APT ETC Improvements

The change from CGI to Java-based ETCs was made in order to standardize the ETCs for all HST instruments, both to simplify development and support, and to provide a more consistent interface for users.

Most results obtained with the new APT ETCs should be close to those calculated with the older versions; however, there are some notable differences and enhancements:

• The new sky background model of Giavalisco, Sahu, & Bohlin (2002), discussed in WFC3 ISR 2002-12, has been implemented for all HST instruments.
• More realistic curves of encircled energy as a function of wavelength have been adopted. This is especially important for the CCD at IR wavelengths, where in-chip scattering puts a large fraction of the detected light in an extended halo.
• Calculations for extended and emission-line sources are significantly more accurate, and relax a number of approximations made in older versions.
• The full complement of supported apertures for each configuration is now included.
• Imaging peakup calculations for point sources are now included in the Target Acquisition ETC.
• Bruzual synthetic spectra are offered in addition to Kurucz models as stellar templates.
• A selectable extraction radius for imaging of point sources has been implemented.
• Rectangular (in addition to square) CCD binning is now available.
• Additional background specification options are offered.
• Total counts are now given for resolution elements rather than lambda-pixels.
• The extended-source lambda-pixel is now 2 pixels high.
• Many additional parameters, particularly for backgrounds and noise, are listed in the APT output page. The time to saturation for CCD images is now also included.