen, $
                   omega=omega,gamma=gamma,degrees=degrees)

          phase: array with the orbital phase points (from 0 to 1)
                 for which the radial velocity is to be computed;
                 if t0 or t90 are given: time in days (same time
                 system as t0 or t90)
          k    : velocity amplitude of the system
          asini: value of a sin i in kilometers
          period: orbital period, in days
          NOTE: either k or  both, asini and period, must be given

          t0   : epoch of periastron (see above, description of "phase" argument)
          t90  : epoch when mean longitude = 90 degrees
          omega: longitude of periastron (little omega; radians,
                 default: 0.)
          eccen: eccentricity (default: 0.)
          gamma: systemic velocity (same units as k or in km/s; default:0.)

          degrees: if set, angular arguments are in degrees instead
                 of radian

      the function returns the radial velocity as a function of the
      phase in the units of k or of  asini/period

      * the eccentricity must be 0<=e<1
      * only one of the arguments t0 and t90 is allowed

      See chapter 3 of
         R.W. Hilditch, An Introduction to Close Binary Stars,
         Cambridge Univ. Press, 2001

 Radial Velocity of HR7000
 (Hilditch, Fig. 3.27; Griffin et al., 1997, Fig. 2)
 npt=100
 phase=findgen(npt)/(npt-1)
 vel=binradvel(phase,k=21.68,gamma=-22.52,eccen=0.372,omega=306.5,/degrees)
 ; Show two orbits for clarity
 pp=[phase,1.+phase]
 vv=[vel,vel]
 plot,pp,vv,xtitle='Orbital Phase',ytitle='Radial Velocity [km/s]'
 xrange=!x.crange
 oplot,xrange,[0.,0.],linestyle=2

 $Log: binradvel.pro,v $
 Revision 1.2  2005/02/18 21:41:23  wilms
 * added t0 and t90 arguments
 Revision 1.1  2002/09/09 14:52:04  wilms
 initial release

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