A Region mask for a radial profile in concentric, elliptical annuli

• select cursor and ellipse. When in the image window, the mouse now has a box shape with an arrow at the upper left corner. The three mouse buttons have been redefined as:

  LEFT - moves the center of the ellipse with the position of the arrow point.

  MIDDLE - sizes the ellipse.

  RIGHT - rotates it.

• position the arrow where the center of the ellipse should be and click on the LEFT button. The ellipse parameters will appear on the window from which SAOimage was initiated.

• size the ellipse by holding the MIDDLE button and dragging the mouse both horizontally and vertically until the desired shape (major and minor axis) is achieved.

• rotate it by holding the RIGHT mouse button and dragging the mouse. Release the button at the desired angle.

• select the annulus button. Mouse buttons are now:

  LEFT -- move region (as before)

  MIDDLE -- add annulus

  RIGHT -- delete annulus

  i.e., the axial ratio and orientation of the ellipse are fixed, only adding (or removing) ellipses of different area is possible.

• obtain different annuli by placing the mouse at some distance from the ellipse and clicking on the MIDDLE button to produce equally spaced, concentric ellipses towards the mouse position. This will work both outside and inside the ellipse. To change the spacing between ellipses, click with the MIDDLE button and drag to the desired position. To remove one or more ellipses use the RIGHT button: the ellipse closest to the cursor position will disappear.

• save the annuli, by typing `s'. The center position and the outermost radial distance along the minor axis will be displayed if the options cursor> region> view and cursor> region> label are ON.

• select region and write, to write the saved region to a file (as above).

Below is an example of the results obtained with the above procedure.

# xdata$rp110590_iml.imh - XRT/PSPC PSF AR LAC
# Thu Jul 25 11:42:57 1991
# shape x, y, [x dimension, y dimension], [angle]
 ELLIPSE(231,314,4.23,17.70,236.864)
 ELLIPSE(231,314,11.72,49.06,236.864) & !ELLIPSE(231,314,4.23,17.70,236.864)
 ELLIPSE(231,314,23.45,98.11,236.864) & !ELLIPSE(231,314,11.72,49.06,236.864)

Note: &! means ``and not''; i.e., an elliptical annulus rather than a solid ellipse.