def W(self,*args,**kwargs):
        """
        NAME:

           W

        PURPOSE:

           return Heliocentric Galactic rectangular z-velocity (aka "W")

        INPUT:

           t - (optional) time at which to get W (can be Quantity)

           obs=[X,Y,Z,vx,vy,vz] - (optional) position and velocity of observer 
                         in the Galactocentric frame
                         (in kpc and km/s) (default=[8.0,0.,0.,0.,220.,0.]; entries can be Quantity)
                         OR Orbit object that corresponds to the orbit
                         of the observer
                         Y is ignored and always assumed to be zero

           ro= (Object-wide default) physical scale for distances to use to convert (can be Quantity)

           vo= (Object-wide default) physical scale for velocities to use to convert (can be Quantity)

        OUTPUT:

           W(t) in km/s

        HISTORY:

           2011-02-24 - Written - Bovy (NYU)

        """
        out= self._orb.W(*args,**kwargs)
        if len(out) == 1: return out[0]
        else: return out
NAME:

           W

        PURPOSE:

           return Heliocentric Galactic rectangular z-velocity (aka "W")

        INPUT:

           t - (optional) time at which to get W (can be Quantity)

           obs=[X,Y,Z,vx,vy,vz] - (optional) position and velocity of observer 
                         in the Galactocentric frame
                         (in kpc and km/s) (default=[8.0,0.,0.,0.,220.,0.]; entries can be Quantity)
                         OR Orbit object that corresponds to the orbit
                         of the observer
                         Y is ignored and always assumed to be zero

           ro= (Object-wide default) physical scale for distances to use to convert (can be Quantity)

           vo= (Object-wide default) physical scale for velocities to use to convert (can be Quantity)

        OUTPUT:

           W(t) in km/s

        HISTORY:

           2011-02-24 - Written - Bovy (NYU)