EMARK: Interactively Specify Ellipse Parameters for Photometry with EMAG

EMARK enables the user to mark with the cursor the radius at which the ellipse parameters to be used by the routine EMAG are to be taken. The image must be displayed, and the PROFILE common block loaded, in order for EMARK to work. It is advisable to have displayed the elliptical isophotes with TVPROF prior to running EMARK.

EMARK will prompt the user to move the cursor to the position (along the major axis) of the ellipse whose shape and orientation is the one desired for use in EMAG photometry. The user then strikes the key "P". A cross will be displayed at this point, and the user will be given the option of choosing another position. Once the user is satisfied with the position chosen, EMARK will compute the distance of this point from the ellipse center. This distance is then loaded into the VISTA variable ERAD.

When EMAG is run with ERAD as a keyword, values of the PROFILE common block near the radius specified by EMARK are averaged in order to obtain the position angles, ellipticities, and centers of the elliptical apertures used by EMAG.

Following the marking of the radius defining ERAD, EMARK asks the user if it is desired to mark the maximum radius for photometry. If so, the user is again prompted to move the cursor to this position and strike the key "P"; again the distance from the center is computed, and loaded into the VISTA variable RMAX.