orbitplot

       make plot of orbit in binary star system. Observers look at
       the orbit from the left and the companion circles the star in
       the clockwise direction

       astronomy

       orbitplot

      a     : semimajor axis of the orbit (default: 1.)
      eccen : Eccentricity of the orbit (default: 0.)
      lonasc: Longitude of ascending node (capital Omega; radians; default:0)
      incl  : Inclination (radians; not used; default: 0.)
      omega : Longitude of periastron (little omega; radians,
              default: 0.)
      position: position of figure in normal coordinates
              (default:0.1,0.1,0.95,0.95)
      space  : fraction of free space around the ellipse (default: 0.05)
      units  : length unit of the plot (i.e., units of semimajor
               axis)
      xtitle, ytitle: title for the x- and y-axis.
              Default (x-, and y-), if set, the units-keyword is ignored
      starrad: radius of the star (same units as semi-major axis)
              if given, a filled circle with radius starrad is drawn,
              if not, a dot at (0,0) designating the position of the
              star is plotted (default; but see keyword nostar)
      starname: name of the central star, overplotted on the star
              (unless nostar-keyword is given)
      phase1: phases to plot symbols on orbit (can be array)
      phase2: ending phase of highlighted orbit segment
              (if phase1 and phase2 are given, draw segment from phase1
              to phase2, NOTE: in this case phase1 must be scalar)
      phasethick: thickness of highlighted ellipse segment (default: 3)
      posdash : draw line perpendicular to ellipse at start and stop
                of highlighted orbit segment
      dirarrow: draw an arrow indicating the direction of motion
                from phase1 to phase2 (note phase2 MUST be greater
                than phase1)
      orbitcol: color for the orbit segment
      compsymbol: symbol to be plotted at the position of the stellar
                  companionorbit, works only if phase2 is not defined
                  (see IDL Help for PSYM, default: 0 (cross))
      symbolsize: sets symbolsize of input compsymbol (default: 1.0)
      shownodes: shows the line of nodes via a dotted line

      nostar: if set, no position or circle is plotted at the
              stellar position
      degrees: if set, the angular input parameters are in DEGREES
      periastron: if set, draw triangular symbol at periastron
      oplot  : if set, the ellipse is drawn in the currently setup
               coordinate system (e.g., for plotting many cometary
               orbits)
      nodata : just setup the figure, do not plot the ellipse
  furthermore, the routine also accepts all keyword parameters of the
  plot and oplot commands via the _extra mechanism, thus allowing one
  to plot, e.g., colored orbits or change the thickness of the
  ellipse that is to be plotted

      none

      a plot is drawn

      the eccentricity must be less than unity; parabolic or
      hyperbolic orbits are not allowed at the moment.

      the ellipse coordinates are computed, then the bounding box
      is determined and the coordinate system is setup in a way that
      the x- and y-coordinates have the same length

 ;
 **********************************
 Orbits of the inner solar system:
 ; Mars
 orbitplot,a= 1.524,eccen=0.093,incl= 1.85,lonasc= 49.58, omega=336.0
 ; Mercury
 orbitplot,a= 0.387,eccen=0.206,incl= 7.00,lonasc= 48.33, omega= 77.5,/oplot
 ; Venus
 orbitplot,a= 0.723,eccen=0.007,incl= 3.39,lonasc= 76.68, omega=131.5,/oplot
 ; Earth
 orbitplot,a= 1.000,eccen=0.017,incl= 0.00,lonasc=-11.26, omega=102.9,/oplot
 stop
 ;
 **********************************
 Orbits of the outer solar system:
 ; Pluto
 orbitplot,a=39.482,eccen=0.249,incl=17.14,lonasc=110.30, omega=224.1
 ; Jupiter
 orbitplot,a= 5.203,eccen=0.048,incl= 1.31,lonasc=100.56, omega= 14.8,/oplot
 ; Saturn
 orbitplot,a= 9.537,eccen=0.054,incl= 2.48,lonasc=113.72, omega= 92.4,/oplot
 ; Uranus
 orbitplot,a=19.191,eccen=0.047,incl= 0.77,lonasc= 74.23, omega=171.0,/oplot
 ; Neptune
 orbitplot,a=30.069,eccen=0.009,incl= 1.77,lonasc=131.72, omega= 45.0,/oplot
 **********************************
 Make PNG of the Vela X-1 system
 set_plot,'Z'
 device,set_resolution=[500,500]
 orbitplot,eccen=0.1885,a=53,omega=150.6,units=textoidl('R_O'), $
   starrad=30.,/degrees,/periastron,starname='HD 77581', $
   position=[0.11,0.11,0.97,0.97],space=0.07
 image=tvrd()
 write_png,'velax1.png',image

 $Log: orbitplot.pro,v $
 Revision 1.5  2005/02/22 15:55:05  wilms
 replaced keyword arrowdir with dirarrow, since it produced a clash
 with IDL's keyword abbreviation mechanism.
 Revision 1.4  2005/02/18 23:28:54  wilms
 added shownodes, arrowdir, phasethick, posdash, nodata and _extra keywords
 Revision 1.3  2003/04/01 07:41:58  gleiss
 added optional inputs compsymbol and symbolsize
 Revision 1.2  2002/09/19 20:55:50  wilms
 added option to highlight orbital segment or specific phases
 Revision 1.1  2002/09/09 14:53:28  wilms
 initial release
 CVS Version 1.3 2003/04/01 gleiss
 added optional inputs compsymbol and symbolsize

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