CalCOS v2.15.4 was installed in OPUS on January 12, 2012. A detailed list of changes related to CALCOS v2.15.4 can be found on the "CALCOS Release Notices" web page at http://www.stsci.edu/hst/cos/pipeline/CALCOSReleaseNotes/notes/). In particular, this version implements two important software changes into the Operations Archive (OPUS Release 2011.3) which are detailed below.
The first change adds a WALKCORR calibration step to CalCOS. The WALKCORR step, and the associated WALKTAB reference file, provide a means to correct the mis-registration of detected photon events, commonly referred to as "walk", caused by gain-sag. The current implementation provides a correction to the detected location based on the pulse height amplitude of each event. Mis-registration can occur in both the dispersion and cross-dispersion directions, x-walk and y-walk, respectively, but to date only y-walk has been observed. Because of this, WALKCORR only corrects for the observed y-walk, and further refinements will be implemented if necessary.
The second new feature is the addition of a TIMELINE extension to corrtag data. For TIME-TAG data, CalCOS will now calculate various statistics about an observation on a second-by-second basis and record them in a new extension. A few of the parameters currently included are the latitude and longitude of HST, the sun's altitude above the horizon, and the strength of geocoronal airglow lines. By using the information included in the TIMELINE extension, and a specifically designed TIMEFILTER module, users can exclude parts of their observations whenever particular parameters become undesirable, e.g. when the sun is above the horizon, or Ly-Alpha is too strong. To access the timefilter module, users will have to download the latest release of STSCI_python available at http://www.stsci.edu/institute/software_hardware/pyraf/stsci_python.