I have a lens flare effect that I want to animate....and not respond to the mouse

I’m using a lens flare…that follows the user’s mouse…but I want to animate it so that it goes from the left side of the screen to the right.

It currently uses…

flare._x = _xmouse;
flare._y = _ymouse;

and it just cycles on this using…
prevFrame();
play();

What would be the best way to animate it…?

Thanks.

and this is how it works…
var x;
var y;
var angle;
var radius;
var big_alpha = 0;
function placeObject (object, expand)
{
// The higher expand is set, the more it will stretch-out from the center
// as the light moves from the center.
object._x = (radius * expand) * Math.cos(angle);
object._y = (radius * expand) * Math.sin(angle);
}

and on the next frame…
radius = Math.sqrt(_x*_x+_y*_y);
angle = Math.atan(_y/_x);
// Correct angle for quadrant.
if (_x < 0) angle = (Math.PI) + angle;
burst1._x = x;
burst2._y = y;
placeObject(burst2, 1);
placeObject(burst3, 0.5);
placeObject(burst4, 1.8);
placeObject(burst5, 0.6);
placeObject(burst6, 1.5);
placeObject(burst7, -0.4);
placeObject(burst8, 1.6);
placeObject(burst9, -0.2);
// Closer to the center, the more alpha there is.
big_alpha = 100 - radius;
if (big_alpha < 0) big_alpha = 0;
bigburst._alpha = big_alpha;